Gnathiidae Leach 1814, n. sp.
Creators: name: Ota, Yuzo
Publisher: name: Zenodo
Year: 2014
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Gnathiidae

description: Family Gnathiidae Leach, 1814
Genus Gnathia Leach, 1814
Gnathia albipalpebrata n. sp. (Figs. 1–4, 12 A, B, 13A, B)
Material examined. Holotype: NSMT-Cr22965, adult male (total length 10.0 mm) here designated, gill chambers of Triaenodon obesus (Rüppell, 1837), gill net in Nakagusuku Bay (26°12′N, 127°49′E), Okinawa-jima Island, Southwestern Japan, 12 Sept. 2009. Paratypes: NSMT-Cr22966, 2 male adults, 2 female adults, 12 third-stage praniza larva, from the same host and locality as the holotype.
[Additional Material/other records]: NSMT-Cr22967, 4 male adults, 1 female adults, and 2 third-stage praniza larvae from gill chambers of Triaenodon obesus (Rüppell, 1837), caught by line fishing off Ishigaki-jima Island (24°28′N, 124°18′E), 5 Sept. 2008.
Description. Adult male (Figs 1, 2). Body 9.1–10.3 mm (mean ± SD; 9.6 ± 0.5 mm, n = 7) covered with long setae. Pigmentation of live specimens white or light brown; digestive organs brown due to congealed host blood. Head (Fig. 1 A–C) covered with tubercles, rectangular with posterior margin slightly concave. Frontal border almost straight. Mediofrontal process slightly curved and slightly dentate, and central notch often visible. Two frontolateral processes with 4 setae. Two apexes of ventral frontal margin slightly visible in dorsal view. Dorsal sulcus not reach half-length of head and shallow U-shaped. Eyes composed with 41 ocelli. Supraocular lobe not prominent with slightly dentate apex. Accessory supraocular lobe acute.
Pereonites 1−3 (Fig. 1 A, C) sparsely covered with tubercles. Pereonite 1 short, not fused with head, reaching lateral margin of head. Widths and lengths of pereonites 2 and 3 same. Pereonite 4 with constriction anteriorly, and anterolateral lobes and anteromedial lobe with several setae. Areae laterales and lobi laterals not prominent on pereonites 5 and 6, respectively. Pereonite 7 short and narrow, overlapping pleonite 1.
Pleonites 1-5 (Fig. 1 A) almost equal length, fringed with long setae on posterior central and lateral margins of each segment. Epimera not prominent.
Pleotelson (Fig. 1 D) covered with pectinate scales. Lateral margin acutely narrow near basis and almost straight posteriorly. Distal apex without pair of spine. Each lateral surface bears 3 or 5 long setae placed randomly. One pair of setae on medial surface and distal apex, respectively.
Mandible (Fig. 1 B, C) pliers-liked shape with prominent basal neck. Mandible length reaches approximately two-third 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.
Antennule (Fig. 1 E) composed with 3 basal and 5 flagellar articles. One, 3, and 1 penicillate setae on distal margins of basal articles 1, 2, and 3, respectively. One penicillate seta on flagellar article 1. One aesthetasc on flagellar article 3, 4, and 5 respectively. Flagellar article 5 terminating in 3 setae.
Antenna (Fig. 1 F) composed with 4 basal and 7 flagellar articles. Two and 3 feather-like bristles on peduncle 3 and 4, respectively. 1–3 setae on distal margins of flagellar articles 1–6. Article 7 terminates in 4 setae.
Maxilliped (Fig. 2 A) composed with basis and 4 palp articles. Basis fringed with setae. Endite fringed with setae on apex, extending to palp article 1. Six, 8, 5, and 8 plumose setae on external margins of palp articles 1–4, respectively. Three setae on internal margin of palp article 4.
Pylopod (Fig. 2 B) 3 articles. Article 1 with 3 areolae, 49 plumose setae on internal margin, 2 setae near basis, and 3 setae on distal margin. Article 2 circular with 12 setae on distal margin and 1 seta on external margin. Article 3 minute.
Pereopod 2 (Fig. 2 C) covered with setae and pectinate scales visible on ischium, merus, and carpus. Basis oblong with 2 penicillate setae and 9 spines on dorsal margin. Ischium shorter than basis, becoming broader distally. Merus length approximately half ischium length. Carpus slightly shorter than merus, with 1 denticulate compound seta on distal margin, 3 tubercles on inner margin. Propodus rectangular, bearing 2 denticulate compound setae on inner-mid and inner-distal margins. Dactylus terminal unguis robust and ventral claws. Pereopod 3 almost same in morphology as pereopod 2. Basis of pereopod 4 and 6 more stout than that of pereopod 2. Pereopod 5 lacks tubercles on basis.
Pleopod 2 (Fig. 2 D). Protopod covered with scales on lateral margin, 1 seta on outer distal corner, and 2 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 with total of 6 simple and plumose setae. Pleopod 1–5 ranged from 8–9 on exopods and 6–8 setae on endopods. Appendix masculina nearly extends to half-length of endopod.
Uropod (Fig. 1 D) fringed with fine setae laterally. Basis covered with pectinate scales. Both rami subequal in length, and extend beyond apex of pleotelson. Exopod with total of 26 or 27 setae and endopod with total 13 or 14 setae. Plumose setae reduced. Six penicillate setae on dorsal endopod.
Penes (Fig. 2 E) 2 contiguous papillae medially fused.
Adult female (Fig. 3). Body (Fig. 3 A) 7.6–7.8 mm (7.7 ± 0.1 mm, n = 2) scarcely covered with long setae. Head (Fig. 3 A, B) with several setae. Frontal border concave. Pereon swollen with 2 sutures between pereonite 4–6. Pereonite 1 not fused to cephalosome. Pereonite 3 wider than pereonite 2, reaching lateral margins. Lateral shields of pereopods 2–6 visible dorsally. Pleonites 1–5 (Fig. 3 A) each with 4–8 setae on lateral and posterior margin, and 4–6 setae on dorsal surface. Pleotelson (Fig. 3 C) covered with pectinate scales and deformed. Lateral margin acutely narrow near basis and almost straight posteriorly. One pair of setae on dorsal surface, lateral margins, and distal margin, respectively.
Antennae (Fig. 3 D, E) with fewer number of setae than those of male adult. Flagellar articles antenna composed with 6 segments. Maxilliped (Fig. 3 F) composed with 2 basal articles and 4 palps. Number of plumose setae 8 on basal article 2, 5 on palp 1, 8 on palp 2, 8 on palp 3, and 7 in palp 4. One seta on inner distal margin of palp 1. Pylopod (Fig. 3 G) composed with 3 articles. Inner margins of article 1 and 2 covered with pectinate scales. Article 3 semicircular. Pylopodal oostegate oval with fine setae on posterior margin. Pereopods (Fig. 3 H) shorter and narrower than those of male adult. Pereopods 4–6 about 1.3 times longer than pereopods 2 and 3. Pleopods (Fig. 3 I) reduced setae: 7–9 and 6–8 simple or plumose setae on exopods and endopods, respectively. Exopods as long as endopods in all pleopods. Uropodal rami (Fig. 3 C) covered with pectinate scales and subequal in length, and extend beyond apex of pleotelson. Exopod with total of 25 or 26 setae and endopod with total 14 setae. Plumose setae reduced. Five penicillate setae on dorsal endopod.
Third-stage praniza larva (Figs 4, 12 A, B, 13A, B). Body (Figs 3 A, 10A, B) 6.8–9.3 mm (8.3 ± 0.7 mm, n = 10) with fully swollen thorax. In live specimens, orange pigmentations on head, pleonites and external margin of uropodal exopod. White spots often scattered on dorsal thorax. Eyes red. Inner margins of eyes fringed with distinct white lines. Pigmentation lost in ethanol.
Head (Fig. 4 A, B) semicircular, length approximately two third width. Clypeus projects nearly anteriorly, length approximately 0.5 head length and 1.23 mandible length exposed in dorsal view, lateral margin distally concave with distinct proximal convexity and then converging anteriorly. Eyes approximately 0.81 times of head length and its inner margin not reaching basis of antennae. Pereonite 1 (Fig. 4 B) axially thin, length less than basal width of head. Pereonite 2 with 1 seta on laterally. Pereonite 3 posteriorly concave. Lateral shields (remnant tergites) of pereonites 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. 4 A) lengths subequal. Small seta not visible on lateral margin of each segment in dorsal view. Pleotelson (Fig. 4 C) slightly narrow near basis and slightly convex on lateral margin. Three pairs of setae on dorsal surface and one pair of seta on apex. Pair of spine on apex.
Antennula (Fig. 4 D) composed with 3 basal and 4 flagellar articles. External margins of basal article 2 and 3 fringed with fine setae. One penicillate seta on flagellar article 4. Antenna (Fig. 4 E) composed with 4 basal and 7 flagellar articles. Basal article 3 and 4 fringed with fine setae.
Mandible (Fig. 4 F) with 8 teeth. Paragnath (Fig. 4 G) slightly curve. Maxillula (Fig. 3 H) with 7 teeth. Maxilliped (Figs. 4 I, 13A, B) composed with 2 basal and 2 palp articles. Basal article 1 lacks pectinate scales. Basal article 2 with coupling hook near elongated endite. Palp article 1 with long seta near basis and 3 teeth on tip. Palp article 2 bifurcate; external part with 4 setae and 1 spine, and inner part with 2 teeth and 1 seta. Pereopod 1 (Fig. 4 J) with distinct spine on distal margin of ischium. Carpus reduced, triangular with 1 small seta. Propodus with 1 seta on distal margin. Dactylus strongly curved. Pereopods (Fig. 4 K) with fewer setae and more slender than those of male adult. Two denticulate compound setae on distal margin of carpus. Propodus of pereopods 5 and 6 longer than that of pereopods 2–4. Pleopod 2 (Fig. 4 L) with fan-shaped rami. Both rami fringed with setae. Eight or 9 plumose setae on exopod. Seven and 8 plumose setae on endopod. Uropodal rami (Fig. 4 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 adults; each seta longer and densely fringed with fine setules.
Etymology. The specific name albipalpebrata is derived from the Latin meaning “white (= albi) eyelid (= palpebrata)”, referring to inner margins of eyes fringed with white distinct line of larva.
Remarks. Gnathia, with more than 100 species, has the highest number of species of any genus in the family (Schotte et al. 2008 onward). Seven new species have been recently collected from elasmobranch hosts and described. They have distinctive characters compared with other Gnathia species. These seven species have large bodies: 4.9–6.1 mm in Gnathia pantherina Smit & Basson, 2002; 7.6 mm in G. capillata Nunomura & Honma, 2004; 5.7–8.3 mm in G. grandilaris Coetzee, Smit, Grutter & Davies, 2008; 4.0– 5.4 mm in G. trimaculata Coetzee, Smit, Grutter & Davies, 2009; 3.9–5.8 mm in G. m a c u l o s a Ota & Hirose, 2009a; 9.0–10.0 mm in G. nubila Ota & Hirose, 2009b; and 6.8–8.7 mm in G. teruyukiae Ota, 2011, whereas most other Gnathia species do not reach 4.0 mm in body length (Monod 1926; Holdich & Harrison 1980; Svavarsson & Bruce 2012). Except G. teruyukiae, the body surfaces of the remaining six species are covered with long setae and the anterior parts of their bodies are covered with tubercles. Except G. capillata, the exopods on the uropods of the remaining six species possess more than 11 setae, while other Gnathia species have <10 setae (Smit & Basson 2002; Nunomura & Honma 2004; Coetzee et al. 2008, 2009; Ota & Hirose 2009a, 2009b; Ota 2011).
Gnathia albipalpebrata n. sp. is distinguished from other Gnathia species by a large body size (> 9.0 mm), entire body bearing long setae, heads and pereonites 1–3 with tubercles, round mediofrontal process, frontolateral processes, slender pleotelson bearing several setae on the lateral margin, and> 10 setae on the uropodal rami. Gnathia albipalpebrata n. sp. is most similar to Gnathia parvirostrata n. sp. because frontal borders of them are almost straight, 5 frontal processes on frontal border are visible in dorsal margin, pleotelson shapes are slender triangular, and pylopods of them are almost same shapes. However, G. parvirostrata n. sp. has slenderer body and has smaller head than G. albipalpebrata n. sp. Head length (from the base of the antenna to the posterior margin of the head), excluding the mandibles (from the base of the antenna to the apex of the pleotelson), is 1.9–2.2 (average ± SD = 2.0 ± 0.2, n = 2) times the body length in G. parvirostrata n. sp. but 1.9–2.6 (2.2 ± 0.2, n = 7) times the body length in the present species. The average head width (maximum width of head) is 2.8–3.0 (3.0 ± 0.1, n = 2) times the body length, excluding the mandibles, in G. parvirostrata n. sp. but 3.0–3.6 (3.3 ± 0.2, n = 7) times the body length in the present species.
The morphology of female adult has been described in 33 Gnathia species. Recent papers provide detail descriptions with drawings of appendages (e.g. Smit et al. 2002; Ota & Hirose 2009a; Farquharson et al. 2012). Female adult of G. albipalpebrata n. sp. had slightly concave frontal border, was scarcely covered with long setae, and had narrow pleotelson. These characters are well correspond with female adults of G. maculosa, G. nubila, and G. dejimagi n. sp. However, body length of female adult of G. maculosa is 4.1–5.5 mm, while G. albipalpebrata n. sp. is 7.6–7.8 mm, and G. maculosa has 8 setae on frontal border, while G. albipalpebrata n. sp. has 3 setae (Ota & Hirose 2009a). Female adult of G. nubila has 2 spots on frontal border and more than 10 setae presents near the eyes, while 3 setae in G. albipalpebrata n. sp. (Ota & Hirose 2009b). Body length of female adult of G. dejimagi n. sp. is 9.0 mm, while G. albipalpebrata n. sp. is 7.6–7.8 mm, and pleopodal rami of G. dejimagi n. sp. are oval shape, while those of G. albipalpebrata n. sp. are fan shape.
The morphology of gnathiid larvae is generally similar in most species but the shape of the head and pleotelson, the number of setae on the uropodal rami, and the number of teeth on the mouthparts is possible interspecific character. Furthermore, some species have distinct pigmentation patterns when living, which are useful for species identification of larvae (Smit & Davies 2004; Wilson et al. 2011). The third-stage praniza larvae of G. albipalpebrata n. sp. had white spots on the swollen thorax and distinct white lines fringed the inner margins of the eyes. White spots on a swollen thorax have also been observed in G. m a c u l o s a and G. parvirostrata n. sp. but the spots had a stronger contrast in the present species. Gnathia albipalpebrata n. sp. was distinguished from other species on the basis of the pleotelson, which was slightly convex with a smooth lateral margin, while its apex had two spines. This pleotelson shape was most similar to the pleotelson shape of G. teruyukiae, although the pleotelson of G. teruyukiae is shorter and the two spines on the apex are smaller (Ota 2011).
description: Published as part of Ota, Yuzo, 2014, Three new gnathiid species with larvae ectoparasitic on coastal sharks from southwestern Japan (Crustacea: Isopoda), pp. 478-500 in Zootaxa 3857 (4) on pages 479-485, DOI: 10.11646/zootaxa.3857.4.2, http://zenodo.org/record/227582