Angustopelta robusta, Ng, Peter K. L. & Castro, Peter, 2016

Ng, Peter K. L. & Castro, Peter, 2016, Revision of the family Chasmocarcinidae Serène, 1964 (Crustacea, Brachyura, Goneplacoidea), Zootaxa 4209 (1), pp. 1-182 : 61-63

Angustopelta robusta n. sp.

( Figs. 12 A, B; 13A‒F; 24F; 31G; 41G, H; 42A‒C; 52G; 59F, J; 74A‒E; 87C; 91C; 101F)

Type material. Holotype male (9.3 × 10.7 mm) (MNHN-IU-2010-5616), Vanuatu, Big Bay , BOA 1 stn CP2435, 14°51’10”S 166°53’80”E, 773‒900 m, 0 9.09.2005.

Paratypes: Vanuatu, MUSORSTOM 8: 1 male (10.0 × 12.6 mm) (MNHN-IU-2013-9042), stn CP1075, 15°53’S, 167°27’E, 944‒948 m, 04.10.1994 ; 6 males, 5 females (MNHN-IU-2013-9041), 2 males, 2 females (ZRC 2015.254, ex MNHN-IU-2013-9041), stn CP1080, 15°57’S, 167°28’E, 799‒850 m, 05.10.1994; 1 male (10.9 × 12.5 mm) (MNHN-IU-2013-9043), no other data.—SANTO 2006: 1 male (12.3 × 13.3 mm) (ZRC 2015.255) [photographed], NE Tutuba I., stn AT60, 15°33.1’S, 167°22.0’E, 880‒953 m, 03.10.2006; 1 male (8.7 × 9.1 mm) (ZRC 2015.256), W. Malo I., stn AT61, 15°39.2’S, 167°01.4’E, 266‒281 m, 0 4.10.2006.

Diagnosis. Carapace ( Figs. 12 A, B; 101F) subtrapezoidal, convex, 1.1 wider than long; front bilobed, with shallow median cleft; minutely granular, without distinct lobes; anterolateral margins arcuate, round tubercle on each margin (may be absent). Eye peduncle ( Fig. 24 F) filling orbit, short, immobile; cornea pigmented. Epistome ( Fig. 24 F) semicircular median lobe with deep median fissure, semicircular lateral margins. Third maxilliped ( Fig. 31 G) merus subcircular, ischium rectangular, slightly longer than merus. Proportionally short ambulatory legs but length varies slightly; P5 merus 0.7 cl in holotype ( Fig. 42 A‒C). Chelipeds ( Figs. 12 A, B; 41G, H; 101F) subequal in length, slightly dissimilar in female, heteromorphic in males; fingers of minor chela ( Fig. 41 H) subcircular in cross-section, gently tapering to tip, scissor-like, cutting margins with few sharp teeth. Ventral surface of cheliped merus with 4 teeth, additional smaller teeth or large tubercles on outer margin, large tooth on distal inner margin, additional tooth on median portion may be present in some individuals. Inner margin of cheliped carpus with sharp tooth ( Fig. 12 A, B). Fused thoracic sternites 1, 2 ( Fig. 52 G) transversely narrow, long. Press-button for pleonal holding present as 2 small, short tubercles posterior to thoracic sternal suture 4/5, one near edge of sterno-pleonal cavity, one just outside ( Fig. 59 J). Male pleon ( Figs. 52 G; 59F) with proportionally short telson. G1 ( Fig. 74 A‒D) stout, distal segment slightly curved, with short to long spinules, tuft of setae just before tip. G2 ( Fig. 74 E) about half G1 length, curved, slender, distal segment proportionally long, curved. Female telson ( Fig. 87 C) proportionally short. Vulvae ( Fig. 91 C) relatively close together, located on outer margins of cavity close to suture 5/6.

Colour. The carapace is a pale, light brownish-pink and white to brownish white pereiopods after cleaning of live specimens ( Fig. 101 F).

Etymology. The name is derived from the Latin robusta for “stout,” alluding to the relatively large size and stocky appearance of the species.

Remarks. The new species has a round, tooth-like tubercle on the anterolateral margin of the carapace, whereas a distinctive tooth is usually present in A. aurita and no tubercle or tooth is present in A. cribrorum . The presence of a distinct tubercle in the new species, however, is a variable one, absent or very low in three of the 20 males examined and in five of 16 females examined. It is not related to overall size, and may simply be due to variation or erosion of the tubercle due to wear and tear. In one specimen (female 9.6 × 11.0 mm, MNHN-IU-2013- 9041), there is also small sharp granule on the subhepatic region that is visible from dorsal view ( Figs. 12 A, B; 13A, B, E, F). This is absent in other specimens although the surface of this region is uneven and covered with low granules. The anterolateral margin of A. modesta n. sp. has a low granule (sometimes undiscernible) that never develops into a tubercle.

Angustopelta robusta n. sp. possesses a unique double press-button of the male pleonal holding, consisting of two tubercles on each side of the pleon posterior to the thoracic sternal suture 4/5, one visible outside edge of sterno-pleonal cavity, the second adjacent to it inside the cavity ( Fig. 59 J). This is unusual and present in all male specimens of this species examined, even for small specimens. The function of the second exposed tubercle is unknown. The press-button of its three conspecifics consists of only one tubercle, which may be large as in A. cribrorum ( Fig. 59 I).

The ambulatory legs of the new species ( Figs. 12 A, B; 42A‒C) are clearly shorter than in A. aurita ( Fig. 11 B, C) and A. cribrorum ( Fig. 11 D, E), the P5 merus of the folded leg almost reaching the orbits in these two species but only to the tubercle on the anterolateral margin, if present, in the new species. The shorter legs, together with a slightly broader anterior third of the carapace, give the new species a more stout appearance than its congeners.

Distribution. Only known from Vanuatu, southwestern Pacific Ocean. Depth: 266‒ 953 m.

Figures

FIGURE 11. Overall dorsal view of species of Angustopelta n. gen. A, A. aurita, Philippines: holotype female 18.9 × 19.1 mm (USNM 46405); B, A. aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.250); C, A. aurita, Philippines: female 8.7 × 10.0 mm (ZRC 2015.253); D, A. cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); E, F, A. cribrorum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214).

FIGURE 12. Overall dorsal view of species of Angustopelta n. gen. A, A. robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); B, A. robusta n. sp., Vanuatu: paratype female 13.4 × 15.1 mm (MNHN-IU- 2010 - 5616); C, A. modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038); D, A. modesta n. sp., Solomon Islands: paratype male 11.5 × 13.2 mm (MNHU-IU- 2013 - 9039); E, A. modesta n. sp., Solomon Islands: paratype female 13.1 × 15.3 mm (ZRC 2015.258); F, A. modesta n. sp., Solomon Islands: paratype male 8.7 × 9.8 mm (MNHN-IU- 2013 - 9038); G, A. modesta n. sp., Solomon Islands: paratype male 6.1 × 6.4 mm (MNHN-IU- 2013 - 9038); H, A. aff. modesta n. sp., Papua New Guinea: female 9.0 × 10.2 mm (ZRC 2015.259).

FIGURE 24. Frontal view of species of Hephthopelta and Angustopelta n. gen. A, Hephthopelta lugubris, Australia: male 7.9 × 8.3 mm (NMV J 61081); B, Hephthopelta occidentalis n. sp., Madagascar: holotype male 6.1 × 6.6 mm with sacculinid (MNHN-IU- 2010 - 1031); C, Angustopelta aurita, Philippines: holotype female 18.9 × 19.1 mm (USNM 46405); D, Angustopelta aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.251); E, Angustopelta cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); F, Angustopelta robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); G, Angustopelta modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038); H, Angustopelta aff. modesta n. sp., Papua New Guinea: female 9.0 × 10.2 mm (ZRC 2015.259).

FIGURE 31. Third maxilliped of species of Hephthopelta and Angustopelta n. gen. A, B, Hephthopelta lugubris, Australia: male 7.9 × 8.3 mm (NMV J 61081); C, Hephthopelta occidentalis n. sp., Madagascar: holotype male 6.1 × 6.6 mm with sacculinid (MNHN-IU- 2010 - 1031); D, Angustopelta aurita, Philippines: holotype female 18.9 × 19.1 mm (USNM 46405); E, Angustopelta aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.250); F, Angustopelta cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); G, Angustopelta robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); H, Angustopelta modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038); I, Angustopelta modesta n. sp., Solomon Islands: paratype male 11.5 × 13.2 mm (MNHU-IU- 2013 - 9039).

FIGURE 41. Chelae of species of Angustopelta n. gen. A, B, A. aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.250); C, D, A. cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); E, F, A. cribrorum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214); G, H, A. robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); I, J, A. modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038).

FIGURE 42. P 4, P 5, and merus of cheliped of species of Angustopelta n. gen. A, A. robusta n. sp., Vanuatu: paratype male 12.3 × 13.3 mm (ZRC 2015.255); B, A. robusta n. sp., Vanuatu: paratype female 13.4 × 15.1 mm (MNHN-IU- 2010 - 5616); C, A. robusta n. sp., Vanuatu: paratype male 12.5 × 14.8 mm (MNHN-IU- 2013 - 9041); D, A. modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038); E, A. modesta n. sp., Solomon Islands: paratype female 13.1 × 15.3 mm (ZRC 2015.258); F, A. aff. modesta n. sp., Papua New Guinea: female 9.3 × 9.9 mm (MNHN-IU- 2011 - 3307); G, Hephthopelta lugubris, Papua New Guinea: female 9.8 × 10.9 mm (MNHN-IU- 2011 - 2657), major cheliped; H, Angustopelta aurita, Philippines: female 10.9 × 12.7 mm (ZRC 2015.248), minor cheliped; I, Tenagopelta pacifica n. sp., Indonesia: male 11.0 × 12.4 mm (MNHU-IU- 2013 - 9053), minor cheliped; J, Chinommatia cavimanus, Philippines: male 9.7 × 11.5 mm (ZRC 2015.234), minor cheliped; K, Chinommatia cavimanus, Philippines: male 7.6 × 9.3 mm (ZRC 2015.231), minor cheliped; L, Notopelta mortenseni, Indonesia: holotype male 5.0 × 6.9 mm (ZMUC CRU- 7397), major cheliped; M, Statommatia apta, Philippines: males 8.5 × 10.3 mm (ZRC 2015.237), minor cheliped; N, Statommatia malagasy n. sp., Madagascar: male 8.8 × 11.0 mm (MNHN-IU- 2010 - 4370 b), minor cheliped.

FIGURE 52. Anterior thoracic sternum and male pleon of species of Hephthopelta and Angustopelta n. gen. A, Hephthopelta lugubris, Australia: male 7.9 × 8.3 mm (NMV J 61081); B, C, Hephthopelta occidentalis, Madagascar: holotype male 6.1 × 6.6 mm with sacculinid (MNHN-IU- 2010 - 1031); D, Angustopelta aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.250); E, Angustopelta cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); F, A. cribrorum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214); G, Angustopelta robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); H, A. modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038).

FIGURE 59. Thoracic sternites 7 and 8, male pleon and sterno-pleonal cavity of species of Hephthopelta and Angustopelta n. gen. A, Hephthopelta lugubris, Australia: male 7.9 × 8.3 mm (NMV J 61081); B, Hephthopelta lugubris, Solomon Is: male 8.3 × 9.1 mm (MNHN-IU- 2013 - 9040); C, Hephthopelta occidentalis n. sp., Madagascar: holotype male 6.1 × 6.6 mm with sacculinid (MNHN-IU- 2010 - 1031); D, Angustopelta aurita, Philippines: male 9.2 × 10.6 mm (ZRC 2015.250); E, Angustopelta cribrorum, Japan: holotype male 13.6 × 14.9 mm (USNM 46388); F, Angustopelta robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); G, Angustopelta modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038); H, Angustopelta modesta n. sp., Solomon Islands: paratype male 11.5 × 13.2 mm (MNHU- IU- 2013 - 9039); I, Angustopelta cribrorum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214); J, Angustopelta robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616). Abbreviations: pb = press buttom male pleonal locking mechanism.

FIGURE 74. Gonopods of species of Angustopelta n. gen. A, C ‒ E, A. robusta n. sp., Vanuatu: holotype male 9.3 × 10.7 mm (MNHN-IU- 2010 - 5616); B, A. robusta n. sp., Vanuatu: paratype male 12.3 × 13.3 mm (ZRC 2015.255); F ‒ I, A. modesta n. sp., Solomon Islands: holotype male 13.3 × 15.1 mm (MNHU-IU- 2013 - 9038). A, B, F, ventral view of left G 1; C, D, G, H, distal part of left G 1; E, I, left G 2. Scales: A, B, E, F, I = 0.5 mm; C, D, G, H = 0.1 mm.

FIGURE 87. Female thoracic sternum and pleon of species of Hephthopelta, Angustopelta n. gen., Chinommatia n. gen. and Notopelta n. gen. A, Hephthopelta lugubris, Australia: ovigerous female 6.3 × 6.6 mm (NMV J 61083); B, Angustopelta aurita, Philippines: female 8.7 × 10.0 mm (ZRC 2015.253); C, Angustopelta robusta n. sp., Vanuatu: paratype female 13.4 × 15.1 mm (MNHN-IU- 2010 - 5616); D, Chinommatia cavimanus, Philippines: female 7.6 × 9.0 mm (ZRC 2015.228); E, Chinommatia bruuni, Malaysia: female 5.5 × 7.2 mm (ZRC 2013.0020); F, G, Notopelta mortenseni, Indonesia: female 5.9 × 4.1 mm (ZMUC CRU- 007768). Vulvae exposed in E, G.

FIGURE 91. Vulvae of species of Hephthopelta, Angustopelta n. gen., Chinommatia n. gen., Statommatia n. gen. and Tenagopelta n. gen. A, Hephthopelta lugubris, Australia: ovigerous female 6.3 × 6.6 mm (NMV J 61083); B, Angustopelta aurita, Philippines: female 8.7 × 10.0 mm (ZRC 2015.253); C, Angustopelta robusta n. sp., Vanuatu: paratype female 13.4 × 15.1 mm (MNHN-IU- 2010 - 5616); D, Chinommatia cavimanus, Philippines: female 7.6 × 9.0 mm (ZRC 2015.228); E, Statommatia apta, Philippines: female 8.5 × 10.6 mm (ZRC 2015.238); F, Statommatia malagasy n. sp., Madagascar: paratype female 9.4 × 8.1 mm (ZRC 2015.215); G, Tenagopelta pacifica n. sp., Philippines: female 9.2 × 10.4 mm (ZRC 2015.187); H, Tenagopelta brachyphallus n. sp., Australia: female 6.9 × 7.6 mm (NMV J 61680).

FIGURE 101. Angustopelta n. gen. A, Angustopelta aurita, Philippines: female 11.8 × 10.2 mm (ZRC 2015.249) [P. K. L. Ng]; B, Angustopelta aurita, Philippines: female 11.8 × 10.4 mm (ZRC 2015.249) [P. K. L. Ng]; C, Angustopelta aurita, Philippines: male 7.7 × 9.5 mm (ZRC 2015.248) [T. - Y. Chan]; D, Angustopelta aurita, Philippines: female 10.9 × 12.7 mm (ZRC 2015.248) [T. - Y. Chan]; E, Angustopelta criborum, Taiwan: male 9.9 × 11.6 mm (ZRC 2015.214) [T. - Y. Chan]; F, Angustopelta robusta n. sp., Vanuatu: paratype male 8.7 × 9.1 mm (ZRC 2015.256) [T. - Y. Chan].