Pleopodias elongatus Richardson, 1910, by monotypy.

Body elongate; cephalon slightly immersed in pereonite 1, posterior margin not trilobed; eyes large and distinct. Rostrum folded back, lying between antennula bases, not concealing basal articles. Antennula long and narrow, extending past cephalon posterior margins; antenna longer than antennula, extending to or beyond pereonite 2, articles 3–6 elongate. Pereon most narrow at pereonite 1; pleon narrower than pereon with pleonites progressively getting narrower from pleonite 1 to 5; pleotelson elongate, 1.2–1.8 times longer than wide. Pereonite 2 shortest in length, pereonite 6 longest. Uropods long and narrow, extending beyond the posterior margin of the pleotelson. Pereopod 7 longer than other pereopods with the merus, carpus and propodus on pereonite 7 elongated.

Pleopodias can be identified by the long antennae, with the antennula shorter than the antenna; body most narrow at pereonite 1; narrow pleon with the width of the pleonites decreasing from pereonite 1 to 5; pereopod 7 longer and more elongate than other pereopods; uropods extending past the posterior margin of the pleotelson; and a longer than wide pleotelson.

The original diagnosis for this genus was provided by Richardson (1910) but was based on the only species known at that time, P. elongatus. In his report on a Pleopodias sp. from the Andaman Islands, Barnard (1936) pointed out that of some of the generic characters used by Richardson to define the genus (i.e. antennula articles 2 and 3 expanded, and pleopods visible in dorsal view) were shared with Anilocra Leach, 1818 and thus not very informative. Bruce (1987) revised both Pleopodias and Anilocra simultaneously and was able to provide a number of differences between the two genera. According to Bruce (1987), Pleopodias has a narrow pleon, getting strongly narrower towards the posterior (not always narrower in Anilocra); antennula articles 4–8 are elongate (not in Anilocra); large robust setae on the maxilla and the medial lobe is distinct (acute, simple robust setae and the maxilla is partially fused in Anilocra); article 3 of the mandible palp is slim and longer than article 2 (article is stout and short in Anilocra); and pereopod 7 with more robust setae than observed in Anilocra. Bruce (1987) also included mouthpart and pleopod morphology in the generic diagnosis of Pleopodias, however, as not all species have these characters noted, we have refrained from adding them into the currently revised diagnosis.

This key is based on the morphological characters of the gravid female:

Female holotype of Pleopodias superatus (26.5 mm TL, 10.4 mm W), caught in a shrimp net off Honshu Island, Japan, 11 April 1969 (USNM 231069).

Holotype. Non-ovigerous female, collected from the East-China Sea (Sea of Japan), from the body of Diaphus coeruleus (TINRO AGK 74190). Paratypes. Non-ovigerous females, same information as holotype (TINRO APK 74191–74195). Not examined.

Figure 1. 

Pleopodias diaphus Avdeev, 1975 (USNM 231069), female (26 mm), (originally designated as the holotype of Pleopodias superatus Williams & Williams, 1986). A dorsal view B dorsal view of pereonite 1 and cephalon C pereopod 1 D ventral view of cephalon E pereopod 7 F dorsal view of pleon and pleotelson G lateral view.

Female holotype of Pleopodias superatus. Length 26.5 mm, width 10.4 mm.

Body oval, 2.4 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.8 times longer than wide, visible from dorsal view, subtriangular. Frontal margin truncate, thickened and ventrally folded. Eyes oval with distinct margins; one eye 0.3 times width of cephalon, 0.4 times length of cephalon. Pereonite 1 smooth, anterior border slightly indented, anterolateral angle narrowly rounded, extending to middle of the eye. Posterior margins of pereonites 1–4 smooth and straight, 5–7 slightly curved laterally, posterior margin of pereonite 7 produced medially. Coxae 2–3 narrow, with posteroventral angles rounded; 4–7 small and narrow, not extending past pereonite margin. Pereonites 1–5 increasing in length and width; 6–7 decreasing in length and width. Pereonite 7 partially overlapping pleonite 1. Pleonites posterior margin smooth, mostly concave. Pleonite 1 widest, visible in dorsal view. Pleonite 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 narrowly rounded. Pleonites 3–5 progressively getting smaller; pleonite 5 not overlapped by lateral margins of pleonite 4, posterior margin slightly concave. Pleotelson 1.8 times as long as anterior width, dorsal surface slightly depressed, lateral margins straight, posterior margin with medial notch.

Antennula thinner and shorter than antenna, contiguous bases, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; articles 2–3 expanded; extending to pereonite 2. Antenna consisting of 12 articles; extending to middle of pereonite 3. Pereopod 1 basis 1.6 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with straight proximal margin; propodus 1.2 times as long as wide; dactylus slender, 1.5 times as long as propodus, 2.4 times as long as basal width. Pereopod 7 longer than other pereopods, basis 2.2 times as long as greatest width; ischium 0.8 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.2 times as long as wide, 0.5 times as long as ischium; carpus 0.9 times as long as wide, 0.4 times as long as ischium, without bulbous protrusion; propodus with numerous acute robust setae, 2.6 times as long as wide, 0.8 times as long as ischium; dactylus slender, 0.8 times as long as propodus, 3.3 times as long as basal width. Uropod longer than the pleotelson, rami subequal. Endopod apically rounded. Exopod apically narrowly rounded.

Sea of Japan (Avdeev 1975) and off Honshu, Japan (Williams and Williams 1986; Yamauchi 2009).

Anterior to the dorsal fin of Diaphus coeruleus (Blue lantern fish) (Avdeev 1975).

Pleopodias diaphus has an ovate shape, contiguous antennula bases, and an emarginated pleotelson posterior margin. The uropod rami are approximately the same length and the eyes are large (each eye approximately a third of the cephalon width).

It was originally described from Japan, with several drawings and a brief description in Russian. In 1986, Williams and Williams described a new species, Pleopodias superatus which shared many similarities with P. diaphus. After comparisons of the notched pleotelson as well as the antennae and somatic morphology, Bruce and Harrison-Nelson (1988) synonymised it with P. diaphus. Despite numerous attempts, the type specimens of P. diaphus could not be obtained for inclusion in the present study; however, the types do exist and the species is eminently recognisable from the original illustrations and is therefore not a nomen dubium or species inquirenda. Avdeev (1975) reported the types as immature females but both the size and drawings indicate they are still adult females (non-ovigerous) and therefore suitable for a valid species description. Both species (P. diaphus and P. superatus) are well illustrated, readily recognised, from the same region, and appear identical, thus the synonymy of the two species by Bruce and Harrison-Nelson (1988) is here upheld until a detailed redescription of the original type material of P. diaphus indicates otherwise.

As the type material for P. diaphus could not be obtained the redescription provided here is based on the holotype of P. superatus housed at USNM. This redescription includes updated measurements and characteristics which are comparable to the other Pleopodias species in this paper. This modern description of the type material of P. superatus will also aid future research into its current status as junior synonym of P. diaphus.

Pleopods and mouthparts of specimens identified as P. diaphus were drawn and described by Yamauchi (2009). The specimens Yamauchi (2009) examined largely conformed to the above description; however, the body size differed with the three more recent samples (12–27 mm in length) being more slender (3.4–3.9 times as long as wide).

Holotype. Ovigerous female (20 mm), off Matocot Point, Philippine Islands, 8 June 1908, 170 fathoms (= 311 m depth), station 5268, coll. U .S. Bureau of Fisheries Albatross Philippine Expedition 1907-08 (USNM 40917). Also noted: bottom third of the pleotelson folded in.

Figure 2. 

Pleopodias elongatus Richardson, 1910 (USNM 40917), female holotype (20 mm). A dorsal view B dorsal view of pereonite 1 and cephalon C pereonite 7 D pereopod 1 E dorsal view of pleon and pleotelson F lateral view G ventral view of cephalon.

Female holotype. Length 20 mm, width 7.5 mm.

Body elongate, 2.7 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 4 and pereonite 5, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.7 times longer than wide, visible from dorsal view, subtriangular. Frontal margin thickened, ventrally folded and truncate. Eyes oval with distinct margins, one eye 0.25 times width of cephalon; 0.4 times length of cephalon. Pereonite 1 smooth, anterior border straight, anterolateral angle acute, anteriorly produced, extending to one third of the eye. Posterior margins of pereonites smooth and slightly curved laterally. Coxae 2–4 narrow, with posteroventral angles rounded; 5–7 small and narrow, not extending past pereonite margin, with posteroventral angles curved. Pereonites 1–4 increasing in length and width; 5–7 decreasing in length and width. Pleonites posterior margin smooth, mostly concave. Pleonite 1 widest, visible in dorsal view. Pleonite 1 and 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 rounded. Pleonites 3–5 progressively getting smaller; pleonite 5 not overlapped by lateral margins of pleonite 4, posterior margin straight. Pleotelson 1.6 times as long as anterior width, dorsal surface slightly depressed, lateral margins weakly convex, posterior margin rounded and damaged.

Antennula thinner than antenna, length longer than antenna, bases narrowly separated, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; articles 2–3 expanded; extending to middle of pereonite 1. Antenna consisting of 11 articles; extending to middle of pereonite 2. Pereopod 1 basis 1.6 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with straight proximal margin; propodus 1.4 times as long as wide; dactylus moderately slender, 1.3 times as long as propodus, 2.4 times as long as basal width. Pereopod 7 longer than other pereopods, basis 2.3 times as long as greatest width; ischium 0.8 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.3 times as long as wide, 0.4 times as long as ischium; carpus 1.3 times as long as wide, 0.4 times as long as ischium, with slight bulbous protrusion; propodus 3.3 times as long as wide, 0.8 times as long as ischium; dactylus slender, 0.9 times as long as propodus, 3.7 times as long as basal width. Uropod longer than the pleotelson, rami subequal. Endopod apically slightly pointed. Exopod apically narrowly rounded.

Not known.

Philippine Islands (Richardson 1910; Bruce 1987).

Pleopodias elongatus can be distinguished by the small eyes (each eye a quarter of the cephalon width), antennula bases narrowly separated, antenna extending to the middle of pereonite 2, rounded pleotelson, and uropod rami approximately the same length.

The only other species recorded from the Pacific is P. diaphus (from Japan). Pleopodias elongatus differs from P. diaphus in having antennula bases narrowly separated (P. diaphus bases in contact), shorter antenna (P. diaphus antenna extend to posterior of pereonite 3), absence of robust setae on propodus of pereopod 7 (P. diaphus has numerous acute robust setae), a rounded pleotelson (P. diaphus pleotelson subquadrate with a deeply emarginated medial notch), and smaller eyes (P. diaphus eyes cover a third of the cephalon width).

Holotype. Female (28 mm TL, 11 mm W), 9 July 1883, collected from the Talisman, St. DR71 (dredge), 640 m depth, coast of Sudan, MNHN-IU-2014-12188 (= MNHN-Is2460). Also noted: the specimen is black with the pleotelson folded in.

Figure 3. 

Pleopodias vigilans Richardson, 1911 (MNHN-IU-2014-12188), female holotype (28 mm). A dorsal view B ventral view of cephalon C pereopod 1 D dorsal view of pereonite 1, pereonite 2 and cephalon E dorsal view of pleon and pleotelson F pereopod 7 G lateral view.

Female holotype. Length 28 mm, width 11 mm.

Body elongate, 2.9 times as long as greatest width, dorsal surfaces slightly bumpy, widest at pereonite 4, most narrow at pereonite 1. Cephalon 0.6 times longer than wide, visible from dorsal view, subtriangular. Frontal margin thickened, ventrally folded and truncate. Eyes not clearly defined; one eye 0.4 times width of cephalon, 0.6 times length of cephalon. Pereonite 1 smooth, anterior border slightly irregular, anterolateral angle narrowly rounded. Posterior margins of pereonites smooth and straight. Coxae 2–3 wide, with posteroventral angles rounded; 4–7 small and narrow, extending past pereonite margin. Pereonites 1–4 increasing in length and width; 5–7 decreasing in length and width. Pleonites posterior margin not smooth, mostly concave. Pleonite 1 widest, slightly visible in dorsal view. Pleonite 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 rounded. Pleonites 3–5 progressively getting smaller; pleonite 5 with posterolateral angles rounded, posterior margin produced medially. Pleotelson 1.2 times as long as anterior width, dorsal surface slightly depressed, lateral margins posteriorly narrow, posterior margin converging to rounded caudomedial point.

Antennula thinner and shorter than antenna, bases widely separated, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; extending past the posterior margin of cephalon. Antenna consisting of 11 articles, extending to posterior of pereonite 2. Pereopod 1 basis 1.6 times as long as greatest width; ischium 0.7 times as long as basis; merus proximal margin without bulbous protrusion; carpus with straight proximal margin; propodus 1.5 times as long as wide; dactylus slender, 1.8 times as long as propodus. Pereopod 7 longer than other pereopods, basis 2.4 times as long as greatest width; ischium 0.6 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.3 times as long as wide, 0.6 times as long as ischium; carpus 1.1 times as long as wide, 0.4 times as long as ischium, without bulbous protrusion; propodus 2.3 times as long as wide, 0.9 times as long as ischium; dactylus slender, 1.1 times as long as propodus, 3.7 times as long as basal width. Uropod longer than the pleotelson; peduncle 0.4 times longer than rami, peduncle lateral margin without setae, apices broadly rounded. Endopod apically rounded, 3.5 times as long as greatest width. Exopod extending beyond posterior of endopod, 5 times as long as greatest width, apically rounded.

Sudan (Richardson 1911).

Not known.

Pleopodias vigilans can be identified by the antennula bases being widely separated, large eyes occupying majority of the cephalon, antenna extending to posterior of pereonite 2, uropodal exopod longer than endopod, and rounded pleotelson with a caudomedial point.

Only one specimen of this species has ever been collected. Due to the age and condition of the specimen, it was not possible to see some of the characters usually associated with Pleopodias (i.e. robust setae on pereopod 7 etc.).

No figures of the specimen were provided in the original description, and as no other collections have been made since, no drawings of the specimen have ever been produced. This redescription provides the first illustrated figures of P. vigilans and will help future identifications of this species. Fresh collections of this species could prove valuable in adding to this information, along with information on the mouthparts and pleopods of this species.

Holotype. Female (30mm TL; 9mm W), RV Africana Cruise 060 (34°46.6'S 18°02.5'E), Station A7033-060-14-03M, South Africa, 14 March 1988, 702m depth (SAMC A088881). Paratype. Male (20mm TL; 5 mm W), same info as holotype (SAMC A43478).

Figure 4. 

Pleopodias nielbrucei sp. n. (SAMC A088881), female holotype (30 mm). A dorsal view B dorsal view of pereonite 1 and cephalon C uropod D pereopod 1 E pereopod 2 F pereopod 6 G ventral view of cephalon H dorsal view of pleon and pleotelson I pereopod 7 J lateral view.

Figure 5. 

Pleopodias nielbrucei sp. n. (SAMC A43478), male paratype (20 mm). A dorsal view B dorsal view of pleon and pleotelson C dorsal view of pereonite 1 and cephalon D ventral view of cephalon E pereopod 1 F pereopod 7 G lateral view.

Female holotype. Length 30 mm, width 9 mm.

Body narrow, 3.3 times as long as greatest width, dorsal surfaces smooth and polished in appearance, widest at pereonite 5, most narrow at pereonite 1, lateral margins subparallel. Cephalon 0.7 times longer than wide, visible from dorsal view, subtriangular. Frontal margin thickened, ventrally folded and truncate. Eyes oval with distinct margins, one eye almost 0.5 times width of cephalon; 0.6 times length of cephalon. Pereonite 1 smooth, anterior border slightly indented, anterolateral angle narrowly rounded, extend to one third of the eye. Posterior margins of pereonites smooth and slightly curved laterally. Coxae 2–3 wide, with posteroventral angles rounded; 4–7 small and narrow, not extending past pereonite margin. Pereonites 1–5 increasing in length and width; 6–7 decreasing in length and width. Pleonites posterior margin smooth, mostly concave. Pleonite 1 widest, visible in dorsal view. Pleonite 2 not overlapped by pereonite 7; posterolateral angles of pleonite 2 narrowly rounded. Pleonites 3–5 similar in form to pleonite 2; pleonite 5 not overlapped by lateral margins of pleonite 4, posterior margin produced medially. Pleotelson 1.2 times as long as anterior width, dorsal surface slightly depressed, lateral margins straight, posterior margin subtruncate.

Antennula thinner and shorter than antenna, bases widely separated, consisting of 8 articles; peduncle articles 1 and 2 distinct and articulated; extending to anterior of pereonite 1. Antenna consisting of 11 articles, extending to middle of pereonite 2. Pereopod 1 basis 1.4 times as long as greatest width; ischium 0.7 times as long as basis; merus with simple setae, proximal margin without bulbous protrusion; carpus with rounded proximal margin; propodus 1.5 times as long as wide; dactylus moderately slender, 1.7 times as long as propodus, 3.3 times as long as basal width. Pereopod 2 propodus 1.4 times as long as wide; merus with simple setae; dactylus 1.7 times as long as propodus. Pereopod 6 basis twice as long as greatest width, ischium 0.6 times as long as basis, propodus 1.7 times as long as wide, dactylus 1.8 times as long as propodus. Pereopod 7 longer than other pereopods, basis 2.3 times as long as greatest width; ischium 0.8 times as long as basis, without protrusions; merus proximal margin without bulbous protrusion, 1.2 times as long as wide, 0.6 times as long as ischium; carpus with numerous acute robust setae, 1.4 times as long as wide, 0.5 times as long as ischium, without bulbous protrusion; propodus with numerous acute robust setae, 2.8 times as long as wide, as long as ischium; dactylus slender, as long as propodus, 3.5 times as long as basal width. Uropod longer than the pleotelson, peduncle 0.4 times longer than rami, peduncle lateral margin without setae. Endopod apically slightly pointed, 5 times as long as greatest width, terminating without setae. Exopod extending beyond posterior of endopod, apically narrowly rounded, terminating without setae.

Male paratype. Length 20 mm, width 5 mm.

Male similar to female but smaller. Body rectangular, body 3.5 times as long as wide. Antennula bases separated, consisting of 8 articles, extending to posterior margin of cephalon. Antenna consisting of 12 articles, extending to middle of pereonite 2. Eyes slightly separated, one eye almost 0.5 times width of cephalon; 0.7 times length of cephalon.

Named in honour of Dr Niel Bruce, in recognition of his significant contribution to the taxonomy of isopods, specifically that of fish parasitic cymothoids.

Off the coast of Cape Town, South Africa.

Not known.

Pleopodias nielbrucei sp. n. can be identified by the narrow body, large eyes covering majority of the cephalon (almost in contact), antennula bases wide apart, antenna extending to middle of pereonite 2, subtruncate pleotelson, pereopod 7 with numerous acute robust setae on the propodus as well as the carpus, and the uropodal exopod longer than the endopod.

This is the first named Pleopodias species from the southern hemisphere (not including the unknown Pleopodias sp. mentioned below). It differs from the other three known species in having larger eyes and a more elongate body, as well as a shorter and more quadrate pleotelson and antennula bases which are further apart than the other species. Pleopodias nielbrucei sp. n. also has a less graduated pleon (the pleonites do not decrease in width from pleonite 1 to 5 as prominently as P. diaphus and P. elongatus).

Ovigerous female (14.5 mm TL), 232 km north of Port Hedland, Western Australia, 10 Oct 1982, 298-300 m depth, coll: L. Marsh & S. Slack-Smith on FRV Soela (WAM 607-80). Also noted: Specimen is crushed within the tube. Not examined.

Ovigerous female (15.5 mm TL), 370–419 fathoms, north of Andaman Islands (14°13'N; 93°40'E). Not examined.

Andaman Islands and Australia (Barnard 1936; Bruce 1987).

Not known.

Bruce (1987) reported what appears to be an undescribed Pleopodias species; however, the Australian specimen is crushed and the whereabouts of Barnard’s specimen is unknown. This species differs from P. elongatus (which it was originally identified as by Barnard) in having a sub-truncate and very narrow pleotelson, uropods which extend to the posterior margin of the pleotelson, antennula bases contiguous, a shorter rostrum, larger eyes, and a less laterally rounded pereonite 7. A tentative description of the Australian specimen was provided by Bruce (1987) but more specimens (in good condition) are required in order to describe the species.