Nerocila exocoeti Pillai, 1954

Aneesh, Panakkool-Thamban, Helna, Ammeri Kottarathil, Valarmathi, Kandasamy, Chandra, Kailash & Mitra, Santanu, 2017, Redescription of Nerocila exocoeti Pillai, 1954 (Crustacea: Isopoda: Cymothoidae) parasitic on beloniform (Exocoetidae and Hemiramphidae) hosts with Nerocila madrasensis Ramakrishna & Ramaniah, 1978 placed into synonymy, Zootaxa 4365 (3), pp. 385-394 : 387-392

Nerocila exocoeti Pillai, 1954

( Figs 1–7 )

Nerocila exocoeti Pillai 1954: 12 –13, fig. 6.— Kurochkin 1980: 289; Bruce 1987: 404; Bruce & Harrison-Nelson 1988: 592 – 593, fig. 4; Bruce & Bowman 1989:1; Trilles 1994: 89; Kensley 2001: 233; Sivasubramanian et al. 2011: 99 –101, figs 1– 4; Aneesh 2014: 23 –62, figs 2.9 c–d; Trilles, Rameshkumar & Ravichandran 2013: 1273 –1286, figs. 2c, 7a–i, 8, 9. Nerocila madrasensis Ramakrishna & Ramaniah, 1978: 177 –180, figs 1–3 (new synonymy).

Materials examined. Type material: Neotype —1♀, 28 mm, ovigerous, Parangipettai, southeastern coast of India from Exocoetus volitans Linnaeus (Exocoetidae) , deposited in MNHN by J.P. Trilles, coll. Rameshkumar on 12 April 2011 (MNHN-IU-2009-1937).

Holotype — 1 ♀, 27 mm, ovig., Madras (Tamil Nadu), from Hemiramphus sp. coll. P. Venkata Ramaniah, (C - 1680/2) ; Paratypes — 2 ♀, 26 mm, ovig., 24 mm partially molted, Madras (Tamil Nadu), coll. P. Venkata Ramaniah, (C - 1681/2) [originally deposited as Nerocila madrasensis by Ramakrishna & Ramaniah (1978)]

Non type material: 1 ♀, 26 mm, ovig., Marina Beach fish landing centre, Chennai, India, 13°05'N, 80°28'E, Bay of Bengal, from Parexocoetus brachypterus (Richardson) (Exocoetidae) , coll. P.T. Aneesh on 22 April 2017 (C - 7151/ 2); 1 ♀, 26 mm, ovig., Ayyikkara fish landing centre, 11°51'N, 75°22'E, Malabar Coast of Kerala, India from Rhynchorhamphus malabaricus (Hemiramphidae) coll. P.T. Aneesh & A.K. Helna on 8 August 2017 (C-7152/2).

Description. Female. Body symmetrical, about 2.4–2.8 times as long as wide, widest at pereonite 5–6. Cephalon longer than wide, anterior margin rounded; eyes with facets not much developed and indistinct. All coxae visible in dorsal view, 2–4, produced into rounded processes, not exceeding beyond posterior margin of pereonites; coxae 5–7 longer than the anterior and the posterior margin acute, extending beyond posterior of pereonites. Pereonites 1 and 5–6 longest, 2–4 subequal; pereonite 7 slightly shorter than 6; posterior angles of pereonites 1–5 not produced; postero-lateral angles of pereonite 6 reduced and 7 produced posteriorly as a pointed process. Pereonites 5–6 widest and slightly wider than pereonite 7. Pleonites all visible, pleonite 1 shortest, pleonite 5 longest and widest, pleonies 2–4 subequal; Ventro-lateral margins of pleonites 1–2 posteriorly directed and acute, extending beyond the pleonite 5; pleonites 3–5 lateral margins weakly acute. Pleotelson 1.1 times as wide as long, lateral margins convex.

Antennula distinctly stouter than antenna, 8 articled, distal margin of articles 5–7 with cluster of esthetes, article 8 with 4–6 terminal esthetes.

Antenna, 10–11 articled, decreasing gradually in width, article 7–10 with distal setae and article 2 and 3 with 3 elongated setae.

Mandible palp, article 1 longest and widest and article 3 with 4–5 marginal setae and one long apical recurved seta.

Maxillula with 4 apical spines slightly recurved.

Bi-lobed maxilla with 2 spines on median lobe and 1 spine on lateral lobe.

Maxilliped with oostegial lobe with many plumose setae and a palp with 2 apical and one lateral small recurved spines on article 3.

Pereopods gradually increase in size from 1 to 7. Pereopods 1–6 without marginal robust setae, dactylus longer than propodus; propodus of pereopod 7 with 5–7 marginal spines.

Pleopods not distinctly visible in dorsal view; pleopod 1–2, endopod without lobes, protopod medial margin of pleopod 1 with few plumose setae. Pleopod 2 with appendix masculina about half the length of endopod; endopod of pleopod 3 with a single lobe, 4 with 2–3 lobes and pleopod 5 with several lobes and several large folds. Proximo-medial lobe of pleopod 3-5 well-developed and folded.

Uropod rami slender, tapering and sub-linear exopod and endopod, exopod about two times longer than endopod. Endopod extending scarcely beyond the posterior margin of pleotelson and exopod extending far beyond it.

Brood pouch with 4 pairs of overlapping oostegites arising from the bases of pereopods 2, 3, 4 and 6. Number of eggs or larvae per brood pouch ranges from 130 to 300 according to the size of the female.

Size. Ovigerous female (16–28; avg. 26 mm), non-ovigerous female (13–26; avg. 22 mm).

Colour. Steel blue.

Host. Scomberomorus multiradiatus (Scombridae) (may be from gut contents); Parexocoetus brachypterus and Exocoetus volitans (Exocoetidae) ; Hemiramphus sp. and Rhynchorhamphus malabaricus (Hemiramphidae) ( Pillai 1954; Ramakrishna & Ramaniah 1978; Bruce & Harrisson-Nelson 1988; Sivasubramanian et al. 2011; Trilles et al. 2013; Aneesh 2014).

Distribution. Trivandrum (Kerala, India) ( Pillai 1954); Madras (Tamil Nadu, India) ( Ramakrishna & Ramaniah 1978; present study); Papua New Guinea, Indonesia and from Taiwan ( Bruce & Harrisson-Nelson 1988); Parangipettai, Southeastern coast of India ( Sivasubramanian et al. 2011; Trilles et al. 2013); Malabar Coast, Kerala ( Aneesh 2014; present study).

Remarks. Nerocila exocoeti can be easily distinguished from the other known species of the genus Nerocila by the following characters: short coxae, postero-lateral angles of the first five pereonites not posteriorly produced, those of 6–7 reduced, cephalon sub-quadrate with anterior border straight; first antenna composed of eight articles and endopod of uropod half the size of exopod. Nerocila exocoeti exhibits oligoxenous host specificity towards beloniform fishes; Parexocoetus brachypterus and Exocoetus volitans (Exocoetidae) ; Hemiramphus sp. and Rhynchorhamphus malabaricus (Hemiramphidae) are the identified hosts for the species. So far, only N. exocoeti and N. trichiuri have been collected from fishes belonging to the family Exocoetidae and both of these species are readily distinguished from each other. In N. exocoeti the uropods are much longer, exopod and endopod extending far beyond the distal margin of pleotelson. In N. trichiuri the coxae and postero-lateral angles of pereonites bluntly rounded and the live specimens of N. trichiuri are pale in colour.

In conclusion, the present study re-described the species based on the neotype collected from exocoetid host, Parexocoetus brachypterus and also compared the material collected from hemiramphid hosts; such as Hemiramphus sp. and Rhynchorhamphus malabaricus and also thoroughly examined the type materials (holotype and two paratypes) of Nerocila madrasensis . All morphological characters of Nerocila exocoeti collected from hemiramphid host ( Rhynchorhamphus malabaricus ) and the type material of Nerocila madrasensis collected from Hemiramphus sp. showed substantial similarity to Nerocila exocoeti collected from exocoetid host ( Parexocoetus brachypterus ). The present study clearly states that the Nerocila madrasensis described from Madras sea shore waters, by Ramakrishna &Ramaniah, (1978) should be treated as a synonym of Nerocila exocoeti Pillai, 1954 .

Figures

FIGURE1. Nerocila exocoeti Pillai, 1954, Femaleneotype (28 mm,ovig.) (MNHN-IU-2009-1937).A, dorsal view; B,ventral view; C, lateral view; D, cephalon.

FIGURE 2. Nerocila exocoeti Pillai, 1954, from Parexocoetus brachypterus (Richardson) (Exocoetidae), female (26 mm, ovig.) (C-7151/2). A, dorsal view; B, ventral view; C, lateral view.

FIGURE 3. Nerocila exocoeti Pillai, 1954, from Parexocoetus brachypterus (Richardson) (Exocoetidae), female (26 mm, ovig.) (C-7151/2). A, dorsal view; B, ventral view; C, lateral view; D, cephalon; E, antennula; F, antenna; G, mandible; H, mandible palp apical segment; I, maxillula; J, maxilla; K, maxilliped of non-ovigerous female; L, maxilliped of ovigerous female; M, distal segment of maxilliped palp.

FIGURE 4. Nerocila exocoeti Pillai, 1954, from Parexocoetus brachypterus (Richardson) (Exocoetidae), female (26 mm, ovig.) (C-7151/2). A–G, pereopods 1–7; H, brood pouch; I–M, pleopods 1–5; N, uropods and pleotelson; O, uropod rami.

FIGURE 5. Nerocila madrasensis described by Ramakrishna & Ramaniah (1978); A–E, female, holotype (C-1680/2), F–J, female, paratype(C-1681/2). A, dorsal view; B, ventral view; C, lateral view; D, cephalon; E, posterior region, F, dorsolateral view; G, ventral view; H, dorsal view of female (partially molted); I, cephalon;J, posterior region.

FIGURE 6. Nerocila exocoeti Pillai, 1954, collected from Rhynchorhamphus malabaricus, female (26 mm, ovig.)(C-7152/2). A–E, alcohol preserved, A, dorsal view:B, ventral view; C, lateral view; D, posterior region: E, anterior region, F, dorsal view, live/fresh color; G–H, live on host fish Rhynchorhamphus malabaricus.

FIGURE 7. Nerocila exocoeti Pillai, 1954, collected from Rhynchorhamphus malabaricus female (26 mm, ovig.)(C-7152/2). A, dorsal view; B, ventral view; C, lateral view; D, cephalon; E, antennula; F, antenna; G, uropods and pleotelson.