Nephropsis pygmaea, Chang & Chan & Kumar, 2020

Chang, Su-Ching, Chan, Tin-Yam & Kumar, Appukuttannair Biju, 2020, Deep-sea clawed lobster Nephropsis stewarti Wood-Mason, 1872 species complex in the Indo-West Pacific (Crustacea, Decapoda, Nephropidae), with description of a new species, ZooKeys 1008, pp. 37-60 : 37

Nephropsis pygmaea sp. nov. Figures 3 , 5C, D

Nephropsis stewarti .- Holthuis 1991: 45 (in part); Chang and Chan 2019: 50 (in part). [not Wood-Mason 1872].

Nephropsis stewarti ? Nephropsis stewarti .- Macpherson 1990: 312 (in part). [not Wood-Mason 1872]

Material examined.

Holotype: Taiwan • male cl 25.6 mm; Donggang, Pingtung County, commercial trawler, 22°11.880'N, 120°22.213'E, 630 m, 2 Oct. 2014 (NTOU M01898).

Paratypes: Taiwan • 1 male cl 23.4 mm; Donggang fishing port, Pingtung County, commercial trawler, Jul. 1975 (NTOU M02164) • 1 male cl 21.1 mm, 6 females cl 19.5-26.2 mm; 3 May. 1991 (NTOU M02168) • 2 males cl 19.2 and 21.7 mm; 14 May. 1991 (NTOU M02169) • 1 male cl 22.4 mm; 4 Jun. 1995 (NTOU M02173) • 1 male cl 21.8 mm; 27 Dec. 1997 (NTOU M02175).

Other material.

Philippines • 4 males cl 12.5-18.1 mm, 1 female cl 19.1 mm; PANGLAO 2005 stn CP2333, 09°38.2'N, 123°43.5'E, 596-565.5 m, 22 May 2005 (NTOU M02253) • 1 male cl 16.2 mm; stn CP2335, 09°34.3'N, 123°37.8'E, 733-743 m, 22 May 2005 (NTOU M02254) • 1 male cl 14.9 mm, 2 females cl 20.0 and 22.1 mm; stn CP2336, 09°32.4'N, 123°39.3'E, 757-729 m, 22 May 2005 (NTOU M02255) • 1 male cl 12.0 mm, 1 female cl 22.9 mm; stn CP2341, 09°24.5'N, 123°49.7'E, 712-888 m, 23 May 2005 (NTOU M02256) • 1 female cl 11.1 mm; stn CP2351, 09°30.7'N, 124°3.0'E, 810-830 m, 24 May 2005 (NTOU M02257) • 1 male cl 9.0 mm; stn CP2352, 09°27.3'N, 124°3.1'E, 1260-1761 m, 24 May 2005 (NTOU M02258) • 3 males cl 11.8-20.4 mm, 5 females cl 15.7-28.0 mm; stn CP2358, 08°52.1'N, 123°37.1'E, 569-597 m, 26 May 2005 (NTOU M02259) • 1 male cl 16.2 mm; stn CP2358, 08°52.1'N, 123°37.1'E, 569-597 m, 26 May 2005 (NTOU M02260) • 6 males cl 10.4-21.9 mm, 1 ovigerous female cl 22.9 mm, 11 females cl 10.3-25.3 mm; stn CP2389, 09°27.9'N, 123°38.4'E, 784-782 m, 30 May 2005 (NTOU M02261) • 1 male cl 19.6 mm, 2 females cl 19.5 and 19.6 mm; stn CP2390, 09°27.4'N, 123°43.1'E, 627-613 m, 30 May 2005 (NTOU M02262) • 2 males cl 17.6 and 23.8 mm; stn CP2397, 09°34.9'N, 123°41.7'E, 669-712 m, 31 May 2005 (NTOU M02263) • 1 male cl 24.0 mm; stn CP2398, 09°32.6'N, 123°40.5'E, 731-741 m, 31 May 2005 (NTOU M02264) • 2 males cl 16.4 and 19.4 mm; stn CP2405, 09°39.0'N, 123°46.1'E, 387-310 m, 1 Jun. 2005 (NTOU M02265) • 1 female cl 16.6 mm; northern coast of Panglao Island, Jul. 2004-May. 2005 (NTOU M02266).

Diagnosis.

Rostrum bearing one pair of lateral teeth usually situated behind mid-length of rostrum. Carapace with subdorsal carinae granulate and lacking distinct spine; supraorbital and antennal spines strong; post-supraorbital spine absent; postcervical groove U-shaped in dorsal view; intermediate carina indistinct and lateral carina moderately developed. Large cheliped (pereiopod I) with inner surface of palm granular, lacking distinct spine; carpus with strong distoventral, ventro-outer (rarely absent) and dorso-inner distal spines, outer surface without distinct spine, inner surface bearing one or rarely two spines on dorsal margin; merus armed with anteroventral and subdistal dorsal spines, lacking subdistal outer spine or sharp tubercle. Pleon finely granulate, without mid-dorsal carina, pleura each with unarmed anterior margin. Telson without erected dorsal spine near base. Uropodal exopods with complete diaeresis.

Description.

Body covered with long or short pubescence, those on anterior two pereiopods, dorsal carapace, and pleonal tergum quite dense. Carapace finely granulated (Fig. 3A, B ); rostrum 0.5-0.9 × carapace length (proportionally longer in small individuals), bearing 1 pair of lateral teeth usually situated behind mid-length of rostrum, median groove extending anteriorly beyond lateral rostral teeth; subdorsal carinae granulate and lacking distinct spine; strong supraorbital and antennal spines present; post-supraorbital spine absent; cervical, postcervical, and hepatic groove well marked, with postcervical groove U-shaped in dorsal view; intermediate carina indistinct and lateral carina moderately developed; gastric tubercle near supraorbital spines, 0.3-0.4 × distance between gastric tubercle and postcervical groove; distance between orbital margin and postcervical groove 1.5-1.8 × distance between postcervical groove and posterior margin of carapace.

Large cheliped (pereiopod I) generally granulate (Fig. 3C-E ); fingers 0.9-1.5 (mostly 1.0-1.3) × as long as palm; chela 2.6-4.1 (usually 2.8-3.2) × as long as wide and similar in both sexes, inner surface of palm granular but lacking distinct spine; carpus with strong distoventral spine, ventro-outer spine (rarely absent) and dorso-inner distal spine, outer surface without distinct spine, inner surface bearing 1 (mostly) or 2 spines on dorsal margin; merus armed with distoventral spine and subdistal dorsal spine, lacking subdistal outer spine or sharp tubercle. Pereiopod II chelate, smooth, carpus 0.5-0.7 × palm length. Pereiopod III generally similar to pereiopod II but less stout; carpus 0.4-0.6 × as long as palm; merus 1.6-2.2 (mostly 1.7-2.0) × as long as carpus. Pereiopods IV and V smooth, not chelate; dactyli 0.5-0.8 (mostly 0.5-0.7) × as long as propodi.

Entire pleon finely granulate (Fig. 3A, B ), without mid-dorsal carina but bearing indistinct and medially interrupted transverse groove on tergites II-V and sometimes also on tergite I; pleura each with unarmed anterior margin, that of pleuron II strongly convex while those of pleura III-V only slightly convex, all terminating ventrally into sharp spine. Telson without erected dorsal spine near base.

Uropod generally smooth, exopods with distinct complete diaeresis.

Eggs spherical, 1.8-2.0 mm in diameter.

Color in life.

Body generally whitish to pinkish white (Fig. 5C, D ), with pleon sometimes pinkish orange. Eyes whitish. Anterodorsal carapace pinkish orange. Rostrum and antennal flagella pinkish orange to orange red. Antennular flagella and maxilliped III orange red. Large cheliped whitish to pinkish orange, distal parts of fingers always pinkish orange. Pereiopods II-V whitish with distal segments orange red or entirely orange red. Pleopods whitish to orange red. Tail fan whitish, sometimes with median parts rose red. Pubescence grayish brown.

Etymology.

The Latin Nephropsis pygmaea (little) refers to the much smaller size of this species compared with other species in the N. stewarti species complex.

Distribution.

Western Pacific and known with certainty from southern Taiwan and the Philippines, at depths of 310-888 m, and perhaps as shallow as 170 m (see “Remarks”).

Remarks.

This smaller form restricted to the northwestern Pacific has a maximum carapace length of 28.0 mm (NTOU M02259), with females bearing eggs attaining only 22.9 mm in the carapace length (NTOU M02261). The largest specimens of N. stewarti and N. grandis is 54 mm ( Dineshbabu 2008) and 64.1 mm (present material) in the carapace length, respectively. The smallest ovigerous females recorded for N. stewarti and N. grandis are of carapace lengths approximately 24 mm (total length 80 mm, Dineshbabu 2008) and 38 mm (body length 105 mm, Chan and Yu 1988), respectively. Other than the difference in body size, N. pygmaea sp. nov. is unique in the N. stewarti species complex in that it lacks the subdistal outer spine or sharp tubercle on the merus of the large cheliped (Fig. 3C, D ), which are present in N. stewarti and N. grandis (Figs 1C, D , 2C, D ).

In spite of the restricted distribution to the northwestern Pacific, N. pygmaea sp. nov. is genetically closer to N. stewarti than N. grandis . The lowest 16S sequence divergence between N. pygmaea sp. nov. and N. stewarti is 3.8%, whereas the sequence divergence is almost double (7.5%) between N. pygmaea sp. nov. and N. grandis . Morphologically, N. pygmaea sp. nov. is also generally more similar to N. stewarti in the surface of the pleonal tergites distinctly granular (Figs 1A, B , 3A, B ), and the large cheliped is relatively less spiny (with inner surface of palm and outer surface of carpus lacking distinct spine; Figs 1C, E , 3C, E ). As such a male specimen from the Philippines (NTOU M02260) has the granules arranged somewhat like a median carina on the pleon, as in some Indian N. stewarti specimens. Nevertheless, N. pygmaea sp. nov. can also be separated from N. stewarti by the intermediate carina on the carapace indistinct (Fig. 3A, B ; vs. well-marked, Fig. 1A, B ), rostral teeth usually located posterior to the mid-length of the rostrum (Fig. 3A, B ; vs. usually at mid-length of the rostrum, Fig. 1A, B ), and the inner surface of the carpus of the large cheliped usually armed with one or occasionally two spines along the dorsal margin (Fig. 3C ; vs. usually two to four spines, rarely one spine, Fig. 1C ). Of the 62 specimens examined for N. pygmaea sp. nov., only 10 (16.1%) have two spines instead of one on the dorsal margin of the inner surface of the carpus of the large cheliped.

The present materials from southern Taiwan and the Philippines are generally very similar. Only one specimen (NTOU M02168) has three teeth instead of one on the right side of the rostrum. As both N. grandis and N. pygmaea sp. nov. occur in the Philippines, it is necessary to re-examine the Philippines " N. stewarti " material reported by Macpherson (1990) to determine their exact identities. Although most of the Philippines specimens described by Macpherson (1990) are rather small, a few of them (eg. carapace length, including rostrum, 70 mm, equivalent to a carapace length of approximately 47 mm) are larger than the present largest specimen (cl 28 mm) of N. pygmaea sp. nov. Moreover, a Philippines specimen identified by Macpherson (1990) was obtained from a depth of 170-200 m, exceptionally shallow for species of Nephropsis . Reexamination of this specimen may eventually reveal that the present species or N. grandis extends to such shallow depth.

Figures

Figure 1. Nephropsis stewarti Wood-Mason, 1872, Andaman Sea, RV ' Dr. Fridtjof Nansen' stn 135, neotype male cl 46.2 mm (NTOU M 02249) A carapace and pleon, dorsal B same, lateral C left pereiopod I, chela to distal part of merus, dorsal D same, lateral E same, ventral. Pubescence and setae omitted ● Position of spines on inner surface of palm ◇ position of spines on dorsal margin of outer surface of carpus ♦ position of spines on dorsal margin of inner surface of carpus ⏹ dorso-inner distal spine of carpus △ ventro-outer distal spine of carpus ◻ distoventral spine ✰ subdistal dorsal spine of merus ★ position of subdistal outer spine of merus.

Figure 2. Nephropsis grandis Zarenkov, 2006, Tanimbar Islands, Arafura Sea, KARUBAR stn CP 59, neotype male cl 64.1 mm (MNHN IU- 2017 - 9001) A carapace and pleon, dorsal B same, lateral C left pereiopod I, chela to distal part of merus, dorsal D same, lateral E same, ventral. Pubescence and setae omitted ● Position of spines on inner surface of palm ◇ position of spines on dorsal margin of outer surface ♦ position of spines on dorsal margin of inner surface ⏹ dorso-inner distal spine of carpus △ ventro-outer distal spine of carpus ◻ distoventral spine ✰ subdistal dorsal spine of merus ★ position of subdistal outer spine of merus.

Figure 3. Nephropsis pygmaea sp. nov., Donggang, Pingtung County, Taiwan, holotype male cl 25.6 mm (NTOU M 01898) A carapace and pleon, dorsal B same, lateral C left pereiopod I, chela to distal part of merus, dorsal D same, lateral E same, ventral, pubescence and setae omitted ● position of spines on inner surface of palm ◇ position of spines on dorsal margin of outer surface ♦ position of spines on dorsal margin of inner surface ⏹ dorso-inner distal spine of carpus △ ventro-outer distal spine of carpus ◻ distoventral spine ✰ subdistal dorsal spine of merus, ★ position of subdistal outer spine of merus.

Figure 5. A, B N. grandis Zarenkov, 2006, Dasi fishing port, Taiwan, male cl 45.3 mm (NTOU M 02171) C, D N. pygmaea sp. nov., Donggang fishing port, Taiwan, paratype female cl 24.4 mm (NTOU M 02168) A, C dorsal habitus B, D lateral habitus.