Galathella solivagus, Kilgallen, 2009

Kilgallen, Niamh M., 2009, New species of lysianassoid Amphipoda (Crustacea) associated with seamounts, marine canyons and cold seeps of New Zealand, Zootaxa 2298 (1), pp. 1-30 : 25-29

Galathella solivagus sp. nov.

( Figures 17–19 )

Type material. Holotype, non-ovigerous female, 8 mm, NIWA 31940 , LM9 cold seep, Omakere Ridge, Hikurangi Margin, 40º03.4’S, 177º48.63’E, 1124 m (Stn. SO 191-2/56), collected by TV-Grab.

Etymology. The specific name ‘solivagus’ is from the Latin meaning ‘wandering alone’, and is used here as the holotype was the only specimen collected.

Diagnosis. Mandible molar weakly triturative, palp attached centrally. Maxilla 1 outer plate with setalteeth in a 7/4 crown arrangement. Maxilliped outer plate reaching to palp article 4. Gnathopod 1 subchelate; coxa 1 shorter than coxa 2 and slightly tapering posterodistally; ischium elongate. Epimeron 3 posterodistal corner produced, forming small spine. Telson deeply cleft.

Description of female holotype. Antenna 1 subequal to antenna 2, primary flagellum 11-articulate, article 1 distinctly elongate with 2-field callynophore; accessory flagellum 4-articulate. Antenna 2 less than 40% of body length; flagellum 10-articulate. Calceoli absent. Eyes apparently absent. Lateral cephalic lobes subquadrate. Mouthparts forming quadrate bundle. Epistome and upper lip separate, epistome slightly produced in front of upper lip. Mandible incisor smooth; lacinia mobilis present on left mandible only; setal row present; molar weakly triturative; palp attached centrally. Maxilla 1 outer plate with 11 setal-teeth in a 7/ 4 crown arrangement; palp present, 2-articulate. Maxilla 2 inner plate without oblique setae. Maxilliped palp 4-articulate, article 4 well developed, without unguis; outer plate large, reaching to palp article 4, with weak, small apical robust setae; inner plate well developed, greater than half the length of outer plate.

Coxae 1–3 posterodistal corner with slight notch with inserted seta. Gnathopod 1 subchelate; coxa 1 large, slightly shorter than coxa 2, slightly tapering posterodistally, rounded distally; basis with setal fringe; ischium elongate, about twice as long as broad; carpus long, subequal in length to propodus; propodus margins subparallel, palm slightly acute, minutely denticulate and defined by robust seta at posterodistal corner; dactylus fitting palm, without accessory tooth. Gnathopod 2 subchelate; carpus about 1.5 × propodus length; dactylus moderately developed. Pereopod 3 merus weakly expanded anterodistally and longer than carpus; carpus moderately robust, shorter than propodus; propodus slender, with blunt, locking robust seta at posterodistal corner. Pereopod 4 coxa with moderately developed posterodistal lobe; merus weakly expanded anterodistally and longer than carpus; carpus slender, slightly shorter than propodus; propodus slender, with blunt, locking robust seta at posterodistal corner. Coxa 5 equilobate; pereopod 5 basis slightly longer than broad, crenate posteriorly; merus moderately expanded posterodistally. Pereopod 6 basis distinctly longer than broad, posterior margin slightly crenate, producing slight posterodistal lobe, not reaching merus. Pereopod 7 basis distinctly longer than broad, anterior margin slightly concave, posterior margin crenate and slightly expanded, posterodistally produced, not reaching merus; merus barely expanded posteriorly. Gills on gnathopod 2 to pereopod 6.

Epimeron 1 anterodistal corner quadrate. Epimeron 2 posterodistal corner quadrate. Epimeron 3 posterodistal corner produced, forming a small spine. Urosomite 1 with distinct dorsal depression and rounded hump. Uropod 1 peduncle subequal in length to rami; rami subequal in length (based on right uropod, not illustrated). Uropod 2 peduncle slightly shorter than rami; rami subequal in length, inner ramus without marginal constriction (based on right uropod, not illustrated). Uropod 3 peduncle distinctly shorter than rami; rami distinctly unequal in length, outer ramus 2-articulate, article 2 about 0.25 × length of article 1, inner ramus extending to article 2 of outer ramus. Telson distinctly longer than broad, deeply cleft.

Length. 8 mm.

Distribution. New Zealand: Omakere Ridge, Hikurangi Margin; 1124 m.

Ecology. Associated with sediments in the vicinity of a cold seep.

Remarks. Galathella solivagus sp. nov. differs from its four known congeners in having a long maxilliped outer plate that reaches almost to article 4 of the palp, lateral cephalic lobes that are not as rounded or down-turning, and a more strongly developed posterior lobe on coxa 4. It differs from G. bassiana Lowry & Stoddart, 1995a , G. palana Lowry & Stoddart, 1995a , and G. latipes ( Ledoyer, 1986) in having more slender pereopods 5–7. Galathella bassiana and G. latipes lack the small epimeron 3 spine present in this species, and the telson of the former species is not as deeply cleft. Galathella palana has a simple gnathopod 1, not subchelate as in this new species. Galathella solivagus sp. nov., G. palana , and G. bassiana also differ from the type species of the genus, G. galatheae ( Dahl, 1959) , in having an elongate ischium on gnathopod 1. The genus thus seems to be quite morphologically diverse, for example the gnathopod 1 has states ranging from simple to strongly subchelate with an ischium that may be short or long, the mandibular molar can be setose with a small triturating surface or not setose with a strong triturating surface, the epimeron 3 posterodistal corner may be producing a small spine or be narrowly rounded, and the telson may be moderately to deeply cleft. Therefore, while G. solivagus differs in some characters from its congeners, it nonetheless conforms to the diagnostic characters of the genus as currently defined. Thus, for the present, it warrants inclusion in the genus Galathella , though the possibility remains that in the future it should be removed to another genus once additional material is uncovered and a revision of the genus carried out.

Figures

FIGURE 17. Galathella solivagus sp. nov., holotype, female, 8 mm, NIWA 31940. A, head and anterior pereonites; B, urosome and epimeron 3; C, antenna 1; D, antenna 2; E, maxilla 2; F, maxilla 1; G, right mandible; H, left mandible; I, maxilliped palp and outer plate; J, maxilliped inner plate. Scale bars: a = 1 mm (figs A, B); b = 0.3 mm (figs C, D); c = 0.1 mm (figs E–J).

FIGURE 18. Galathella solivagus sp. nov., holotype, female, 8 mm, NIWA 31940. A, gnathopod 1; B, gnathopod 2; C, pereopod 3; D, pereopod 4. Scale bar = 0.5 mm.

FIGURE 19. Galathella solivagus sp. nov., holotype, female, 8 mm, NIWA 31940. A, pereopod 5; B, pereopod 6; C, pereopod 7; D, telson; E, left uropod 1; F, left uropod 2; G, uropod 3. Scale bars: a = 0.5 mm (figs A–C); b = 0.4 mm (figs D–G).