Torbenella mensae, Macpherson & Rodríguez-Flores & Machordom, 2023

Macpherson, Enrique, Rodríguez-Flores, Paula C. & Machordom, Annie, 2023, Integrative approach to describe new species of squat lobsters of the genera Heteronida Baba & de Saint Laurent, 1996 and Torbenella Baba, 2008 (Decapoda, Munididae) from the Southwestern Pacific Ocean, European Journal of Taxonomy 860 (1), pp. 116-140 : 132-136

Torbenella mensae sp. nov.

urn:lsid:zoobank.org:act:1D01DE3B-C8B9-4316-8457-33EE2B7B9526

Fig. 5

Torbenella aff. orbis 2.— Machordom et al. 2022: table 2.

Etymology

The name ‘ mensae ’ refers to one of the southern hemisphere constellations (the Table Mountain).

Material examined

Holotype PAPUA-NEW GUINEA • ♂ (7.2 mm); MADEEP stn DW4312; 09°50′ S, 151°34′ E; 120–280 m depth; 3 May 2014; GenBank no.: COI: OP215691 , 16S: OP196030 , 18S: OP 196288 ; MNHN-IU-2016-3004 .

Description

CARAPACE. Slightly wider than long. Transverse ridges with dense, very short setae, not medially interrupted. Scales and secondary striae absent between main striae. Gastric region with 2 main epigastric spines, each behind supraocular spine; 3–5 additional minute spines on each lateral side; some small spines at base of rostrum and in parahepatic, hepatic and anterior branchial regions; one small postcervical spine on each side. Orbit with iridescent mesial, rounded mound, lateral limit slightly defined. Frontal margins concave. Lateral margins slightly convex. Anterolateral spine well developed, at anterolateral angle, reaching level of sinus between rostrum and supraocular spines. One small marginal spine anterior to cervical groove. Branchial margins with 4 small spines. Rostrum spiniform, less than half as long as remaining carapace, reaching end of corneae, straight, and directed slightly upwards. Supraocular spines not reaching midlength of rostral spine and falling short of end of corneae, subparallel, directed slightly upwards.

THORACIC STERNUM. Smooth, without striae, except a few on sternite 4. Sternite 3 3.2 times as wide as long; sternite 4 3.6 times as wide as long, twice wider than sternite 3. Anterior margin of sternite 4 contiguous to entire posterior margin of sternite 3.

ABDOMEN. Somites 2–4 each with 2 median spines on anterior ridge; posterior ridge of somite 4 unarmed. Somites 2–3 each with 3 transverse ridges and several scales in addition to anterior ridge. Somite 4 with a few striae.

EYES. Eyes large, corneae dilated, maximum diameter 0.4 times distance between bases of anterolateral spines.

ANTENNULE. Article 1 (distal spines excluded) about one-third carapace length, elongate, barely reaching end of corneae, with 2 short distal spines, distomesial spine shorter than distolateral spine; lateral margin unarmed, bearing numerous long plumose setae.

ANTENNA. Article 1 with prolonged, strong mesial process, exceeding antennular peduncle, lateral border with long plumose setae; article 2 with 2 distal spines, distomesial slightly larger than distolateral, not reaching end of article 3; article 3 with minute distomesial spine, article 4 unarmed.

MXP3. Ischium about 1.5 times length of merus, distoventrally produced to spine. Merus with well developed median spine on flexor margin, extensor margin unarmed.

P1. Lost.

P2–3 (P4 lost). Moderately long and slender, squamous, with dense short setae on scales, and some long iridescent setae along extensor margins of all articles. P2 2.8 times carapace length. Meri shorter posteriorly (P3 merus 0.9 times length of P2 merus); P2 merus 1.2 times carapace length, 8.5 times as long as wide, 1.6 times as long as P2 propodus; P3 merus 4.0 times as long as wide. Extensor margins of P2–3 meri with row of small proximally diminishing spines; flexor margins with distal spines followed proximally by several eminences; lateral sides unarmed. Carpi with several spines on extensor margin; flexor margin ending in blunt point. P2 propodus 8 times as long as wide; extensor margin unarmed; flexor margin with 9 slender movable spines, without fixed distal spine. P2 dactylus long and slender, 7.5 times as long as wide, length 0.8 times that of propodus; flexor margin with 4 movable spinules along proximal half.

Genetic data

COI, 16S and 18S were successfully sequenced. CO1 provided the maximum divergence between T. mensae sp. nov. and T. aequabilis sp. nov. (15.17%). The minimum value for this gene and species was 12.87% with respect to T. crateris sp. nov. Torbenella mensae sp. nov. appeared in the phylogenetic reconstruction as a sister species of T. calvata ( Fig. 7 ), but with a low support (pp = 0.62).

Remarks

Torbenella lupi sp. nov., T. mensae sp. nov. and T. orbis ( Baba, 2005) are unique in the genus in having the presence of spines along the anterior ridge of the abdominal somite 2. Torbenella mensae is easily distinguished from the other 2 species by the wider thoracic sternite 3 (more than 3 times as wide as long) and the absence of spines on the posterior ridge of the abdominal somite 4. The other species have the thoracic sternite 3 moderately wide, less than 3 times as wide as long, and the posterior ridge of the abdominal somite 4 usually with small median spines.

Torbenella lupi sp. nov. and T. orbis were found at the same station in Papua-New Guinea. Torbenella lupi is distinguished from T. orbis by having spinules on the flexor margin of the P2–4 dactyli, which are absent in T. orbis . Furthermore, these articles are more slender in T. orbis than in the new species (7.5 vs 5.5 times as long as wide).

The genetic differences among the three species were: 13.28% for COI between T. mensae and T. lupi sp. nov., and 14.70% between T. mensae and T. orbis (COI) , and pairwise distance of 11.12% for 16S between T. mensae and T. orbis ; sequence data for 16S was not available for T. lupi .

Distribution

Papua-New Guinea, between depths of 120 and 280 m.

Figures

Fig. 5. Torbenella mensae sp. nov., holotype, ♂, CL = 7.2 mm (MNHN-IU-2016-3004), Papua-New Guinea. A. Carapace and abdomen, dorsal view. B. Sternal plastron. C. Cephalic region, showing antennular and antennal peduncles, ventral view. D. Left Mxp3, lateral view. E. Left P2, lateral view. F. Dactylus of left P2, lateral view. G. Right P3, lateral view. Scale bar: A–B, E, G = 2.0 mm; C–D, F = 1.0 mm.

Fig. 7. Bayesian phylogenetic inference based on four concatenated gene fragments (COI, 16S, 18S and PEPCK). Numbers on branches indicated the posterior probability supports.