Elthusa arnoglossi, Trilles & Justine, 2006

Trilles, Jean-Paul & Justine, Jean-Lou, 2006, Elthusa arnoglossi sp. nov. (Crustacea: Isopoda: Cymothoidae), a branchial parasite of flatfishes (Bothidae) from the Chesterfield Islands, New Caledonia, Zootaxa 1338 (1), pp. 57-68 : 59-66

Elthusa arnoglossi sp. nov.

( Figs 1–4 )

Material examined

Holotype. ♀ (ovig, 11.0 mm), MNHN –Is 5893. Chesterfield Islands , Banc Nova Nord, EBISCO cruise, RV Alis, station CP 2539, 10 October 2005, 22°20'S, 159°24' E, depth 315–320 m.

Paratypes. Allotype, ♂ (7.0 mm), MNHN –Is 5894; 23 ♀ (16 ovig, TL 9.0–13.0 mm; 7 non-ovig, TL 10.5–13.0 mm); 2 intermediate stages (8.5–9.0 mm); 4 ♂ (6.5, 7.0, 7.5 and 8.5 mm), MNHN –Is 5895, 5896, 5897, 5898. Parasite collection number JNC1639 .

Type-host

Arnoglossus sp. The fish specimens could not be identified at the species level and are either Arnoglossus polyspilus ( Günther, 1880) or A. japonicus Hubbs, 1915 ( Pleuronectiformes , Bothidae ). They are deposited in the collections of the MNHN under number 2006–0759.

Site of attachment

The female occurs only in the lower gill chamber, attached to the branchial arches, with the head facing the buccal cavity; the male usually settles beneath the female.

Etymology The species name is derived from that of the host genus, Arnoglossus . Description of ovigerous and non-ovigerous females ( Figs 1A–C , 2A–O , 4A–F )

Body about 1.5 times as long as wide, widest at pereonite 4, asymmetrical, deeply twisted to the right side. Pereon slightly vaulted at the level of pereonites 2–4.

Cephalon about 1.6 times as wide as long, roughly triangular, anterior margin acute in dorsal view, with minute rostral point, posterior margin broadly rounded, not enclosed in the pereonite 1. Eyes about 0.5 times width of cephalon, ovate, black. Coxal plates of pereonites 2–7 more or less visible in dorsal view.

Pereon broad, about 1.15 as wide as long, always twisted to the right side. Pereonite 1 longest, 2–4 progressively decreasing in length, 5–7 shortest and subequal in length. Posterior margin of pereonite 7 deeply curved. Pereonites 3–4 are expanded on the right side compared to the left.

Pleon about 1.8 as wide as long; all pleonites visible; pleonite 1 shorter and narrower than others, partially covered by pereonite 7; pleonites 2–5 progressively narrower towards posterior, 2–4 subequal in length, 5 longest with posterior margin widely bisinuate. Pleotelson hemispherical, about 1.6 times as wide as long, posterior margin rounded.

Brood pouch (filled with eggs, embryos or manca larvae) of the ovigerous female is prominent in lateral view and made up of five pairs of alternatively overlapping oostegites arising from sternites 1–5, anterior pair partly overlapping mouth parts.

Antennule much shorter than antenna, with 8 articles, reaching posterior of cephalon, basal articles nearly in contact; Antenna with bases wide apart, composed of 18 articles, extending to or beyond posterior margin of pereonite 1, proximal article 6 sometimes with 2 plumose setae respectively on the anterodistal and posterodistal angles. Mandible incisor acute but reduced, molar prominent; palp slender, article 1 widest and article 2 longest, sometimes with only a single setae on distolateral margin of article 3. Maxillule with 1 large and 3 small spines. Maxilla with 3 blunt spines on lateral lobe in ovigerous female ( Fig. 2H ), 2 of which longer, recurved and acute in non-ovigerous female ( Fig. 2I ). Maxilliped with oostegial lobe bearing some plumose setae and distal article of palp with 2 blunted spines in ovigerous female ( Fig. 2C–D ), recurved and acute in non-ovigerous ( Fig. 2E–F ).

Pereopods almost similar with distinctly dilated merus, humped, decreasing slightly in size from pereopod 1 to 7, dactyli short and basis without carina. Propodus of all pereopods short, about as long as combined lengths of merus and carpus; ischium of pereopods 1–3 about 0.6–0.7 length of basis; ischium and basis of pereopods 4–7 nearly subequal.

Pleopods with all rami lamellar, decreasing progressively in size, exopod slightly larger than endopod; all pleopods without coupling hooks on peduncle medial margin and folding or accessory lobes on endopod.

Uropods short, almost reaching posterior margin of pleotelson, biramous, rami unequal, exopod shorter than endopod, apices blunted pointed.

Description of male ( Figs 1D , 3A–P , 4G–L )

Smaller than the female. Body roughly bilaterally symmetrical, about 2.1 as long as wide, widest at pereonite 3.

Cephalon subtriangular about 1.7 as wide as long, slightly immersed in pereonite 1, anterior margin in blunted point. Eyes visible, about 0.6 times width of cephalon.

Pereonites 1–3 distinctly longer and wider than 4–7 subequal in length but decreasing progressively in width. Coxae of pereonite 2–7 more or less visible in dorsal view.

Pleon about 1.6 as wide as long and about 0.45 width of pereon, lateral margins subparallel. All pleonites visible, pleonite 1 shorter than others, 2–4 subequal in length, fifth slightly longest with posterior margin widely bisinuate. Pleotelson about 0.5 times as long as wide, subtriangular to posteriorly round.

Antennule and antenna similar to female, but antennule with some very little setae on distal margin of articles 1–5 and antenna extending to the pereonite 3. Mouthparts similar to female but mandible palp article 3 sometimes with more setae.

All pereopods sub-similar, without dilated merus, but dactyli 1–3 relatively longest.

Pleopod 2 with appendix masculina, approximately 0.7 as long as endopod.

Uropod rami subequal, bluntly rounded, exopod larger than endopod, extending to posterior of pleotelson.

Manca larvae 1 ( Fig. 1E )

The specimen reproduced in Figure 1E is at the intramarsupial stage 1 (manca larvae 1 or pulli 1) with 7 pereonites but only 6 pereopods and characterized by: enlarged cephalon, sub-triangular; ovate pereon and narrowed pleon with sub-parallel margins; acute pleotelson with posterior margin rounded; uropods short, both rami broadly rounded, not reaching posterior margin of pleotelson.

Colour Female and male yellowish.

Size range

Ovig ♀: 9.0– 13 mm in body length; non-ovig ♀: 10.5-13.0 mm; intermediate stage: 8.5–9.0 mm; ♂: 6.5–8.5 mm.

Remarks

The genus Elthusa Schioedte & Meinert, 1884 , briefly defined in Latin by the Danish authors, was recently clearly redefined by Bruce (1990) who at that time recognized 25 species, including several incompletely described and characterized. Twenty eight species are now recognized, most species (24) being known from the Pacific or Indo-Pacific area. Only 4 species are reported from the Atlantic Ocean.

Host identity remains unknown for several species of Elthusa but five species are known to parasitize pleuronectiform fishes, either specifically [ E. parabothi from Bothidae ( Trilles & Justine 2004) , E. samariscii from Samaridae ( Shiino 1951; Biju Kumar & Bruce 1997), E. methepia from Achiridae ( Schioedte & Meinert 1884) ] or occasionally [ E. raynaudii from Pleuronectidae ( Chilton 1911) , E. vulgaris from Paralichthyidae ( Ho 1975; Brusca 1978)]. E. parabothi was previously reported from Parabothus kiensis ( Tanaka, 1918) . So, E. arnoglossi is the second species of Elthusa described from the host family Bothidae . However, this species is the first cymothoid collected on gills of flatfishes of the genus Arnoglossus .

Elthusa arnoglossi can be easily distinguished from most of the species of the genus that have a bilaterally symmetrical body ( E. alvaradoensis , E. atlantniroi , E. caudata , E. menziesi , E. neocytta , E. ochotensis , E. puhi , E. raynaudii , E. sacciger , E. samoensis , E. splendida , E. tropicalis , E. turgidula , E. vulgaris ) or only weakly asymmetrical ( E. californica , E. foveolata , E. frontalis , E. intermedia , E. methepia , E. myripristae , E. philippinensis and E. parabothi ). Four species ( E. nanoides , E. propinqua , E. samariscii and E. sigani ) are distinctly asymmetrical. From them, only one species, E. samariscii , first described by Shiino (1951) and recently redescribed by Biju Kumar & Bruce (1997) show some similarity to E. arnoglossi . However, E. arnoglossi can be separated from this species by: female body more asymmetrical, dissimilar in shape and always deeply twisted only to the right side while E. samariscii is slightly twisted to one side or another (dextral or sinistral); antenna composed of 18 articles (only 12 for E. samariscii ) extending to or beyond margin of pereonite 1(instead of posterior margin of cephalon); all pereopods with a distinctly dilated merus lacking in E. samariscii ; uropods longer and almost reaching posterior margin of pleotelson (instead barely reaching beyond anterior quarter of pleotelson); male body with pereonite 1–3 relatively wider and longer beside others (character not related to the isopods moulting process); antenna with 18 articles instead of 12; pleopod 2 with appendix masculina distinctly longer and uropods reaching posterior margin of pleotelson

Figures

FIGURE 1. Elthusa arnoglossi sp. nov. A–C, holotype, ♀, ovigerous. A, dorsal view; B, lateral view; C, ventral view; D, allotype, ♂. E, manca larva 1. Scale bars: 2 mm (A–D); 0.5 mm (E).

FIGURE 2. Elthusa arnoglossi sp. nov., paratype ♀, ovigerous. A, antennule; B, antenna; C, maxilliped; D, maxilliped apex; G, maxillule; H, maxilla; J, mandible; K–L, pereopods 1–2; M–O, pereopods 5–7; paratype ♀, non-ovigerous. E, maxilliped; F, maxilliped, apex; I, maxilla. Scale bars: 0.5 mm (A, B, C, K, L, M, N, O); 0.2 mm (E); 0.1 mm (F, G, H, I, J); 0.05mm (D).

FIGURE 3. Elthusa arnoglossi sp. nov., paratype ♂. A, antennule; B, antenna; C, maxilliped; D, maxillule, apex; E, maxilla; F, maxilla, apex; G, mandible; H–I, mandible palp, apex; J–P, pereopods 1–7. Scale bars: 0.5 mm (A, B, J, K, L, M, N, O, P); 0.2 mm (G); 0.1 mm (C, E); 0.05 mm (D, F, H, I).

FIGURE 4. Elthusa arnoglossi sp. nov., paratype ♀, ovigerous. A–E, pleopods 1–5; F, uropod; paratype ♂: G–K, pleopods 1–5; L, uropod. Scale bar: 0.5 mm (A–L).