Gnathia grandilaris Coetzee, Smit, Grutter & Davis, 2008

Ota, Yuzo & Hirose, Euichi, 2009, Gnathia nubila n. sp. and a new record of Gnathia grandilaris (Crustacea, Isopoda, Gnathiidae) that parasitizes elasmobranchs from Okinawan coastal waters, Japan, Zootaxa 2238, pp. 43-55 : 51-54

Gnathia grandilaris Coetzee, Smit, Grutter & Davis, 2008

Material examined. Six males, 2 females, and 14 larvae (NSMT-Cr 20882) and 5 males, 1 female, and 13 larvae ( NMV J60145 ) from gill filaments, gill arches, and buccal cavity of Himantura sp. commercially caught in a fixed net (Toya Fishing Port), off Yomitan (26°21’N, 127°42’E), 19 August 2008, coll. Y. Ota. Two males, 2 females, and 2 unfed larvae, from gill filaments, gill arches, and buccal cavity of pink whipray Himantura fai Jordan & Seale, 1906 caught commercially in fixed net, off Yomitan, 15 May 2008, coll. Y. Ota (NSMT-Cr 20881). Two males and 2 females from gill filaments and gill arches of bluespotted maskray Dasyatis kuhlii (Müller & Henle, 1841) , caught by commercial gill net (Umino Fishing Port), Nakagusuku Bay (26°N, 127°E), 2 June 2007, coll. Y. Ota ( NMV J60146 ).

Description. Female ( Fig. 5 ). Body 5.9–8.8 mm (7.6 ± 0.9 mm, n = 7). Pigmentation of live specimens white.

Cephalosome ( Fig. 5 A, B). Cephalosome with several setae; length two-thirds of width. Frontal margin straight. Eyes well developed.

Pereonites ( Fig. 5 A). Pereonites 2–6 with several setae on lateral margins and lateral shields. Pereonite 1 ( Fig. 5 B) very short, not fused, and convex anteriorly. Lateral shields of pereopods 4–6 visible dorsally.

Pleonites ( Fig. 5 A) with several setae, subequal in length. Pleotelson ( Fig. 5 C) triangular and narrow, with 1 pair of setae on apex.

Antennae. Antenna 1 ( Fig. 5 D). Two feather-like bristles on distal margin of peduncle 2. One feather-like bristle on flagellar articles 1 and 4. One aesthetasc on articles 2–4. Antenna 2 ( Fig. 5 E). Peduncle 3 has 2 feather-like bristles.

Maxilliped ( Fig. 5 F). Inner margin fringed with fine setae. Endite reaches half length of palp article 1. Five, 7, 11, 7, and 7 plumose setae on basis and articles 1, 2, 3, and 4, respectively. Oostegite fringed by fine setae.

Pylopod ( Fig. 5 G). Article 1 with suture covered with scales and fine setae. Articles 1 and 2 fringed by fine setae on inner margins. Article 2 elliptical. Article 3 minute. Oostegite oval.

Pereopods ( Fig. 5 H). Pereopod 2 bears fine setae on inner margin except for basis and bears long setae on lateral margins except for dactylus. Basis oblong; bears 2 feather-like bristles on outer margin. Ischium becoming larger distally, pectinate scales on inner margin. Carpus rectangular with 1 serrate spine on inner margin. Propodus rectangular. All pereopods similar in setation. Pereopods 5 and 6 larger than pereopods 2–4.

Pleopod ( Fig. 5 I). Exopods and endopods fan-shaped, with from 8–9 and from 6–9 setae on distal margins of exopods and endopods, respectively. All pleopods subequal in shape.

Uropod ( Fig. 5 C). Both rami subequal in shape and extending slightly beyond apex of pleotelson. Exopod bears 15 setae on margin. Endopod bears 9 setae on margin.

Remarks. Among congeners, females of G. grandilaris are most similar to those of G. m a c u l o s a, which was recorded from the same location. However, in G. m a c u l o s a, the frontal border is slightly concave and the total length is shorter (4.1– 5.5 mm; Ota & Hirose, 2009) than in G. grandilaris (5.9–8.8 mm).

Although males do not differ in morphology between the GBR and the Ryukyus ( Fig. 6 A), the larval pleotelsons on Ryukyus specimens are wider than those of GBR specimens ( Fig. 6 B, C).

The distribution range of gnathiid species is uncertain because most species have been recorded only once. Gnathia trimaculata was originally recorded from the GBR ( Coetzee et al. 2009); we collected this species as a new record for Japan ( Ota & Hirose, 2009). Thus, G. trimaculata probably has a wide distribution between the GBR and Ryukyus ( Ota & Hirose, 2009). Gnathia grandilaris is the second species of the genus known to occur in both regions. More records from other areas are required for future in-depth considerations of gnathiid distribution ranges.

Figures

FIGURE 5. Gnathia grandilaris n. sp., female (NSMT-Cr 20881). (A) Body in dorsal view. (B) Left eye and frontal border. (C) Pleotelson. (D) Antenna 1. (E) Antenna 2. (F) Maxilliped. (G) Pylopod, Su; suture of article 1, Oo; oostegite. (H) Pereopod 2. (I) Pleopod 2.

FIGURE 6. Gnathia grandilaris n. sp., male, 10.1 mm (A; NSMT-Cr 20881) and immature praniza larva, 7.6 mm (B, C; NSMT-Cr 20882). (A) Male in dorsal view. (B) Larva in dorsal view. (C) Pleotelson of larva.