Pasiphaea unispinosa Wood-Mason 1892

Pasiphaea unispinosa Wood-Mason, 1892

Figs 1, 2

Pasiphaea unispinosa wood-Mason, 1892: pl. 3, fig. 7.—wood-Mason & Alcock 1893: 163 (type locality: 7 miles SE by S of Ross Island, Andaman Sea, 265 fathoms).— Alcock 1901: 60.— De Man 1920: 3 (list).— Burukovsky 1976: 22 (key); 1993: 37, figs 2, 8–13; 1996: 843 (table).— Burukovsky & Romensky 1987: 58 (table).— Hayashi 2004: 367. Not Pasiphaea unispinosa: Calman 1939: 186.

Not Pasiphaea unispinosa: Hayashi 1990: 403, figs 192e, j, 193. (= Pasiphaea sirenkoi Burukovsky, 1987)

Material examined. Andaman Sea, RV “Dr. Fridtjof Nansen”, stn 68, 14°06.22’N, 94°31.81’E, 457 m, 4 April 2015, beam trawl, 1 female (cl 37.5 mm), NTOU M02040.

Description. Body strongly compressed laterally; integument rather firm, glabrous.

Rostrum (Fig. 1 A, B) relatively small for genus, arising posterior to frontal margin of carapace, terminating in tiny spine directed forward and falling short of carapace frontal margin; anterior margin slightly sinuous. Carapace (Fig. 1 A, B) 2.1 times longer than deep; rostrum and postrostral region strongly compressed laterally; dorsal margin gently sinuous in lateral view, distinctly carinate in anterior 0.8 (edge of dorsal carina blunt), rounded in posterior 0.2; frontal margin slightly convex; lateral face with obsolete ridge extending from postorbital region to hepatic region; hepatic region with very shallow depression; branchial region with clearly demarcated longitudinal ridge (branchial ridge) extending from hepatic region to near posterolateral margin and short branched ridge extending obliquely from hepatic region; suborbital lobe roundly triangular; antennal lobe obtusely triangular; branchiostegal spine small, submarginal, shortly buttressed, tip overreaching anterolateral margin of carapace; branchiostegal sinus broad, deep.

Pleon (Fig. 1 C) with somite 1 rounded dorsally (Fig. 1 D); terga of pleomeres 2 (Fig. 1 D) and 3 (Fig. 1 E) generally flattened, lateral margins delimited by blunt carinae; tergum of pleomere 4 slightly widened posteriorly, tricarinate with blunt middorsal and lateral carinae; tergum of pleomere 5 also bluntly tricarinate in posterior 0.7 and rounded in anterior 0.3; no posterodorsal median spine on pleomeres 3–5; posterodorsal margin of pleomere 5 deeply concave. Pleuron 1 rounded; pleuron 2 broadly rounded; pleura 3–5 each with roundly angled anteroventral margin; ventral margin of pleuron 5 faintly sinuous. Pleomere 6 1.2 times as long as somite 5, 1.6 times longer than deep; dorsal surface bluntly carinate in anterior 0.6, flattened in posterior 0.4, posterodorsal margin convex, without spine (Fig. 1 F); lateral face with well delimited, curved carina. Telson damaged (Fig. 1 C); dorsal surface of preserved part faintly grooved in midline.

Cornea (Fig. 1 A) darkly pigmented, slightly wider than eyestalk.

Antennular peduncle (Fig. 1 A) moderately stout, reaching distal 0.3 of antennal scale; stylocerite strongly compressed laterally, not reaching distal margin of article 1, terminating in tiny spine dorsodistally.

Antenna (Fig. 1 A, G) with basicerite bearing small ventrolateral distal spine. Antennal scale reaching distal end of thickened aesthetasc-bearing portion of outer antennular flagellum, narrowing distally, 0.4 times as long as carapace, 3.0 times as long as wide; lateral margin evenly convex, terminating in small tooth slightly overreaching narrow, rounded distal lamella.

Mouthparts typical of genus (not dissected). Maxilliped 3 endopod (Fig. 2 A) slightly overreaching distal margin of antennal scale; ultimate article 1.7 times longer than penultimate article (= carpus); antepenultimate article with sinuous dorsal margin; exopod slightly overreaching distal margin of antepenultimate article.

Pereopod 1 (Fig. 2 B) overreaching antennal scale by half-length of chela. Fingers strongly curved distally, crossing, 0.7 times as long as palm, cutting edges finely pectinate. Palm about 3.6 times longer than wide, bearing 1 minute spiniform setae located at about midlength on mesial face adjacent to flexor margin (Fig. 2 C). Carpus with extensor distal margin produced in subacute triangular process, flexor distal margin produced in small spine. Merus unarmed on ventral margin. Ischium unarmed on ventral margin. Basis with sharp ventrodistal spine directed, ventral margin evenly concave. Exopod overreaching midlength of merus.

Pereopod 2 (Fig. 2 D) overreaching first pereopod by length of fingers. Fingers strongly curved distally, crossing, 0.7 times as long as palm, cutting edges finely pectinate. Palm tapering distally, 4.2 times longer than greatest width; mesial face without spiniform setae. Carpus with triangular tooth dorsally on distolateral margin, flexor distal margin produced in sharp, spine-like tooth. Merus with 1 spiniform seta on ventral margin, arising at about distal 0.4. Ischium unarmed on ventral margin. Basis with tiny ventrodistal spine. Exopod not reaching midlength of merus.

Pereopod 3 (Fig. 2 E) damaged in both sides, but preserved part typical of genus. Pereopod 4 (Fig. 2 F) shortest, reaching level of distal margin of basis of pereopod 2; dactylus short, 0.4 times as long as propodus, rounded distally, with row of setae becoming longer distally; propodus with dense row of short setae on flexor margin; exopod reaching distal end of merus. Pereopod 5 (Fig. 2 G) falling far short of midlength of merus of pereopod 2; dactylus suboval in shape, with fringe of long setae on distal half of margins; exopod reaching distal end of carpus.

Branchial formula typical of genus (cf. Hayashi 2004); pleurobranch on thoracomere 8 slightly smaller than arthrobranch on thoracomere 6 (above base of pereopod 3), distinctly lamellate.

Pleopods and uropod (Fig. 1 C) also typical of genus, without distinctive features.

Colour in life. Not known.

Remarks. Pasiphaea unispinosa was originally described on the basis of two female specimens (syntypes) collected from the Andaman Sea (7 miles SE by S of Ross Island). Alcock (1901) briefly described the species with the syntypes and three additional lots from the Andaman Sea, Bay of Bengal and Arabian Sea. Since then, P. unispinosa has been recorded from the Gulf of Aden (Calman 1939), Ryukyu Islands (off Amami-ohshima Island), Japan (Hayashi 1990) and off Sokotra, western part of the Arabian Sea (Burukovsky 1993). Hayashi (2004), who reviewed species of the Pasiphaea cristata Spence Bate, 1888 group, mentioned P. unispinosa, although no specimens referable to the species were available to him. He clarified that the specimen from the Gulf of Aden, identified with P. unispinosa by Calman (1939), did not represent the species, though that identification was not satisfactorily determined. Furthermore, Hayashi (2004, 2007) showed that the specimen from off Amami-ohshima Island, Ryukyu Islands, he had identified with P. unispinosa (cf. Hayashi 1990), was actually P. sirenkoi Burukovsky, 1987.

The present topotypic specimen from the Andaman Sea agrees with the brief descriptions by Wood-Mason (1893) and Alcock (1901) in the carinate dorsal margin of the carapace, the presence of a blunt lateral carina on the carapace, extending from the postorbital region to the hepatic region, the deep pleomere 6, the unarmed merus of pereopod 1 and the merus of pereopod 2 armed with one spiniform seta. Hayashi (2004) demonstrated that the structure of the pleonal tergites provides diagnostic characters for species differentiation in Pasiphaea, and diagnosed P. unispinosa as having “Abdominal somites dorsally rounded”. Our examination of the present specimen, however, has clarified that the structure of the pleonal tergites is more complicated in the species, as described and illustrated herewith.

In the structure of the tergites of pleomeres 4 and 5 and the general armature of the meri of pereopods 1 and 2, P. unispinosa is similar to P. merriami Schmitt, 1931 from the western Atlantic. Nevertheless, P. unispinosa differs from P. merriami in the distinctly carinate dorsal mid-line of the carapace (the postrostral carina extending to the posterior 0.2 of the carapace) and the possession of a deep branchiostegal sinus. In P. merriami, the carapace dorsum is rounded in the posterior 0.7; the branchiostegal sinus is quite shallow, hardly recognizable (Hayashi 2004). Furthermore, the rostrum is less acuminate in P. unispinosa than in P. merriami, with a slightly sinuous anterior margin. Details of the tergal structure of pleomeres 2, 3 and 6 are also different between the two species. In P. unispinosa, the terga of pleomeres 2 and 3 are nearly flat, without trace of a middorsal carina, whereas in P. merriami, there is a blunt middorsal carina on those terga; the dorsal surface of pleomere 6 is bluntly carinate in the anterior 0.6 and flat in the posterior 0.4 in P. unispinosa, while having a middorsal groove extending almost over the entire length of the somite in P. merriami.

We concur Hayashi’s (2004) opinion that the specimen from the Gulf of Aden, identified with P. unispinosa by Calman (1939), is not P. unispinosa.

Distribution. Known only from the Indian Ocean: Andaman Sea, Bay of Bengal, and Arabian Sea; 365–1133 m.