Gnathia sifae, Svavarsson, 2006

Svavarsson, Jörundur, 2006, New species of Gnathiidae (Crustacea, Isopoda, Cymothoida) from seamounts off northern New Zealand, Zootaxa 1173, pp. 39-56 : 47-55

Gnathia sifae sp. nov.

( Figs 6–10 )

Material examined

Holotype. male, 8.8 mm, stn. TAN 0107/001, 19 May 2001, 35º44.51’S, 178º30.20’E, epibenthic sled, 260­470 m, scoria rubble ( NIWA 22442 ) . Paratypes. Stn. TAN 0107 /001, 19 May 2001, 35º44.51’S, 178º30.20’E, epibenthic sled, 260–470 m, scoria rubble, 92 males ( NIWA 22443 ; IMNH 2005.05.11); stn. TAN 0107 /224, 23 May 2001, 35º44.35’S, 178º29.74’E, 200–500 m, scoria rubble, 6 males ( NIWA 22444 ) .

Other non­type material. Stn. TAN. 0107/001, 19 May 2001, 35º44.51’S, 178º30.20’E, epibenthic sled, 260–470 m, scoria rubble, 19 females and 6 larvae (NIWA 22445); stn. TAN 0107/224, 23 May 2001, 35º44.35’S, 178º29.74’E, 200–500 m, scoria rubble, 1 female and 1 larva (NIWA 22446).

Diagnosis

Frontal border with distinct mediofrontal process, with several notches. Eyes large. Mandible moderately curved, armed carina, with fine dentations and smooth long blade. Pereonite 5 with areae laterales, pereonite 6 with lobi laterales. Pereopods with projections laterally near ventral margin, holding rounded cuticular extensions. Basis of pereopod 4 dorsodistally with 2 processes.

Description

Body length 7.0– 8.8 mm. Body about 2.6 times as long as wide ( Fig. 6 ). Cephalosome ( Fig. 7 A–C) semi­pentagonal, about 0.7 times as long as wide, lateral margins convex. Numerous fine granules on cephalosome. Frontal border with distinct mediofrontal process, mediofrontal process with several notches and several fine setae, broad dorsal sulcus. Supraocular lobe long, pointed. Posterior median tubercle present. Weak paraocular ornamentation. Eyes well developed, elongated, lateral and sessile, eyes length (full length seen in lateral view) 0.4 times cephalosome length. Pereon ( Fig. 6 ) evenly sided, with several long setae along body, numerous fine granules anteriorly on pereonites, pereonites subequal in width, widest at pereonites 2 and 3, about 1.1 times wider than cephalosome. Pereonite 1 dorsally reaching lateral margins, only partially obscured by cephalon. Pereonite 2 slightly wider than pereonite 1, pereonite 5 with areae laterales, pereonite 6 with weak lobi laterales, pereonite 7 narrow. Pleonites ( Fig. 6 ) subequal, pleonal epimeria prominent on pleonites 2 to 4, fine row of setae posteriorly on all pleonites.

Antenna 1 ( Fig. 7D ) short, smaller than antenna 2; second and third articles of peduncle with few plumose setae distally, 3 plumose setae medially. Flagellum with 5 articles; about 0.9 times as long as article 3 of peduncle; first article small, few fine setae and aesthetascs on distal articles.

Antenna 2 ( Fig. 7E ) about 2 times longer than antenna 1; peduncle 3 and 4 with few long, plumose setae distally, several slender setae medioventrally; flagellum with 7 articles, flagellum about 1.7 times as long as peduncle article 4.

Mandible ( Fig. 7 A­C, F) about 0.4 times as long as cephalon width, moderately curved, armed carina, with fine dentations; smooth long blade.

Maxilliped ( Fig. 7G ) with 5 articles; external margin of article 1 fringed with fine, small setae; external margins of articles 2–5 with stout plumose setae, 7 on article 2, 9 on article 3, 6 on article 4, around 13 setae on external margin and distally on article 5; endite reaching article 3, with 4 coupling hooks ( Fig. 7H ).

Pylopod ( Fig. 7I ) with 3 articles, external and internal margins fringed with fine setae; article 1 about 1.4 times longer than wide, lateral and posterior margins form obtuse angle, external margin of article 1 with about 66 plumose setae, plumose setae intermediate and similar in size, simple setae present on distal end and on internal margin; second article with fringed with fine setae, few simple setae distally; third article minute ( Fig. 7J ).

Pereopods ( Figs 8–9 ) similar is shape, with numerous long plumose setae on basis, long setae distally on merus, ischium and carpus. Several fine seta laterodistally on propodus; robust seta medioventrally and ventrodistally; rounded projections laterally near ventral margin, holding rounded cuticular extensions. Basis of pereopod 4 dorsodistally with 2 processes ( Fig. 9A ).

Pleopod 1 ( Fig. 10A ) protopod with 3 coupling hooks. Endopod 2.1 times longer than wide, distally with 7 plumose setae, longest plumose setae 0.5 times endopod length; exopod 0.8 times endopod length, 2 times longer than wide, distally with 10 plumose setae, longest plumose setae 0.75 times exopod length.

Pleopod 2 ( Fig. 10B ) protopod with 2 coupling hooks, appendix masculina short, curved. Endopod 2.2 times longer than wide, distally with 8 plumose setae, longest plumose setae 0.4 times endopod length; exopod 0.9 times endopod length, 1.9 times longer than wide, distally with 11 plumose setae, longest plumose setae 0.7 times exopod length.

Pleopod 3 ( Fig. 10C ) protopod with 2 coupling hooks. Endopod 2 times longer than wide, distally with 8 plumose setae, longest plumose setae 0.6 times endopod length; exopod 0.7 times endopod length, 1.9 times longer than wide, distally with 11 plumose setae, longest plumose setae 0.7 times exopod length.

Pleopods 4 and 5 similar to pleopod 3; with same number of plumose setae and coupling hooks.

Pleotelson ( Fig. 10D ) 1.3 times longer than wide, strongly concave near insertion of uropods, slightly concave about one third from distal end, lateral margins with cuticular extensions; 2 setae posteriorly near lateral margins; distally 2 setae.

Uropodal ( Fig. 10D ) endopod about as long as exopod, about 3.3 times longer than wide, fringed with about 9 plumose setae on distomedial margin and on apex, longest plumose setae about as long as endopod, few long simple seta laterodistally, 2 broom­like setae on dorsal surface near proximal end, 1 broom­like seta near distal end. Exopod about 4.6 times as long as wide, fringed with few plumose setae mediodistally and distally, few simple setae laterally and laterodistally.

Etymology The species is named in honour of my wife, Sif, for her understanding and patience towards my scientific work over the years.

Remarks

Gnathia sifae sp. nov. is easily distinguished from all other New Zealand gnathiid species in having a distinct mediofrontal process on the cephalon, but no frontolateral processes. It is further clearly distinguished from the co­occurring species, Caecognathia nieli sp. nov., in having relatively larger eyes and of different shape, in the presence of lateral projections on the pereopods and in the shape of the appendix masculina. The species is in some ways similar to Caecognathia polythrix ( Monod, 1926) . In addition to having the above mentioned mediofrontal process, G. sifae is considerable larger than C. polythrix (adult males 2.3–2.8 mm). The latter species is generally more tuberculate, for instance at the lateroventral surface of the cephalon, which is smooth in G. sifae .

G. sifae was found in large numbers in scoria rubble on the Rumble III seamount sitting to the north of the Bay of Plenty, New Zealand.

Distribution North of Bay of Plenty, New Zealand.

Discussion

The isopod fauna of New Zealand is still fairly poorly known, although some families and genera have received attention recently (e.g. Bruce 2002, 2003, 2004a, 2004b, 2004c, 2005; Just & Wilson 2004; Merrin 2004). This is particularly true for the gnathiid isopods, of which only eight species have previously been recorded from New Zealand. Six of these species were reported during the first part of last century by Monod (1926): Caecognathia polythrix ( Monod, 1926) , C. regalis ( Monod, 1926) , C. pacifica ( Monod, 1926) , C. akaroensis ( Monod, 1926) , Thaumastognathia diceros Monod, 1926 and Gnathia brachyuropus Monod, 1926 , the latter known only from a praniza larva. The species described by Monod were all collected in fairly shallow waters: T. diceros , C. regalis and C. polythrix at the Three Kings at 118 m, C. akaroensis at Akaroa harbour at 10 m, and C. pacifica in Coleville Channel at 64 m. Gnathia brachyuropus was observed at Akaroa (10 m) and Lyttelton harbours. Much later Cohen & Poore (1994) reported Bathygnathia tapinoma Cohen & Poore, 1994 and B. vollenhovia Cohen & Poore, 1994 from deep water, both from a depth of 924 m off the west coast of the South Island ( Cohen & Poore 1994). The New Zealand gnathiid fauna is presumably still quite under­sampled, in particular in deeper waters.

The present paper adds two species to the New Zealand gnathiid fauna, bringing the total to 10 known species. There is no information available on which fish species these gnathiids parasitize during their larval praniza stage. It is not unlikely that the orange roughy ( H. atlanticus ) is among the hosts, being very abundant on seamounts in New Zealand waters ( Bull et al. 2001).

Figures

FIGURE 6. Gnathia sifae sp. nov. A. Male holotype, 8.8 mm (NIWA 22442). A, body (pleonites down turned). B, pleonites and pleotelson (slightly down turned). Scale: 0.5 mm.

FIGURE 7. Gnathia sifae sp. nov. Male paratype, 7.6 mm (NIWA 22443). A, cephalosome, dorsal view. B, cephalosome, lateral view. C, anterior part of cephalosome, ventral view. D, antenna 1. E, antenna 2. F, mandible. G, maxilliped (fine setulose on large setae omitted from large setae). H, coupling hooks of maxilliped. I, pylopod (fine setulose on large setae omitted from large setae). J, third article of pylopod.

FIGURE 8. Gnathia sifae sp. nov. Male paratype, 7.6 mm (NIWA 22443). A, pereopod 2. B, dactylus of pereopod 2. C, pereopod 3.

FIGURE 9. Gnathia sifae sp. nov. Male paratype, 7.6 mm (NIWA 22443). A, pereopod 4. B, pereopod 5. C, pereopod 6.

FIGURE 10. Gnathia sifae sp. nov. Male paratype, 7.6 mm (NIWA 22443). A, pleopod 1. B, pleopod 2. C, pleopod 3. D, uropods and pleotelson.