Galathea nicobarica, Tiwari & Padate & Cubelio & Osawa, 2022

Tiwari, Shivam, Padate, Vinay P., Cubelio, Sherine Sonia & Osawa, Masayuki, 2022, Two new species of the genus Galathea Fabricius, 1793 (Crustacea: Decapoda Anomura: Galatheidae) from the Andaman Sea, India, Zootaxa 5219 (2), pp. 175-184 : 177-180

Galathea nicobarica sp. nov.

urn:lsid:zoobank.org:act:E56310EE-74D4-4753-8A10-75CF2F159007

( Figs. 2A , 3 )

Type material. Holotype: ovigerous female ( IO /SS/ANO/00144; PCL 3.8 mm, CW 3.6 mm), Andaman Sea , off Car Nicobar Island, FORVSS stn. 334II05, 9.24°N, 92.92°E, 315 m depth, Naturalist’s dredge, coll. Vinu Jacob, 28 January 2015.

Diagnosis. Carapace slightly longer than wide; dorsal surface glabrous in general, with transverse rows of interrupted ridges (epigastric row composed of short scaly ridges, 1 complete row on protogastric region, 2 rows on mesogastric region, 3 irregular rows on posterior half), no spines on gastric region and on hepatic regions and margins; anterolateral spine overreaching tip of lateral limit of orbit, but not reaching tip of basal lateral tooth of rostrum; lateral margin with no small spine between anterolateral spine and anteriormost spine of branchial margin; branchial margin with 4 spines. Rostrum broadly triangular, with 4 shallowly incised small teeth. Pterygostomian flap without spines on upper margin and surface. Abdominal tergite 2 with 2 long transverse ridges, tergite 3 with 1 long transverse ridge, tergites 4–6 smooth. Antennular article 1 with well-developed distomesial spine. Antennal article 1 with distomesial spine reaching distal end of article 4. Mxp3 merus with 2 flexor marginal spines and small disto-extensor spine, distal spine larger than proximal spine; dactylus roundly truncate. P1 palm relatively broad, 1.4 times as long as wide, dorsomesial margin with row of small spines; fingers equal in length to palm, opposable margins of fingers spooned. Epipods absent from P1–4.

Description. Carapace (PCL) 1.1 times as long as wide, surface nearly horizontal from anterior to posterior. Dorsal surface without setae; epigastric ridge composed of 2 short scales, without spines; 1 complete protogastric ridge, 2 indistinct mesogastric ridges interrupted medially, metagastric ridges apparently absent. Mid-transverse ridge uninterrupted, preceded by shallow cervical groove, and followed by 3 irregular transverse rows of short ridges on posterior half; median ridge of anteriormost row longest. Anterior branch of cervical groove poorly developed. Lateral margins gently convex, with 5 spines decreasing in size posteriorly; first anterolateral, well-developed, overreaching tip of lateral limit of orbit, not reaching tip of proximalmost lateral tooth of rostrum; 2 anterior and 2 posterior branchial spines. Lateral limit of orbit ending in small spine; infraorbital margin unarmed ( Figs. 2A , 3A, B ). Rostrum broadly triangular; length 1.1 times width, 0.4 PCL; width 0.4 CW; distance between distalmost lateral incisions 0.3 of that between proximalmost incisions; dorsal surface nearly horizontal in lateral view, without setae; lateral margins with 4 shallowly incised small teeth ( Figs. 2A , 3A, B ).

Pterygostomian flap unarmed but with undulate ridges bearing short setae on surface; dorsal margin unarmed; anterior margin rounded, with slightly longer setae ( Fig. 3B ).

Thoracic sternum as long as wide, lateral extremities gently divergent posteriorly. Sternite 3 2.5 times as wide as long, with 2 lobes anteriorly separated by V-shaped, shallow median notch; anterior margins of lobes faintly crenulated. Sternite 4 weakly concave on anterior margin; anterior width approximately as large as sternite 3; surface with pair of short striae anterolaterally and 1 undulate stria posteromedially ( Fig. 3C ).

Abdominal tergite 2 with 2 long transverse ridges, anterior ridge corresponding to dorso-anterior margin. Tergite 3 with 1 transverse ridge ( Fig. 3A ). Tergites 4–6 smooth on surfaces. Tergite 6 with posteromedian margin gently concave ( Fig. 3D ). Telson incompletely subdivided ( Fig. 3D ).

Ocular peduncle about 1.2 times as long as wide, maximum corneal diameter 0.8 times rostrum width ( Fig. 3A ).

Antennular article 1 with 3 well developed distal spines; distomesial and distolateral spines subequal in size, distodorsal spine largest ( Fig. 3E ).

Antennal article 1 with distomesial spine reaching distal margin of article 4; article 2 with well-developed distomesial and distolateral spines subequal in size, not reaching distal margin of article 3; article 3 with small distomesial spine; article 4 unarmed ( Fig. 3E ).

Mxp3 ischium with small distoflexor spine; extensor margin ending in acute angle; crista dentata with 26 denticles. Merus slightly longer than ischium (measured on lateral midline); flexor margin with 2 spines, distal spine distinctly longer than proximal; extensor margin with 1 distal spine and smaller subdistal spine. Carpus to dactylus unarmed. Propodus relatively broad. Dactylus short, roundly truncate; distal margin broad ( Fig. 3F ).

P1 unequal (left and right P1 1.6 and 1.4 PCL, respectively) covered with finely setiferous scales and with sparse long plumose setae. Merus 0.6 (left) and 0.5 (right) PCL, 1.7 (left) and 1.8 (right) times length of carpus; dorsal surface with 3 dorsolateral spines arranged in arc, dorsomesial margin with 3 spines, distomesial spine strongest, dorsodistal margin with 1 median spine; mesial surface with strong subdistal spine; ventral surface with distomesial spine followed by smaller spine. Carpus 0.9 (left) and 1.2 (right) times length of palm, 1.5 (left) and 1.6 (right) times longer than wide; dorsal surface with row of 5 and 4 spines, distomesial spine strongest; mesial surface with 2 spines, distal spine larger; ventrodistal margin with row of 3 small spines. Palm relatively broad, 1.4 (left) and 1.3 (right) times as long as wide, lateral and mesial margins subparallel, gently converging proximally; dorsal surface with small spine at dactylar articulation, dorsomesial margin with row of 4 small spines, lateral margin with 2 distal spines; ventral surface with 1 spinule at dactylar articulation. Fingers equal in length to palm (left) and 1.2 times longer than palm (right), spooned; opposable margins slightly gaping, each with low blunt tooth on proximal half; distal margin rounded, with row of small blunt teeth; dactylus with 1 proximal spinule on dorsomesial surface ( Fig. 3G, H ).

P2–4 missing. Epipods absent from P1–4.

Etymology. The species name is derived from the type locality.

Remarks. Although the present specimen is partially damaged and lacks all ambulatory legs, we treat it as a new species because of the different morphological characters of the carapace and third maxilliped. Galathea nicobarica sp. nov. is morphologically close to G. rubromaculata Miyake & Baba, 1967a , known from Japan, Korea and the Philippines, in having the carapace with only a few long transverse ridges but no spines or covering of short setae on the gastric region and no small spine between the anterolateral and anteriormost branchial spines, the rostrum being relatively broad and with four shallowly incised small teeth on each lateral margin, the antennular article 1 with 3 well developed distal spines, the antennal article 1 with the distomesial spine reaching the distal end of the article 4, and the P1 without an epipod (cf. Miyake & Baba 1967a; Baba 1988; Kim et al. 2016). However, the present new species is distinguishable from G. rubromaculata by the branchial margin of the carapace with four instead of five spines. The flexor marginal armature of Mxp3 merus of G. rubromaculata varies between the holotype from Japan (southwest off Nagasaki, Kyushu; Miyake & Baba 1967a) and specimens from Japan (Sagami Bay, comparative material for the present study) and Korea ( Kim et al. 2016). The two flexor marginal spines of Mxp3 merus are equal in size in the holotype, but the distal spine is distinctly larger than the proximal spine in the other Japanese and Korean specimens, which is similar to the holotype of the present new species (cf. Miyake & Baba 1967a; Kim et al. 2016; present study).

Galathea nicobarica sp. nov. has a roundly truncate Mxp3 dactylus which has been only known in G. kuboi Miyake & Baba, 1967b recorded from Japan, Philippines, and Indonesia, among the congeneric species ( Miyake & Baba 1967b; Baba 1988, 2005). Galathea kuboi is clearly different from the new species by numerous short setae and no distinct transverse ridges on the carapace (cf. Baba 2005). The Japanese specimens of G. rubromaculata examined in the present study also have a comparatively wide Mxp3 dactylus, but the shape of the article is oblong ( Fig. 3J ) rather than truncate as in G. nicobarica sp. nov. and G. kuboi .

Distribution. Presently only known from Andaman Sea, 315 m depth ( Fig. 1 ).

Figures

FIGURE 1. Map of the study area indicating collection sites in Indian EEZ. 1, Galathea nicobarica sp. nov.; 2, Galathea tirmiziae sp. nov.

FIGURE 2. Habitus, dorsal view. A, Galathea nicobarica sp. nov., holotype, ovigerous female (IO/SS/ANO/00144; PCL 3.8 mm, CW 3.6 mm); B, Galathea tirmizii sp. nov., holotype, female, (IO/SS/ANO/00129; PCL 3.0 mm, CW 2.9 mm). Scale bars: 2 mm.

FIGURE 3. Galathea nicobarica sp. nov., holotype, ovigerous female (IO/SS/ANO/00144; PCL 3.8 mm, CW 3.6 mm) (A–I); Galathea rubromaculata Miyake & Baba, 1967a, male (CBM-ZC 14502; PCL 4.8 mm) (J). A, carapace, dorsal view (left lateral and right posterior parts partially damaged); B, carapace and pterygostomian flap, left lateral view; C, thoracic sternum, ventral view; D, telson, external view; E, left eye, antennular article 1 and antennal peduncle, ventral view; F, J, right Mxp3, lateral view; G, left P1, dorsal view; H, left P1, ventral view; I, left P5 dactylus, lateral view. Scale bars: A, B, G, H= 2.0 mm; C–F, I = 0.5 mm; J = 1.0 mm.