Gnathia dejimagi, Ota, Yuzo, 2014

Ota, Yuzo, 2014, Three new gnathiid species with larvae ectoparasitic on coastal sharks from southwestern Japan (Crustacea: Isopoda), Zootaxa 3857 (4), pp. 478-500 : 491-499

Gnathia dejimagi n. sp.

( Figs 8–11 , 12 E, F, 13E, F)

Material examined. Holotype: NSMT-Cr22970, adult male, here designated, (total length 14.4 mm), gill chambers of Triaenodon obesus (Rüppell, 1837) , caught by gill net in Nakagusuku Bay (26°12′N, 127°49′E), Okinawa-jima Island, Southwestern Japan, 30 June 2008. Paratypes: NSMT-Cr22971, 1 male adult, 1 female adult, and 4 third-stage zuphea larva, from the same host and localities as the holotype; NSMT-Cr22972, 5 male adults, 1 female adult, and 4 third-stage praniza larvae, gill cambers of Nebrius ferrugineus (Lesson, 1831) , caught by line fishing off Ishigaki-jima Island, southwestern Japan. (24°28′N, 124°18′E), 12 Sept. 2009; NSMT-Cr22973, 7 third-stage praniza larvae, gill chambers of N. ferrugineus , caught by line fishing off Ishigaki-jima Island, southwestern Japan. (24°28′N, 124°18′E), 11 Sept. 2010.

Description. Adult male ( Figs. 8 , 9 ). Body 11.9–14.4 mm (mean ± SD; 13.1 ± 0.9 mm, n = 7) covered with long setae. Pigmentation of live specimens white; digestive organs brown due to congealed host blood.

Head ( Fig. 8 A–C) covered with tubercles, rectangular with posterior margin slightly concave. Frontal border almost straight. Mediofrontal process acute or slightly bifid with dentate or smooth apex. Two frontolateral processes with several setae. Two apexes of ventral frontal margin slightly visible in dorsal view. Dorsal sulcus deep and narrow, reaching half length of head. Eyes composed with 48 ocelli. Supraocular lobe not prominent with dentate apex. Accessory supraocular lobe acute.

Pereonites 1–4 ( Fig. 8 A, C) densely covered with tubercles. Pereonite 1 short, not fused with head, reaching lateral margin of head. Widths and lengths of pereonites 2 and 3 almost same. Pereonite 4 with constriction anteriorly, and anterolateral lobes and anteromedial lobe with tubercles and setae. Pereonites 5 and 6 with areae laterales and lobi laterals, respectively. Pereonite 7 short and narrow, overlapping pleonite 1.

Pleonites 1–5 ( Fig. 8 A) almost equal length and narrower posteriorly, fringed with long setae on lateral and posterior margins of each segment. Epimera visible on each segment in dorsal view.

Pleotelson ( Fig. 8 D) covered with pectinate scales. Lateral margin acutely narrow near basis and slightly convex. Distal apex smooth. Six or 7 setae on lateral surface, and 2 pair of setae on near basis and 1 pair of seta on medial surface and distal apex.

Mandible (Fis. 8A–C) pliers-liked shape with prominent basal neck. Mandible length extends half-length of head in dorsal view. Apex curved inward. One mandibular seta presents near armed carina on mid-dorsal surface. Erisma visible in dorsal view.

Antennula ( Fig. 8 E) composed with 3 basal and 5 flagellar articles. One, 3, and 1 feather-like bristle on distal margins of basal article 1, 2, and 3, respectively. One feather-like bristle on flagellar article 1. One aesthetasc on flagellar article 3, 4, and 5, respectively. Flagellar article 5 terminating in 1 seta.

Antenna ( Fig. 8 F) composed with 4 basal and 7 flagellar articles. One and 3 feather-like bristles on basal 3 and 4, respectively. 1–4 setae on distal margins of flagellar articles 1–6. Article 7 terminates in 3 setae.

Maxilliped ( Fig. 9 A) composed with basis and 4 palp articles. Basis fringed with fine setae. Endite just reach distal margin of palp article 1. Seven, 11, 6, and 8 plumose setae on external margins of palp articles 1–4, respectively. One seta on internal margin of palp article 4. One plumose seta on inner margin of palp 1 and 2, respectively. No plumose seta on inner margin of right maxilliped.

Pylopod ( Fig. 9 B) 3 articles. Article 1 with 2 areolae, 60 plumose setae on internal margin, 2 setae near basis, and 10 setae on distal margin. Article 2 elliptical with 21 setae. Article 3 minute.

Pereopod 2 ( Fig. 9 C) fringed with fine setae on outer margin. Basis oblong with several long setae, 2 featherlike bristles, and 2 protrusions on inner margin. Ischium becoming larger distally with several setae. Propodus bearing 2 denticulate compound spines on inner-mid and inner-distal margins. Dactylus terminating in unguis and ventral claw. Pereopod 3 almost same morphology as pereopod 2. Basis and ischium of pereopods 4–6 longer and stouter than those of pereopod 2, and tubercles present on inner margins of basis and ischium of pereopods 4–6.

Pleopod 2 ( Fig. 9 D) with reduced setae. Protopod covered with pectinate scales and fringed with fine setae on inner margin and 1 seta on outer distal corner and coupling hooks on inner margin. Both rami not fringed with fine setae. Exopod fan shaped with total 9 of simple and plumose setae. Endopod oval shaped with total of 7 simple and plumose setae. The number of setae of all pleopods ranged 8 or 9 on exopods and 7 or 8 setae on endopods. Appendix masculina of pleopod 2 not extending half-length of endopod.

Uropod ( Fig. 8 D) covered with pectinate scales on basis. Both rami subequal in length, and extend beyond apex of pleotelson. Exopod with total of 22 or 24 simple and plumose setae and endopod with total of 13 simple and plumose setae. Plumose setae reduced. Four feather-like bristles on dorsal endopod.

Penes ( Fig. 9 E) fused with 2 contiguous papillae.

Female adult ( Fig. 10 ). Body ( Fig. 10 A) 9.0 mm, covered with long setae.

Head ( Fig. 10 A, B) with 1 pair of seta on central surface. Frontal border slightly concave with thick lateral margin. Liner protrusion with 9 setae on central surface of frontal border. Pereon swollen with 2 sutures between pereonite 4–6. Central part of pereonites 1 and 2 not visible in dorsal view but reaching lateral margins. Pereonite 3 visible in dorsal view. Lateral shields of pereopods 2–6 visible dorsally. Pleonites 1–5 ( Fig. 10 A) each with 2–7 setae on lateral and posterior margin, and 4–6 setae on dorsal surface. Pleotelson ( Fig. 10 C) not covered with pectinate scales. Lateral margin slightly convex. One pair of setae on dorsal surface. No setae on distal apex. Antennae ( Fig. 10 D, E) with fewer number of setae than those of male adult. Maxilliped ( Fig. 10 F) composed with basal article and 4 palps. Number of plumose setae 8 on basal article, 8 on palp 1, 11 on palp 2, 10 on palp 3, and 11 in palp 4. One seta on inner distal margin of palp 1. Pylopod ( Fig. 10 G) composed with 3 articles. Inner margins of article 1 and 2 covered with scales. Article 3 semicircular. Pylopodal oostegate oval with pectinate scales on anterior part. Pereopods ( Fig. 10 H) shorter than those of male adult. Pereopods 3 and 4 almost same morphologies as pereopod 2. Pereopods 5 and 6 about 1.2 times longer than pereopod 2, and merus of pereopod 5 and 6 has 3 distinct tubercles. Pleopods ( Fig. 10 I) reduced setae: 6–11 and 4–8 simple or plumose setae on exopods and endopods, respectively. Exopods of pleopods 3–5 fan shaped and other exopods and endopods oval shaped. Uropodal rami ( Fig. 10 C) subequal in length. Exopod with total of 25 or 26 setae and extend beyond apex of pleotelson. Endopod with total 14 setae and not reach apex of pleotelson. Plumose setae reduced. Six penicillate setae on dorsal endopod.

Third-stage praniza larva ( Figs. 11 , 12 E, F, 13E, F). Body ( Figs 9 A, 10E, F) 8.9–12.8 mm (11.4 ± 1.0 mm, n = 10) with fully swollen thorax. In live specimens, red pigmentations regularly formed on head, pleonites and basis of pleotelson. White cloud-like pattern on dorsal thorax. Eyes red. The pigmentation disappeared in ethanol.

Head ( Fig. 11 A, B) semicircular with slightly concave posterior margin, approximately two third length of width. Clypeus almost straight anteriorly, approximately 0.34 times of head length and 1.4 times of mandible length exposed in dorsal view. Eyes approximately 0.83 times of head length and its inner margin reaches basis of antennae. Pereonite 1 ( Fig. 11 B) short. Pereonite 2 with seta on laterally. Pereonite 3 posteriorly concave. Lateral shields of pereopods 4–6 visible in dorsal view, elliptical. Fully swollen part (from anterior margin of pereonite 4 to distal apex of lateral shield of pereonite 6) approximately 2.4 times as wide as long. Pleonites ( Fig. 11 A) subequal in each length. Small seta visible on lateral margin of each segment in dorsal view.

Pleotelson ( Fig. 11 C) slightly narrow near basis, almost straight, and dentate on lateral margin. Pair of setae on dorsal surface and apex, respectively. Apex round without spine.

Antennula ( Fig. 11 D) composed with 3 basal and 4 flagellar articles. Basal article 2 and 3 fringed with fine setae. Several scales visible on flagellar article 2. Antenna ( Fig. 11 E) composed with 4 basal and 7 flagellar articles. Fine setae fringe external margin of basal article 3 and external and internal margins of 4.

Mandible ( Fig. 11 F) with 7 teeth. Paragnath ( Fig. 11 G) slightly curved inward. Maxillula ( Fig. 11 H) with 7 teeth. Maxilliped ( Figs. 11 I, 13E, F) composed with 2 basal articles and 2 palps. Basal article 2 with coupling hook near elongated endite. Palp 1 with long seta near basis, fringed with fine setae on external margin, 3 teeth on distal apex. Palp article 2 bifurcate; external part with 4 setae and 1 spine, and inner part with 1 tooth and seta. Pereopod 1 ( Fig. 11 J) has distinct protrusion on distal margin of merus. Carpus reduced.

Pereopod 2 ( Fig. 11 K) with fewer setae and more slender than those of male adult. Pectinate scales visible on carpus and propodus. One denticulate compound spine on distal margin of merus. Pereopod 3 almost same morphologies as pereopod 2. Pereopods 4–6 about 1.3 times as long as pereopod 2. Pleopod 2 ( Fig. 11 L) with fanshaped rami. Both rami fringed with fine setae. Eight or 9 plumose setae on exopod. Six and 8 plumose setae on endopod. Uropod ( Fig. 11 C) not reach apex of pleotelson. Exopod with 6 setae and 4 plumose setae. Endopod with 3 setae and 6 plumose setae. Plumose setae of pleopodal and uropodal rami more developed than those of male adult; each seta longer and densely fringed with fine setae.

Etymology. The specific name dejimagi is derived from the Okinawan regional dialect meaning “extremely (= deji ) large (= magi)”, referring to large body size.

Remarks. Gnathia dejimagi n. sp. is distinguishable by a large body size (> 11.9 mm), variable shapes of the mediofrontal processes, posterior margins of pleonites fringed with long setae, epimera visible in the dorsal pleonites, round apex of the pleotelson, and relatively large number of plumose setae on the pylopod (60 setae). Gnathia dejimagi n. sp. is most similar to G. nubila in terms of its large body (> 9.0 mm), the shape of the frontal border, and the presence of epimera on the pleonites. The apex of the pleotelson, however, is acute in G. nubila but was round in G. dejimagi n. sp. ( Ota & Hirose 2009b).

Morphology of female adult of G. dejimagi n. sp. is distinguishable by body covered with long setae, slightly concave frontal border, and narrow pleotelson. These characters are well correspond with female adults of G. albipalpebrata n. sp., G. masulosa , and G. nubila . The differences between G. d e j i m a g i n. sp. and G. albipalpebrata n. sp. were referred in Remarks of G. albipalpebrata n. sp. Female adult of G. m a c u l o s a is much smaller than that of G. d e j i m a g i n. sp. (4.1–5.5 mm vs. 9.0 mm) ( Ota & Hirose 2009a). Female adult of G. nubila is easily distinguish from G. dejimagi n. sp. by 2 spots on frontal border ( Ota & Hirose 2009b).

A live specimen of the third-stage praniza larva had a cloud-like white pattern on its swollen thorax. This pattern is visible on G. nubila and G. grandilaris but G. nubila has a distinct white line on the ventral thorax ( Ota & Hirose 2009b) while G. grandilaris has white spots on the dorsal thorax ( Coetzee et al. 2008). Gnathia dejimagi n. sp. had relatively large eyes and the inner margins of the eyes reached the base of the antenna while the distal margins were close to the base of the antenna. In most other species, the inner margins of the eyes do not reach the base of the antenna and the base of the antenna and the distal margin of the eyes are separated by a space (Smit & Davies 2002; Coetzee et al. 2009; Ota & Hirose 2009a; Ota, 2011). Gnathia grandilaris also has relatively large eyes but its pleotelson is narrower than that of the present species ( Coetzee et al. 2008).

Figures

FIGURE 8. Gnathia dejimagi n. sp., holotype, male adult (NSMT Cr- 22970, total length, 14.4 mm): A, body, dorsal view; B, frontal border with mandibles and eye, dorsal view (broken line shows mediofrontal process of paratypes, Cr- 22972; C, head, lateral view; D, pleotelson, dorsal view; E, left antennula; F, left antenna.

FIGURE 9. Gnathia dejimagi n. sp., holotype, male adult (NSMT Cr- 22970, total length, 14.4 mm): A, left maxilliped, ventral view; B, left pylopod, ventral view; C, left pereopod 2, lateral view; D, left pleopod 2, ventral view; E, penes, ventral view.

FIGURE 10. Gnathia dejimagi n. sp., paratype, female adult (NSMT Cr- 22971, total length, 9.0 mm): A, body, dorsal view; B, frontal border, dorsal view; C, pleotelson, dorsal view.

FIGURE 11. Gnathia dejimagi n. sp., paratype, third-stage larva (NSMT Cr- 22971, total length, 11.3 mm); A, body, dorsal view; B, head, dorsal view; C, pleotelson, dorsal view; D, left antennula; E, left antenna; F, mandible; G, paragnath; H, maxillula; I, maxilliped; J, pereopod 1; K, left pereopod 2; L, left pleopod 2. En = endite.

FIGURE 12. Live specimens of third-stage praniza larvae: A and B, Gnathia albipalpebrata n. sp.; C and D, Gnathia parvirostrata n. sp.; E and F, Gnathia dejimagi n. sp. Scale = 1 mm.