Deep-sea squat lobsters of the Munidopsis serricornis complex in the Indo-West Pacific with descriptions of six new species (Crustacea: Decapoda: Munidopsidae)

The deep-sea squat lobster, Munidopsis serricornis (Lovén, 1852), originally described from the north-eastern Atlantic, has long been considered near cosmopolitan with numerous reports also from the western Pacific and northern Indian Ocean. These Indo-West Pacific records are reviewed along with new material from seamounts throughout the region. Munidopsis serricornis sensu stricto is restricted to the Atlantic Ocean. Six new species are described from the Indo-West Pacific: M. alcocki sp. nov. from the central to western Indian Ocean; M. atlantis sp. nov., from the Southwest Indian Ridge; M. macphersoni sp. nov. from the Austral Islands, French Polynesia; M. spiridonovi sp. nov. from the western Indian Ocean; M. nias sp. nov. from southern Indonesia and the Nicobar Islands; and M. pyrochela sp. nov. from New Zealand, Australia and the Southwest Indian Ridge.

Description. Carapace: Moderately convex from side to side; sparsely covered with short, fine setae; surface of anterior half smooth, with few scattered, fine short striae; surface of posterior half with fine distinct striae. Cervical groove indistinct. Epigastric spines absent. Posterior orbital margins transverse to slightly oblique, outer orbital spine prominent. Frontal margins oblique; anterolateral spine similar to outer orbital spine. Lateral margins broadly convex; with 2 spines on anterior branchial margin and spine at junction of anterior and posterior branchial margins. Rostrum broad, 0.3-0.4 pcl; trifid distally; apex slightly deflected dorsally; median carina distinct; lateral proximal margin convex. Posterior margin unarmed. Pterygostomian flap with short diagonal striae; anterior margin blunt, angular.
Antenna: Basal article with triangular mesial and lateral tooth, neither overreaching article 2. Article 2 with strong distolateral spine, reaching beyond midlength but not apex of article 3. Article 3 with short distomesial spine. Article 4 with lateral triangular projection. Flagellum as long as cl.
Munidopsis alcocki is most similar to M. serricornis from the Western Atlantic and M. modesta Benedict, 1902 from the eastern Pacific in lacking epigastric spines but is readily distinguished by its minutely rather than strongly spinose extensor margins on the meri of the walking legs. Diagnosis. Rostrum broad, flat, medially carinate, trifid distally. Carapace with pair of epigastric spines, otherwise unarmed dorsally; surface of dorsal half with granules and short rugae; lateral margins with 4 spines (1 anterolateral, 3 branchial); posterior orbital margin transverse; outer orbital spine distinct. Abdominal tergites unarmed. Telson with 8 plates. Maxilliped 3 merus flexor margin with 2 spines. Cheliped carpus length twice width, dorsal surface unarmed. Walking leg meri irregular to serrated along extensor margin; dactylus flexor margin with movable spines, and more slender movable spine at base of corneous unguis. Pereopods without epipods.

Distribution
Description. Carapace: Moderately convex from side to side; surface with few scattered short setae, almost glabrous; surface of anterior half with granules and small rugae or short striae; surface of posterior half with short striae. Cervical groove indistinct. Pair of epigastric spines flanked by short scales. Posterior orbital margins transverse, outer orbital spine prominent. Frontal margins oblique, concave; anterolateral spine similar to outer orbital spine. Lateral margins subparallel; with 2 spines on anterior branchial margin and blunt spine at junction of anterior and posterior branchial margins. Rostrum broad, 0.4 pcl; trifid distally; apex horizontal; median carina distinct; lateral proximal margin weakly convex, tapering. Posterior margin unarmed, shallowly concave medially. Pterygostomian flap with short diagonal striae posteriorly and short rugae anteriorly; anterior margin blunt, angular.
Pereopods 2-4: Slightly compressed; decreasing in length posteriorly; with scattered, setose striae. Merus elongate; length 3.4 times width (pereopod 2) to 2.8 (pereopod 4); extensor margin irregular to serrated but not spinose; distal extensor margin with large distal spine; flexor margin irregular but not spinose except for triangular distal spine. Carpus with distal extensor spine and irregular to serrated margin; low, irregular, dorsal carina. Propodus extensor margin irregular, unarmed; flexor margin with movable spine at distal one-third and paired movable spines distally adjacent to dactylar articulation. Dactylus about two-thirds propodus length; extensor margin with scattered setae, unarmed; flexor margin with 9 or 10 low triangular teeth, each bearing corneous movable spine and more slender movable spine at base of corneous unguis. Epipods absent.

Colour in life. Unknown.
Etymology. From the type locality, Atlantis Bank; used as a noun in apposition.

Remarks.
Munidopsis atlantis sp. nov. is most similar to M. comarge and M. ternaria in the combination of a granulated and rugose anterior half of the carapace and serrated but not spinose extensor meral margins of the walking legs. It resembles M. ternaria (and differs from M. comarge) in having epigastric spines and differs from both species in having lateral carapace spines behind the anterolateral spine. Munidopsis atlantis and M. macphersoni differ in the number of lateral spines on the carapace behind the anterolateral spine, three in the latter, four in the former. Munidopsis atlantis is also superficially similar to M. crinita Faxon, 1893, from the eastern Pacific in sharing the presence of epigastric spines and unarmed extensor margins of the meri of the walking legs, but is readily distinguished by the glabrous or sparsely setose, rather than, densely setose body and chelipeds. Macpherson et al. (2014)  Diagnosis. Rostrum broad, flat, medially carinate, trifid distally. Carapace with pair of epigastric spines, otherwise unarmed dorsally; surface of dorsal half with granules and short rugae; lateral margins with 5 spines (1 anterolateral, 4 branchial); posterior orbital margin transverse; outer orbital spine distinct. Abdominal tergites unarmed. Telson with 8 plates. Maxilliped 3 merus flexor margin with 2 or more spines. Cheliped carpus length less than twice width, dorsal surface unarmed. Walking leg meri spinose along extensor margin; dactylus flexor margin with movable spines and more slender movable spine at base of corneous unguis. Pereopods without epipods.

Description.
Carapace: Moderately convex from side to side; surface with few scattered short setae, almost glabrous; surface of anterior half with granules and small rugae or short striae; surface of posterior half with short striae. Cervical groove indistinct. Pair of epigastric spines. Posterior orbital margins transverse, outer orbital spine prominent. Frontal margins oblique, slightly concave; anterolateral spine similar to outer orbital spine. Lateral margins broadly convex; with 3 blunt spines on anterior branchial margin and spine at junction of anterior and posterior branchial margins. Rostrum broad, slightly less than 0.5 pcl; trifid distally; apex slightly deflected dorsally; median carina distinct; lateral proximal margin convex. Posterior margin unarmed. Pterygostomian flap with short diagonal striae; anterior margin blunt, angular.
Antenna: Basal article with triangular mesial and lateral tooth, neither overreaching article 2. Article 2 with strong distolateral spine, reaching midlength of article 3. Articles 3 and 4 unarmed. Flagellum slightly longer than pcl.
Pereopod 1 (cheliped): Cheliped elongate, 2.7 pcl, simple golden setae, most numerous on dorsal and ventral margins; subcylindrical to ovate. Ischium with dorsal spine; without ventral spine. Merus with row of 5 or 6 small, graded dorsal spines along proximal half and large distal dorsal spine; mesial margin with 2 large spines, one distally at carpal articulation, one at distal one-third of margin; ventromesial margin with small proximal spine and strong distal spine. Carpus about 1.8 times longer than wide; mesial margin with distal and subdistal spine, latter largest; small dorsodistal and ventrodistal spine. Propodus unarmed, palm about 2.5 times as long as wide; mesial margin of palm longer than dactylus. Pollex and dactylus occlusal margins crenulated, apices with interlocking teeth. Epipod absent.
Pereopod 2-3 (pereopod 4 unknown): Slightly compressed; decreasing in length posteriorly; with scattered, setose striae. Merus elongate; length about 3.4 times width (pereopod 2); extensor margin with short upright spines; distal extensor margin with large distal spine; flexor margin irregular but not spinose except for strong distal spine. Carpus with distal extensor spine and serrated margin; with low, irregular, dorsal carina. Propodus extensor margin straight, unarmed; flexor margin with movable spine at distal one-third and paired movable spines distally adjacent to dactylar articulation. Dactylus about two-thirds propodus length; extensor margin with scattered setae, unarmed; flexor margin with 8 low triangular teeth, each bearing corneous movable spine and more slender movable spine at base of corneous unguis. Epipods absent.

Remarks
Eye: Ocular peduncle sparsely setose; movable; partially concealed by rostrum. Cornea subglobular, slightly wider than peduncle. Slender spine adjacent to lateral margin of eye.
Antennule: Basal article squat, with 2 distolateral spines, dorsal shorter; distomesial margin with short triangular tooth. Antenna: Basal article with triangular mesial and lateral tooth, neither overreaching article 2. Article 2 with strong distolateral and distomesial spine, former reaching beyond midlength of article 3. Article 3 with mesial spine. Article 4 with triangular lateral projection. Flagellum about as long as pcl.
Pereopod 1 (cheliped): Elongate, 2.3 pcl in both sexes, simple golden setae, most numerous on dorsal and ventral margins; subcylindrical to ovate. Ischium with ventrodistal spine and dorsal spine. Merus with longitudinal row of 4-6 graded dorsal spines and large distal dorsal spine; mesial margin with 1 or 2 large spines, one distally at carpal articulation, one at distal one-fourth of margin (absent in female paratypes); ventromesial margin with proximal row of 3 proximal spines (first spine smallest) and strong distal spine. Carpus 1.2-1.5 times longer than wide; mesial margin with distal and subdistal spine, latter largest; dorsodistal and ventrodistal spine; occasionally with small lateral distal spine. Propodus unarmed, palm about twice as long as wide; mesial margin of palm longer than dactylus. Pollex and dactylus occlusal margins crenulated, apices with interlocking teeth. Epipod absent.

Colour in life. Unknown.
Etymology. Named after the type locality, Nias, Indonesia; used as a noun in apposition.

Remarks. Records of Munidopsis tridentata from off
Sumatra, Indonesia (Doflein & Balss, 1913) collected by the Valdivia, are referrable to M. nias sp. nov. Munidopsis nias sp. nov. is most similar to M. acuminata Benedict, 1902 (type locality: western Atlantic, off South Carolina) and M. pubescens Macpherson, 2007 (type locality: Madagascar) in sharing the broad, subquadrate, distally tridentate rostrum; unarmed dorsal surface of the carapace and abdomen; seven telson plates; short, squat, pereopods 2-4 with the length of the pereopod 2 merus not more than 2.5 times the width (versus about 3-4 times width) and two distal spines on the carpus. The new species differs from M. acuminata in lacking the epipod on the cheliped, having a straight or convex rather than slightly concave dorsal margin on the cheliped dactylus ( Fig 4A, 5A, B) and the smooth versus rugose surface on the anterior half of the carapace. Munidopsis nias differs from M. pubescens in the smooth versus rugose anterior carapace surface, having a row of prominent spines on the extensor margin of the carpus of pereopods 2-4, a row of dorsal spines on the merus of the chelipeds and more extensive striation on the branchial regions of the carapace. Variation in the type series of M. nias is slight, the main adult difference being in the number of mesial spines on the cheliped merus: two in the male holotype, one in the female paratypes. The juvenile female (pcl 4.0 mm) (Fig. 5A) has rudimentary pleopods and differs chiefly from the adults in having relatively more pronounced carapace spines, proportionally shorter chelipeds (twice pcl), fewer mesial and ventromesial spines on the merus of the chelipeds, and a proportionally shorter cheliped palm (slightly shorter than the dactylus versus longer in adults).
In addition to Indonesian material identified here as M. nias sp. nov., Doflein & Balss (1913) also reported material from off East Africa under the name M. tridentata. Given the strong similarities between M. nias and M. pubescens, Doflein & Balss' (1913) East African records are probably referable to the latter species. Baba & Poore's (2002: fig.  6D, 7C, 8C, 9E) record of M. serricornis from off Nias, Indonesia (Valdivia stn 198, 677 m), is referrable to M. nias. Material reported by Laurie (1926) as M. tridentata from Saya de Malha could not be located for the present study (Matt Lowe, pers. com., UMC), but are tentatively referred to M. pubescens Macpherson, 2007, described from Madagascar. Laurie's (1926 account was brief, but consistent with M. pubescens: the extensor margins of the meri of the walking legs are spinose, the carpi of the walking legs have two distal spines and only a single longitudinal row of spines on the cheliped merus (always two or three rows in M. nias). The Saya de Malha specimens probably also lacked epigastric spines as in M. pubescens; were epigastric spines present, they would almost certainly have been mentioned given Laurie's (1926) succinct but detailed account of carapace and pereopodal spination. Saya de Malha is also geographically adjacent to the type locality of M. pubescens, Madagascar.
Antenna: Basal article with triangular mesial and lateral tooth, neither overreaching article 2. Article 2 with strong distolateral spine, reaching beyond midlength but not apex of article 3. Article 3 with distomesial spine. Article 4 with Maxilliped 3: Dactylus, propodus and carpus unarmed. Merus extensor margin with 2 small, blunt to acute tubercles and distal spine; flexor margin with 2 large triangular spines proximally and 1 or 2 smaller spines distally. Ischium longer than wide, with distal flexor and extensor spine.

Colour in life.
Carapace and abdomen off-white; lateral margins and ridges with pale orange-brown marks. Chelipeds deep orange-red. Walking legs off-white. Cornea pale pink. The holotype is depicted in colour by Poore et al. (2011, pl. 23F).
Etymology. Derived from the Latin pyro, fire and chela, alluding to the orange-red chelipeds of the new species.

Remarks.
Most previous records of M. serricornis from southeastern Australia are based on M. pyrochela sp. nov. (see Baba & Poore, 2002;Ahyong & Poore, 2004). Munidopsis pyrochela is readily distinguished from M. serricornis, however, by the presence of epigastric spines on the carapace and the colour in life, in which the carapace and walking legs are whitish rather than orange. Of the serricornis-complex species, M. pyrochela sp. nov. most closely resembles those having a pair of epigastric spines and spinose extensor margins of the walking legs, namely M. spiridonovi sp. nov., M. mina Benedict, 1902 from the eastern Pacific, and two western Atlantic species, M. tridens (A. Milne-Edwards, 1880) and M. transtridens Pequegnat & Pequegnat, 1971. Munidopsis pyrochela differs from M. transtridens in the less slender cheliped carpus with a length less than twice the width (versus about 2.5-3 times width). From M. mina, M. pyrochela is readily distinguished by the presence of a prominent spine on the mesial margin of the carpus of the cheliped in addition to a small distal spine adjacent to the propodal articulation, rather than only a small distal spine. From M. tridens, M. pyrochela differs in having eight rather than seven telson plates, and three instead of two longitudinal rows of spines on the merus of the cheliped.
The presence of epigastric and lateral carapace spines is remarkably consistent in M. pyrochela, being present in all specimens including the smallest specimen examined (male, pcl 4.9 mm, NIWA 53274). The larger western Indian Ocean specimen (male, pcl 12.6 mm, OUMNH.ZC.2013-01-008) initially appeared to lack epigastric spines, but close inspection revealed that the spines were broken. Australian and New Zealand specimens usually have an irregular or serrated extensor carpal margin on the walking legs, but on pereopods 2 and 3, up to three of these serrations may be developed as spines, as in the two western Indian Ocean specimens. A specimen from The Snares (NIWA 19199) and a western Indian Ocean specimen (AM P92563) are the smallest ovigerous females at pcl 10.3 mm and pcl 10.2 mm, respectively.
The strongly disjunct distribution of M. pyrochela, between southern Australia and the western Indian Ocean, is conspicuous. The level of sampling from intermediate localities in the southern Indian Ocean, however, is presently inadequate to determine if the disjunction is real or artefactual. Material from both regions are similar, the two western Indian Ocean specimens being less setose dorsally than the Australian and New Zealand examples; the significance of these differences requires further study, especially given the apparent distributional disjunction. A similar disjunction applies also to the deep-water caridean shrimp, Leontocaris bulga Taylor & Poore, which is known from Tasmania and off southeast Africa (Komai & Chan, 2010).
Munidopsis pyrochela is a common seamount species and the most southerly occurring species of the serricornis complex, ranging into Subantarctic waters. The typical habitat of M. pyrochela remains to be confirmed, although the holotype was collected from a crevice in a hexactinellid glass sponge Farrea similaris Reiswig & Kelly, and other specimens were collected together with various other species of hexactinellids. Munidopsis pyrochela has not yet been confirmed from deepwater corals, unlike M. serricornis, which is a known associate of the arborescent Lophelia pertusa in the northern Atlantic (Lavaleye et al., 2009).
Distribution. Southwest Indian Ridge (Middle of What Seamount), New Zealand and south-eastern Australia, ranging in the east from the southern Kermadec Ridge and The Snares, south to the Macquarie Ridge and westwards to Tasmania including the South Tasman Rise and Cascade Plateau; 392-1414, usually 900-1000 m.

Description of adults.
Carapace: Moderately convex from side to side; covered with short, fine setae; surface of anterior half with granules and short rugae; surface of posterior half with short rugae and distinct striae. Cervical groove indistinct. Pair of epigastric spines. Posterior orbital margins transverse to slightly oblique, outer orbital spine prominent. Frontal margins oblique, slightly concave; anterolateral spine similar to outer orbital spine. Lateral margins broadly convex; with 2 spines on anterior branchial margin and spine at junction of anterior and posterior branchial margins. Rostrum broad, 0.4 pcl; trifid distally; apex horizontal or slightly deflected dorsally; median carina distinct; lateral proximal margin convex. Posterior margin unarmed, medially emarginated. Pterygostomian flap with short diagonal striae; anterior margin blunt, angular.
Antenna: Basal article with triangular mesial and lateral tooth, neither overreaching article 2. Article 2 with strong distolateral spine, reaching midlength but not apex of article 3. Article 3 with distomesial spine. Article 4 unarmed. Flagellum slightly shorter than pcl.

Colour in life. Unknown.
Etymology. Named for Vassily Spiridonov, for kindly making material available for study and for his important contributions to decapod systematics.   Mayo, 1974), but differs in having a markedly less setose carapace (sparse, short scarcely visible setae versus long prominent setae) and more elongate chelipeds in adults. The proportional length of the cheliped palm in adult M. spiridonovi is about 1.5 times dactyl length (versus 1.3 or less in M. transtridens), the cheliped merus is distinctly longer than pcl (almost as long as cl) rather than being about as long as pcl, and the cheliped length is greater than 3.6 pcl compared to about 3.0 pcl. Variation between the male and female type specimens is slight, being most marked in the sexually dimorphic chelae in which the male cheliped fingers have a distinct versus slight gape (Fig. 7A, 8L). The carpus of the cheliped of the holotype has a dorsal row of two spines on the right side, four on the left (Fig. 8A, J). The male paratype has six dorsal carpal spines. The merus of maxilliped 3 is armed with three flexor spines, of which the distalmost ranges from smaller than to as large as the other two spines (Fig.  7E, 8K). The two juvenile females from the Southeast Indian Ridge (Fig. 8A-J), although lacking the row of carpal spines on the cheliped, are presently assigned to M. spiridonovi. They agree well with the adults in almost all features, but have a row of raised angular, dorsal prominences on the cheliped carpus rather than spines, an unarmed carpal extensor margin (excluding the distal spine) on pereopod 2, less prominent meral extensor spines on the walking legs, and a proportionally shorter cheliped in which the length is about 2.5 pcl with merus slightly shorter than pcl and palm about 1.2 times dactylus length. Although these juveniles potentially represent a different species in which diagnostic characters are yet to be fully expressed, each of the aforementioned differences between adults and juveniles are consistent with expected allometric changes in M. spiridonovi, and parallel changes in M. transtridens, which may also have a dorsal row of carpal spines on the cheliped in adults (Pequegnat & Pequegnat, 1971;Mayo, 1974;Tavares et al., 2008).

Distribution. Western Indian Ocean from seamounts on the
Coco-de-Mer Ridge and the Southeast Indian Ridge, near Amsterdam Island; 940-1680 m.

Discussion
The discovery of six new Munidopsis serricornis-complex species documented here demonstrates the wide distribution of the group throughout the Indo-West Pacific. The majority of serricornis-complex species share a rostrum with typically convex margins, unarmed or spinose carapace margins, seven or eight (usually eight) telson plates, two or more prominent flexor spines on the maxilliped 3 merus, all pereopods without epipods, presence of a slender flexor spine or thick seta arising from the base of (and usually lying against) the unguis of pereopods 2-4. These include M. serricornis (Lovén, 1852), M. crinita Faxon, 1893, M. mina Benedict, 1902, M. modesta Benedict, 1902, M. tridens (A. Milne-Edwards, 1880, M. transtridens Pequegnat & Pequegnat, 1971, from the Atlanto-East Pacific, and M. pyrochela sp. nov., M. alcocki sp. nov., M. spiridonovi sp. nov., M. ternaria Macpherson, 2007, M. comarge Taylor, Ahyong &Andreakis, 2010, M. macphersoni sp. nov. andM. atlantis sp. nov., from the Indo-West Pacific. Munidopsis treis Ahyong & Poore, 2004 is superficially similar to M. serricornis on the basis of its trifid rostrum and unarmed dorsal surface but is excluded from the serricornis complex; it differs from all other serricornis-complex species in having the posterior orbital margins and frontal margins of the carapace in-line and sloping posteriorly at the same angle, as in M. trifida Henderson, 1885, andM. kareenae Ahyong, 2013. Within the serricornis complex, three species (M. acuminata Benedict, 1902, M. pubescens Macpherson, 2007, andM. nias sp. nov.) differ from remaining species in the combination of a relatively short, broad, subquadrate rostrum, absence of epigastric spines, seven telson plates, cheliped with or without an epipod, one or two (usually one) flexor spines on the merus of maxilliped 3, proportionally short, squat pereopods with the pereopod 2 merus length not more than 2.5 times the width, in having two distal spines on the carpus of the walking legs, and absence of a slender flexor spine or thick seta arising from the base of the unguis of pereopods 2-4. Munidopsis acuminata Benedict, 1902, M. pubescens Macpherson, 2007, andM. nias sp. nov. form a discrete group within the serricornis complex suggesting common ancestry of the three species.
Present results demonstrate that Munidopsis serricornis is not cosmopolitan, but restricted to the Atlantic Ocean. All previous Indo-Pacific records of M. serricornis are referrable to other species, most of which are newly described here: M. alcocki sp. nov., M. pyrochela sp. nov. and M. nias sp. nov. Other new species described herein have been discovered de novo: M. atlantis sp. nov., M. macphersoni sp. nov. and M. spiridonovi sp. nov.
Records of Munidopsis serricornis (as M. tridentata) from the Philippines and south-eastern Indonesia by Baba (1988Baba ( , 2005 are referrable to M. comarge and M. ternaria, respectively (USNM specimens re-examined in 2013). Similarly, the New Zealand records of M. comarge  are here referred to M. ternaria (NIWA specimens re-examined in 2013). Thus, M. comarge ranges from southern and western Australia to the Philippines and Taiwan, and M. ternaria ranges from New Zealand to New Caledonia and southeastern Indonesia (Osawa et  Table 1.