Gnathia parvirostrata, 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 : 486-487

Gnathia parvirostrata n. sp.

( Figs. 5–7 , 12 C, D, 13C, D)

Material examined. Holotype: NSMT-Cr22968, adult male, here designated, (total length 11.1 mm), gill chambers of Galeocerdo cuvier (Péron & Lesueur, 1822) , caught by line fishing off Ishigaki-jima Island (24°28′N, 124°18′E), 6 Sept. 2008. Paratypes: NSMT-Cr22969, 1 male adult, 6 third-stage praniza larvae, from the same host and locality as the holotype.

Description. Adult male ( Figs. 5 , 6 ). Body ( Fig. 5 A) 10.6 and 11.1 mm and covered with long setae. Pigmentation of live specimens white; digestive organs brown due to congealed host blood.

Head ( Fig. 5 A–C) covered with tubercles, rectangular with posterior margin slightly concave. Frontal border almost straight. Mediofrontal process not elongated. Two frontolateral processes with several setae and tubercles on tips. Two apexes of ventral frontal margin slightly visible in dorsal view. Dorsal sulcus deep U-shaped and just reaching about half-length of. Eyes composed with 45 ocelli. Paraocular ornamentation highly raised in lateral view. Supraocular lobe prominent with slightly dentate apex. Accessory supraocular lobe acute.

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

Pleonites 1–5 ( Fig. 5 A) almost equal length and width, fringed with long setae on posterior central and lateral margins of each segment. Epimera not prominent.

Pleotelson ( Fig. 5 D) covered with pectinate scales. Lateral margin acutely narrow near basis and almost straight posteriorly. Distal apex without spine. One pair of small seta near basis, central surface, and distal apex, respectively. Four pair of long setae near lateral margin.

Mandible ( Fig. 5 A–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.

Antennula ( Fig. 5 E) composed with 3 basal and 5 flagellar articles. Two, 3, and 1 penicillate setae on distal margins of 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 2 setae.

Antenna ( Fig. 5 F) composed with 4 basal and 7 flagellar articles. One and 4 feather-like bristles on basal 3 and 4, respectively. One or 2 setae on distal margins of flagellar articles 1–6. Article 7 terminates in 4 setae.

Maxilliped ( Fig. 6 A) composed with basis and 4 palp articles. Basis fringed with fine setae. Endite extends palp article 1. Six, 7, 4, and 9 plumose setae on external margins of palp articles 1–4, respectively. Five setae on internal margin of palp article 4.

Pylopod ( Fig. 6 B) 3 articles. Article 1with 2 areolae, 44 plumose setae on internal margin, and 2 setae near basis. Three small spines and 4 setae on distal margin of article I. Article 2 circular with 10 setae. Article 3 minute.

Pereopod 2 ( Fig. 6 C) covered with pectinate scales visible on ischium, carpus, and propodus. Outer margins of basis, ischium, and merus fringed with fine setae. Basis oblong with many long setae, 2 feather-like bristles, and 10 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 of pereopod 2. Propodus of pereopods 4–6 longer than that of pereopod 2.

Pleopod 2 ( Fig. 6 D) with reduced setae. Protopod covered with scales and fringed with fine setae, 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 6–9 setae on endopods. Appendix masculina of pleopod 2 slightly extends half-length of endopod.

Uropod ( Fig. 5 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 28 setae and endopod with total 12 or 13 setae. Plumose setae reduced. Four or 5 feather-like bristles on dorsal endopod.

Penes ( Fig. 3 E) fused with 2 contiguous papillae.

Third-stage praniza larva ( Figs 7 , 12 C, D). Body ( Figs 6 A, 12C, D, 13C, D) 6.6–8.5 mm (7.8 ± 0.9 mm, n = 5) with fully swollen thorax. In live specimens, orange pigmentations on head, pleonites and external margin of exopod of uropod. White spots scattered on dorsal thorax. Eyes light orange. The pigmentation disappeared in ethanol.

Head ( Fig. 7 A, B) circular with almost straight posterior margin, approximately two-third length of width. Clypeus concave anteriorly, approximately 0.24 times of head length and 0.32 times of mandible length exposed in dorsal view. Eyes approximately 0.73 times of head length and its inner margin not reaching basis of antennae. Pereonite 1 ( Fig. 7 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 3.3 times as wide as long. Pleonites ( Fig. 7 A) subequal in each length. Small seta not visible on lateral margin of each segment in dorsal view. Pleotelson ( Fig. 7 C) narrow near basis and slightly convex on lateral margin. Scales visible on dorsal surface. Lateral margin fringed with fine setae. Two pairs of setae on dorsal surface and one pair of seta on apex. Apex not acute fringing with fine setae. Apex with pair of small spine.

Antennula ( Fig. 7 D) composed with 3 basal and 4 flagellar articles. External margins of basal article 2 and 3, and flagellar article 2 fringed with fine setae. Antenna ( Fig. 7 E) composed with 4 basal and 7 flagellar articles.

Mandible ( Fig. 7 F) with 7 teeth. Paragnath ( Fig. 7 G) slightly curved. Maxillula ( Fig. 7 H) with 7 teeth. Maxilliped ( Figs. 7 I, 13C, D) composed with 2 basal and 2 palp articles. Basal article 2 with coupling hook near elongated endite. Palp article 1 with long seta near basis and smooth tip without teeth. Palp article 2 separated into 2 parts distally; external part with 5 setae and 1 spine, and inner part with 1 tooth and seta. Pereopod 1 ( Fig. 7 J) pereopodal shape. Distinct protrusion on distal margin of merus. Caprus reduced with small seta.

Pereopod 3 ( Fig. 7 K) with fewer setae and more slender than those of male adult. Pectinate scales not visible. Pereopod 2 almost same morphology as pereopod 3. Pereopods 4–6 entirely larger and basis of them stouter than pereopod 2. Distinct tubercle presents on inner margin of pereopod 5. Pleopod 2 ( Fig. 7 L) with fan-shaped rami. External margin of basis without seta. Both rami fringed with fine setae. Eight or 9 plumose setae on exopod. Seven and 8 plumose setae on endopod. Uropod ( Fig. 7 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 parvirostrata is derived from the Latin meaning “small (= parvi) rostrum (= rostrata)”, referring to distinct short clypeus of larva.

Remarks. Gnathia parvirostrata n. sp. can be distinguished from other Gnathia species by a large body size (> 8.0 mm), entire body covered with long setae, head and pereonites 1–4 with tubercles, round mediofrontal process, frontolateral processes, slender pleotelson bearing long random setae, and> 10 setae on the uropodal rami. The morphology of G. parvirostrata n. sp. is most similar to that of G. albipalpebrata n. sp. but the differences between G. parvirostrata n. sp. and G. albipalpebrata n. sp. were referred in the previous remarks. Gnathia parvirostrata n. sp. also similar to G. grandilaris because of the shape of the frontal border and the pleotelson. In G. grandilaris , the mediofrontal process is slightly elongated and the tips of the ventral frontal border are not visible in dorsal view; however, in G. parvirostrata n. sp., the mediofrontal processes are not elongated and the distal margin of the ventral frontal border are visible in dorsal view. The outer margin of the pylopod is sinuous in G. grandilaris ( Coetzee et al. 2008) , but is almost straight in G. parvirostrata n. sp.

The third-stage praniza larvae of G. parvirostrata n. sp. were easily distinguishable from other species because of their short clypeus and most mandibular parts being exposed in the dorsal view. With regard to live specimens, the other species had red eyes while the present species had light orange eyes. The swollen thorax of the present species had white spots. The third-stage praniza larvae of G. m a c u l o s a and G. aureamaculosa Ferreira & Smit, 2009 also have white spots on their swollen thorax but they are smaller (<5.8 mm in G. m a c u l o s a and <3.1 mm in G. aureamaculosa but> 6.6 mm in the present species) ( Ota & Hirose 2009a; Ferreira et al. 2009).

Figures

FIGURE 3. Gnathia albipalpebrata n. sp., paratype, female adult (NSMT Cr- 22966, total length, 7.8 mm): A, body, dorsal view; B, frontal border, dorsal view; C, pleotelson, dorsal view. P 1 = pereonite 1.

FIGURE 5. Gnathia parvirostrata n. sp., holotype, male adult (NSMT Cr- 22968, total length, 11.1 mm): A, body, dorsal view; B, head with mandibles, dorsal view (broken line shows mediofrontal process of paratype, NSMT Cr- 22969); C, head, lateral view; D, pleotelson, dorsal view; E, left antennula; F, left antenna.

FIGURE 6. Gnathia parvirostrata n. sp., holotype, male adult (NSMT Cr- 22968, total length, 11.1 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 7. Gnathia parvirostrata n. sp., paratype, third-stage larva (NSMT Cr- 22969, total length, 8.4 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 I; K, left pereopod 3; 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.