Nesaea: Leach (1814).

Prochonaesea: Hesse (1873).

Sorrentosphaera: Verhoeff (1944).

Eubranchiate sphaeromatid with body approximately elliptical. Anteriorly, cephalosome separating the bases of the antennules. Eyes set slightly into pereonal tergite 1. Coxal plates of pereonites 1–7 separated from tergites by sutures.The seventh somite is overlapped by the sixth in adult males (stage 8), with the pleura extended postero-laterally into two small processes, which vary in shape according to species. Pleotelson domed or keeled, and terminating in an obvious terminal foramen, which may be enclosed forming a tube. Antennular peduncle articles 1 and 2 dilated and juxtaposed to ventral margins of cephalosome. All pereopods ambulatory. Both rami of pleopods 1-3 bearing margin of plumose setae. Endopods of uropod fused with protopods and juxtaposed to pleotelsonic margin; exopods posteriorly directed. Sexual dimorphism pronounced. Adult male with pereonal tergite 6 longer than those preceding, posterior margin with an elongate, posteriorly directed process either side of the mid-line (the bidentate process). Posterior part of pleotelson with central boss. Penes small, separate. Endopod of pleopod 2 lacking appendix masculina. Female with pereonal tergite 7 similar to those preceding and lacking bidentate process; pleotelson smooth. Ovigerous female with ventral marsupium, formed from four pairs of lamellae, which arise from pereonites 1-4. Mouthparts strongly metamorphosed.

Oniscus bidentatus Adams, 1800

Oniscus bidentatus: Adams (1800).

Naesa bidentata: Leach (1815).

Dynamene bidentata: Holdich (1968a, b, c, 1969, 1970, 1971, 1976); Kussakin (1979); Harrison and Ellis (1991).

An extensive synonymy was given by Holdich (1968a, c) for citations prior to 1968.

Specimens have been examined from 129 locations in the NE Atlantic, mainly from the British Isles, Channel Islands, France, Spain, Portugal and Morocco – see the Suppl. materials 1 and 2. A number of literature records have been included where the diagrams clearly indicate this species. In addition, there are 76 records from the NBN database.

Body convex; in stage 8 males the pleotelsonic boss is large and bilobed, the two halves are separated by a wide v-shaped groove; the arms of the bidentate process taper to a point, and are sparsely rugose dorsally (Fig. 2A–B). In stage 7 females the pleotelsonic dome is smoothly rounded in side view and the pleotelsonic foramen is open and flush with the edge of the pleotelson (Fig. 3A–B). In populations from Atlantic coasts the smooth outline of the pleotelsonic dome in females and juveniles is key to separating this species from D. magnitorata and D. edwardsi, where it is keeled in side view. Further details are provided by the scanning electron microscope pictures of the posterior body of a stage 8 male and a stage 7 female in Holdich (1976).

Figure 2. 

Main features of adult males (stage 8) of the NE Atlantic-Black Sea axis Dynamene spp. A, B D. bidentata (S. Wales). Arrows indicate shape of the bidentate process (A), uropods (A, B) and pleotelsonic boss (B) C, D D. magnitorata (Roscoff, France). Arrows indicate shape of the bidentate process (C), the uropods (C, D) and the pleotelsonic boss (C, D). Note the difference in the shape of the boss and the ends of the arms of the bidentate process to those of D. bidentata E, F D. edwardsi (E Canaries F Azores). Arrows indicate shape of the bidentate process (E, F), uropods (F) and pleotelsonic boss (E, F). Specimen in E shows relatively little dorso-lateral setation, whilst that in F is hirsute. Note the differences in the shape of the boss and the tips of the arms of the bidentate process compared to those of D. bidentata and D. magnitorata G, H D. bifida (France, Mediterranean). Arrows indicate shape of the bidentate process (G, H), uropodal exopod (H) and pleotelsonic boss (G). Note the large accessory process on each arm of the bidentate process, the small sessile pleotelsonic boss and the long narrow uropodal exopods I D. tubicauda (Bay of Naples, Italy). Arrows indicate the unique body shape, tubular respiratory channel, peg-like pleotelsonic bosses, and the curved uropodal exopods J, K D. bicolor (Bay of Naples, Italy). Arrows indicate shape of the bidentate process (J), and pleotelsonic boss (J, K). Note in particular the rugose nature of the dorsal surface of the bidentate arms, and the triangular shape of each half of the boss – in specimens from the Black Sea the boss is of a similar shape but much less prominent.

Figure 3. 

Main features of females and juveniles of the NE Atlantic-Black Sea axis Dynamene spp. A, B Dynamene bidentata (S. Wales). Arrows indicate smooth outline of pleotelsonic dome (A) and non-tubular pleotelsonic foramen (B) C, D Dynamene magnitorata (Roscoff, France). Arrows indicate angular outline of pleotelsonic dome (C), posterior extension of pleotelsonic keel and non-tubular pleotelsonic foramen (D) E, F, G Dynamene edwardsi (Italy). Arrows indicate angular outline of pleotelsonic dome (E) with central bulge (E, F, G) and tubular pleotelsonic foramen. (E and F from Naples, Italy G hirsute female from the Venice Lagoon, Italy) H, I Dynamene bicolor (Naples, Italy). Arrows indicate angular outline of pleotelsonic dome (I) and non-tubular pleotelsonic foramen (H) J, K Dynamene tubicauda (Ischia, Italy). Arrows indicate flattened epimera surrounding body that give this species a unique body shape (J, K) and the tubular pleotelsonic foramen (J, K) L, M. Dynamene bifida (Ischia, Italy). Arrows indicate smooth outline to pleotelsonic dome (L) and pleotelsonic foramen at end of short tube (M).

Adult males (stage 8) typically 7.0 × 3.0 mm, although specimens 10 mm in length have been seen; pre-ovigerous females (stage 7) typically 6.0 × 2.9 mm.

There are eight life-history stages in both males and females (Holdich 1968b). Sexual dimorphism becomes apparent in stage 6 males with the appearance of a very small bidentate process, this increases in size at the seventh, and is fully developed by the eighth and terminal stage (Figs 1D, 4–lower row 6–8). This process is absent from juveniles and females (Figs 1A-B, 4–upper row 6–8, 2A–M). Juveniles and females up to and including stage 7 are very similar to each other morphologically. At the moult to stage 8 females become ovigerous and are very similar morphologically between the species. Their mouthparts are strongly metamorphosed, and they die after releasing their broods (Hansen 1905, Holdich 1968b, 1971). Stage 8 males live for two breeding seasons, at least in the British Isles, and remain in their cryptic habitat for the entire period without apparently feeding (Holdich 1971). Those in their second year are recognizable from the growths of algae, and sometimes serpulids, on the pleotelson.

Figure 4. 

Dorsal views of the posterior halves of the bodies of various life history stages (5–8) of Dynamene bidentata. 5 juvenile Upper row female stages 6, 7, 8 (ovigerous) Lower row male stages 6, 7, 8. Adapted from Holdich 1968b.

All stages can be found on a wide variety of mid- to lower littoral algae, and also in rock pools in the upper littoral zone. Fenwick (pers. comm., July 2016) has found this species commonly amongst lower shore and sublittoral coralline algae in Cornwall, and he has also recorded adults from under large lower shore pebbles. Stage 7 females and stage 8 males move from the algae into cryptic habitats, such as crevices and empty barnacle tests, particularly Balanus perforatus, to breed (Holdich 1970, 1976). Stage 7 females moult into stage 8 females within such a habitat and reach peak numbers in April/May each year (Holdich 1968b).

Some degree of camouflage in the algal habitat is given by green, yellow and brown ‘uniformis’ phenotypic varieties, and this is enhanced by the development in some individuals of patterns of white or red, dorsal, non-adaptable chromatophores (Tinturier-Hamelin 1962, 1967, Holdich 1969, Arrontes 2009). In the past some workers have given specific status to the red and green colour varieties, e.g. rubra and viridis (see Holdich 1968c). Adult males are particularly colourful when found amongst red algae on the lower shore, with the margins of the body segments and uropods bordered in orange.

The distribution of this species shown in Holdich (1970, 1974) has been extended by the present study. It occurs from the Shetland Islands to Tarfaya in western Morocco and Tenerife and Gran Canaria in the Canary Islands, which are the only two records of the species in Macaronesia (Fig. 5A). Within this range D. bidentata occurs in the north, northwest (including the outer islands), west and south coasts (as far as the Isle of Wight) of Great Britain, around Northern and Southern Ireland, the Channel Islands, northwest France, Atlantic Iberian Peninsula and in northwest Africa. Arrontes (1991) cites D. bidentata as being the most abundant isopod species on shores in northern Spain. It is the only species present in the British Isles (with the exception of a single record of D. magnitorata in southern England). It is particularly common in SW England and SW Wales, especially where the large barnacle, Balanus perforatus is present. There is one recent record for north-eastern England, which may be the result of a stranding, as are records for The Netherlands, where it is not considered indigenous (Holthuis 1956). The closest record to the Mediterranean of D. bidentata is Tarifa, in southern Spain (Guerra-García et al. 2011, Izquierdo and Guerra-García 2011, Guerra-García et al. 2012, Torrecilla-Roca and Guerra-García 2012).

Figure 5. 

Distribution of Dynamene species along the NE Atlantic-Black Sea axis based on material validated during the present study. A Dynamene bidentata B Dynamene bicolor C Dynamene bifida D Dynamene edwardsi E Dynamene magnitorata F Dynamene tubicauda.

Maggiore and Fresi (1984) described D. bidentata from the Gulf of Naples (publishing descriptions and figures), and several authors (e.g., Castelló and Carballo 2001, Castellanos et al. 2003, Junoy and Castelló 2003) have used Maggiore and Fresi’s (1984) observations to justify their findings of D. bidentata in the Mediterranean. Yet, examination of the single specimen found by Maggiore and Fresi (1984) showed that it was in fact a D. magnitorata.

A lot of confusion regarding the identification of D. bidentata was caused by Torelli (1930) who figured what she called D. bidentata (a stage 8 male and a stage 8 ovigerous female), from the Bay of Naples, Italy. Omer-Cooper and Rawson (1934) used Torelli’s figures to illustrate D. bidentata from Britain, which was then proliferated in some British identification guides, e.g., Barrett and Yonge (1964), although this has been corrected in more modern guides, e.g., Hayward and Ryland (1995). Pauli (1954) also used Torelli’s figures to illustrate D. bidentata from the Black Sea. Holdich (1968a) collected material from Naples and decided that Torelli’s figures were in fact of a new species, commonly found in the Bay of Naples, which he named D. torelliae Holdich, 1968. However, Kussakin (1979) decided that D. torelliae was in fact synonymous with D. bicolor (Rathke, 1837). This species was in fact unknown to Holdich at the time of his studies.

Databases we have consulted indicate that D. bidentata commonly occurs around Northern and Southern Ireland. However, we could only find one modern published record, i.e., de Grave and Holmes (1998) from Lough Hyne in County Cork.

Unlike most other isopods, stage 8 male Dynamene bidentata do not have appendix masculina on the endopods of the second pair of pleopods, this is also the case in the other Dynamene species. This phenomenon has also been noted by Messana (2004) in Sphaeroma terebrans Bate, 1866. It is very difficult to observe mating in Dynamene due to the cryptic habitat of the adults. It is probable that sperm are released directly into the marsupium as the eggs are laid.

Campecopea bicolor: Rathke (1837).

Dynamene bidentata: Torelli (1930); Omer-Cooper and Rawson (1934); Pauli (1954); Holthuis (1956); Barrett and Yonge (1964); [not D. bidentata of Adams (1800)].

Dynamene torelliae: Holdich (1968, 1970).

Dynamene bicolor: Kussakin (1979); Maggiore and Fresi (1984).

Specimens have been examined from 48 locations in 12 countries in the Mediterranean and Black Seas - see the Suppl. materials 1 and 2. A number of literature records have been included where the diagrams clearly indicate this species.

In stage 8 males the pleotelsonic boss is comprised of two right-angled triangular structures separated by a deep groove (however, the boss may be very low lying in some specimens, e.g., those from the Black Sea); the arms of bidentate process taper to a point and are rugose dorsally (Fig. 2J–K). In stage 7 females the pleotelsonic dome is keeled in side view and the pleotelsonic foramen is flush with the edge of the pleotelson (Fig. 3H, I). The females of this species are very difficult to separate from those of D. magnitorata. Maggiore and Fresi (1984) provide a complete description of D. bicolor.

Adult males (stage 8) typically 3.5 × 1.5 mm, pre-ovigerous females (stage 7) typically 3.0 × 1.3 mm.

Nothing is known of the life-history, other than the fact that sexual dimorphism occurs with males developing the bidentate process characteristic of the genus.

Juveniles are usually found in shallow water on a variety of algae down to 3.0 m and adults in empty Balanus tests, in mussel beds, in rock crevices, within sponges, and under rocks throughout the Mediterranean. However, occasionally they have been found in deeper water, e.g., off the island of Chios (Greece) specimens were collected from Cystoseira at depths from 0.5 – 30 m (see Suppl. material 1).

As with D. bidentata, some degree of camouflage in the algal habitat is given by yellow or dull green ‘uniformis’ phenotypic varieties, and this is enhanced by the development in some individuals of patterns of white or red, dorsal, non-adaptable chromatophores (Holdich 1969).

The distribution of this species shown in Holdich (1970) has been extended by the present study. It is the most commonly recorded Dynamene species in the Mediterranean, occurring from the Balearic Islands in the west to the coast of Israel in the east, although there are only a few records for the North African coast (Fig. 5B). It has been frequently recorded around the Greek islands and mainland coast of both Greece and Turkey. The most northerly record is for Croatia in the Aegean Sea. It has also been recorded for a number of countries around the Black Sea (Bulgaria, Romania, Turkey and Georgia) (Fig. 5B). Most records in the literature refer to D. torelliae, which is now considered synonymous with D. bicolor.

Many records exist, both published and unpublished, for Dynamene bicolor (usually as ‘D. torelliae’) in the Mediterranean Sea, particularly from the coasts of Spain, France, Italy and Greece (Holdich 1970, Bakir et al. 2014). However, its presence in Egypt and Israel was unreported until now. Previous observations indicated its presence in the Black Sea (Kussakin 1979), where it was thought to be the only Dynamene species present (Gönlügür-Demirci and Katağan 2004). On comparing specimens from the Black and Mediterranean Seas the current authors have accepted the decision of Kussakin (1979) that D. torelliae and D. bicolor are synonymous. However, it is clear that some of the specimens from the Black Sea have a reduced pleotelsonic boss, and the two may eventually turn out to be separate species when more material is examined. Kirkim et al. (2006) commented on the form of the pleotelsonic boss, stating that this can vary from two small projections to a well-formed boss in specimens of ‘D. torelliae’ from the Aegean Sea. Rathke’s (1837) drawings of D. bicolor show the posterior halves of a female and a stage 7 male. The male has two joined hemispherical pleotelsonic bosses, which are similar to those found in the same stage of ‘D. torelliae’ and unlike that of D. edwardsi the other species in the region, which is single.

Dynamene bifida: Torelli (1930).

Dynamene bifida: Holdich (1968, 1970).

Specimens were examined from seven locations in Spain, Greece, France, Italy and Turkey in the Mediterranean – see the Suppl. materials 1 and 2. A number of literature records have been included where the diagrams clearly indicate this species.

In stage 8 males each arm of the bidentate process is large, tapering and with a well-developed, downwardly-directed accessory process a quarter of the way from the apex; the pleotelsonic boss is very small with raised pointed corners (Fig. 2G–H). In stage 7 females the pleotelsonic dome is smoothly rounded in side view and the pleotelsonic foramen is at the end of short tube (Fig. 3L–M).

Adult males (stage 8) typically 5.0 × 3.0 mm, although a specimen of 7.0 mm length has been seen; pre-ovigerous females (stage 7) typically 4.0 × 2.0 mm.

Nothing is known of the life-history of this species, other than the fact that sexual dimorphism occurs with males developing the bidentate process characteristic of the genus.

Adults, including stage 8 females, were found among Hydroides unicata colonies and other cryptic habitats in the Bay of Naples (Torelli 1930, Holdich 1970). Ledoyer (1962) recorded it from Ulva lactuca at Endoume, southern France, and Holthuis (unpublished records) from rocky shores amongst algae at 0.0–1.0 m at Banyuls-sur-Mer. The latter record included stage 8 females.

All specimens seen were a pale, sandy yellow. No polychromatism was observed.

The distribution of this species shown in Holdich (1970) has been extended by the present study. It has a widespread distribution in the Mediterranean stretching from southern Spain to Turkey (Fig. 5C).

Originally described by Torelli (1930) from the Bay of Naples, males of this distinctive, and sometimes large, species has been infrequently recorded, and females even less so. The accessory process on each arm of the bidentate process is similar to that found in the Australian species, D. ramuscula (Holdich and Harrison 1980). The fact that ovigerous females were found amongst shallow-water algae raises questions about the life-history of this species, although in the Bay of Naples this stage has been recorded with males in more protective habitats.

Naesa edwardsi: Lucas (1849).

Dynamene hanseni: Monod (1923).

Dynamene edwardsi: Holdich (1968a, 1970); Harrison (1982).

Dynamene bidentata: Picker and Griffiths (2011).

An extensive synonymy was given by Holdich (1968a, c) for citations prior to 1968.

Specimens were examined from 89 locations in NE Atlantic, Mediterranean, Adriatic, Aegean and Red Seas – see Suppl. materials 1 and 2. A number of literature records, e.g., the Suez Canal, have been included where the diagrams clearly indicate this species.

Nothing is known of the life-history of this species, other than the fact that sexual dimorphism occurs with males developing the bidentate process characteristic of the genus.

Body convex; in stage 8 males the apices of arms of the bidentate process are swollen, each with a short, downwardly-directed spur; the pleotelsonic boss is plate-like with two forward-facing pegs; the body exhibits various degree of setation (Fig. 2E–F), e.g., specimens examined from the Balearic Islands (Spain) and the island of Chios (Greece) are somewhat different from other D. edwardsi seen by us in being very hirsute, with a pronounced developing boss and respiratory tube in the stage 7 males. In stage 7 females the pleotelsonic dome is keeled in side view, with a median protuberance; the pleotelsonic foramen is at the end of a short tube (Fig. 3E–G). Further details are provided by the scanning electron microscope pictures of the posterior body of a stage 8 male and a stage 7 female in Holdich (1976). See keys to stage 8 males and stage 7 females.

Adult males (Stage 8) typically 5.5 × 2.25 mm; pre-ovigerous females (stage 7) typically 3.0 × 1.1 mm, specimens of 4.4 × 2.3 mm have been seen from the Venice Lagoon, Italy.

Juveniles and adults have been found amongst a variety brown, green and red algae in the littoral and sublittoral zones, sometimes in conjunction with D. bicolor in the Mediterranean, and with D. bidentata and D. magnitorata on Atlantic coasts. Adults have also been recorded from amongst mussels and tube worm colonies and barnacle tests in the Bay of Naples (Torelli 1930, Holdich 1970), and elsewhere in the Mediterranean (e.g., Rivosecchi 1961, Bellan-Santini 1962). It has been found associated with encrusting matter on solid surfaces in some harbours and canals. On occasions it has been found amongst the ‘trottoir’ on steep-sided cliffs as deep as 10 m. Monod (1932) recorded it from coralline and fucoid algae on the coast of NW Africa. In the Azores, adults have been recorded from empty Chthamalus stellatus tests attached to lower shore cobbles, along with Campecopea lusitanica. In West Portugal (Buarcos) it is present with D. bidentata and D. magnitorata. However, while D. bidentata adults were present in barnacles, no D. edwardsi were found inside barnacles, only among intertidal algae and on a few ‘small’ algae in shaded crevices at 0-1 m. Also, they were not present among mussels. Unusually, adults, including stage 8 females, were found in upper shore sandstone crevices, along with Campecopea hirsuta, in southern Portugal.

The general body colour is a dull grey-green, individuals sometimes exhibit polychromatism caused by patterns of white, dorsal, non-adaptable chromatophores as seen in some of the other species (Holdich 1969).

The distribution of this species shown in Holdich (1970) has been extended by the present study. It is the most meridional of the Atlantic species, occurring from Galicia in north-western Spain to Nouadhibou in Mauritania (Fig. 5D). This is the currently known southern limit of Dynamene species of the NE Atlantic-Black Sea axis. It is widespread in the Macaronesian islands and in the eastern and western Mediterranean (Fig. 5D). The most northerly record comes from the Venice Lagoon in the Adriatic Sea. It is also the only Dynamene species recorded from the Red Sea, in the Gulf of Aqaba (Fig. 5D). Glynn (1972) recorded a species that is clearly D. edwardsi from the Suez Canal. Picker and Griffiths (2011) have recorded this species (as D. bidentata) from South Africa.

Dynamene edwardsi occupies a wide vertical range in the littoral zone on NE Atlantic shores, and from the littoral zone down to 10 m in the Mediterranean. In recent field work, it was found to be very abundant in the Canary Islands and Madeira archipelago, whereas D. magnitorata was more common in the Azores and D. edwardsi rare. It is the most southerly of the Dynamene species extending down the West African coast to Mauritania and the only record for tropical waters. Glynn (1972) suggested that D. edwardsi has migrated from the Mediterranean throughout the whole length of the canal. Our study has shown that it has now reached the Gulf of Aqaba in the Red Sea

The records for the Suez Canal and Red Sea are interesting as they show movement from the Mediterranean Sea into the Red Sea, whilst many marine species are moving in the opposite direction (Galil et al. 2014). No Dynamene species have yet been recorded from the Indian Ocean (Schotte and Kensley 2005). However, a stage 8 male has been recorded from Port Elizabeth harbour in South Africa by Picker and Griffiths (2011). They suggest that it may have been introduced as a fouling organism or in ballast water. It is known that this species can be transported amongst fouling organisms on ships, as evidenced by the finding a stage 8 male on a ship in Tangiers harbour (Morocco) (see Suppl. material 1).

This species is variable in its morphology and particularly in the degree of hirsuteness. It may be that some of the specimens collected from the Balearic and Greek islands are in fact a new species, but more material is needed to prove this. Ideally, a molecular genetic analysis needs to be carried out on Mediterranean and Adriatic specimens. Such a technique applied to specimens from some NE Atlantic coasts and Macaronesian islands has shown that a number of cryptic species may be present (Vieira et al. 2015).

Dynamene magnitorata: Holdich (1968).

Dynamene bidentata: Monod (1932); Maggiore and Fresi (1984).

Dynamene magnitorata: Holdich (1968a, 1970, 1976).

Specimens were examined from 52 locations in the NE Atlantic, and four countries in the Mediterranean – see the Suppl. materials 1 and 2. A number of literature records have been included where the diagrams clearly indicate this species.

Body convex; in stage 8 males the pleotelsonic boss is large, bilobed, with the two halves separated by a narrow groove; the arms of the bidentate process are of similar width along their lengths and are dorsally tuberculate (Holdich 1976, fig. 3A, B; Fig. 2C–D in this paper). In stage 7 females the pleotelsonic dome is keeled in side view and the pleotelsonic foramen is flush with the edge of the pleotelson (Fig. 3C–D). Further details are provided by the scanning electron microscope pictures of the posterior body of a stage 8 male and a stage 7 female in Holdich (1976). The females of this species are very difficult to separate from those of D. bicolor. See keys to stage 8 males and stage 7 females.

Adult males (stage 8) typically 4.25 × 2.25 mm, pre-ovigerous females (stage 7) typically 4.0 × 2.0 mm.

A comparison of the life-histories of D. bidentata and D. magnitorata from two Atlantic coast locations was made by Holdich (1976). Only a limited number of D. magnitorata specimens were available but it showed that this species has a similar sequence of seasonal events (see description for D. bidentata). However, whereas D. bidentata stage 8 males live for two breeding seasons, those of D. magnitorata may only live for one.

A mid- to lower littoral and shallow sublittoral species, although sometimes recorded from deeper water. Its range occasionally overlaps that of D. bidentata. Juveniles are found associated with a wide range of littoral and shallow water algae, particularly Corallina sp., Rhodomenia palmata, Chondrus cripspus and Gigartina stellata. Adults have been found in empty tests of Balanus crenatus, amongst ascidians, and in channels within sponges (including those associated with eel grass beds). In the Roscoff region (northern France) adults were frequently found within the encrusting sponge, Halichondria sp. In the Azores (São Miguel island) adults have been found sublittorally in the empty tests of Megabalanus azoricus, as well as intertidally among algae on the islands of Terceira, São Miguel and Santa Maria. On Fuerteventura (Canary Islands) adult males were caught using a surface dip net. In the Chafarinas Islands off Mediterranean Morocco they have been recorded from 0.0m down to 20.0 m on a variety of algae. Like Dynamene bidentata (Harvey et al. 1973), D. magnitorata adults were found to have a tolerance to high air temperatures, i.e., 38 °C (Holdich 1976). However, survival at 5 °C was much lower for D. magnitorata compared to D. bidentata (Holdich 1976) and this may be the reason it has not colonized more northerly regions.

Individuals exhibit a wide variety of colours, often matching the colour of their background, the predominant colours being coralline-pink and brown, rather than the greens and yellows seen in D. bidentata. Individuals sometimes exhibit polychromatism caused by white, dorsal, non-adaptable chromatophores, as seen some other species (Holdich 1969, 1976).

The distribution of this species shown in Holdich (1970) has been extended by the present study. It has been recorded from southern England (a single specimen only that may be the result of a stranding), the Channel Islands, around the coasts of Brittany, the Atlantic Iberian Peninsula and northwest Africa, the islands of the Azores, Canary Islands and Madeira in the Macaronesian archipelagos, and in the Mediterranean along the European and African coasts, and also Egypt (Fig. 5E).

Almost all the Dynamene specimens found in the Azores during recent field work belonged to D. magnitorata. However, Dynamene was less prevalent in the benthic community when comparing with Canaries and Portugal (pers. obs., unpublished data). Maggiore and Fresi (1984) described D. bidentata from the Bay of Naples, but in fact examination of the specimen showed it to be a male D. magnitorata. If the author’s had compared an actual D. bidentata with their specimen then they would have realized this, particular as it is so much smaller than any known D. bidentata specimen. Dynamene magnitorata has only rarely been recorded in the Mediterranean, i.e. twice in Spain, and once in each of Egypt, Italy, Monaco and Tunisia, although it was found to be common on the Chafarinas Islands off Morocco (Castellanos et al. 2003) (see Suppl. material 1).

Dynamene tubicauda Holdich (1968).

Dynamene tubicauda: Holdich (1968a, 1970); Lombardo (1984); Borg et al. (2006).

Specimens were examined from six Italian locations in the Bay of Naples and off the island of Elba, and one location off Malta - see the Suppl. materials 1 and 2. A number of literature records from Sicily have been included as the diagrams clearly indicate this species (Lombardo 1984).

The morphology of this species is unique amongst the known Dynamene species - in stage 8 males the pereon length and width are similar; the epimera and front of the head form a shelf; the antennular peduncle is expanded; there are two widely separated, peg-like pleotelsonic bosses; and the pleotelsonic foramen is at the end of a ventrally-closed tube (Fig. 2I). In stage 7 females the body is also flattened with the epimera forming a shelf round the body; the pleotelsonic foramen is at the end of a well-developed tube (Figs 3J–K). See keys to stage 8 males and stage 7 females.

Adult males (stage 8) typically 3.0 × 2.0 mm, pre-ovigerous females (stage 7) typically 2.5 × 2.0 mm.

Nothing is known of the life-history of this species, other than the fact that sexual dimorphism occurs with males developing the bidentate process characteristic of the genus. Holdich (1968) only recorded males, but both sexes have been recorded in the present study. Lombardo (1984) was the first to describe the adult female.

This species has been found between 2-30 m amongst algae in muddy/sandy and coralline habitats, rock scrapings, freely swimming at 30 m, and also in sea grass meadows (Lombardo 1984, Borg et al. 2006).

Pale yellow. No polychromatism was observed.

The distribution of this species shown in Holdich (1970) has been extended by the present study. However, it appears to be restricted to the eastern Mediterranean, having only been recorded off the west coast of Italy (Holdich 1968), Sicily (Lombardo 1984) and Malta (Borg et al. 2006) (Fig. 5F). The most northerly record is for the island of Elba and the most southerly is off Malta.

The distribution of this species is the most restricted of all the Dynamene species along the NE Atlantic-Black Sea axis. Considering the large number of samples examined during this study this restricted distribution is most likely real. Its unusual flattened shape and the position of the pleotelsonic foramen at the end of a tube, even in adult males, may be an adaptation to inhabiting sediments.

Two stage 8 males. See the Suppl. materials 1 and 2.

The bilobed pleotelsonic boss has a posteriorly-directed spine not seen in any other stage 8 males. The uropodal exopod is wide and the body markedly hirsute.

Known only from the stomach contents of a black scorpionfish Scorpaena porcus.

Known only known from NW Aegean Sea.

Only two specimens have been found, both stage 8 males, and both from the stomach contents of a black scorpionfish, Scorpaena porcus. This could well be a new species of Dynamene, but more material is needed to confirm this. It may even be related to the hirsute specimens found in the Balearic Islands and the Greek island of Chios. The fish is known to be a bottom feeder in the Black Sea, close to where the specimen came from, which was in the NW Aegean, where it occurs at 20–40 m depth (Başçïnar and Saǧlam 2009). Rafrafi-Nouira et al. (2016) examined the diet of S. porcus from waters off the coast of Tunisia, but the only isopods they found were listed as unidentified.