Barybrotes indus Schioedte and Meinert, 1879

Vigneshwaran, P., Ravichandrana, S. & Kumar Ajith ,, T. T., 2022, Redescription of the monotypic micro-predatory isopod genera Alitropus H. Milne Edwards, 1840 and Barybrotes Schioedte & Meinert, 1879 (Isopoda, Cymothoida), with a taxonomic key to the Cymothooidea Leach, 1814 from India, Journal of Natural History 55 (45 - 46), pp. 2909-2934 : 2924-2926

Barybrotes indus Schioedte and Meinert, 1879

( Figures 6–10 )

Barybrotes indus Schioedte and Meinert, 1879: 281–283 , pl. III, figs 1–10, pl. IV, fig. 1. — Stebbing, 1893: 347. — Monod, 1934: 10, pl. 11–17. — Barnard, 1936: 157. — Pillai, 1954: 8. — Pillai 1967: 278–279, pl. II 2, fig. 6.

Barybrotes agilis Schioedte and Meinert, 1879: 283–284 , pl. III, figs 11–13. — Hansen, 1890: 167–169, pl. IX, figs 3–3s. — Richardson, 1910: 8. — Nierstrasz, 1931: 177.

Type and locality. The holotype is held at Zoological Museum , Natural History Museum of Denmark, University of Copenhagen (NHMD-84636 (previously ZMUC-CRU-6792)). The original description states that the type locality is in the Bay of Bengal; the detailed station information, 6°22 ʹ N, 95°54 ʹ E, clearly puts the locality in the Indonesian part of the Andaman Sea.

Material examined. Holotype: Female (22 mm), coll. Schiödte and Meinert ( NHMD- 84636); syntype: 1 female, Sumatra, Java Sea, 3°25 ʹ S, 106°50 ʹ E, coll. Andréa, 1869 (NHMD-81765 (previously ZMUC-CRU-3917)).

Non-type: 1 female (21 mm) Cauda , Nha Trang , Vietnam, 13 May 1929 (NHMD-263602); 1 ovigerous female with eggs (21 mm) Andaman Sea, Thailand, 79 m, 14 January 1966 (NHMD-263603); 1 ovigerous female (20 mm) Parangipettai (11.5084°N, 79.7568°E) 18 August 2017 from Strophidon sathete (Hamilton, 1822) (ZSI/ MBRC D1-553 ); 5 females (18–24 mm) Parangipettai (11.5084°N, 79.7568°E), 12 September 2016, from Muraenesox cinereus (Forsskål, 1775) ( CAS / MBRM C-301 to C-305 ), coll. P. Vigneshwaran.

Redescription of female ( Figures 6–10 ). Body ( Figures 6 (a) and 7(a,b)) almost parallelsided, about 4.5 times as long as wide, longest between pereonites 4–6. Cephalon is semicircular, with a small anteromedian rostrum projecting between the bases of the antennules. Eyes large, almost contiguous, 0.6 times width of the cephalon. Pereonite 1 longer than pereonites 2 and 3, subequal to cephalon; pereonites 4–6 longer than others; pereonite 7 shorter, subequal to 3 and 4. Coxae ( Figures 6 (c) and 8(a)) 2–4 well developed, partially visible in dorsal view; coxae 5–7 well developed, extending beyond posterior margin of respective pereonites. All pleonites visible dorsally, pleonites 1–3 subequal in length and width, lateral margin of pleonite 4 produced posteriorly and overlapping pleonite 5. Pleotelson ( Figure 6 (e)) sub-truncate apically and dorsally convex in welldeveloped female, with 6–7 spines and long setae.

Antennula ( Figure 8 (b)) extending to middle of the eye, stouter than the antenna; peduncle with 5 articles, articles 1 and 2 widest and others decreasing in width progressively, article 5 longest; proximal segment large and visible dorsally with a plumose spine on distal inferior margin; flagellum with 6 articles; distal composite flagellar articles with three clusters of setae, distal articles with few terminal aesthetasc setae. Antenna ( Figure 8 (c)) extending to middle of pereonite 6, peduncle 5-segmented, distal peduncular segment with 2 plumose setae on distal inferior margin; flagellum has 33–36 articles, each article with setae on its distal inferior and distal superior margins. Frontal lamina is clubshaped.

Mandible ( Figure 8 (d)) with a tridentate incisor process; reduced molar process; lamellar; lacinia mobilis and spine row absent, represented by 1 or 2 setae; palp 3-segmented, proximal segment longest, distal margin setose, middle and distal segments with a comb of setae. Maxilla ( Figure 8 (f)) long narrow, simple minute lobe, lacking robust setae, with 2 hook-like spines latero-distally and 7 recurved spines apically. Maxilliped ( Figure 8 (g)) endite absent; palp with 4 articles, article 2 elongate, about 2.9 times proximal width, articles 2–4 with hooked robust setae; article 4 smallest, apex bears 5 curved hook-like spines and 3 slender minute spines.

Pereopods 1–3 ( Figure 9 (a–c)) with prehensile dactylus, about as long as or longer than propodus; superior distal margins of ischium and merus strongly produced and setose; inferior lateral margins of merus, carpus and propodus also bears fringed sensory spines; dactylus falcate, uniunguiculate. Pereopod 2 ( Figure 9 (b)) propodus with 6 robust setae on palm. Pereopod 3 ( Figure 9 (c)) ischium anterodistal angle produced, but not as produced as on pereopods 1 and 2, similar to pereopod 4, propodus with 1 robust seta on palm.

Pereopods 4–7 with flattened basis, with superior and inferior margins provided with continuous row of long plumose setae. Pereopod 4 ( Figure 9 (d, e)) merus anterodistal angle produced with 3 rows of 8, 6 and 3 robust setae, respectively, on palm. Pereopod 6 ( Figure 9 (f)) basis anterior margin sinuate; medial carina with plumose seta; posterior margin convex, plumose seta present. Ischium anterior margin with slender seta; posterior margin with 1 robust seta, plumose seta present. Merus posterior margin with 4 robust setae, slender seta present. Carpus posterior margin with 3 robust setae, slender seta absent. Propodus longer than carpus; posterior margin with 3 robust setae, slender seta absent.

Pereopod 7 ( Figure 10 (a)) basis anterior margin sinuate; medial carina with plumose seta along entire length; posterior margin convex, plumose seta present. Ischium anterior margin with slender seta; posterior margin without robust seta, plumose seta present. Merus anterior margin with slender seta; posterior margin without robust seta, slender seta present. Carpus posterior margin without robust seta, slender seta present. Propodus longer than carpus; posterior margin with 6 robust setae, slender seta present.

Pleopods ( Figure 10 (b–e)) rami lamellar, without ridges or folding, with plumose marginal setae on both rami of pleopods 1 and 2, setation reduced on endopods of pleopods 3 and 4; pleopod 5 endopod with setae. Pleopod 2 ( Figure 10 (c)) appendix masculina: extending subequal to the tip of endopod, 1.01 times length of endopod; margins very slightly curved laterally; slender; apex not at angle to adjacent margins, bluntly rounded.

Uropod ( Figure 7 (d)) falls short of pleotelson apex, exopod with acute apex bearing 7 marginal spines and numerous long setae; endopod with rounded apex, bearing 9 spines and long setae marginally.

Variation. The number of robust setae on the pleotelson is most often 8 but may range between 6 and 12 – 6 in the holotype (NHMD-84636); 10 in the syntype specimens from the Sumatra , Java Sea (NHMD-81765); 12 in specimens from Southeast coast of India Bay of Bengal (ZSI/MBRC D1-553 ). The antennae reach the posterior of pereonite 4 in the holotype specimen, whereas in other material they extend approximately halfway along pereonite 3. All of the specimens examined, other than the holotype of B. indus , have an angular pleotelson as described for this species by Schioedte and Meinert (1879). Specimens from the Southeast coast of Indian Bay of Bengal (ZSI/MBRC D1-553 ) have a complete interocular furrow and indistinct coxal furrows on all coxae.

Distribution. Barybrotes indus is widely distributed from the Indian Ocean – East Africa/ Kenya, India, Malaysia, Indonesia and Thailand ( Schioedte and Meinert 1879; Hansen 1890; Monod 1934; Pillai 1954, 1967; Bruce 2009; present study) – to the Pacific Ocean – Philippines ( Richardson 1910) and Vietnam ( Bruce 2009).

Prey. The present material was collected from slender giant moray S. sathete (Hamilton, 1822) , dagger-tooth pike conger M. cinereus (Forsskål, 1775) and mangrove red snapper Lutjanus argentimaculatus (Forsskål, 1775) . Pillai (1967) reported this species from the gills of giant devil ray Mobula diabolus (as Mobula mobular (Bonnaterre, 1788)) .

The juveniles are ectoparasitic on fishes until they attain sexual maturity. The adults are, however, free-living and cling to fish only for the purpose of feeding.

Remarks. Barybrotes indus can be identified by the elongate body with an evenly vaulted dorsum; the cephalon anterior margin semicircular, with a small anteromedian process projecting between the bases of the antennule; pereonites 4–6 large, with a prominent lateral groove running inwards; pleotelson elongate triangular and dorsally arched, its apex, in adult specimen, subtruncate and armed with 6 strong spines; frontal lamina clubshaped; inner lobe of the maxilla with a pair of setae at the base of the large seta.

Barybrotes indus was first reported from the Bay of Bengal by Schioedte and Meinert (1879). Since then, it has been recorded from the Indian Ocean and Pacific Ocean (East Africa to Vietnam; see ‘Distribution’) Bruce (2009). Nevertheless, its mouthparts and somatic appendages were not fully illustrated until Bruce (2009) published his work on the marine fauna of New Zealand. Inasmuch as certain fine structures of possible taxonomic significance were not found in Bruce’s re-evaluation of B. indus , a full description of our Indian specimens is provided. After Schioedte and Meinert’s (1879) Latin description, B. indus was mentioned in a few publications, such as Monod (1934), Barnard (1936), Pillai (1967) and Bruce (2009), but there is no detailed description of this species. This has led to much confusion about the species and its validity has frequently been questioned. The first step in answering this question was to provide a complete redescription of B. indus along with precise and detailed drawings of all appendages, and views that were previously unavailable, all of which are given here. The present redescription confirms the validity of B. indus as a valid species based on the available information.

Figures

Figure 6. Barybrotes indus Schioedte and Meinert, 1879, ovigerous female (20.0 mm; ZSI/MBRC D1- 553). (a) Dorsal view; (b) ventral view; (c) lateral view; (d) ventral view of cephalon with mouth parts; (e) dorsal view of pleon. Please replace in colour figures

Figure 7. Barybrotes indus Schioedte and Meinert, 1879, ovigerous female. (a) Holotype (22.0 mm; NHMD-84636 (previously ZMUC-CRU-6792));(b–d) non-type (20.0 mm; ZSI/MBRC D1-553). (a, b) dorsal view; (c) ventral view of cephalon with mouth parts; (d) uropod.

Figure 8. Barybrotes indus Schioedte and Meinert, 1879, ovigerous female (20.0 mm; ZSI/MBRC D1- 553). (a) Lateral view; (b) antennula; (c) antenna; (d) mandible; (e) maxillule; (f) maxilla; (g) maxilliped.

Figure 9. Barybrotes indus Schioedte and Meinert, 1879, ovigerous female (20.0 mm; ZSI/MBRC D1- 553). (a–d) Pereopods 1–4; (e) pereopod 4 merus ventral view; (f) pereopod 6.

Figure 10. Barybrotes indus Schioedte and Meinert, 1879, ovigerous female (20.0 mm; ZSI/MBRC D1- 553). (a) Pereopod 7; (b–e) pleopods 1, 2, 4, 5, respectively.