Dinochelus, Ahyong & Chan & Bouchet, 2010

Ahyong, Shane T., Chan, Tin-Yam & Bouchet, Philippe, 2010, Mighty claws: a new genus and species of lobster from the Philippine deep sea (Crustacea, Decapoda, Nephropidae), Zoosystema 32 (3), pp. 525-535 : 528

Genus Dinochelus n. gen.

TYPE SPECIES. — Dinochelus ausubeli n. gen., n. sp.

ETYMOLOGY. — From the Greek dinos, meaning terrible, fearful, and chela, meaning claw, alluding to the massive, spinose major claw of the new genus. Gender masculine.

DIAGNOSIS. — Rostrum with lateral spines. Carapace surface with scattered spinules or acute granules, otherwise smooth, without median groove or carina; with small supraorbital spine; orbital fossa obsolete; pterygostomial margin faintly convex, with prominent antennal spine; anterolateral angle rounded, with few small spines or denticles, meeting pterygostomial margin at acute angle; with postcervical, cervical, hepatic, antennal and branchiocardiac grooves. Pleural margins subtruncate to broadly rounded, wider than high; surfaces and margins of pleura 2-5 with laterally minute granules or spinules. Eyes well-developed, elongate, movable, corneal region rounded, unpigmented. Scaphocerite spinose. Epistome fused anteriorly with carapace; inverted T-shaped, with narrow median portion and slender, transverse posterior portion. Mandible with palp. Maxilliped 2 exopod well-developed; epipod absent. Maxilliped 3 exopod well-developed; epipod with well-developed podobranch; with 2 arthrobranchs. Pereopods 1-4 each with epipod and podobranch. Pereopod 5 without epipod or podobranch. Chelipeds strongly dimorphic. Major and minor pereopod 1 palms with numerous spinules; pollex and dactylus with occlusal margins bearing 2 divergent rows of spines. Pereopod 1 minor chela fingers 3 times as long as palm. Uropodal exopod proximal segment with spinose outer margin; distal segment wider than half width of proximal segment. Telson subquadrate; margins and surfaces unarmed.

MONOPHYLY AND RELATIONSHIPS

Dinochelus n. gen. is most closely related to other nephropids formerly placed in Thaumastochelidae , namely species of Thaumastocheles and Thaumastochelopsis . Phylogenetic analyses of partial 12S mitochondrial sequences under both ML and MP recovered identical topologies indicating that Dinochelus n. gen. is sister to the remaining thaumastocheliform nephropids, namely, a clade containing two reciprocally monophyletic clades corresponding to Thaumastocheles and Thaumastochelopsis ( Fig. 1 ).

Dinochelus n. gen. variously shares diagnostic features of both Thaumastocheles and Thaumastochelopsis . With species of Thaumastocheles , Dinochelus n. gen. shares well developed rather than rudimentary exopods on maxillipeds 2 and 3, of which maxilliped 3 also has two rather than one arthrobranchs and a well-developed podobranch; and the distal segment of the uropodal exopod is wider than long instead of small and semicircular. Together with species of Thaumastochelopsis , Dinochelus n. gen. shares movable, well-developed eyes, although it is noteworthy that the eyes of Dinochelus n. gen. are relatively larger than in species of Thaumastochelopsis (cf. Fig. 2B, J ). In species of Thaumastocheles , the eyes are reduced to a fixed, rudimentary stub without a cornea. The well-developed eyes of Dinochelus n. gen. (in common with species of Thaumastochelopsis ), and more complete branchial formula along with the larger uropodal exopod distal segment (in common with species of Thaumastocheles ) is consistent with its phylogenetic position as sister to Thaumastocheles + Thaumastochelopsis . Dinochelus n. gen. exhibits a more “complete” morphology than either Thaumastocheles or Thaumastochelopsis in being less modified. In Thaumastocheles and Thaumastochelopsis , aspects of morphological reduction relative to Dinochelus n. gen. are evident in the various losses of branchiae, reduction of maxillipedal exopods, reduction of the uropodal exopod and degeneration of the eyes.

Although less modified than species of either Thaumastocheles or Thaumastochelopsis , Dinochelus n. gen. differs from both of these genera in having an unusual epistome form ( Fig. 2G, K ). In both Thaumastocheles and Thaumastochelopsis , the median and posterior portions of the epistome are broad, with the median portion wider than one-third the overall epistome width. The basal antennal segments in members of these two genera fit snugly against the anterolateral excavations on either side of the epistome. In contrast, the epistome in Dinochelus n. gen. has slender median and posterior portions, forming a distinctly inverted T-shaped element. The basal antennal segments in Dinochelus n. gen. are proportionally larger than in species of Thaumastocheles and Thaumastochelopsis , but articulate with the anterolateral margins of the epistome via a wide margin of arthrodial membrane. Such an epistomial arrangement as in Dinochelus n. gen. is unique in the Nephropidae .

Figures

FIG. 1. — Maximum likelihood (ML) phylogram of “thaumastochelid” genera based on analysis of mitochondrial 12S rRNA sequences under best fitting model TVM + G. Numbers at nodes indicate bootstrap proportions for analyses under MP (upper) and ML (lower). Outgroups (not shown) were Homarus americanus, Metanephrops japonicus and Nephropsis serrata.

FIG. 2. — A-I, Dinochelus ausubeli n. gen., n. sp., š holotype, pcl 26.1 mm (NMCR); J, K, Thaumastochelopsis brucei Ahyong, Chu & Chan,2007,š holotype,pcl 21.1 mm (AM P49083);A, body,right lateral view;B, J, anterior carapace,dorsal view;C, abdomen,dorsal view; D, right uropodal exopod, ventral view; E, right antenna, dorsal view; F, right antenna, ventral view; G, K, epistome,ventral view; H, right maxilliped 2, lateral view; I, right maxilliped 3, lateral view. Scale bar: A-D, G, 10.0 mm; E, F, H, I, 5.0 mm; J, K, 7.5 mm.