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

Abstract Nephropsis stewarti Wood-Mason, 1872 is the most common species of the deep-sea clawed lobster genus Nephropsis Wood-Mason, 1872 in the Indo-West Pacific. Morphological comparisons and genetic analyses of extensive material referred to this lobster revealed the presence of three species. The three species differ mainly in body size, development of the intermediate carina on the carapace, position of the lateral pair of rostral teeth, whether the pleonal tergum is granulate, and the spination on the large chelipeds. Nephropsis stewarti is restricted to the western central Indian Ocean, and a neotype is selected to fix its identity. The name Nephropsis grandis Zarenkov, 2006 is revived with neotype selection for the large form found in the West Pacific and northwestern Australia. The smaller form from southern Taiwan and the Philippines is described as Nephropsis pygmaeasp. nov.


Introduction
Among the 16 species in the deep-sea clawed lobster genus Nephropsis Wood-Mason, 1872 (Nephropidae) (Chan 2010(Chan , 2019Chang and Chan 2020), the type species N. stewarti Wood-Mason, 1872 is probably the most well-known in the Indo-West Pacific because of its frequent records showing a wide geographical distribution, large size, and presence at shallower depths compared with other congeners (see for example Miyake 1982;Holthuis 1984Holthuis , 1991Baba 1986;Yu 1988, 1993;Macpherson 1990Macpherson , 1993Wadley and Evans 1991;Chan 1997Chan , 1998Jones and Morgan 2002;Zarenkov 2006;Dineshbabu 2008;Radhakrishnan et al. 2019;Chang and Chan 2019). Nephropsis stewarti is a unique species within the genus as it has only one pair of rostral teeth, no distinct spines on the subdorsal carina, a pleon lacking dorsal carina, a telson without erected dorsal spine, and uropodal exopods bearing well-developed diaeresis. Slight differences can be observed among the materials of N. stewarti from various localities (see Macpherson 1993), and Zarenkov (2006) considered a large specimen from the Arafura Sea, north of Australia, as a different species, described as N. grandis Zarenkov, 2006. Zarenkov's (2006 specimen (carapace length, including rostrum, 58 mm) is smaller than N. stewarti in many other localities (e.g., Macpherson 1990Macpherson , 1993Chan 1997;Zarenkov 2006), and the main diagnostic characteristic of N. grandis is the spination of the large chelipeds (see Chang and Chan 2019), which is missing in the holotype of N. stewarti (Wood-Mason 1873, 1874; therefore, Chan (2010Chan ( , 2019 tentatively treated N. grandis as a junior subjective synonym of N. stewarti. Many reports have illustrated the coloration of specimens identified with Nephropsis stewarti (e.g., Miyake 1982;Baba 1986;Yu 1988, 1993;Wadley and Evans 1991;Jones and Morgan 2002;Chang and Chan 2019). The body of N. stewarti was believed to primarily have a whitish color. However, during a recent survey on the decapod crustacean fauna in India carried out by the second author, about 10 N. stewarti specimens were observed in a local fishing port, and all were reddish in color. As N. stewarti was originally described in the Andaman Sea near India, it was suggested that the currently recognized N. stewarti might contain more than one species. This work compared extensive material of N. stewarti from various Indo-West Pacific localities, aided by molecular barcoding genetic analysis (Bucklin et al. 2011), and revealed the presence of three species. Nephropsis stewarti is restricted to the western central Indian Ocean; a neotype is selected to fix its identity. The name Nephropsis grandis can be applied to much of the material from the western Pacific to northwestern Australia; its identity was also fixed by the erection of a neotype. The third, undescribed species, which is smaller in the size compared with the two closely allied species, is present in southern Taiwan and the Philippines; it requires a new name.

Samples
The present study was based mainly on the extensive collection of the N. stewarti species complex deposited at National Taiwan Ocean University, Keelung, Taiwan (NTOU), supplemented with material from the Muséum national d'Histoire naturelle, Paris, France (MNHN); the Department of Aquatic Biology and Fisheries, University of Kerala, India (DABFUK); Natural History Museum and Institute, Chiba, Japan (CBM); and Senckenberg Museum, Frankfurt am Main, Germany (SMF). These materials included topotypic specimens of N. stewarti and N. grandis. Carapace length (cl) was measured dorsally from the orbital margin to the posterior margin of the carapace. The abbreviation (CP) preceding the station number indicates the type of the collecting gear (French beam trawl). Morphological terminology generally follows Macpherson (1990) and Holthuis (1991). Nephropsis stewarti s.l. is well known in the Indo-West Pacific, having many taxonomic accounts or reports, often with only brief descriptions and without mentioning any of the diagnostic characteristics of the three species identified in this study. Therefore, the synonymy provided is restricted to important taxonomic works related to this species complex.

Taxonomy
Description. Body covered with long or short pubescence, rather thick on anterior two pereiopods, dorsal carapace, and pleonal tergum.
Carapace finely granulated (Fig. 1A, B); rostrum 0.4-0.5× as long as carapace, with 1 pair of teeth usually situated near mid-length of rostrum; subdorsal carinae granulate, without distinct spine or tooth-like process; supraorbital and antennal spines well developed, post-supraorbital spine absent; cervical, postcervical, and hepatic grooves present, with post-cervical groove U-shaped in dorsal view; intermediate and lateral carinae both well marked; gastric tubercle located near supraorbital spine, their distance being approximately 0.4× distance between gastric tubercle and post-cervical groove; distance between orbital margin and post-cervical groove 1.2-1.5× longer than the distance between post-cervical groove and posterior margin of carapace.
Entire pleon finely granulate (Fig. 1A, B) without median carina; pleura lacking spine on anterior margins, each terminating ventrally into blunt to sharp spine. Telson without erected dorsal median spine near base. Uropodal exopods with complete diaeresis.
Eggs spherical and 2.2-2.7 mm in diameter. Distribution. Known with certainty in the western to northeastern Indian Ocean from the eastern coast of South Africa to the Andaman Sea. Found at depths of 250-1520 m and perhaps even 1720 m, but mostly less than 1000 m (see Alcock 1901;Macpherson 1990;Zarenkov 2006 fig. 3.22). Eyes and antennal peduncle always whitish. Distal parts of pereiopods II-V, pleopods always reddish. Large cheliped and pleonal tergum, whitish to orange. Pleonal pleura and uropods purple to reddish. Antennal and antennular flagella orange to reddish. Pubescence grayish to reddish. Eggs orange.
Remarks. Although the present Indian specimens have a very reddish color, a comparison with Andaman Sea topotypic specimens and material from Mozambique Channel revealed wide color variations in N. stewarti, from whitish to reddish (Fig. 4). Specimens with different colors in the western and northern Indian Ocean are genetically very similar, with 1.0% or less sequence divergence in 16S (Table 2). However, large genetic divergences (16S sequence divergence 3.8-7.3%) exist between the material from the western and northern Indian Ocean, and that from the western Pacific (including the South China Sea and Arafura Sea) and northwestern Australia (Table  2). Such genetic differences are greater than those between N. rosea Bate, 1888 and N. aculeata Smith, 1881 (3.1-3.7%) and between N. serrata Macpherson, 1993 and N. stewarti s.l. (lowest 2.8%).
Nephropsis grandis, previously considered to be a synonym of N. stewarti, has a type locality in the Arafura Sea (Zarenkov 2006). Of the three characteristics proposed by Zarenkov (2006: table 1) to separate N. grandis from N. stewarti, the shape of the distal part of the rostrum has been shown to be variable. The subdistal outer spine on the merus of the large cheliped is present in all of the western and northern Indian Ocean specimens (   western central Indian Ocean material (with only one exception; a cl 42.3 mm ovigerous female of DABFUK/AR-ACH-10) but mostly in a position distinctly posterior to the middle of the rostrum in the specimens from the western Pacific and northwestern Australia (except in three specimens; one in N. grandis: NTOU M02177, and two in N. pygmaea sp. nov.: NTOU M02168, NTOU M02262).
Nephropsis stewarti was originally described from a single female specimen lacking large chelipeds, and collected from Ross Island of the Andaman Islands (Wood-Mason 1873, 1874). Soon after its discovery, many more specimens of this species were collected in India (see Alcock 1901); however, the holotype (supposed to have registration number 1404) is no longer extant, although having been held by the Zoological Survey of India, Calcutta (S Mitra, Zoological Survey of India, Calcutta, personal communication). As the N. stewarti species complex has now been found to contain at least three species, in order to fix the identity of N. stewarti, a recently collected Andaman Sea specimen (NTOU M02249) with color ( Fig. 4E) and genetic information (Table 1) and that is very close to the type locality, is herein selected as the neotype of this species. The neotype fits well with the description of the holotype (Wood-Mason 1873, 1874), particularly in terms of the eye being rudimentary, bearing one pair of lateral rostral teeth, exopod of uropod with distinct diaeresis, and generally being similar to the figures provided for the holotype (Fig. 1A, B; Wood-Mason 1874: pl. 4-1-3).
Because material from northwestern Australia in the eastern Indian Ocean is now considered to belong to N. grandis instead of N. stewarti, re-examination of the specimens from northeastern Sumatra in the eastern Indian Ocean, reported by Balss (1925), will be necessary to determine if they represent N. stewarti, despite being collected near the type locality of the latter species. Re-examination of the "N. stewarti" material, reported by Chang and Chan (2019), revealed that all but one female (NTOU M02162) from the South China Sea belong to either N. grandis or the new species described below. This particular female specimen has the subdorsal carina on the carapace bearing small spines; therefore, it actually represents N. serrata (also see Tables 1, 2).
Although a red or white body color is thought to be specific for Nephropsis (see Chang and Chan 2019), this is not the case for N. stewarti. The Indian material appears to be much redder (Fig. 4A fig. 3.22) and has more distinct granules on the pleon, sometimes even arranged like a median carina. Thomas (1979), however, mentioned that his N. stewarti material from the Gulf of Mannar had a greenish-yellow color and deep red appendages. Color photographs are available for two of the Andaman Sea specimens examined (NTOU M02249, M02250). One (Fig. 4F) has a rather white body like the Mozambique specimen (MNHN IU-2018-5063, Fig. 4C, D), except for the pereiopods II to V, which are entirely pale purple. The neotype (Fig. 4E) has a body that is generally pale orange (which is intermediate between red and white). Color information on more specimens from different areas of the central western Indian Ocean will be necessary to understand whether material from the same locality also exhibits large variations in body color for this species. Diagnosis. Rostrum armed with a single pair of lateral teeth usually situated posterior to mid-length of rostrum. Carapace with subdorsal carinae granulate, lacking distinct spine; supraorbital and antennal spines present; post-supraorbital spine ab- Large cheliped (pereiopod I) with inner surface of palm usually armed with row of distinct spines; carpus with strong distoventral, ventro-outer distal, and dorso-inner distal spines, inner surface usually with 2-4 spines along dorsal margin and several small spines on ventral margin, both dorsal and ventral margins of outer surface spinose; merus with subdistal dorsal and anteroventral spine, generally also bearing a spine or sharp tubercle on subdistal outer surface. Pleon generally smooth and lacking middorsal carina; pleura each with unarmed anterior margin. Telson without erected middorsal spine near base. Uropodal exopods with complete diaeresis.
Description. Body covered with long or short pubescence, rather thick on dorsal carapace, pleonal tergites and anterior two pereiopods. Carapace finely granulated ( Fig. 2A, B); rostrum 0.4-0.8× as long as carapace (proportionally longer in small individuals), bearing 1 pair of lateral teeth usually situated posterior to mid-length of rostrum; subdorsal carinae granulate, lacking distinct spine; strong supraorbital and antennal spines present; post-supraorbital spine absent; cervical, postcervical, and hepatic groove well-marked, with post-cervical groove U-shaped in dorsal view; intermediate carina weak, indistinct; lateral carina distinct; distance between gastric tubercle and supraorbital spines 0.3-0.4× distance between gastric tubercle and postcervical groove; distance between orbital margin and postcervical groove 1.3-1.5 (rarely 1.6)× distance between post-cervical groove and posterior margin of carapace.
Large cheliped (pereiopod I), generally with smooth surface (Fig. 2C-E); chela 2.7-4.7 (mostly 2.9-3.8)× as long as wide; inner surface of palm generally armed with row of distinct spines except for very small individuals; carpus with strong distoventral spine, ventro-outer distal spine, and dorso-inner distal spine, inner surface having 2-4 spines (sometimes only one in very small individuals) along dorsal margin and several small spines on ventral margin, both dorsal and ventral margins of outer surface spinose (with fewer spines in small young specimens); merus with subdistal dorsal spine and distoventral spine, usually also bearing subdistal outer spine or sharp tubercle. Pereiopod II with carpus 0.5-0.7 (rarely 1)× palm length. Pereiopod III with carpus 0.4-0.5× as long as palm; merus 1.8-2.1× longer than carpus. Pereiopods IV and V with dactyli 0.3-0.6× as long as propodi.
Pleon generally smooth ( Fig. 2A, B), lacking median carina, only tergites I and VI granulate; pleura each with unarmed anterior margin and each terminating ventrally into a blunt or sharp spine. Telson without erected dorsal median spine near base. Uropodal exopods with complete diaeresis.
Eggs spherical and approximately 3 mm in diameter (Chan and Yu 1988). Distribution. Western Pacific and northwestern Australia, known with certainty from Japan, Taiwan, South China Sea, the Philippines, Indonesia (Kai and Tanimbar Islands), Arafura Sea, and northern Australia (Queensland to NW Shelf ); at depths of 312-647 m (Macpherson 1993; present study) and perhaps 170-821 m (see Remarks).
Remarks. Although the western Pacific and northwestern Australia material has been shown to be not the true N. stewarti, molecular genetic analysis suggests that there are two distinct species (16S sequence divergence as high as 7.5-9.4%, even higher than 3.1-6.3% among N. serrata, N. aculeata, and N. rosea; Table 2). Careful comparisons revealed that these two genetic forms differ, detailed as follows. (1) The body size is large in one form (up to cl 64.1 mm, MNHN IU-2017-9001) but much smaller in the other (up to cl 28.0 mm NTOU M02259). (2) Although the pleon is concealed by thick pubescence, the surfaces of tergites II to V is rather smooth in the large size form ( Fig. 2A, B) but distinctly granular in the smaller form (Fig. 3A, B). (3) The large cheliped is also concealed by long pubescence but is more spiny in the large form. In the large form, the carpus is heavily spinose on the outer surface and has 2-4 spines along the dorsal margin of the inner surface (Fig. 2C-E). The inner surface of the palm is also spiny (Fig. 2C, E), except in small young specimens (cl < 20 mm), and the merus generally has a subdistal outer spine or sharp tubercle (Fig. 2C, D) except in one female (MNHN IU-2018-5062). For the large cheliped of the smaller form, the carpus has an outer surface without distinct spines and the inner surface bears only one (mostly) or two spines on the dorsal margin ( Fig. 3C-E). The inner surface of the palm lacks distinct spines (Fig. 3C, E), and there is no subdistal outer spine or sharp tubercle on the merus (Fig. 3C, D).
Nephropsis grandis was described from a single male collected near the Tanimbar Islands in the Arafura Sea (09°07.5'S, 131°14.9'E, Zarenkov 2006). The holotype is a large specimen (carapace length, including rostrum, 58 mm) and its pleonal tergites I-VI are without granules on the surfaces. The large cheliped in the holotype appears to be rather spinous; however, it is difficult to comprehend the exact spination on the various parts from the original description and illustrations. For example, the holotype appears to lack a subdistal outer spine at the merus of the large cheliped (Zarenkov 2006: table 1: subdistal spine on outer surface of merus of cheliped). Nonetheless, the larger form discussed above generally fits the characteristics described for N. grandis, and at present, only the larger form is found in the Arafura Sea. Currently, the holotype of N. grandis (ZMMU Ma 5157) cannot be located in the Zoological Museum of Moscow University (V Spiridonov, personal communication). As there are now three species in the N. stewarti species complex and each has only subtle differences, it is desirable to fix the identity of N. grandis. The current largest specimen (MNHN IU-2017-9001) from the Tanimbar Islands, and with genetic data available, was selected as the neotype of N. grandis, thus affixing this name on the larger form in the West Pacific and northwestern Australia. The neotype was collected from a locality very close to that of the holotype (both in the Arafura Sea) and is generally similar to the original figures provided for the holotype ( Fig. 2A-C ;Zarenkov 2006: figs 5, 6).
Nephropsis grandis is genetically distinct from N. stewarti, with 6.4-7.3% 16S sequence divergence (Table 2). Other than the differences described under the "Remarks" of N. stewarti, these two species also differ in the pleonal tergites II-V, being smooth in N. grandis ( Fig. 2A, B) but granular in N. stewarti (Fig. 1A, B). In Nephropsis grandis the outer surface of the large cheliped carpus is spinose (Fig. 2C-E) but this is only granular and without distinct spines in N. stewarti (Fig. 1C-E). In large specimens, the inner surface of palm of the large cheliped is also spinose in N. grandis (Fig. 2C, E) but still lacks spines in N. stewarti (Fig. 1C, E). Macpherson (1993) suggested that the shape of the large chela might be different among the species in the N. stewarti species complex. However, this is not supported by the present work, even though the large chelae have sexual dimorphism only in N. stewarti.
Nephropsis grandis is widely distributed from Japan to Australia. Photographs of the Japanese specimen identified as "N. stewarti" from Suruga Bay (CBM-ZC 14212) and with a very short 16S sequence for eDNA metabarcoding (LC430805, 163 bp; Komai et al. 2019) is now confirmed to represent N. grandis. The short 16S sequence of this specimen is also identical to the sequence of the present Taiwanese specimens (NTOU M02174, NTOU M00505) assigned to N. grandis. The Japanese specimens (SMF 18328), referred to "N. stewarti" by Zarenkov (2006), are rather small (two males and one female, cl, including rostrum, 32-41mm) but still have a distinct spine on the outer surface of the carpus of the pereiopod I (Zarenkov 2006: fig. 19A); therefore, they likely represent N. grandis instead. The SMF 18328 lot, however, consists of two moderately large specimens (cl 36.0 mm and 46.0 mm). One more lot of "N. stewarti" from Japan is held in the Senckenberg Museum (SMF 24678), and there are three specimens within the lot. Although the number and sex of the specimens in the SMF 24678 lot match those reported for SMF 18328 in Zarenkov (2006), their sizes (cl 27.5-41.0 mm) do not match. Nevertheless, photographs of all five of these Japanese specimens in the Senckenberg Museum clearly show that they are all N. grandis because of the weak intermediate carina, large cheliped with distinct spines on the outer surface of the carpus, and the merus having subdistal outer spine. For the published photographs of Japanese "N. stewarti", the one of Baba (1986: fig. 103) clearly shows the large cheliped with the inner surface of the palm and the outer surface of the carpus bearing distinct spines. The other photograph of Miyake (1982: pl. 26-1) also shows the large cheliped with the outer surface of the carpus armed with distinct spines, although the spination on the inner surface of the palm is unclear because of the covering of thick pubescence. Thus, it appears that only N. grandis is distributed in Japan among the N. stewarti species complex. Among the two sequenced Taiwanese specimens of this species, specimen NTOU M00505 was used in a clawed lobster phylogenetic study (Tshudy et al. 2009) as "N. stewarti" with GenBank no. EU882882, which has a sequence identical to U96086 from a specimen of N. stewarti in Natal, South Africa (Tam and Kornfield 1988). However, re-amplification of the 16S gene of the NTOU M00505 specimen (GenBank no. M302004) revealed that its sequence does not match EU882882 and belongs to the clade of N. grandis instead.
The present work revealed that among the N. stewarti species complex, both N. grandis and N. pygmaea sp. nov. are distributed in southern Taiwan and the Philippines, and the true N. stewarti is restricted to the Indian Ocean. Re-examination of the Philippines material (with a depth range of 170-821 m) reported as "N. stewarti" in Macpherson (1990) is necessary to determine which of these two species they belong to, and whether N. grandis can be found in waters as shallow as 170 m and/or as deep as 821 m. Diagnosis. Rostrum bearing one pair of lateral teeth usually situated behind midlength 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 bear- ing 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 granu-  (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.
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 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 mate- rial) 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.
southern India and hence lead the present study. TYC is also grateful to the University of Kerala for hosting him during his studies in India. Part of the extensive material studied in this work was gathered through many expeditions and they are all gratefully acknowledged. The PANGLAO 2005 deep-sea expedition onboard the research