Maldives: two specimens approx. 20 mm length (MDV/AB/96/23), Vilufushi lagoon, Thaa Atoll, 3 m depth, 31 March 1993, leg. RC Anderson & SG Buttress. – La Réunion: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Globose shell thin, transparent, too small to accommodate body completely; shell 15 mm, living animal up to 25 mm. Body pale green with large and small orange spots, part contained within the shell much darker green than both head and tail. Larger orange spots and patches underlying shell outlined with white or very pale green.

Infrequently, huge mating congregations are observed, with numbers of up to 100 individuals per m² in February 2007 in La Réunion, which lasted approximately one week (P Bidgrain, pers. comm. and http://seaslugs.free.fr/nudibranche/a_intro.htm). These aggregations were not observed again until 2010, but with a much smaller number of animals, only 100 individuals in total (P Bidgrain, pers. comm.).

Haminoea cf. cymbalum has been rarely recorded in the Indian Ocean; it is more common in the western Pacific. Difficulties arise with the name of this well-known species: both Burn (in Marshall and Willan 1999) and Carlson and Hoff (Sea Slug Forum 1999) suggested that the shell representing the type in the MNHN (Paris) is not the same species; therefore this species would take the next available name, which is Haminoea simillina (Pease). Additionally, there are several other species differing in colour, radula, and gizzard plates, so further work is needed; deposits of individual specimens such as these in museums with their descriptions and photographs will ensure that enough material is made available for future workers.

Maldives: 29 mm length (10 mm pres., MDV/AB/96/1), Guraidhoo Channel, South Malé Atoll, 16 m depth, 30 April 1996, leg. RC Anderson & SG Buttress. – Zanzibar: two pres. specimens 15 mm × 2 mm and 19 mm × 9 mm, Bawe Island, underside of Porites head with encrusting Tubastrea and sponges, 7 m depth, June 1995, leg. MD Richmond. – Madagascar: 50 mm × 10 mm (PK-C), Ampangorina, Nosy Komba, on algal-encrusted coral, 3 m depth, 30 January 1992, leg. P Kemp. – Mayotte: photographs of two individuals, 15 mm and 25 mm http://seaslugs.free.fr/nudibranche/a_intro.htm.

These specimens and photographs are among the first records of Chelidonura electra from the Indian Ocean. Chelidonura electra is distinguished by its white body and yellow edges to the parapodia and tails. There are no similar specimens in the Indian Ocean: Chelidonura pallida Risbec is found in the western Pacific and eastern Indian Ocean only; it has not been recorded from the western Indian Ocean. Also white, it has a black line along the edges, followed by an inner orange-yellow band. Gosliner (1980) suggested that Chelidonura electra might be a colour form of Chelidonura pallida, arguing that colour can be variable in a single species but in his recent book (Gosliner et al. 2008) they are treated as separate species, and their different distributions are acknowledged. They are also treated as different species with different reproductive strategies in Anthes and Michiels (2007). Chelidonura amoena Bergh is also found in the eastern Indian Ocean and western Pacific: it is also a large species, translucent white with diffuse yellow margins to the head and tail and dark brown to black speckled pigmentation on the dorsum and parapodia, the latter having yellow anterior and posterior corners (pers. obs., Willan and Cattaneo-Vietti 1995).

Maldives: three specimens, approx. 5-6 mm length pres., Kuredu, Lhaviyani Atoll, on sandy substrate in shallow water, 10-24 March 1998, leg. J Hinterkircher; several individuals, photos only, 1986-1994, J Hinterkircher. – La Réunion: photographs of numerous individuals, 10 - 40 mm http://seaslugs.free.fr/nudibranche/a_intro.htm.

Dark brown to black body with black and orange edging, vivid blue Y- or T-shaped mark on head, small white patch at posterior end of head shield, and large white crescent-shaped mark on posterior shield. The species is rarely recorded in the Indian Ocean, where the pattern is relatively consistent, and somewhat different to those from the Pacific Ocean. Gosliner (1988) comments on the different colour forms, and that two colour forms were recorded mating in South Africa. Chelidonura hirundinina is recorded in the Mauritius - La Réunion region, the type locality, and it has a circumtropical distribution (also found in the Caribbean, Thompson 1977). Most records are from the western Pacific, where it is larger, more abundant, and more variable in colour and pattern, although the variations exhibited by http://seaslugs.free.fr/nudibranche/a_intro.htm are substantial.

Maldives: 15 mm (MDV/AB/96/15, “very dark brown, almost black, white edge anteriorly and blue grey edge to parapodia, with orange-red spots”), Fulidhoo Channel, Felidhoo Atoll, 9 m depth on coral rock, 7 May 1996, leg. RC Anderson & SG Buttress. – Mauritius, La Réunion, and Mayotte: five individuals photographed http://seaslugs.free.fr/nudibranche/a_intro.htm.

Chelidonura punctata appears to be restricted to the western Indian Ocean; to date there are no records of the species occurring in the Red Sea, the Gulf of Aden, the Gulf of Oman, or the Persian Gulf. The similar species found in the Gulf of Eilat (recorded erroneously as Chelidonura punctata in Yonow 2008) and in the Seychelles (pers. obs.) is illustrated here as Chelidonura cf. punctata (Plate 5) for comparison as no specimens are available; it has many small, yellower spots which appear to be slightly raised, lacks the white margins to the parapodia but has broken white markings along the posterior margin of the posterior shield, and the tails are very differently proportioned. It is also appears to be small, but without specimens, identification is impossible.

An interesting paper documenting the feeding habits of Chelidonura punctata in Kenya describes the association between it and an acoel flatworm present on the hard coral Platygyra daedalea (Mangubhai 2007); neither the sea slug nor the flatworm was observed on other coral species. A similar association was observed between Chelidonura livida and Waminoa cf. brickneri in the Red Sea (Yonow 2008).

Maldives: 3 mm pres., Maayafushi, Ari Atoll, shallow water in lagoon, February 1995, leg. J Hinterkircher; photos of two individuals, 1986-1994, J Hinterkircher; 7 mm (5 mm pres., “all black”), Maayafushi Channel, Ari Atoll, 7-17 m depth on sandy slope, 12 October 1994, leg. RC Anderson & SG Buttress.

The collecting notes state that there were “plenty of aglajids, all completely black” in Maayafushi lagoon, up to approximately 10 mm in length, and it is very common in the Maldives (Yonow 1994). This species is recorded throughout the western Indian Ocean as well as in the northern Red Sea, and its extensive variability of colouration is now well known; both specimens demonstrate the all-black colouration (Plate 6) while an additional photo (from another locality in the same atoll) depicts an individual which is black with white marbling, but without the orange spots (Plate 7). Turner and Wilson (2011) have shown that the range of colour morphs show no breeding differences; Chelidonura tsurugensis Baba & Abe, 1959 may be an older name (Yonow in prep.).

Maldives: two specimens, 30 mm and 15 mm pres., Maayafushi Channel, Ari Atoll, 7-17 m depth on sandy slope, 12 October 1994, leg. RC Anderson & SG Buttress.

Maldives: two specimens, 18 mm and 12 mm pres., Maayafushi Channel, Ari Atoll, 7-17 m depth on sandy slope, 12 October 1994, leg. RC Anderson & SG Buttress; 24 mm (MDV/AB/96/5), Fulidhoo lagoon, Felidhoo Atoll, 7 m depth, 03 May 1996, leg. RC Anderson & SG Buttress. – La Réunion, photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. – Tanzania: photograph of single individual, Mafia Island, shallow water, 31 July 2004, A de Villiers.

The photographs on the La Réunion website show mating, egg laying, and egg development during the breeding season, November. This common Indo-West Pacific species known as Philinopsis cyanea, with an extremely variable colour pattern, has an older name, Philinopsis speciosa, which was previously considered as endemic to Hawaii. Rudman (http://www.seaslugforum.net/find/philspec) states that there are no anatomical differences between the two, and Gosliner et al. (2008) have combined them under the older name with no discussion or comment. Pease (1860) described the habit of stressed slugs vomiting perfect shells of Bulla, as recorded for specimens from the Red Sea (Yonow 1992) and Zanzibar (Rudman, Sea Slug Forum). Philinopsis cyanea is formally synonymised with Philinopsis speciosa in this work.

Pale form: Socotra: 10 mm × 5 mm pres. (IT-084, N-171), Rhiy di-Irisal, SE site, 2-8 m depth, 24.II.1999, leg. N Simões. – La Réunion, photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Dark form: Maldives: two specimens approx. 14 mm in length, Hulhulé Island, North Malé Atoll, 12 m depth on orange encrusting sponge on outer reef, 30 July 1995, leg. RC Anderson & SG Buttress (“dark brown with numerous tiny white dots, brown tending to orange, greyish white at margins”); two specimens both 14 mm, Old Shark Point, Thilafalhu Reef, North Malé Atoll, 16 m depth, 18 November 1995, leg. RC Anderson & SG Buttress (“dark brown with numerous fine pale dots; edges of [parapodia] and tentacles pale”); 20 mm (MDV/AB/96/13), Fulidhoo Channel, Felidhoo Atoll, 9 m depth, 07 May 1996, leg. RC Anderson & SG Buttress (“no white spots”). – La Réunion, photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. – Tanzania: photo of one individual, Mafia Island, shallow water, May 2009, A de Villiers.

The dark colour form is common in the Red Sea and western Indian Ocean (Yonow 1994a, Yonow et al. 2002, Yonow 2008) and also occurs in the western Pacific (Gosliner et al. 2008), albeit less frequently. The pale Socotra specimen is well relaxed and preserved: the body is cream coloured with black edging to the rhinophores, oral tentacles, foot, and parapodia. Both colour forms are small, and one is the reverse colour pattern of the other. Although pale Aplysia parvula are recorded to grow to 120 mm (Marshall and Willan 1999), the largest size recorded for the dark colour formis the Maldives specimen listed above at 20 mm. Consistent differences occur in the colour patterns: Aplysia parvula sensu strictu is usually pale green or greenish brown with white marbling and spots, and dark purple-to-black margins on the tentacles and parapodia (Plate 10). The black form is very dark brown or black, sometimes with white speckles, and with pale pink or violet edging to the parapodia and tentacles (Plate 11). The pale form is found in shallow tidal areas with seaweed, while the dark form is found on coral reefs in more exposed areas. Several other colour patterns have been illustrated on the La Réunion website.

The radula of the Socotra specimen has the formula 29 (+2) × 4.7.1.7.4. It is comparable in formula and size to those of the dark form previously examined from the Red Sea (26 (+1) × 4.6.1.6.4: Yonow 2000) and Chagos (26 (+3) × 3.6.1.6.3: Yonow et al. 2002), although it must be stressed that the radulae are not very good diagnostic features for differentiating between species of Aplysia. The shell is also similar in both forms but again, it is variable and therefore not a particularly useful character for determining species of aplysiids.

Zanzibar: 46 × 28 mm pres., Kizimkazi Dimbani reefs, intertidal, June 1994, leg. Suki/MD Richmond. – La Réunion, Mauritius, and Mayotte: photographs of numerous individuals and two shells http://seaslugs.free.fr/nudibranche/a_intro.htm. – Oman: Muscat, 1-12 April 2009, photo S Kahlbrock. – Seychelles: one individual photographed, Lilôt, NW Mahé, 1988-1989, P Kemp.

Examination of the shell (Fig. 2) identifies the Zanzibar specimen as the tropical Indo-Pacific Dolabella auricularia; the specimen had rounded tubercles in life, and these remain on the preserved animal. There are only two species of Dolabella, but to date no recent specimens of Dolabella gigas (Rang) have been recorded. The two species are said to differ in shell morphology and internal characters (Engel 1942, Eales 1946): Bebbington (1974) gave a history of Dolabella gigas and Dolabella auricularia. Engel (1942) listed both species, with slightly different shell morphologies, long and armed or short and unarmed penises, based on one specimen and 13 shells of gigas and many more of auricularia (as scapula). Eales (1946) examined two specimens of Dolabella gigas from India and confirmed the differences in shell morphology but was unable to confirm the presence of spines on the penis.

The radular formulae appear smaller in gigas but it is difficult to make size-for-size comparisons from the literature. This study demonstrates that the shells of three specimens from La Réunion and Zanzibar with rounded tubercles, the external morphology of Dolabella gigas, prove to be identical to Dolabella auricularia (P Bidgrain and M Jay, pers. comm., see http://seaslugs.free.fr/nudibranche/a_intro.htm for shell photos). Looking at the many shells illustrated by Engel (op. cit.) and Eales (op. cit.), there appears to be a clinal variation from one extreme to the other. Smooth and hirsute specimens were recorded together from Mauritius (Yonow and Hayward 1991) and both spiky and warty specimens were recorded from the Maldives (Yonow 1994a); all shells examined were similar, which eliminates the previously divisive external morphologies. It is probable that some of the shells of Dolabella gigas illustrated in the literature are extremes or aberrant; there appears to be only one record of penis spines, which remains unconfirmed. If this is considered an error, any differences between the two species are eliminated: it seems extremely unlikely that there would be two very large species of Dolabella distributed together in the same regions, and both are here considered the same species.

The Maldives specimen and shell listed in Yonow (1994) are deposited in The Natural History Museum, London (NHMUK 20110444), and not in the Australian Museum, Sydney, as stated in that paper due to subsequent postal security regulations.

Socotra: 10 mm curled pres. (St-021, MAP-097), rocks with algae, W of Rhiy di-Diblih, Nogid, S coast, 12 March 1999, leg. M Apel. – Maldives: 60 mm approx. (49 mm pres.), in Tridacna culture tank, Marine Research Section, Malé, North Malé Atoll, 30 December 1995, leg. RC Anderson (“mottled olive green; extruded white gelatinous fluid from posterior siphon”); photos only of several individuals, March 1997, March 1998, March 1999, J Hinterkircher. – Mauritius and La Réunion: numerous individuals with various colours and textures http://seaslugs.free.fr/nudibranche/a_intro.htm. – Seychelles: photo of one individual, Lilôt, NW Mahé, 1988-1989, P Kemp.

Preserved specimen from the Maldives are relaxed, with rhinophores and tentacles well extended, and a distinct flange present around margin; Socotra specimen very contracted and curled up. Colours of living specimens are extremely variable, and the villi may or may not be present; Dolabrifera dolabrifera can grow to 50 mm in length, and is common in the western Indian Ocean and Red Sea in shallow inter- and sub-tidal coastal waters; it has a wide Indo-Pacific distribution.

Socotra: four specimens 15-20 mm preserved lengths (IT-157, RJ-011), 12°18.698'N, 53°48.285'E, 09 April 1999, leg. R Janssen.

Preserved specimens are similar to previously examined material from the Red Sea, severely contracted into spheres with varying amounts of speckling remaining on different specimens. The species is circumtropical, common where it occurs but not often recorded. Records from the western Indian Ocean are summarized by Bebbington (1974); there are no new records apart from those from the Red Sea listed above.

Maldives: 6 mm in length pres., 2 m depth on algal-covered stone, Kuredu, Lhaviyani Atoll, 10-24 March 1998, leg. J Hinterkircher; three specimens collected of many, 50-70 mm live lengths (28-32 mm preserved), on algae growing on floating grouper cage near surface, Kiadhu Tila, Felidhoo Atoll, 23 July 1994, leg. RC Anderson (striations still visible on preserved specimens). – Zanzibar: numerous specimens 10-50 mm pres. lengths, Mazzini, intertidal and low water forming chains on sand and rocks in sea grass beds, 09 September 1993, leg. MD Richmond (numerous villi, very long rhinophores and oral tentacles). – Mauritius, La Réunion, Mayotte, and Madagascar: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. – Oman: Muscat, 01-12 April 2009, photos of several individuals, S Kahlbrock.

Benthic form of this circumglobal species distinguished by fine longitudinal brown-to-black lines usually interrupted by ‘eyespots’ with bright blue centres; tail long, swelling present in middle of body where parapodial lobes enclose large gill and anal siphon; rhinophores and oral tentacles long and slender. Specimens in any given population may have few or numerous villi, and this variation is still visible in the preserved material. It can be locally common in sea grass beds and shallow water, especially during the breeding season, but this does not happen every year (P Bidgrain, pers. comm. and http://seaslugs.free.fr/nudibranche/a_intro.htm).

There is probably only one species of Stylocheilus occurring in two forms, the benthic striated form described and illustrated here, which was known as striatus, and the yellow pelagic form associated with seaweeds currently known as longicauda.

This may be an appropriate location to discuss the problems posed by the aplysiids distributed in the Indo-West Pacific: all species covered in this work are complex and appear to comprise colour forms identified as separate species, as well as having different habitat preferences. Aplysia parvula occurs consistently in at least two forms, the larger pale-coloured shallow water one associated with algae and the tiny black reef form although other colour forms are recorded (http://seaslugs.free.fr/nudibranche/a_intro.htm and http://www.nudipixel.net/species/aplysia_parvula/). It is noted that the radulae and shells were similar, with slight differences. Dolabrifera dolabrifera has been described under many names but has long been recognised as a single species. Many species of Dolabella have been described but were historically resolved to two species, with different external and (possibly) internal morphologies and shells; these are synonymised as one species in this work. The history of Stylocheilus is also complicated, with two very different forms inhabiting very different environments. Clearly the aplysiids are in need of revision, entailing comparison of specimens from different regions and habitats as well as a very thorough review of the literature; it is probable that the numerous species names currently listed will dissolve into fewer, variable species.

Holotype: 12 mm alive, 6.5 × 2.5 mm pres. in alcohol, Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337104.

Paratypes: approx. 12 mm alive, 4 × 3 mm pres. in formalin (dissected), Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337103; 10 mm alive, 4.5 × 2 mm pres. in alcohol, Etang Salé, La Réunion, rocky coast, 1 m depth, 14 December 2009, leg. H. Flodrops, SMF 337205.

A multi-coloured Cyerce with approximately 30 inflated, pustular, angular cerata whose margins are pale violet-blue with creamy orange patches and black spots. The head has an orange band on either side and black spots on its frontal margin. The body and cerata are marbled light green and white. Ventrally, the propodium and metapodium each bear a row of small black dots, the former anteriorly and the latter marginally and posteriorly. Size up to approximately 15–20 mm.

The description of the colour and pattern is based on a series of photographs of the type specimens: body covered in fewer than 30 slightly inflated and tubercular cerata, loosely arranged in transverse rows along each side. Each ceras can be flat or swollen, angular with rounded corners (Fig. 3B, C), semi-translucent beige to green, margins pale blue-violet ‘beaded’ with opaque pale orange pigment, and sub-marginal black spots. The profile is in one plane along the sides but strongly convex at the distal end. Tubercles opaque white, concentrations of larger black spots in lateral swellings. Very few black spots scattered on cerata but yellow spots, olive-green patches, and light green to light brown marbling present. In some photographs, paired dark brown globular patches visible in alcohol-preserved specimens can be seen as circular red-brown patches at bases of cerata (Plate 14, right-hand cerata at level of pericardium). Anterior portion of body marbled: head and rhinophores semi-translucent; eyes clearly visible at bases of rhinophores (Plate 15). Oral tentacles short and recurved. Frontal margin of head with black spots, and behind eyes and rhinophores, coalesced to form a network. Broad orange band on each side of head, outside the black spots. Pericardium immediately behind first two or three rows of cerata, swollen, ochre-coloured, bare of cerata.

The specimens preserved in alcohol are in excellent condition; the paratype in formaldehyde shed 23 larger cerata. It is cream in colour, while the holotype and second paratype are semi-translucent. Dark patch of pigment anterior to swollen pericardium behind rhinophores and faint pigmented patch beyond. Pericardium a large swelling but dissection of paratype in formaldehyde did not reveal vessels and disintegrated with further prodding. Large swollen anal papillae behind right rhinophore near eye in all preserved specimens. Conical penis visible below right rhinophore in alcohol paratype only, no spine apparent at tip. Ventral views well presented in alcohol (Fig. 3A); rhinophores visible, as are head and oral tentacles; propodium with row of black spots along anterior margin, rounded metapodium with a row of black spots all around its edge except anteriorly. Cerata angular with three rounded corners near distal margin. At the base, doughnut-shaped attachment point and small flap beyond (Fig. 3B). Minute pointed papillae located in a band following the contours on both surfaces of the cerata, white in certain angles of light (Fig. 3C). Edges of some preserved cerata appear serrated (Fig. 3C). Brown triangular patch present on flap at base of each ceras in alcohol-preserved specimens. Two dark brown to black bodies inside cerata, formed of very small globules (Fig. 3B, C), near base above and beside attachment point.

Dissection of the formaldehyde-preserved paratype proved impossible as only the outer skin was preserved, the internal organs decomposed. However, the muscular pharynx remained solid and was removed to extract the radula. Radular formula 16 × 0.1.0, nine teeth in the ascending limb and seven teeth in the descending one (fig. 3D). The teeth are typical in shape for Cyerce (e.g. Hamatani (1976) for Cyerce kikutarobabai), and 170 μm in length. The denticles along the cutting edge are paired, with the first denticles at the tip smaller (fig. 3E). Denticles 1-7 increase in size, while denticles 8-10 decrease, and denticle 11 is just a small bump. The teeth are curved along their long axis and fit closely into the next tooth, the denticles leaving indentations in the underlying shaft. In profile, the shaft is shorter and barely narrower than the cusp (fig. 3D, E).

This distinctive species appears to extend throughout the Indo-West Pacific oceans (Gosliner et al. 2008). Cyerce bourbonica sp. n. has also been discussed on the Sea Slug Forum based on photographs from Japan, La Réunion, and possibly Hawaii (http://www.seaslugforum.net/find/cyersp3). It is recorded frequently from La Réunion but only from two localities. Cyerce bourbonica sp. n. is clearly distinguishable from the named species of Cyerce previously recorded from the western Indian Ocean, all three species of which are recorded from Mayotte and/or La Réunion (http://seaslugs.free.fr/nudibranche/a_intro.htm). Cyerce elegans Bergh, 1870, is translucent cream to beige (sometimes red) with rounded swollen cerata. The edges of the cerata glisten with faint iridescent scalloped markings and there is usually a blue spot at the base of each. Cyerce pavonina Bergh, 1888, has curved swollen cerata covered in pustules on both surfaces and is pale greenish brown in colour, and the outer and inner surfaces of the cerata differ in colour. Cyerce nigricans (Pease, 1866) is black and has golden spots and a red band on the cerata.

The species is named ‘bourbonica’ after the original name of the island of La Réunion, the type locality. The island was renamed La Réunion in 1793 after the fall of the House of Bourbon (Spain and Luxembourg currently have Bourbon monarchs), but the name was changed back and forth several times until the French revolution in 1848.

Seychelles: 20 × 5 mm (PK-HH, “10 mm when parapodia are opened”), Whale Rock, on coral rubble, 26 April 1992, leg. P Kemp; numerous photographs from La Réunion, Mauritius, and Mayotte http://seaslugs.free.fr/nudibranche/a_intro.htm.

Body pale green with ocellated black spots and orange patches along edges of parapodia where they were thrown into three permanent folds. Rhinophores marbled green with white pigment dorsally, creamy orange submarginal band, and white distal end. Oral tentacles tipped with white.

The single specimen is well preserved, with the parapodia opened completely. Dorsally, there are large black ovate spots (oval along the horizontal axis) on inner surfaces of parapodia and body. Edges of parapodia scalloped in three places, containing opaque white granular pigment spots along the margin (Fig. 4A), presumably the orange marginal pigment in life. The pericardium is elongated, triangular anteriorly and squared posteriorly, with only two un-branched vessels posteriorly. Ventrally, the foot and head are bilobed; there are fewer smaller spots on the foot and more larger spots on the outer surfaces of the parapodia (Fig. 4B).

This species is recognisable, as evidenced by the internet discussions (http://www.seaslugforum.net/find/elyssp11) and is most probably Pease’s species, described from Tahiti. The many photographs on the internet show slight variations only, and it is remarkable that it has not been recorded before. This is not only the first record for the Indian Ocean, but the first published record since the species was described in 1861. Another specimen measuring 40 mm from Madagascar is lodged in the Natural History Museum, London (NHMUK 20010521, leg. Lindsey Warren) but was not examined by this author.

Kenya: 25 × 11 mm preserved, Vipingo, 25 miles N of Mombasa, rock pool ELW, 23 September 1984, leg. J Hognerud. – Maldives: 9 mm in length (MDV/AB/96/7, specimen disintegrated, no radula located), Fulidhoo Lagoon, Felidhoo Atoll, 10 m depth on sand, 04 May 1996, leg. RC Anderson & SG Buttress. – Zanzibar: 14 × 8 mm preserved, Matemwe Lagoon, in Xenia sp. and sand near encrusted, partly submerged rock with Didemnum molle and Halimeda sp., 01 March 1995, leg. MD Richmond. – Seychelles: 30 × 10 mm alive (PK-A, one of four individuals preserved), Source d’Argent, La Digue, 1 m depth on broken Acropora sp. behind reef in algal growth, 26 January 1992, leg. P Kemp. – La Réunion and Mayotte: photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Plakobranchus ocellatus has been recorded in excess of 35 mm in the Indian Ocean (Rao 1962). The western Indian Ocean specimens examined here conform to the description of Red Sea specimens (Yonow 1990, 2008). Jensen (1992) listed numerous synonyms from the Pacific Ocean, stating that colour pattern and distribution of ocelli are variable in just a single species; however, in 2006 she suggested, “It is possible that a complex of sibling species is involved.”

In the Marshall Islands, an interesting commensal association was observed between Plakobranchus ocellatus and the sea cucumber Holothuria atra (Mercier and Hamel 2005); this is the first report of an opisthobranch occurring on an echinoderm species. The authors provide evidence of a real association between the two animals through a set of well-designed experiments and natural observations. In the Indian Ocean Holothuria atra is also a common species, with a similar habitat to Plakobranchus ocellatus, but there are no observations of a similar association.

Seychelles: 15 × 5 mm (PK-P, “stripy black/mauve rhinophores and body, scattered blue spots, orange line edging parapodia”), Lilôt, NW Mahé, 7 m depth on underside of rock, 25 March 1992, leg. P Kemp; 25 × 5 mm (PK-W, “striations along parapodia but with white edge with orange line, vivid blue spots, rhinophores white with longitudinal stripes and brown orange at tips, orange under mouth”), Lilôt, NW Mahé, 20 m depth under rock, 09 April 1992, leg. P Kemp; photo of one individual, Lilôt, NW Mahé, 1988-1989, P Kemp. – Maldives: three pres. specimens 6 mm, 7 mm, and 12 mm. (MDV/AB/96/10), Miyaru Kandhu, Felidhoo Atoll, 05 May 1996, leg. RC Anderson & SG Buttress; 15 mm (MDV/AB/96/12; badly preserved, no radula found), Fulidhoo Channel, Felidhoo Atoll, 10 m on algae, 07 May 1996, leg. RC Anderson & SG Buttress; photos of two individuals, 1986-1994, J Hinterkircher.

Several colour forms exist in the Indo-West Pacific under the names of bayeri Er. Marcus (1975) and ratna Er. Marcus (1975). Ernst Marcus (1975) named these two species in the same publication based on specimens from the Marshall and Palau Islands: his species were differentiated by the presence or absence of blue spots and the shapes of the radular teeth. As noted in the review by Gosliner (1995), the numerous photographs now available show an overlap in colour pattern; morphologically he thought they had very little to distinguish between them and synonymised ratna with bayeri. The pericardia of bayeri appear to be simpler than those of ratna, but Risbec does not describe or illustrate it for gracilis. The pericardia of these three specimens are illustrated for information, and are clearly variable (Fig. 5). The sizes of the teeth are also variable, with the range of the teeth of bayeri being slightly larger than that of ratna (measured from Jensen 1992 and Gosliner 1995). The form with blue spots is the more common in the Indian Ocean, although the form with orange margins is the only one recorded in Mayotte (http://seaslugs.free.fr/nudibranche/a_intro.htm). All the specimens listed above from the Maldives and the Seychelles had bright blue spots in life (Plate 18), and the Seychelles animals additionally had orange margins (Plate 19).

Thuridilla gracilis (Risbec) was mentioned in a discussion of a new species as being impossible to re-identify (Gosliner 1995), but later, Gosliner (2001) appears to have reconsidered, comparing splendens (Baba) with gracilis, both species having dark brown to black bodies with cream longitudinal lines and reflective blue pigment spots which may be absent in gracilis, and subsequently retaining gracilis as a valid species (Gosliner et al. 2008). Risbec’s drawing and description of a 20 mm specimen from New Caledonia is clearly within the cline between bayeri and ratna in having dark and light green lines on the body and orange tips to the rhinophores, parapodial margins, and oral tentacles. Photographs of many individuals from the type locality, New Caledonia, demonstrate that the specimens occurring at the type locality are well within the extremes shown by bayeri and ratna (Hervé 2010 and pers. comm.). Risbec’s species is here determined as both recognisable and valid, and the name Thuridilla gracilis should take precedence.

Maldives: approx. 10 mm alive (3 mm pres.), Coral Garden on filamentous green algae, Vadhoo Reef, South Malé Atoll, 5 m depth, 14 October 1994, leg. RC Anderson & SG Buttress; specimen disintegrated (no radula found), 7 mm alive, Bathala Island reef, Ari Atoll, 8 m depth, 28 July 1995, leg. SG Buttress & RC Anderson (“colour dark with pale streaks, rhinophores appeared white with red tips”). – La Réunion and Mayotte: numerous individuals 10-15 mm in length http://seaslugs.free.fr/nudibranche/a_intro.htm.

Ground colour grey with hint of purple, covered with yellow spots and pustules, and round black dots. Marginal bands of the parapodia creamy yellow. Head white, forming X-shape into rhinophores anteriorly and body posteriorly; remainder of head and anterior part of body grey-black. Red-orange band at tip of each rhinophore, a distinctive character of the species; in this specimen, the rhinophores were faintly spotted with creamy yellow.

Preserved specimen semi-translucent with no pigment remaining except black spots on body. Parapodia folded over body and frontal margin bilobed (Fig. 6A). Pericardium unusual in Thuridilla vataae in that lateral and posterior vessels are connected. In this specimen, they appear to form a partial ring around the pericardium (Fig. 6A). Ventrally, foot and frontal margin both cleft in preserved specimen (Fig. 6B).

Thuridilla vataae is a small species recorded sporadically from the Indo-West Pacific. Risbec (1928) almost certainly named this species after the bay south of Nouméa, Baie de l’Anse Vata, of which the north-western tip is the collection locality of his single specimen, Rocher à la Voile. The suffix for commemoratives in this case is -ae, hence the spelling vataae. The original spelling is correct and should be maintained.

Maldives, two specimens, both 35 mm (MDV/AB/96/4), Fulidhoo Channel, Felidhoo Atoll, 9 m depth, 02 May 1996, leg. RC Anderson & SG Buttress; 32 mm (MDV/AB/96/14), Fulidhoo Channel, Felidhoo Atoll, 07 May 1996, leg. RC Anderson & SG Buttress; photo of individual, Maaya Tila, Ari Atoll, 6-8 m depth, March 1994, H Voigtmann.

Easily recognised by velvety black body, large orange pustules edged with green especially along frontal margin, black and orange rhinophores, and green gills. The differences between Nembrotha guttata and Nembrotha cristata Bergh are clearly visible in Plate 21. Nembrotha cristata has been previously recorded from the Indian Ocean, but only in the Maldives (Yonow 1994). A third black and pustulose species known from the region is Nembrotha kubaryana, recorded from Mauritius (Yonow and Hayward 1991): it has green pustules but orange gills and rhinophores.

Nembrotha guttata appears to be endemic to the Maldive islands; paler and consistently differently coloured species are recorded from the Philippines (Pola et al. 2008), Indonesia, Australia, Japan (Gosliner et al. 2008) and New Caledonia (Hervé 2010) but need further investigation. Colour patterns appear to be the best physical characters differentiating species of Nembrotha, and the brownish-red spotted pattern with white gills and white pigment between and on the rhinophores currently included in Nembrotha guttata is consistent in pattern and colour; it occurs only in the western Pacific Ocean and is most probably a distinct species.

Maldives: 8 mm (6 mm pres.), Fulidhoo Channel, Felidhoo Atoll, 12 m depth, 24 July 1994, leg. RC Anderson & SG Buttress; photographs of two individuals 12 mm and 20 mm, March 1999, J Hinterkircher. – Tanzania: photographs of a single individual, M’Nazi Bay, Msimbati, near Mtwara, May 1994, IM Horsfall. – La Réunion: several individuals photographed up to 18 mm in length (http://seaslugs.free.fr/nudibranche/a_intro.htm).

Maldives: 11 mm (6 × 2 mm pres.), Old Shark Point, Thilafalhu reef, south end of North Malé Atoll, 10 m depth, 14 August 1995, leg. RC Anderson & SG Buttress.

Animal dark to medium green with some relatively large white spots. Tail extremely long, almost half body length, and body appears to have been smooth. Five small multi-pinnate gills beige with purple tips; rhinophores beige suffused with purple; margins of rhinophore sheaths pale yellow. Flattened oral tentacles visible when crawling.

The preserved specimen is well relaxed: body light blue-green, gills and rhinophores white, rhinophores with 12 lamellae. Marshall and Willan (1990) state that there is no rhinophoral sheath; none is visible on the specimen but the rim of the right rhinophore is visible in Plate 23 where it catches the light. Baba (1967) described and illustrated the genital opening just below the right rhinophore whereas Pola et al. (2006) located it halfway between the gills and the rhinophore; in this specimen, an orange puckered pore also occurs halfway. The collectors noted that the animal laid a light pink spiral egg mass 4 mm in diameter its second night in captivity; it has barely more than three complete whorls laid close together (Plate 23).

Tambja amakusana is recorded for the first time from the Indian Ocean; all literature records to date are listed in the synonymy. The only similarly small species with purple tips to the gills and rhinophores is Tambja limaciformis (Eliot), but this species is usually brick to orange red, with many more white spots, occurring throughout the tropical Indo-West Pacific (e.g. Yonow 2008).

Mauritius: 22 × 8 × 10 mm, Japan Wreck, 25 m depth, 04 March 1990, leg. H Debelius and (poor) photograph of two mating individuals; photographs of three individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Preserved specimen translucent but retains blue pigment in creases on tail, gills, and rhinophores. The species was previously recorded from Mauritius by the author, and appears to be an infrequently encountered species in the western Indian Ocean (see NudiPixel for three records from India, Kenya, and Madagascar).

Maldives: 40 mm (35 × 7 mm pres.), Banana Reef, North Malé Atoll, 10 m depth on yellow sponge, night dive, 28 August 1993, leg. RC Anderson & SG Buttress; one individual photographed/described but not preserved, 63 mm (MDV/AB/96/16), Fulidhoo Channel, Felidhoo Atoll, 10 m depth on bare coral rock, 08 May 1996, RC Anderson & SG Buttress; photographs of one individual, 1986-1994, J Hinterkircher.

This dark colour form of Notodoris gardineri appears to be endemic to the Maldives island group (only one photo from more than 50 available on http://www.nudipixel.net/species/aegires_gardineri/ for example). Otherwise, Notodoris gardineri is common in and restricted to the Pacific, with no records from the western Indian Ocean other than form nigerrima from the Maldives.

Socotra: 40 × 13 mm preserved (IT-157, RJ-011), 12°18.698'N, 53°48.285'E, 09 April 1999, leg. R Janssen. – Tanzania: photographs of two individuals, Mafia Island, shallow water, May 2009, A de Villiers. – La Réunion, Rodriguez, and Mauritius: several individuals photographed http://seaslugs.free.fr/nudibranche/a_intro.htm. – Seychelles: one photographed individual, Lilôt, NW Mahé, 1988-1989, P Kemp.

Socotra: 55 mm pres. length (WPU Rostock, MAR 85, RC-N57), Hadibo, late 1980s, leg. W Wranik. – Yemen: 85 × 60 mm pres., distorted and flattened (WPU Rostock, MAR 85, RC-N16), Al Mukalla, late 1980s, leg. W Wranik. – Kenya: two specimens 60 and 95 mm in length, pres., Vipingo, 25 m N of Mombasa, ELW in rock pools on exposed reef, 23 September 1984, leg. J Hognerud. – Tanzania: photographs of one individual, M’Nazi Bay, Msimbati, near Mtwara, May 1994, IM Horsfall. – Maldives: one juvenile specimen 13 mm (MDV/AB/96/17), Yacht Tila, South Malé Atoll, 25 m depth, 09 May 1996, leg. RC Anderson & SG Buttress; photos of 15 mm juvenile individual, 1986-1994, J Hinterkircher. – La Réunion, Mauritius, Mayotte: photographs of numerous individuals, including juveniles similar to the Maldives specimen examined here (http://seaslugs.free.fr/nudibranche/a_intro.htm) and slides of 27 individuals varying from yellow to mottled pink, M Parmantier. – Seychelles: photos of several individuals including juvenile and sub-adult, Lilôt, NW Mahé, 1988-1989, P Kemp. – Sri Lanka: photographs of one large individual, Unawatuna, S of Galle, on sediment-covered rock, 27 December 2011, S Kahlbrock.

The large specimens and individuals were of the typical Indo-West Pacific colour pattern, blotchy red and cream, especially along the margins. The 13 mm juvenile specimen from the Maldives illustrated here (Plate 26) is well relaxed, and the six gills can be seen to insert into separate openings. The oral tentacles are large rounded lobes, clearly the precursors to the lappets of the adult: these tentacles are huge in comparison to those of a chromodorid (or dorid) of similar size. The rhinophores have 13 lamellae; note that the white edges present in the adults have not yet developed. Another 15 mm juvenile individual was identical in colour pattern, while a slightly larger animal from the Seychelles demonstrated the developing adult colour pattern already had white edges to the 17+ rhinophore lamellae (Plate 27).

The radular formulae of the larger specimens are tabulated below: the sizes listed are of the same dimension of a large lateral tooth – from the tip of the cusp to the flange where the cusp meets the base. There is no relationship between the radular formula and maximum tooth size, nor are they correlated with preserved animal size. A giant Hong Kong specimen is included for comparison, and has the largest teeth but not the largest radula. It had a bubbly texture and was pinkish yellow in life (M Collard pers. comm.; specimen, radula, notes and photographs lodged in the Natural History Museum, London: NHMUK acc. no. 2337 with the “Red Sea Giant”).

Socotra 55 mm pres. 41 × 64.0.64 500 μm

Yemen 85 mm pres. 53 × 93-83.0.83-93 550 μm

Kenya 90 mm pres. 47 × 77.0.77 700 μm

Kenya 95 mm pres. 46 × 79.0.79 450 μm

Hong Kong 190 mm pres. 51 × 67.0.67 800 μm

Yonow (2001) suggested that the uniformly red species in the Red Sea should be assigned to Hexabranchus sanguineus (Rüppell & Leuckart), and that it was distinct from the widespread Indo-Pacific Hexabranchus marginatus (Quoy & Gaimard). The study mentioned in that paper was never published, since the following year a paper analyzing the same problem was published by Valdés (2002): Valdés examined material from the western Indian Ocean and the Pacific, but no Red Sea specimens were included in his analysis, nor were any ‘giants’ but, despite this, he concluded that all Indo-Pacific species were the same, and that only the Caribbean species Hexabranchus morsomus Ev. Marcus & Er. Marcus was distinct.

Zanzibar: 30 mm pres., Matemwe, in sponge, lagoon on east coast, 01 March 1995, leg. MD Richmond. – La Réunion: photographs of one individual, 1990s, M Jay, pers. comm. and http://seaslugs.free.fr/nudibranche/a_intro.htm.

Numerous photographs of living specimen depict an oblong animal slightly broader posteriorly, with pinkish beige gill clump spanning width of animal. Darker central patch extended from just in front of rhinophores to gills, very dark brown where the tubercles were not ringed by white but lighter along the midline where seven large and numerous small tubercles were ringed in white. Many tubercles “frosted” with white pigment, which appears to be a characteristic of living specimens of Hoplodoris grandiflora. Remainder of mantle consisted of paler band of beige tubercles outlined in white; extended white areas formed patches perpendicular to the margin.

Dorsally the preserved specimen still bears distinct hard beige and brown tubercles. The central ones are the largest, and tubercles decrease in size towards the margins. The six gills are multipinnate, and the sheath is scalloped. The rhinophores extend from a raised irregular sheath bearing pinkish beige tubercles. The ventral surfaces of both sole and hyponotum are creamy beige with light brown pigment in the creases, lighter than dorsal tubercles (Fig. 7A). There are small pustules covering the hyponotum but not the sole. The foot is bilaminate for the entire anterior margin extending laterally for a short distance down each side, both laminae are notched, and the oral tentacles are triangular (Fig. 7B).

The radula of the 30 mm preserved specimen has the formula 38-39 × 107.0.107. The first lateral on each side has a long base and a short triangular cusp with a small denticle on each side (Fig. 7C). The remaining teeth have an equally long base with a small flange, but the cusp increases in length (Fig. 7D) and develops serrations along the side (Fig. 7E). The last two or three teeth in each row are very reduced (Fig. 7F).

This species has a widespread distribution in the western Indian Ocean, the Red Sea (Yonow 2008), and the western Pacific (Fahey and Gosliner 2003).

Zanzibar: 10 × 5 mm pres., leg. MD Richmond (California Academy of Sciences, CASIZ 169953). – Kenya: photographs of two individuals, Malindi National Park & Watamu National Park, 5-8 m depth, MD Richmond. – La Réunion, Mauritius, and Mayotte: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Body colour translucent white, yellow to orange-yellow ridges, and several dark spots anteriorly and posteriorly near mantle edge. Foot translucent white with at least one black spot near tip and broad pale yellow margin. Rhinophores long, translucent white with one dark brown spot on stalk; yellow on proximal third, dark brown on distal two-thirds of lamellate portion, white on elongated tip. Six gills white with black band across inner side of each rachis from base to tips of pinnules.

This small species was first recognised by Yonow and Hayward (1991), based upon specimens collected from Mauritius and La Réunion, the type locality. Three specimens from Western Australia (Fahey and Gosliner 2001) extend the range of this species to the eastern Indian Ocean.

Sri Lanka: three pres. specimens 9 × 5 mm, 17 × 10 mm, 20 × 12 mm, and two pres. curled 15 × 10 mm, 15 × 8 mm, Unawatuna, S of Galle, 27-30 December 2010, leg. S Kahlbrock.

The photographs accompanying these five specimens from the type locality are all clearly of the same species: body semi-translucent white with numerous yellow-capped tubercles and few round black spots, tubercles in some specimens arranged in lines approximating ridges of other species of Halgerda. Rhinophores long, tapering; long translucent stalk with black pigment on its posterior surface continuing to lamellate portion, which was black with black knob at tip. First 4-6 lamellae yellow on anterior face and remaining 20-24 lamellae black on all sides. Black spot always present at base of rhinophoral sheath posteriorly in line with black line on stalk, often another black spot laterally or anteriorly. At least one yellow tubercle on rhinophoral pocket rim. The gills distinctive in this species with only four gill branches. Anterior two gills larger than posterior two, inner rachides marked with brown-black line. The anal papilla protruded in some photographs of living specimens, and was identical to Farran’s description of “rather long and tubular, white with a black crenulated margin.”

The preserved specimens are firm, grey-white with pale yellow spots on low tubercles in all but one specimen, which has pale orange spots. All specimens have round black spots. The rhinophoral pockets have a posterior black spot on the rim extending to the mantle on all specimens and an anterior black spot in four specimens. There are black spots on the top of the metapodium, which also has an orange spot at the tip fading into a line along the middle. The branchial pocket is faintly tuberculate and there is always a large round or oval black spot placed anteriorly on the mantle in each specimen, also visible in Plate 30. The gills, retain their black and white markings. The hyponotum is narrow with a few small spots. There are larger spots on the sides of the foot but the sole is bare. The head is reduced, and the mouth is visible with very small rounded tentacles (Fig. 8).

This appears to be the first record in the scientific literature of this species since its description. It was originally described from Sri Lanka, and most photographic records are from the type locality, with a few from Thailand and Burma to the east (NudiPixel and Sea Slug Forum). The species described as Halgerda punctata by Rudman (1978) and Gosliner (1987) were re-identified as Halgerda formosa by Fahey and Gosliner (1999), so it appears no one has found or redescribed Farran’s species.

Kenya: two specimens 15 × 15 mm and 9 × 5 mm, Vipingo, 25 miles N of Mombasa, rock pools at ELW, 23 September 1984, leg. J Hognerud (California Academy of Sciences CASIZ 169945). – Tanzania: photograph of single individual, Mafia Island, shallow water, May 2009, A de Villiers. – Maldives: two specimens 15 mm and 25 mm (MDV/AB/96/11), Foteo Channel, Felidhoo Atoll, 15 m depth, 05 May 1996, leg. RC Anderson & SG Buttress (California Academy of Sciences CASIZ 169996); photos of two individuals, 1986-1994, J Hinterkircher. – Mayotte: photographs of two individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. – Seychelles: photos of two individuals, Lilôt, NW Mahé, 1988-1989, P Kemp.

Easily recognised by pattern of orange ridges enclosing brown depressions speckled with white. Both specimens from Kenya were examined when they were received in 1984: the 15 mm specimen was still yellow-orange, as was the foot; the brown reticulated pattern also remained. Very few spots were present on hyponotum but between the hyponotum and foot, there was a band of brown dots/patches. The smaller specimen retained an orange edge to the mantle and the foot: the dorsum was yellow-orange with the brown pattern remaining; there were more spots on the hyponotum than in the larger animal, and there were spots and patches present in a band between the hyponotum and the foot. The preserved Maldives specimens were also clearly recognizable several years after collection, with the brown reticulated pattern remaining between the ridges as well as the brown spots scattered on the hyponotum.

Halgerda tessellata has a wide Indo-Pacific distribution although, like some species with such a large range, it has a consistently different colour form in the Pacific: a band of white dots is present around the margin and there is dense white pigmentation on the gills (Carlson and Hoff 1993; Yonow in prep.).

Sri Lanka: 13 × 6 mm pres., Unawatuna, S of Galle, SW coast, 28 December 2010, leg. S Kahlbrock. – Gulf of Oman: photos of two individuals, Muscat, Oman, 01-12 April 2009, S Kahlbrock. – La Réunion and Mayotte http://seaslugs.free.fr/nudibranche/a_intro.htm.

The collected specimen was deep yellow in life with a white foot, long white rhinophores, and five white pinnate gills. The tubercles were elongated, and some were rounded whilst others were somewhat pointed; they were yellow basally and pink-red distally.

The specimen is well preserved, with some yellow remaining on the dorsum several months after collection. There is a tubercle in front of and behind each rhinophore, and three tubercles located just in front of the gill pocket. The spicules on the dorsum and in the tubercles are visible, as are the yellow tubercle bases; the distal parts are now white. Ventrally the hyponotum has an orange submarginal band and the submarginal bands of mantle glands are visible. The foot is deeply divided anteriorly, and the oral tentacles are so contracted as to be non-existent (Fig. 9).

This appears to be only the third record of Cadlinella ornatissima in the scientific literature from the Indian Ocean, in addition to photographic records from the Gulf of Eilat (Yonow 2008).

Zanzibar: 36 × 34 mm pres., in Sargassum off reef crest, Matemwe Lagoon, 01 March 1995, leg. MD Richmond (examined 1995: dorsum cream with rusty/orange-brown patches and pigment in creases, knobbly; rhinophores very close together, located far anteriorly; gills located far posteriorly, pocket with six lappets; ventrally with bright rusty ‘rings’ of pigment on hyponotum) (examined 1998: no pigment left except faint marks in creases and tucked-in gills; rings still bright on hyponotum). – Tanzania: photograph of two individuals, Mafia Island, shallow water, 31 December 2003 and 16 October 2005, A de Villiers. – Maldives: 65 mm (47 × 44 mm preserved, MDV/AB/96/19), 13 m depth, Yacht Tila, South Malé Atoll, 09 May 1996 (examined 1998: very well extended, very soft, completely bleached: no marks or colour left; morphology of foot, oral tentacles, and dorsum as above), leg. RC Anderson & SG Buttress. – La Réunion: photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Recognised by its oval shape with scalloped margin, and blurred green, beige, and blue colour pattern. Ventrally, green reticulations and ocelli located in junction between foot and mantle are distinctive. Widespread if infrequently recorded in the tropical Indo-West Pacific.

Kenya: 25 mm in length, preserved, Vipingo, 25 m N of Mombasa, ELW in rock pools on exposed reef, 23 September 1984, leg. J Hognerud (Australian Museum, Sydney, C431128). – Madagascar: 50 × 20 mm (PK-F), Ampangorina, Nosy Komba, 3 m depth in live Acropora, 02 March 1992, leg. and photos P Kemp; photographs of two individuals, Nosy Bé, October 2007, J Hinterkircher. – Tanzania: photographs of two individuals 1994 and Pegasus Wreck, 10 m depth, March 1995, MD Richmond; photographs of two individuals, M’Nazi Bay, Msimbati, near Mtwara, May 1994 and May 1995, IM Horsfall.

A large species, growing to 80 mm in length. Ground colour black, two thick or thin white lines running length of dorsum and joined behind gills forming a loop, not extending to pale orange mantle border anteriorly or posteriorly in any of these specimens but may do so anteriorly in the species. Broad, somewhat crumpled, pale orange tending-to-yellow mantle skirt, separated from the black dorsum by a broad white line. No white line at the margin, visible on the preserved specimen from Madagascar which retains its black, white, and orange bands fifteen years after collection. Gills and rhinophores darker orange than border, arising from pockets with raised orange rims. This species has been recorded from the Red Sea and south along the East African coast only (Yonow 2008); surprisingly, it is not recorded from the Gulfs of Aden or Oman, which show close faunal affinities with the Red Sea.

Persian Gulf: photograph of one individual, Dahwat ad Daffi, Jubail, Saudi Arabia, April 1992, F Krupp; photographs of numerous individuals, 2000-2011, GT Smith; photos of several individuals, Qaruh Island, Kuwait, 2008-2011, M Nithyandanan. – Gulf of Oman: photos of two individuals, Muscat, Oman, 01-12 April 2009, S Kahlbrock; photographs of one individual less than 10 mm, Inchcape 2 (a ship wreck), 20 m depth, 08 January 2010, GT Smith; two individuals, approx. 15 mm, Sharm Rock, 09 January 2010, GT Smith. – Mayotte and La Réunion: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Easily recognised, not to be confused with any other species found in the western Indian Ocean and Red Sea. Large and fleshy with raised, medium-sized bright orange pustules, deep purple rings around rhinophores and gills joined by broken line in the Dahwat ad Daffi individual and the majority of photographs of individuals from the Persian Gulf (Plate 34). In the Gulf, the purple rings are not perfect as in the Red Sea, presenting with gaps, dots, dashes, and extra markings (Plate 35). Mantle margin is of the same purple pigment, foot without purple margin but does have few orange spots on its upper surface; rhinophores and gills purple.

Chromodoris annulata is known from the Red Sea (Yonow 2008) and the east African coastline to South Africa, and is recorded from the Persian Gulf, the Gulf of Oman, La Réunion, and Mayotte for the first time.

Maldives: 30 mm, Bathala Island, Ari Atoll, 28 July 1995, 10 m depth, leg. RC Anderson & SG Buttress (“colour duller and darker than usual”); photographs of several individuals incl. one 5 mm juvenile, March 1997, March 1998, March 1999, J Hinterkircher. – Tanzania: photo of one individual, Mafia Island, shallow water, May 2009, A de Villiers.

Pale blue body with three black lines, black sub-marginal line forming a ring, paler blue to white margin; white and orange rhinophores and six gills with distinctive black marks at base on both sides. There may be a general orange wash dorsally. Recent published records of Chromodoris boucheti are only from the Maldive Islands and Mayotte: Chromodoris boucheti was not found in the Chagos archipelago despite similar sampling techniques, nor has it been recorded from Mauritius, and there is only one record from La Réunion (http://seaslugs.free.fr/nudibranche/a_intro.htm). However, photographs on websites show individuals from Kenya, Tanzania, and South Africa, and this extended distribution is supported by a photograph from Mafia Island, Tanzania (A de Villiers, pers. comm.).

La Réunion: 60 mm (25 × 15 mm pres., #1), Bassin des Hirondelles, St. Gilles les Bains, 05 November 2006, 1-2 m depth, leg. P Bidgrain; 76 mm (37 × 20 mm pres., #2), Bassin des Hirondelles, St. Gilles les Bains, 17 September 2009, 1-2 m depth, leg. P Bidgrain; 75 mm (34 × 17 mm pres., #3), Bassin des Hirondelles, St. Gilles les Bains, 17 September 2009, 1-2 m depth, leg. P Bidgrain [all in permanent shallow pool on granite coast]; numerous photographs as Chromodoris cf. geminus on http://seaslugs.free.fr/nudibranche/a_intro.htm. – Sri Lanka: photographs of two individuals, Unawatuna, S of Galle and Negombo, N of Colombo, 30 December 2010 and 12 January 2011, S Kahlbrock.

The three specimens are well preserved, accompanied by 10-20 photographs each. They were all similar in life, with an ochre dorsum extending towards a white band around the edge of the mantle; the purple margin normally present in the species was lacking in all three. The first specimen (60 mm) was rusty orange, deeper along central dorsum and fading toward edge; creamy white band along margin but no purple edge. Some photographs are of the hyponotum as the animal flapped its margin, and there was no purple crescent or line ventrally. Six large wine-red patches with white annulus outside and white speckles inside. Around edge of rust-coloured area was a ring of small round wine red spots, each also with white ring. Rhinophores white, distal part of frontal surfaces and tips purple: 35 lamellae on right rhinophore, very faint purple wash at tips remaining on preserved specimen. 25 pinnate gills arranged with two ends of an arc spiralling inwards: each is triangular, flat surface white and translucent pinnae on other two surfaces. Both branchial and rhinophoral pockets slightly raised, orange in life. Foot and digitate oral tentacles white, but upper lamina of foot very faintly purple; no spots ventrally.

Specimen 2 (76 mm) was deeper orange in life, with more brown centrally and more yellow-orange marginally than specimen 1; faint submarginal band of yellow-orange before white margin. 13 large brown-red spots encircled with white, few smaller ones arranged irregularly around central patch. Additionally, this specimen had some white patches outside and amongst the small spots. 22 gills all had purple tips; rhinophores had more extensive purple pigment than those of specimen 1. Foot yellow-orange posteriorly followed by white band around margin. Ventrally foot bilaminate for its entire anterior margin (Fig. 10A). This specimen was dissected to remove the radula: body wall of foot thick and rose-red internally, digestive gland dark brown-pink while buccal mass white with pink tint. Muscles were very strong, glistening pink; reproductive system opaque white. The radula is large, but the teeth are minute: the largest laterals measure 100 μm (Fig. 10C). The formula is 58 (+2) × 56.1.56. There is a much reduced median thickening in some of the older rows (Fig. 10D). The first lateral bears a small rounded denticle on each side of a sharp cusp. The next 12 laterals have 10-12 weak denticles along the cusp (Fig. 10D). The remaining teeth are simply hook-shaped, blunt and rounded at the old end of the radula (Fig. 10E) but with extremely long sharp cusps at the newer end. Most of the jaw elements are simple unicuspid structures, with a single slightly curved cusp; very few are bicuspid.

Specimen 3 (75 mm) was dark like specimen 2, with 19 gills tipped in purple; rhinophores dark violet, with many closely spaced lamellae (Plate 37). Orange raised rhinophoral pocket rims can be seen in the plate. Ventrally, top of foot white with dark spots, violet margin on upper lamina of foot, white oral tentacles; orange-yellow marking posteriorly but no purple margin; faint orange line in crease between hyponotum and foot. Conical oral tentacles of preserved specimen visible in Fig. 10B, although left one is difficult to see. Margin of anterior foot distinctive, with the two laminae quite separated and extending across entire margin.

Many photographs of additional individuals from La Réunion as well as those from Sri Lanka (Plate 38) clearly belong to the same species. Variations range from large to small spots with solid to diffuse pigmentation, wine-red to almost black-red in colour, all with white ocelli; the presence or absence of smaller spots with a very broad to ‘normal’ white marginal band; a violet margin is very rarely present in the La Réunion individuals but present on the Sri Lanka individuals. Ventrally, there is also some variability, from pure white to having a (faint or dark) rusty orange line along the crease between the foot and the hyponotum, from no spots to few spots on the foot below this line, and there may or may not be an orange patch on the tail. The Sri Lanka individuals had a very faint purple line on the foot margin.

The specimens are all distinctive in preservative, either alcohol or formaldehyde: they are violet-purple to plum red-violet, and all have a thick undulating mantle skirt (including that from Chagos, see Yonow et al. 2002: 854). The gills spiral inwards at their ends and are triangular in section, with lamellae on two sides. The foot is broad anteriorly. No mantle glands are visible in any of the specimens.

Rudman (1987) initially synonymised Eliot’s species Chromodoris cavae with Kelaart’s Chromodoris tennentana (p. 44) but subsequently separated them into two species (http://www.seaslugforum.net/showall/chrotenn). Gosliner et al. (2008) retain this species as distinct from both Chromodoris tennentana and Chromodoris leopardus. Willan, based on 21 photographs on NudiPixel (http://www.nudipixel.net/species/chromodoris_tennentana/) decided that all variations belong to one species which is simply very variable from the western Indian Ocean to the West Pacific. However, the preserved specimens (including the one from Chagos, Yonow et al. 2002) are violet when preserved while all preserved tennentana (p. 44 and Yonow et al. 2002: 845) and leopardus (Yonow 2001: 23) are translucent. The gills in tennentana are flattened and simply pinnate (see p. 44) or sub-quadrangular (Rudman 1987: 364) while the gills of leopardus are triangular (Rudman 1987: 388); the gills of cavae are triangular. The gills and rhinophores of tennentana are coloured ochre with white tips, those of leopardus are tipped in violet (the gills rarely have an ochre rachis), and those of cavae are violet or tipped with violet. No mantle glands are visible in the preserved specimens of cavae, whereas they are obvious in tennentana (p. 44 and Fig. 11) and form a band around the mantle in leopardus (Rudman 1987).

Comparison of the radulae of tennentana, vicina, leopardus, cf. leopardus, and one La Réunion specimen show only slight variations in morphology but large differences in tooth size; the sizes listed are of the same dimension of a lateral tooth – from the tip of the cusp to the flange where the cusp meets the base.

20 mm alive (Rudman, tennentana) 40(+2) × 37.0.37 40 µm

36 mm alive (Edmunds, vicina = tennentana) 52 × 49.1.49 60 µm

59 mm alive (Rudman, leopardus) 74(+2) × 61.0.61 90 µm

34 mm alive (Yonow et al., cf. leopardus = cavae) 52 × 62.1.62 25 µm

80 mm alive (this paper, cavae) 58(+2) × 56.1.56 100µm

The three specimens examined from La Réunion belong to a form of Chromodoris cavae in which the violet mantle margin is lacking; of the additional photographs of a further 25 individuals from La Réunion and Mauritius (P Bidgrain, pers. comm., H. Flodrops, pers. comm., and http://seaslugs.free.fr/nudibranche/a_intro.htm) all but one individual lack the violet margin on both the mantle and the foot. The Chagos specimens both had a pale purple margin to the mantle (Yonow et al. 2002) as did the individuals from Sri Lanka (Plate 38). Chromodoris cavae differs from both Chromodoris tennentana and Chromodoris leopardus in numerous features, all discussed above, and it is here removed from the synonymy of Chromodoris tennentana. Chromodoris cavae is recorded from Chagos, Sri Lanka, La Réunion, Zanzibar, and South Africa, indicating a western Indian Ocean distribution.

Seychelles: 20 × 7 mm (PK-Z), 5 m depth under rock, off Ade’s house, Lilôt, NW Mahé, 10 April 1992, leg. P Kemp (specimen retains orange gills and rhinophores, examined 2009) and photos of one larger individual, P Kemp. – La Réunion and Mayotte: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

It is exciting to be recording this species once more; there is one other published record from South Africa as Chromodoris geometrica (Gosliner 1987), and many photographs from La Réunion and Mayotte (http://seaslugs.free.fr/nudibranche/a_intro.htm), where it has been observed growing to 40 mm and spawning. This species displays ontogenetic changes: larger specimens are very irregularly pustulose, and the symmetrical violet markings around the large, regularly distributed, creamy yellow pustules of the juveniles (Plate 39) are sometimes reduced to just short dashes on each side in the large animals (Plate 40). In the larger specimens, the anterior ventral violet crescent of the smaller animals becomes a fiery orange-red (Plate 40). Most internet records are from the western Indian Ocean; a couple of photographs from west Thailand need confirmation (NudiPixel and Sea Slug Forum).

Maldives: 10 mm (8 × 3 mm pres.), 12 m depth, Banana Reef, North Malé Atoll, 19 November 1995, leg. SG Buttress & RC Anderson (“dorsal surface creamy green with white dots, spots, and faint lines; margin orange with purple spots and white dots; larger purple spots inside margin; rhinophores and gills cream”). – Oman: photographs of one individual, Muscat, 01-12 April 2009, S Kahlbrock. – Sri Lanka: photographs of one individual, Unawatuna, S of Galle, 28 December 2010, S Kahlbrock.

The single specimen is accompanied by a photograph reproduced here (Plate 41) and is not of the typical colour pattern. The white lines were represented by a series of dots and dashes, forming an irregular scalloped line around the central dorsal hump, contiguous to an orange band containing larger purple spots and smaller white dots. Purple spots coalesced to form small patches. Some white dots and dashes within this central region, but only vaguely indicate a median. The five simply pinnate gills, rhinophores, and top of the tail all bore opaque white markings: the gills and the rhinophores as a core, and the tail as a white band centrally tapering on the long metapodium. Two individuals photographed in Oman and Sri Lanka have an identical pattern of distinct marginal bands of orange and lilac, the lilac bearing rounded purple spots (Plate 42). There is one white line dorsally splitting around the branchial pocket. One photograph shows the red-violet spots located between the foot and the hyponotum, characteristic of this species.

The preserved specimen is well extended but badly preserved. It is translucent white, and the black digestive gland is visible through the thin epidermis, as is the white intestine loop. The translucent white metapodium is long and pointed.

This is the first literature record of the species from the western Indian Ocean. There have been photographs made available on Sea Slug Forum and NudiPixel only from Sri Lanka, with all other records being further east from Christmas Island and the western Pacific.

Maldives: 15 mm, Banana Reef, North Malé Atoll, 12 m depth, 19 November 1995, leg. SG Buttress & RC Anderson, and photos of another individual, RCA. – Mayotte: photographs of numerous individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

The small specimen illustrated in Plate 43 was very dark brown, with a few large pustules distributed centrally and marginally, and speckled greenish-yellow gills and rhinophores: Maldives specimens are usually darker brown than individuals from other localities. It is noteworthy that the only Indian Ocean specimens available are once again from the Maldive Islands. Currently, the only photographic records from anywhere else in the Indian Ocean are from Mayotte (http://seaslugs.free.fr/nudibranche/a_intro.htm), although there are other internet photos of this Indo-West Pacific species from Tanzania and South Africa (Sea Slug Forum) and the Maldives, Kenya, and Madagascar (NudiPixel).

Maldives: 25 mm, Fulidhoo Channel, Felidhoo Atoll, 10 m depth, 24 April 1994, leg. RC Anderson & SG Buttress; photographs of one individual 40 mm, March 1999, J Hinterkircher. – Sri Lanka: photographs of mating pair, Negombo, N of Colombo, 16 January 2011, S Kahlbrock.

Kenya: six specimens 15-20 mm pres. lengths, Vipingo, 25 miles N of Mombasa, ELW in rock pools on exposed reef, 23 September 1984, leg. J Hognerud (Australian Museum, Sydney, C431127). – Tanzania: photographs of two individuals, 1994, and reef flat, Matemwe, August 1993, MD Richmond; photo of one individual, Mafia Island, shallow water, May 2009, A de Villiers. – La Réunion: photograph of single individual, P Bidgrain, pers. comm.

The preserved specimens were blue in life with a broad pale orange mantle skirt and a distinctive orange patch in the centre of the dorsum, bisected by a longitudinal black line. All published records are listed above, and indicate that this species is known only from eastern Africa: Chromodoris hamiltoni has not been recorded from any of the island groups except La Réunion. It is similar only to Chromodoris quadricolor (see below), but usually lacks the distinctive white line between the black outermost line and the orange margin, the orange margin is paler and slightly more pink, and usually it has additional patches of orange and/or black dorsally. It is a much more variable species than Chromodoris quadricolor.

Socotra: 20 × 9 mm pres. (St-190, F-59), Abd al-Kuri, Khaisat en Naum, western tip, 10 April 1999, leg. U Zajonz.

There are no photographs accompanying the Socotra specimen, but the preserved specimen is semi-relaxed (examined 2009), with dark orange rhinophores and gills. The mantle is black with two white stripes fading to cream with a faint orange tinge on the dorsum. There is a relatively broad white band between the black dorsum and the orange marginal band (cf. Chromodoris hamiltoni above, which normally does not have this white separation, and Chromodoris elisabethina Bergh, which has a fine white line). The white line at the very edge of the margin can still be seen (cf. Chromodoris africana p. 34 which does not have this white line). There are two black stripes on the sides of the foot, and the foot retains an orange margin. The preserved specimen is identical to specimens collected from the Red Sea in 1990: Chromodoris quadricolor appears to hold its colour extremely well in formaldehyde.

Originally described from the Red Sea, its presence in Socotra is not unexpected: Rudman (1977) had specimens from Tanzania and Yonow et al. (2002) subsequently reported specimens from Chagos. Yonow et al (2002) discussed the similarities with Chromodoris elisabethina: five specimens from that collection were correctly attributed to Chromodoris quadricolor (Chag96/42, 96/51, 96/52a, 96/52b, 96/52c, and 96/87, colour figure 11f); however, two specimens are here reassigned to Chromodoris elisabethina (Chag96/16 and 96/87, colour figure 11e, and radular preparation, fig. 12a, b). Re-examination of the specimens and additional colour slides revealed that these animals both had darker patches located centrally as well as behind the rhinophores, clearly visible in the figure of specimen Chag96/87e in Yonow et al. 2002 (fig. 11e) and typical of Chromodoris elisabethina. The yellow margin differs in colour from that of the more orange rhinophores and gills, another characteristic of Chromodoris elisabethina and visible in the illustrations. Chromodoris elisabethina is more likely to have more black lines than quadricolor: Chromodoris quadricolor normally only has three black lines on the dorsum, and the Red Sea specimens with more black lines have been identified as Chromodoris strigata Rudman (Yonow 2008). Chromodoris quadricolor is restricted to the Red Sea, where it is very common, apart from isolated specimen records from Socotra, Tanzania, and Chagos.

Seychelles: 8 × 5 mm pres. (PK–BB), Lilôt, NW Mahé, 17 m depth on algal-encrusted rock, 26 April 1992, leg. P Kemp (mantle glands obvious on preserved specimen). – Madagascar: photos of one juvenile, 10 mm in length, Nosy Bé, October 2007, J Hinterkircher.

The Seychelles specimen has the typical colour pattern: a central patchy ochre-brown dorsum with ocellated violet spots, a creamy sub-marginal band with orange and purple spots, a blue-violet margin, and ochre rhinophores and gills. The specimen preserved in formaldehyde is translucent, with a rosy-orange and black gut. The flat translucent mantle skirt is extended, white mantle glands visible in a band along the edge: most are irregular in shape, some are stellate (Fig. 11A). Gills translucent, flat, and very simply pinnate; oral tentacles digitiform (Fig. 11B). The similarities and differences between this species and Chromodoris cavae, removed from synonymy of Chromodoris tennentana, are discussed under that species (see p. 36).

Seychelles: 30 × 15 mm (PK-N), Horseshoe Rock, Lilôt, NW Mahé, 15 m depth on algal-encrusted rock, 24 March 1992, leg. P Kemp (“pink with dark blue edging”; the preserved specimen is brick red with a green margin). – Maldives: 15 mm (7 mm pres.), 5 m depth on coral encrusted with algae and sponge, Maayafushi, South Malé Atoll, March 1997, leg. J Hinterkircher. – Persian Gulf: photograph of one individual, Dahwat ad Daffi, Jubail, Saudi Arabia, April 1992, F Krupp. – Kenya: 30 mm long pres., Vipingo, 25 m N of Mombasa, ELW in rock pools on exposed reef, 23 September 1984, leg. J Hognerud (preserved animal more orange and purple than red and blue-green) (Australian Museum, Sydney, lost?). – Tanzania: photographs of two individuals, Mafia Island, shallow water, May 2009, A de Villiers. – Sri Lanka: photographs of one individual, Unawatuna, south of Galle, 01 January 2011, S Kahlbrock.

Maldives: approx. 20 mm alive (11 × 5 mm pres.), Bathala Island, Ari Atoll, 11 m depth, night dive, 27 July 1995, leg. SG Buttress & RC Anderson. – Persian Gulf: photographs of two individuals, Dahwat ad Daffi, April 1992, and N of Abu Ali, 26 May 1992, Jubail, Saudi Arabia, F Krupp; photo of three individuals, Muscat, Oman, 01-12 April 2009, S Kahlbrock. – La Réunion: photos of several individuals 6-20 mm http://seaslugs.free.fr/nudibranche/a_intro.htm. – Seychelles: photographs of one individual, Lilôt, NW Mahé, 1988-1989, P Kemp. – Sri Lanka: photographs of two individuals, Unawatuna, S of Galle, 03 January 2011, S Kahlbrock.

The preserved specimen is well relaxed: it is opaque white, and no markings remain; the digestive system is not visible through the skin. Twelve gills are extended: the rachis is flat on the outside and lamellae face inwards on the two other sides. In life, the lamellae can be seen to extend laterally. One photograph from Oman (S Kahlbrock, pers. comm.) depicts the individual beginning to lay an egg mass, a flat white ribbon laid on its edge.

This species appears to be present but rarely recorded in the western Indian Ocean: Rudman (1984) had one only specimen from Tanzania; the specimen above is a first record for the Maldives (Plate 48), and new photographic records are presented here from the Persian Gulf, Gulf of Oman, Seychelles, La Réunion (http://seaslugs.free.fr/nudibranche/a_intro.htm), and Sri Lanka.

Sri Lanka: 13 × 5 mm pres., Unawatuna, S of Galle, 27 December 2010, leg. and photos S Kahlbrock.

This description of the live animal is based on many photographs of the specimen: dorsum broad with narrow mantle overlap; skirt thick with single pair of permanent undulations. Dorsum grey to off-white with irregularly shaped white, slightly raised pustules. Mantle skirt whiter than dorsum with only a few small white pustules; margin lemon-yellow. Rhinophores very small: distal half translucent lemon-yellow, proximal half paler translucent yellow, posteriorly an opaque line brighter yellow towards the tip. Simply pinnate gills translucent white with opaque white line on each side of rachis, red tips, and short red line running down from tips.

The preserved specimen is semi-translucent grey with irregular opaque white spots, slight crumpling of mantle around each. Mantle skirt with thickened margin, no coloured or thickened margin on skirt or foot. Long rhinophores translucent grey with white line and white tip, lamellae indistinct. Gills retracted but the red ends visible though translucent skin and open pocket.

This is the first record in the scientific literature of Glossodoris undaurum from the western Indian Ocean. There are book and internet records from South Africa, Kenya, Oman, and La Réunion. There are several named and un-named species occurring in the Indian Ocean, but these differ externally in the combination of margin, rhinophore, and gill colouration: collection of specimens will enable comparisons. It may be that some are colour variations but this cannot be established at present.

Seychelles: 15 × 5 mm (PK-DD), Lilôt, NW Mahé, 17 m depth on granite wall, 26 April 1992, leg. P Kemp. – Maldives: 15 mm length, Maayafushi, Ari Atoll, 3m depth, on coral rubble encrusted with algae and sponges, March 1997, leg. J Hinterkircher. – La Réunion, Mauritius, and Mayotte: numerous photographs http://seaslugs.free.fr/nudibranche/a_intro.htm. – Sri Lanka: photographs of one individual, Unawatuna, S of Galle, 27 December 2010, S Kahlbrock.

Elongated body with spatulate head. Translucent body with opaque white markings comprising several longitudinal white lines on dorsum and small white dots on orange-red margin. Magenta spots and patches between dorsal white lines. Foot translucent with magenta spots and patches, and small white dots. Rhinophores distinctive with white core bearing two red bands. Gills small, held upright, red proximally and white distally.

Small specimens are similar to several species of Thorunna, such as Thorunna australis (Risbec), recorded only from South Africa in the western Indian Ocean: it also has orange bands on the gills and rhinophores but the white markings are limited to one or two lines on the dorsum. Thorunna florens (Baba) also has similar gills and rhinophores but has purple spots around the margin as well as an orange border to the frontal margin, and it is limited to the western Pacific. Several un-named species are illustrated in Gosliner et al. (2008) but at present they are only known from few localities in the western Pacific.

La Réunion: 30 mm (24 × 10 mm pres.) on wall of cave, Etang Salé les Bains, 38 m depth, 21 December 2010, leg. H Flodrops; 35 mm (23 × 10 mm pres.), Sec Jaune, Saint-Leu, 12 m depth (night dive), 30 December 2010, leg. H Flodrops. – Mauritius: photographs only of three individuals, 1990’s, M. Parmantier pers. comm. and http://seaslugs.free.fr/nudibranche/a_intro.htm. – Sri Lanka: three specimens 11 × 5 mm, 13 × 4 mm, and 16 × 7 mm all pres., Unawatuna, S of Galle, 29 December 2010, and Negombo, N of Colombo, 16 January 2011, leg. S Kahlbrock; photo of one individual, Pigeon Island, Trincomalee, 16 m depth, April 1995, RC Anderson.

All five specimens are of the original colour form as described and illustrated by Collingwood (1881) and reproduced on Plate 51: dorsum mauve with central orange tinge and distinct narrow white margin; gills and rhinophores bright orange with magenta bases, gills raised high on a peduncle. La Réunion specimens pale violet with white margin, bicoloured gills and rhinophores (Plate 52). Smaller Sri Lanka specimens with rosier orange central dorsum (Plate 53). Seven gills in La Réunion specimens and nine in Sri Lanka specimens. In some photographs, the peculiar arrangement described and illustrated by Collingwood (Plate 51, "fig. 17") is visible, in which the gills are connected: the last two or three gills on each side are joined at the base and there are three single central ones (Fig. 12A). Anal papilla protruded as a tube in most images showing open gills, same colour as mantle. Gills bright orange but deep magenta where connected basally. Pockets of both rhinophores and gills uniformly coloured with mantle; raised rim translucent. White marginal line present on both surfaces as well as edge of mantle.

The specimens are well preserved, solid with a high profile, the metapodium extending beyond the posterior mantle margin. All five specimens retain the white line around the margin but no mantle glands are evident. The gills are extended in the La Réunion specimens, and each gill is almost round in section. Those of the 35 mm specimen are still pink, especially at the base (April 2011). The head is rounded with small oral tentacles identical to that figured for Risbecia apolegma Yonow (2002, fig. 11). The rosy hue remains on the dorsum, rhinophores, and gills of the Sri Lanka material several months after collection. The radula of the 16 mm Sri Lankan specimen examined had a formula of 72 × 100.0.100. All teeth are denticulate: there is no median thickening; the first 10 laterals in each row are recurved: the main cusp has a strong “brow ridge” with 1 or 2 very small denticles on each side (Fig. 12B). The majority of the laterals rapidly become straighter with a large cusp bearing 5 or 6 small denticles along its edge; the largest cusp measures at least 100 μm. In the last 5-7 teeth of this group, the first denticle next to the main cusp is doubled (Fig. 12C, D), even in the newest row (Fig. 12E). The final 10 teeth of each row rapidly reduce in size of cusp and denticles to become almost rounded; however, the double first denticle persists (Fig. 12F). The jaw rodlets of Risbecia bullockii have a slightly curved point with a swollen base.

Much controversy surrounds the identity of this species, here recorded from the Indian Ocean for the second time: photographs from La Réunion and Mauritius are also amethystine violet, intensifying anteriorly and posteriorly, a thin, bright white line is present around the mantle but not around the foot, and the gills and rhinophores are orange with magenta at the base (http://seaslugs.free.fr/nudibranche/a_intro.htm); these are identical to Collingwood’s illustration. Controversy also surrounded the description of Risbecia apolegma Yonow, 2002: Rudman stated on Sea Slug Forum that he could “find no anatomical grounds to place this ‘species’ in the genus Risbecia” while also querying its distinction from Hypselodoris “bullocki” (sic). However, in the numerous pages showing variations in colour pattern he stated that “unpublished studies of the anatomy show that it should probably be placed in the genus Risbecia.” Examination of the radula of the La Réunion specimen, re-examination of all micrographs of the radulae of Risbecia apolegma and of Risbecia pulchella (see below) show that they are all very similar and bear the diagnostic features as described by Rudman (1984). None of these teeth has the bicuspid laterals typical of the genus Hypselodoris; another character they have in common is that there are fewer rows than teeth per half row, in contrast to a statement by Gosliner and Johnson (1999) to the opposite effect. The teeth of Risbecia apolegma have a single large cusp with 5-6 denticles, the first of which faintly shows the division that is so obvious in bullockii and pulchella. Whether one assigns apolegma to Risbecia or Hypselodoris, it is clearly different from bullockii and a valid species based on radular morphology and consistent colour pattern.

Coincidentally, a recent paper by Johnson (2010) presented a phylogenetic tree placing Hypselodoris bullockii with Risbecia imperialis and Risbecia tryoni. Several species of Hypselodoris have a high body profile and an elevated gill peduncle, of which Hypselodoris regina Ev. Marcus & Er. Marcus is found along the East African coastline: the gills in this species nearly always form a goblet shape unlike those of Risbecia bullockii, which are similar to those of Risbecia apolegma.

Seychelles: 50 × 25 mm, one of two animals on algal-encrusted rock, Bug Rock, Brissare, 05 April 1992, leg. P Kemp; photographs of several individuals, Lilôt, NW Mahé, 1988-1989, P Kemp. – Gulf of Oman: photos of two individuals trailing, Muscat, 01-12 April 2009, S Kahlbrock; photographs of pairs, Musandam, 13 May 2009, trailing pair, Siri Island, 15 m depth, 13 May 2009, trailing pair, Anemone Garden, just off Khorfakkan, 8 Jan 2012, GT Smith. – La Réunion, Mauritius, Mayotte: photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

The radular formula is 83 (+3) × 90-95.0.95-90: there is no median tooth. The first 7-8 laterals are duck bill shaped with a large denticle on the outside (Fig. 13A). The central laterals increase rapidly in size to a cusp length of approximately 75 μm bearing 4-5 denticles, of which the first is divided (Fig. 13B). The last 3-4 laterals in each row are very reduced with a rounded main cusp and multiple denticles (Fig. 13C).

Sri Lanka: 5 × 4 mm pres., Pigeon Island, Trincomalee, 16 m depth, April 1995, leg. SG Buttress & RC Anderson.

The single specimen appears to have been stocky with little mantle overlap in life. Margin permanently convoluted with three indentations: one behind rhinophores, largest in centre of body, one just beyond gills. Colour opaque white with violet pigment concentrated around edges and on head around and between rhinophores. Thin sub-marginal white line around the violet, followed by translucent margin with orange in patches and in permanent folds, most especially the central one in which there was orange pigment overlying the submarginal white line. Rhinophores very large with translucent stalk and white core covered in 13 orange-red lamellae; rhinophoral pockets with low violet rim. Eight gills simply pinnate, arranged in circle around anal papilla; white ‘core’ and orange lamellae; orange line along both inner and outer edges of each gill. Foot pale violet, darker concentration of violet in band around metapodium.

The preserved specimen is translucent cream, with a thin mantle skirt. The rhinophores are retracted but some of the gills are extended: they are simply pinnate. The foot is convoluted laterally but anteriorly it is relaxed. The bilaminate margin spans the entire width and the upper lamina is notched. The oral tentacles are plump rounded structures (Fig. 14).

This specimen differs from Thorunna horologia, also found in the western Indian Ocean: horologia is opaque white with red marginal and orange-yellow sub-marginal lines, a single deep indentation which is red, and a white foot with a violet band on the margin (Rudman 1984, Gosliner et al. 2008).

Socotra: 17 × 10 mm pres. (IT-177, RJ-032), 12°41.326'N, 54°05.175'E, 14 April 1999, leg. R Janssen. – Persian Gulf: four pres. specimens 17 × 10 mm, 15 × 12 mm, 16 × 10 mm, and 9 × 5 mm, Rescue Centre, Jubail, Saudi Arabia, 09 December 1991, leg. D Fiege; photographs of one individual, Dahwat al Musallamiya, Jubail, Saudi Arabia, 25 November 1991, F Krupp. – La Réunion: photographs of four individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

Both Dendrodoris nigra and Dendrodoris fumata are found in similar habitats in the western Indian Ocean, and both species are present in these collections. Two colour forms occur in the Indo-West Pacific, a grey form and an orange/red form, the latter being much more common in the Indian Ocean (pers. obs., Brodie et al. 1997). As there were no colour photographs accompanying these specimens but photographs of uncollected individuals from the same region (Plate 56), identification is based on the morphology and colour in preservative, considerably different from that of Dendrodoris nigra (see also discussion for Dendrodoris nigra below) and other dendrodorids (see below). The Dendrodoris fumata specimens are contracted and semi-translucent; one is slightly lumpy but they are otherwise smooth and domed with a wide mantle skirt.

A third species of Dendrodoris is present in the Persian Gulf material: the preserved animals are very different from both Dendrodoris fumata and Dendrodoris nigra, but there are no notes or photographs of the living material for adequate comparison or identification (Abu Ali, 28 March 1992). In preservative, these two specimens measure 10 × 8 mm and 15 × 9 mm. They are both translucent beige-yellow and may have been pustular (? possibly Dendrodoris coronata Kay & Young). Both have very prominent raised rhinophoral and branchial sheaths; the smaller specimen has 9 extended simply pinnate gills and the rhinophoral pockets are crumpled in both specimens. Ventrally, the foot is broad and squared anteriorly with two laminae, and the ridge-like oral tentacles meet medially as in all dendrodorids.

Socotra: two pres. specimens 18 × 13 mm and 16 × 9 mm (IT-177, RJ-032; the smaller has a white submarginal band), 12°41.326'N, 54°05.175'E, 14 April 1999, leg. R Janssen. – Maldives: two specimens 16 × 4 mm and 19 × 5 mm (MDV/AB/96/6), found separately under rocks, Fulidhoo Lagoon, Felidhoo Atoll, 04 May 1996, leg. RC Anderson & SG Buttress; photo of one red individual, 1986-1994, J Hinterkircher. – Zanzibar: 30 × 15 mm pres. (“black, frilly skirt, domed dorsum, no white specks”), in coral rock, 1994, leg. MD Richmond. – Gulf of Oman: photo of three individuals, Muscat, 01-12 April 2009, S Kahlbrock. – Seychelles, one individual photographed, Lilôt, NW Mahé, 1988-1989, P Kemp. – La Réunion, Mauritius, and Mayotte: photographs of several individuals http://seaslugs.free.fr/nudibranche/a_intro.htm.

The preserved specimens of Dendrodoris nigra are all black, a little longer and thinner, and much firmer than Dendrodoris fumata, which has a thinner but more extensive mantle skirt. In the two Socotra specimens of Dendrodoris nigra, black or dark grey in preservative ten years later, the large white mantle glands are still clearly visible; additionally, in the smaller specimen, there is a substantial and distinct white submarginal band, presumably red in life. The two Maldives specimens of Dendrodoris nigra are relaxed and also retain their small white spots (examined 15 years later). The gills and rhinophores are extended and the gill clump is relatively small. The photograph of the only non-black Dendrodoris nigra from the Maldives is clearly a juvenile: it had a narrow mantle skirt and was pale translucent red with small white spots and flecks as well as a black marginal band (Plate 58). The gill clump was small (but translucent red), the tri-coloured rhinophores were translucent red basally, black distally, with a large white knob at the tip; these are characters typical of Dendrodoris nigra, reviewed by Brodie et al. (1997) based on Pacific specimens. Dendrodoris fumata is never black, nor does it have white spots or glands on the dorsum (Brodie and Calado 2006).

Holotype: Persian Gulf (Saudi Arabia): 25 × 17 mm pres., Jubail, Dahwat ad Daffi, 03 April 1992, leg. F Krupp, SMF 337105.

Creamy yellow elongate oval body with ochre gills and charcoal black rhinophores. Variously sized spiculose tubercles are covered in opaque white lines, with some fainter ones extending from the tubercles to the mantle.

The photograph depicts an elongate oval animal with a wrinkled and damaged margin in life. Dorsum covered in tubercles, themselves covered and sometimes faintly linked to each other with fine white lines. Body was creamy yellow, plumose gills ochre in colour, darker than dorsum, but the rhinophores were black: the stalk was translucent cream and the approximately 15 fine lamellae were charcoal black. The midline on each side and the tip were dusty white. The gut was visible through the skin, opaque creamy orange with black patches.

The preserved specimen has a pink cast and is semi-translucent. Surprisingly, the retracted rhinophores are no longer black, and not visible by translucence through the pockets or the body wall. The tubercles are full of spicules. Tubercles are largest centrally and become progressively smaller toward the margin (Plate 59); in preservative, many are mushroom-shaped. The margin itself is rather thick (and damaged on the right side). Ventrally, the anterior margin of the foot is simple, not bilaminate, and there is a fold under the mouth (Fig. 15).

The single specimen is unlike any species of Doriopsilla published to date, and different from the photographs available in books and on the internet. The most similar species is Doriopsilla miniata (Alder & Hancock), described from India and occurring throughout the Indo-West Pacific in a wide range of colours from nearly white to bright orange. Usually, there are tracings of white lines crossing the dorsum transversely but these may be absent. More critically, the gills and rhinophores of Doriopsilla miniata are the same colour as the dorsum or a little darker and this, amongst other characteristics, distinguishes this new species. An un-named species of Doriopsilla similar to Doriopsilla nigrocera sp. n. is illustrated in Gosliner et al. (2008), Apte (2009), and Apte et al. (2010) in which only the tubercles are covered in white lines; however, this species has rhinophores and gills the same colour as the mantle and not black and may simply be a colour form of Doriopsilla miniata. These animals were recorded from South Africa and India, but remain unidentified.

The specific epithet refers to the very distinctive black rhinophores, unique to this species of Doriopsilla.

Maldives: 35 mm in length (MDV/AB/96/20), 14 m depth, Banana Reef, North Malé Atoll, 10 May 1996, leg. RC Anderson & SG Buttress; photos of several individuals 30-40 mm, March 1999, J Hinterkircher. – La Réunion and Mauritius: numerous photographs of many individuals http://seaslugs.free.fr/nudibranche/a_intro.htm. – Tanzania: photographs of three individuals, Mafia Island, shallow water, March 2004 and May 2009, A de Villiers. – Seychelles: photo of one individual, Lilôt, NW Mahé, 1988-1989, P Kemp.

The single specimen is not of the typical western Indian Ocean colour pattern, but more like the animals found in the eastern Indian Ocean and is therefore illustrated here. All other photos are of the typical colour form (as described by Yonow 1994), and range in size from 22 mm to 60 mm in length. The longitudinal pattern of black lines is lacking in this specimen and only transverse rays to the margin are present, connected to each other and crossing the dorsum. There are usually no tubercles on the black lines but if present, these are only small pustules. Ground colour granular blue-white, with more blue pigment present around margin; larger tubercles orange-yellow and arranged in three lines of partially contiguous tubercles along centre of dorsum; in the marginal area, row of single orange-yellow tubercles on each side followed by smaller ones.

Socotra: two specimens, both 27 × 12 mm pres. (St. 018, GR-22), Qualansiyah Bay 12°41.026'N, 53°28.309'E, 10 March 1999, leg. G Reinicke.

This is the first record of Phyllidia (Fryeria) picta in the western Indian Ocean, identified by colour pattern and ventral anus. The colour pattern does not appear to differ from that found in the western and central Pacific: the white-in-life areas around the tubercles are now grey-white, and the orange-in-life tubercles are a dirty yellow colour. There are three rows of individual tubercles which are not contiguous (as in marindica, see above) although the white bases of two or three tubercles may merge along the central line (Fig. 16A). Ventrally, the anterior foot margin is divided and the oral tentacles are triangular (Fig. 16B). The two specimens differ from preserved specimens of marindica (above) and Phyllidia (Fryeria) rueppelii Bergh, from the Red Sea: the black pigment covers much more of the dorsum in Phyllidia (Fryeria) picta, extending to the margin in rays. The black areas in Phyllidia (Fryeria) picta are smooth, while they are tuberculate in Phyllidia (Fryeria) rueppelii and small pustules may be present in the black areas of Phyllidia (Fryeria) marindica. All three species, however, are similar in having three central lines of orange tubercles, orange rhinophores, and a ventral anus.

Maldives: 25 mm in length, Dhigu Tila, near Gulhi, South Malé Atoll, 12 m depth, 14 October 1994, leg. SG Buttress & RC Anderson; 28 × 12 mm, Bathala Island, Ari Atoll, 6 m depth, 28 July 1995, leg. SG Buttress & RC Anderson; 15 × 7 mm pres. (“light grey with black lines, rhinophores and last tubercle yellow”), Bathala Island, Ari Atoll, 10 m depth, 27 July 1995, leg. SG Buttress & RC Anderson; photographs of many individuals, 25-40 mm, March 1997, March 1998, March 1999, J Hinterkircher. – Sri Lanka: photos of two individuals, Negombo, N of Colombo, April 1995, RC Anderson; photos of one individual, Unawatuna, S of Galle, 27 December 2010, S Kahlbrock.

The preserved 15 mm juvenile is in perfect condition and easily recognised as Phyllidia alyta. Broken black line present on sole of foot despite its small size (Fig. 17A), but only two of the four longitudinal dorsal black lines are complete (Plate 61). Three rows of tubercles on midline between start of two lines: central row of tubercles joined by low ridge and only the last tubercle orange. Black crossbar between rhinophores lacking. Two larger specimens typical, with four dorsal black lines, black bar between rhinophores, and ventral broken black line. Foot thickened and concave anteriorly, and triangular tentacles bear groove along each outer side (Fig. 17B). Hyponotum hatched with spicules, dorsal black pigment showing through.

It is probable that the species described by Eliot (1906) is Phyllidia alyta: he distinguishes it from Phyllidia varicosa (he had specimens of both), and Phyllidia alyta is the only other species in the Indian Ocean with linearly-arranged orange tubercles and black lines dorsally in combination with a black line on the sole of the foot. This species appears to be restricted to the western Indian Ocean; there are only two internet records from south western Thailand on NudiPixel.

Madagascar: 65 × 25 mm (PK-C), Ampangorina, Nosy Komba, 1 m depth on Acropora, 30 January 1992, leg. P Kemp. – Tanzania: photographs of two individuals, Mafia Island, shallow water, 15 January 2005 and 04 July 2005, A de Villiers. – Seychelles: 32 × 12 mm (PK-FF), Lilôt, NW Mahé, 15 m on encrusted coral, 26 April 1992, leg. P Kemp; 32 × 15 mm preserved (NHMUK acc. no. 2222), slightly curled, east side of East Channel, Aldabra, 1 m depth in coral, 25 September 1967, leg. JD Taylor; 49 × 15 mm preserved (NHMUK acc. no. 2222), Passe Femme, Aldabra, in shallow water beneath coral, 29 November 1967, leg. JD Taylor. – Maldives: 23 × 11 mm preserved (NHMUK ref. M/02/B/42), Gan, 04 September 1964, PSD Maldive Islands Expedition. – La Réunion and Mayotte: numerous individuals photographed, 20-45 mm in length http://seaslugs.free.fr/nudibranche/a_intro.htm.

Ground colour granular blue-white with three black lines: median line containing orange-tipped tubercles, two smooth lateral lines. Lateral lines normally meet anteriorly, and extend to margin usually as U-shape, but remain separated posteriorly. Outside the black lines, mantle bears tubercles, black flecks, and smaller scattered pustules toward edge; larger tubercles may have orange tips. Rhinophores bright orange, up to 16 lamellae; row of orange tubercles originates behind each rhinophore. Ventrally, propodium notched or deeply concave; all specimens have long tapering oral tentacles, grooved laterally and bearing black pigment on dorsal surfaces extending ventrally onto bases.

These specimens and photographed individuals belong to the typical form of Phyllidia coelestis, a commonly recorded species in the western Indian Ocean and occurring as far south as South Africa. Another group of specimens also identified as Phyllidia coelestis (Brunckhorst 1989, 1993; Yonow 2011 as dark form) has a central oval region where the ground colour is black and only a marginal band around it is blue-white. The edge of the central black area is irregular and may form short rays extending a little way into the blue-white margin, identical to that of Phyllidia (Fryeria) picta (p. 56), but this form has not been found in the western Indian Ocean.

Maldives: single specimen 15 mm (11 × 6 mm pres.), Dhigu Tila, near Gulhi, South Malé Atoll, 12 m depth, 14 October 1994, leg. SG Buttress & RC Anderson. – Madagascar: photo of one individual, Nosy Bé, 12-14 m depth, 25 July 2010, S Bachel (http://seaslugs.free.fr/nudibranche/a_intro.htm). – Mayotte: photo of one individual, Ilot Blanc de Mtsamboro, 4 m depth, 30 Dec 2010, M Deuss (http://seaslugs.free.fr/nudibranche/a_intro.htm).

Elongated oval animal with granular white ground colour and three black lines connected anteriorly around rhinophores but not posteriorly; central one shortest and widest. Tubercles present in black areas. Three main rows of orange-tipped tubercles in life, middle ones located along central black line, lateral ones between black lines. Several isolated orange-tipped tubercles outside black lines within marginal band of granular white, which also contains non-orange tubercles. Ring of rounded black spots at edge of granular white and bordering the orange margin. Rhinophores same orange colour as tubercles and margin; anal papilla faintly orange. When the colour images of the living specimen are magnified, a completely separate band is visible around the margin, which is translucent when not pigmented with orange (Plate 63).

The preserved specimen does not retain any orange pigmentation. The tubercles located on the black lines are clearly spiculose, while those located on white areas are covered by granular pigment (Fig. 18A). The anus is very difficult to see, located far posteriorly and not on a tubercle. Ventrally, the anterior margin of the foot appears to be concave; the oral tentacles are conical (Fig. 18B).

Brunckhorst (1993) described this species from one juvenile specimen (15 mm) from the eastern Indian Ocean and nine specimens (11-30 mm) from the West Pacific but it has been recorded to 45 mm in eastern Australia (Cobb and Willan 2006). This first record from the Maldives records its distribution in the western Indian Ocean, and photographs from the Maldives and Kenya are available on NudiPixel. Phyllidia schupporum Fahrner & Schrödl (2000) was originally described from the Red Sea and compared to Phyllidia exquisita; it is the most similar species but it has very high spiculose tubercles (see also Yonow 2008). The numerous photographs now available on the internet show that there are several similar species but, of those with three to four black lines and granular white colour pattern most similar to the holotype of Phyllidia exquisita, variations occur from no orange margin to fragmented and complete orange margins, and these can in all probability be assigned to exquisita. Until specimens of the other illustrated forms are examined, their identities must remain unconfirmed.

Maldives: 11 × 6 mm pres. (NY-142, orange with black triangles), Fulidhoo House Reef, Felidhoo Atoll, 20 m depth, 12 January 1991, leg. N Yonow; 14 × 7 mm pres. (SH-65, “bright yellow” with black ring), Maaya Tila, Ari Atoll, 16 m depth, August 1991, leg. S Harwood; 17 × 7 mm pres. (“yellow with black” ring), Hans’ Place, North Malé Atoll, 23 m depth, 3 November 1994, leg. SG Buttress & RC Anderson; photographs only of two individuals together, 10 mm approx. lengths (yellow with black ring), 12 m depth, July 1992, J Hinterkircher.

Phyllidia koehleri is a small species (the largest recorded size is 17 mm preserved length, above), bright yellow or orange, with a central longitudinal black line and a black ring, solid or broken, encompassing the anus and rhinophores. Body oval with single raised ridge behind each rhinophore, either side of central black line. Apart from two strong central ridges and tiny single tubercles covering skirt, the mantle is smooth. Broad central black band extending from behind the rhinophores to the anus, black ring then encloses central area (Plate 64); colour in life of these specimens yellow. Sometimes, as in one specimen, the black ring is broken into dashes which form bases of black triangular rays extending to margin (Plate 65); colour of this specimen orange but both patterns occur in both colours in images on the internet. There may be a few black spots in the marginal band and the orange form appears more tuberculate than the yellow ringed form. Rhinophores same colour as body, yellow or orange depending on body colour, extremely long and thin, bearing little more than 10 diagonal lamellae. Anal papilla translucent, extending from raised rim at junction of two ridges very near the posterior border, surrounded by some small tubercles. Ventrally, foot white in life, but hyponotum and gills yellow or orange in life. Anterior margin of foot notched, head white, and large oral tentacles triangular, grooved on outer margins, tipped with orange in life (Fig. 19A-C).

Internally, all specimens are similar, and illustrated here (Fig. 19D-F). The pharyngeal bulb is conical and slightly asymmetrical. Its posterior surface is glandular, the ventral projections a little longer than the dorsal ones. The oesophagus is very long, exiting the bulb posteriorly and bending anteriorly to pass through the nerve ring sitting on the bulb.