Gnathia nubila, Ota, Yuzo & Hirose, Euichi, 2009

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 : 44-51

publication ID	https://doi.org/ 10.5281/zenodo.190468
DOI	https://doi.org/10.5281/zenodo.6225850
persistent identifier	https://treatment.plazi.org/id/817F87E0-FFF1-FC31-679A-F9C7FEEC6404
treatment provided by	Plazi
scientific name	Gnathia nubila
status	sp. nov.

Treatment

Gnathia nubila View in CoL n. sp.

( Figs. 1–3 View FIGURE 1 View FIGURE 2 View FIGURE 3 , 6 View FIGURE 6 A, B)

Material examined. Holotype. 9.1 mm (NSMT-Cr 20878), from gill filaments and gill arches of spotted eagle ray Aetobatus narinari (Euphrasen, 1790) caught by commercial fishing (boat out of Hama Fishing Port), Nakagusuku Bay (26°N, 127°E), Okinawa Island, Ryukyu Archipelago, southwestern Japan. 30 November 2007, coll. Y. Ota.

Paratypes. Two males and 4 females from the same fish host as the holotype ( NSMT Cr 20879). One male and 19 larvae from gill filaments and gill arches of A. narinari caught by commercial fishing (Okinawa City Fishing Port), Nakagusuku Bay (26°N, 127°E), 13 September 2006, coll. Y. Ota (NSMT-Cr 20880).

Description. Male ( Figs. 1 View FIGURE 1 , 2 View FIGURE 2 ). Body 9.0–10.0 mm (9.3 ± 0.5 mm, n = 4). Pigmentation of live specimens white; digestive organs black due to congealed host blood.

Cephalosome ( Fig. 1 View FIGURE 1 A–C). Cephalosome covered with tubercles and setae, almost square with posterior margin convex, about one-fifth of total length. Posterior median tubercle prominent. Frontal border medially opened by 2 frontolateral processes with tubercles and several submarginal setae. Apex of mediofrontal process bifit and dentate ( Fig. 1 View FIGURE 1 D). Eyes well developed, about one-fourth length of cephalosome. Supraocular lobe low, not acute. Dorsal sulcus deep and narrow.

Pereon ( Fig. 1 View FIGURE 1 A). All pereonite lengths about half of total length. Pereonite 1 short, not fused, reaching lateral margin of cephalosome. Pereonites 2–6, sparsely covered with setae and tubercles. Widths of pereonites 2, 3, and 4 similar. Pereonite 2 as long as pereonite 3 and slightly shorter than pereonite 4. Anterior constriction and anterolateral lobe present on pereonite 4. Pereonites 5 and 6 combined subequal in length to pereonites 2–4 combined. Areae laterales and lobi laterals present on pereonites 5 and 6, respectively. Pereonite 7 short and narrow, overlapping pleonite 1.

Pleon ( Fig. 1 View FIGURE 1 A). Lateral margins of pleonites 1–5 fringed with long setae. Lengths of pleonites and pleotelson about one-quarter of total length. Epimera prominent on pleonites 3–5.

Pleotelson ( Fig. 1 View FIGURE 1 D). Pleotelson narrow, covered with pectinate scales. Eight setae on lateral margin and 1 pair of setae on both dorsal surface and distal apex.

Mandible ( Fig. 1 View FIGURE 1 E). Mandible length two-thirds of cephalosome length. Apex curved inward. One mandibular seta present near armed carina on mid-dorsal surface. Dentate blade occupies about two-fifths of mandible length. Basal neck and erisma prominent.

Antennae. Antenna 1 ( Fig. 1 View FIGURE 1 F). Peduncle articles 2 and 3 covered with pectinate scales. Three, 4, and 1 feather-like bristles on distal margins of peduncles 1, 2, and 3, respectively. One seta on internal margins of peduncle 2, and several setae on external and distal margins of peduncle 3. Flagellar articles bearing an aesthetasc on both articles 3 and 4. One seta on distal margin of article 3. Article 5 with 1 feather-like bristle terminating in 3 setae and 1 aesthetasc. Antenna 2 ( Fig. 1 View FIGURE 1 G). Two feather-like bristles and several setae present on peduncle 4. A few setae present on distal margins of flagellar articles 1–6. Article 7 terminates in 5 setae.

Maxilliped ( Fig. 2 View FIGURE 2 A). Endite reaches distal margin of palp article 1. Palp articles 1, 2, 3, and 4 bearing 6, 8, 5, and 9 plumose setae on external margins, respectively. Article 4 terminates in 4 simple setae.

Pylopod ( Fig. 2 View FIGURE 2 B). Pylopod 3 articled. Several setae present on distal margins of articles 1 and 2. Article 1 large and elliptical, with 2 areolae, and 76 plumose setae on internal margin. A few setae and 1 feather-like bristle present near outer margin. Article 2 circular and fringed with fine setae. Article 3 minute.

Pereopods ( Fig. 2 View FIGURE 2 C). Pereopod 2 bearing many setae; longer on outer margin than on inner. Pectinate scales on each article except basis; fine setae on inner margins of all articles. Basis oblong, bearing 2 featherlike bristles on outer margin. Ischium similar in length to basis, becoming larger distally. Merus about half length of ischium. Carpus rectangular and similar in length to merus. Propodus rectangular, about 1.2 times longer than carpus; bearing 2 spines on inner-mid and inner-distal margins. Dactylus with a few setae, terminating in unguis. Length of dactylus and unguis combined about half that of propodus. All pereopods similar in shape, size, and setation.

Pleopods ( Fig. 2 View FIGURE 2 D). Pleopodal peduncle inner margin fringed with fine setae. One seta on outer distal corner, and a coupling hook on inner margin. Both pleopodal rami oval and equal in length. All pleopods subequal in shape. From 7 to 9 plumose setae and 1 simple seta (pl. 1, 2, 4) on exopods: pleopod 1; 7 plumose setae, pl. 2–4; 8, pl. 5; 9. From 4 to 8 pumose setae and 1 simple seta (pl. 2, 3) on endopods: pleopod 1; 6 plumose setae, pl. 2; 4, pl. 3–5; 8. Appendix masculina extending beyond half length of pleopod 2 endopod.

Uropods ( Fig. 1 View FIGURE 1 D). Both rami subequal in length, extending beyond apex of pleotelson. Exopod bearing 19 setae and 7 plumose setae on external and internal margins, respectively. Endopod bearing 9 setae and 9 plumose setae on external and internal margins, respectively. Several feather-like bristles on dorsal surface.

Penes ( Fig. 2 View FIGURE 2 E). Penes composed of 2 contiguous papillae and not prominent.

Female ( Fig. 3 View FIGURE 3 ). Body 7.4–8.0 mm (7.7 ± 0.3 mm, n = 4). Pigmentation of live specimens white.

Cephalosome ( Fig. 3 View FIGURE 3 A–C). Cephalosome with several setae. Frontal margin slightly convex; pair of spots present.

Pereon ( Fig. 3 View FIGURE 3 A, B). Pereonite 1 short, not fused, with central part protruding forward. Pereonites 3–6 oval, with 2 sutures, widths about two-thirds of lengths. Lateral shields of pereopods 4–6 visible dorsally.

Pleon ( Fig. 3 View FIGURE 3 A, B). Several setae on pleonites 1–5 subequal in length. Pleotelson ( Fig. 3 View FIGURE 3 D). Two pairs of setae on lateral margin and apex.

Antennae ( Fig. 3 View FIGURE 3 E, F). Setae on peduncle articles of both antennae fewer than in male. No pectinate scales on peduncle articles.

Maxilliped ( Fig. 3 View FIGURE 3 G). Inner margin of basis and endite covered with pectinate scales. Endite reaches half length of palp article 1. Nine, 7, 9, 6, and 8 plumose setae on basis and articles 1, 2, 3, and 4, respectively. Oostegite elliptical.

Pylopod ( Fig. 3 View FIGURE 3 H). Pylopod composed of 3 articles. Articles 1 and 2 covered with pectinate scales and fringed with fine setae on inner margins. Article 1 with suture bears 10 setae on lateral and distal margins. Article 2 rectangular, bearing 6 setae on distal margin. Article 3 minute.

Pereopods ( Fig. 3 View FIGURE 3 I). Pereopods bear fewer setae than those of male; not covered with pectinate scales.

Pereopods 5 and 6 larger than other pereopods.

Pleopod ( Fig. 3 View FIGURE 3 J). One aesthetasc on outer margin of peduncle. Exopods and endopods oval, with 8 (exopods) or 6 (endopods) setae on distal margins, all vestigial. All pleopods subequal in shape.

Uropod ( Fig. 3 View FIGURE 3 D). Uropodal rami slightly extended beyond apex of pleotelson. Exopod bears 19–21 setae on margin. Endopod bears 14–15 setae on margin.

Immature praniza larva ( Figs. 4 View FIGURE 4 , 7 View FIGURE 7 A, B). Body 7.6–9.7 mm (8.4 ± 0.6 mm, n = 19). Dorsal thorax of live specimens black with white cloud-like pattern ( Fig. 7 View FIGURE 7 A); ventral thorax has distinct white line ( Fig. 7 View FIGURE 7 B). Distinct brown spot on eyes. Lateral margins of pleonites have brown pattern (see Fig. 7 View FIGURE 7 A).

Cephalosome ( Fig. 4 View FIGURE 4 A). Triangular, length same as width. Anterior margin of labrum straight. Eyes occupying half length of cephalosome.

Pereon ( Fig. 4 View FIGURE 4 A, B). Pereonite 1 short. Pereonite 2 subequal in width to pereonite 3, with convex anterior margin. Pereonite 3 slightly longer than pereonite 2. Lateral shields of pereopods 4–6 visible in dorsal view, elliptical.

Pleon ( Fig. 4 View FIGURE 4 A). Pleonites 1–4 subequal in length and slightly shorter than pleonite 5. Pleotelson ( Fig. 4 View FIGURE 4 C) with dentate lateral margin, bearing 3 pairs of setae on dorsal surface and apex.

Antennae ( Fig. 4 View FIGURE 4 D, E). Internal margins of peduncles 2 and 3 of antenna 1 fringed with fine setae. Internal margins of peduncles 3 and 4 of antenna 2 fringed by fine setae.

Mouth parts. Mandible ( Fig. 4 View FIGURE 4 F) with 9 teeth. Maxillule ( Fig. 4 View FIGURE 4 G) with 2 slender articles, fine setae on outer margin projecting to posterior, 7 teeth on apex. Paragnath ( Fig. 4 View FIGURE 4 H) slightly curved. Maxilliped ( Fig. 4 View FIGURE 4 I) composed of basis and 2-articled palp. Basis with 1 coupling hook on inner margin and endite with 1 seta. Apex of palp 1 slightly dentate. Apex of palp 2 divided into 2 parts; 1 seta and 1 tooth on inner apex, 5 setae and 1 spine on outer part. Gnathopod ( Fig. 4 View FIGURE 4 J) pereopodal in shape with reduced carpus. One projection on distal margin of merus. Propodus with distal bulbous protrusion. Dactylus terminating in sharp, pointed unguis.

Pereopods. Pereopod 2 ( Fig. 4 View FIGURE 4 K) more slender than that of male. Inner margins of carpus and propodus covered with pectinate scales.

Pleopods ( Fig. 4 View FIGURE 4 L). Exopod fan-shaped with 7–9 plumose setae on distal margins. Endopod rectangular and as large as exopod; 7 or 8 plumose setae on distal margins. All pleopods subequal in shape.

Uropod ( Fig. 4 View FIGURE 4 C) just reaches apex of pleotelson. Exopod bears 6 setae and 4 plumose setae on margin. Endopod bears 2 setae and 7 plumose setae on margin.

Etymology. The specific name nubila is derived from the Latin meaning “cloudy”, referring to the larval thorax pattern.

Remarks. Among Gnathia species described so far worldwide, the body length, and shape of the cephalosome and pleotelson of male G. nubila is most similar to those of G. grandilaris . However, the mediofrontal process of G. grandilaris is triangular-shaped lobe and conical ( Coetzee et al. 2008) ( G. grandilaris has the bifit one). Because G. trimaculata and G. m a c u l o s a have been found from this area ( Ota & Hirose, 2009), these species may be found with G. nubila , but they are distinguished from G. nubila by the following features. Gnathia trimaculata has a mediofrontal process on the frontal border and a more slender pylopod ( Coetzee et al. 2009). Gnathia maculosa is smaller (3.9–5.8 mm) and lacks a mediofrontal process ( Ota & Hirose, 2009).

Frontal borders of G. n o t o s t i g m a Cohen & Poore, 1994 and G. c o o k i Müller, 1989 are also similar in shape to that of G. nubila . However, G. notostigma has very pronounced paraocular tubercles and wider pleotelson ( Cohen & Poore, 1994). Gnathia cooki has long and basally broadened penes and a wider pleotelson ( Müller, 1989).

Because species descriptions of gnathiids have traditionally been based on the morphology of adult males, detailed descriptions of larvae and female adults are lacking in many literatures. Females of the genus Gnathia have been described in detail for the following species: G. firingae , G. c a m u r i p e n i s, G. limicola , G. m a c u l o s a, G. a f r i c a n a, G. pantherina , G. p i l o s u s, G. gurjanovae , and G. trimaculata ( Müller, 1991; Smit & Basson, 2002; Smit et al. 2002; Tanaka, 2004; Golovan, 2006; Ota et al. 2007; Coetzee et al. 2008; Ota & Hirose, 2009).

Gnathia maculosa View in CoL most closely resembles G. nubila View in CoL . However, the frontal border of G. nubila View in CoL has a pair of spots, the pleopodal rami are oval, and the body is larger (7.4–8.0 mm). The pleopodal rami of G. m a c u l o s a are fan-shaped, and the body length is smaller (4.4–5.5 mm) than that of G. nubila ( Ota & Hirose, 2009) View in CoL .

Detail descriptions of praniza larvae were limited worldwide; G. firingae View in CoL , G. africana View in CoL , G. pantherina View in CoL , G. camuripenis View in CoL , G. limicola View in CoL , G. capillata View in CoL , G. grandilaris View in CoL , G. trimaculata View in CoL , and G. m a c u l o s a ( Müller, 1991; Smit et al., 1999; Smit & Basson, 2002; Tanaka, 2004; Nunomura & Honma, 2004; Ota et al., 2007; Coetzee et al., 2008, 2009; Ota & Hirose, 2009). Among the gnathiid larvae described so far, G. nubila View in CoL is most similar to G. grandilaris View in CoL . However, G. grandilaris View in CoL lacks a distinct brown spot on the eyes and a distinct white line on the ventral thorax, and it has a shorter pleotelson ( Coetzee et al. 2008). Gnathia capillata View in CoL , G. trimaculata View in CoL , and G. maculosa View in CoL larvae have all been found as ectoparasites on elasmobranchs from Japan; these 3 species are distinguishable from G. nubila View in CoL as follows. Gnathia capillata View in CoL has a wider pleotelson, and its pereonite 4 is distinctively separated from pereonites 5 and 6 ( Nunomura & Honma, 2004). Gnathia trimaculata View in CoL has yellow-greenish color with black spots on the thorax and its shorter pleotelson ( Coetzee et al. 2009). Gnathia maculosa View in CoL has wider pleotelson, shorter body length in the immature stage (4.2–5.8 mm), and white speckled or dappled pattern on the thorax ( Ota & Hirose, 2009).

Praniza larvae of G. c a m u r i p e n i s and G. limicola have also been described from the Ryukyus. Gnathia nubila is easy to distinguish from these 2 species by the following criteria: the body lengths of immature G. camuripenis and G. limicola are 3 mm, and the pleotelson is wider and not elongated ( Tanaka, 2004; Ota et al. 2007).