Trapezionida brevitas, Macpherson & Rodríguez-Flores & Machordom, 2024

Macpherson, Enrique, Rodriguez-Flores, Paula C. & Machordom, Annie, 2024, DNA barcoding and morphology revealed the existence of seven new species of squat lobsters in the family Munididae (Decapoda, Galatheoidea) in the southwestern Pacific, ZooKeys 1188, pp. 91-123 : 91

Trapezionida brevitas sp. nov.

Fig. 4

Trapezionida aff. fornacis : Machordom et al. 2022: table 2, suppl. figs S1-S6.

Material.

Holotype: New Caledonia. Smib 8 Stn DW 163, 28 January 1993, 24°49.12'S, 168°08.93'E, 310-460 m: male, 4.1 mm (MNHN-IU-2017-1336) . Paratype: New Caledonia. Norfolk 2 Stn DW 2024, 21 October 2003, 23°27.92'S, 167°50.90'E, 370-371 m: 1 male, 4.6 mm (MNHN-IU-2014-13973) .

Description.

Carapace: Slightly longer than broad, moderately convex, with a few secondary striae and scales between main transverse ridges. Dorsal ridges with dense short plumose setae and a few scattered long iridescent setae. Gastric region with four pairs of epigastric spines, longest pair behind supraocular spines, one pair between largest pair of spines. One parahepatic, two branchial dorsal and one postcervical spine on each side. Frontal margins oblique. Lateral margins slightly convex. First lateral spine at anterolateral angle, moderately long, clearly not reaching level of sinus between rostrum and supraocular spines; one-two small spines in front of anterior branch of cervical groove; end of anterior branch of cervical groove without tuft of iridescent setae. Branchial margins slightly convex, with four spines. Rostrum spiniform, ~ 0.6 × length of remaining carapace, slightly upwards directed, dorsally slightly carinated. Supraocular spines reaching midlength of rostrum and not reaching end of cornea, slightly divergent, directed slightly upwards. Pterygostomian region unarmed, ending in blunt angle.

Thoracic sternum: 0.8 × as long as broad. Surface of thoracic sternites IV-VI smooth. Sternite IV trapezoidal, anterior margin contiguous to sternite III along ¾ of its length. Sternite III 3.5 × as wide as long; sternite IV 2.5 × as wide as long, and 2.3 × as wide as sternite III.

Pleon: Anterior ridge of pleomere tergites unarmed; tergites II and III each with one uninterrupted transverse ridge on tergite behind anterior ridge, absent on tergites IV and V; some iridescent setae on each side of anterior ridges of tergites; posteromedian margin of tergite VI straight.

Eye: Ocular peduncle as long as broad. Cornea dilated, maximum corneal diameter 0.4 distance between bases of anterolateral spines.

Antennule: Article 1 (distal spines excluded) ~ 0.3 × carapace length, 2 × as long as wide (excluding spines), slightly exceeding end of cornea, with two distal spines, distomesial subequal or slightly longer than distolateral; two spines on lateral margin, proximal one short, located at midlength of segment, distal one long, nearly reaching end of distolateral spine.

Antenna: Article 1 with distomesial spine slightly exceeding distal margin of article 2. Article 2 with subequal distomesial and distolateral spines, nearly reaching end of article 3. Article 3 unarmed.

Mxp3: Ischium with strong distal spine on flexor margin. Merus shorter than ischium; flexor margin with 2 spines, proximal stronger than distal; extensor margin with small distal spine. Carpus unarmed.

P1: 3.5-3.7 × carapace length, with minute scales, short plumose setae on each scale, and some scattered long spines. Merus 1.3 × length of carapace, 2.2 × as long as carpus, with some dorsal and mesial spines, distomesial spine strong, not reaching first quarter of carpus. Carpus 0.8 length of palm, 2.3 × as long as broad, with some spines along mesial and dorsal sides. Palm 1.8-2.3 × as long as broad, with some small dorsal spines; row of spines along mesial and lateral margins. Fingers as long as palm; movable with small proximal spine at base, otherwise unarmed, with minute distal spine on fixed finger.

P2-P4: Moderately long and slender, covered with setose scales, with some long plumose setae and some long iridescent setae along extensor margin of articles. P2 2.0 × carapace length. Meri shorter posteriorly (P3 merus 0.9 × length of P2 merus, P4 merus 0.8 × length of P3 merus); P2 merus 0.8 × length of carapace, 4.2 × as long as broad, 1.4 × as long as P2 propodus; P3 merus 4.5 ×as long as broad, 1.3 × length of P3 propodus; P4 merus 3.5 × as long as broad, 1.1 × length of P4 propodus. Extensor margins of P2-P3 meri with row of seven-eight proximally diminishing spines, one small distal spine on P4; flexor margins distally with one-two spines followed proximally by several eminences; lateral sides unarmed. Carpi with three spines on extensor margin of P2-P3, one minute distal spine on P4; lateral surface with several granules sub-paralleling extensor margin on P2-P4; flexor margin with distal spine. Propodi 4.5-5.5 × as long as broad; extensor margin unarmed; flexor margin with four-ten slender movable spines on P2-P4, distal end with one minute fixed spine. Dactyli slender, length 0.6 that of propodi; flexor margin with six-seven movable spinules, without spinule at base of unguis, distal third unarmed; P2 dactylus 4.0 × as long as wide. P4 merocarpal articulation reaching anterior end of cervical groove; P4 merus> ½ length of P2 merus.

Genetic data.

COI, 16S.

Etymology.

From the Latin, Trapezionida brevitas , shortness, in reference to the small size of the species.

Remarks.

Trapezionida brevitas belongs to the group of species having four spines on the branchial lateral margins of the carapace, frontal margins oblique, thoracic sternites without granules or carinae, anterior ridge of the pleomeres II and III tergites unarmed, article 1 of antennule with subequal distal spines or distomesial spine slightly longer than distolateral, extensor margin of Mxp3 merus with small distal spine and flexor margin of P2-P4 dactyli with spinules along entire margin. The new species is closely related to T. fornacis (Macpherson, 2006) and T. descensa (Macpherson, 2006), both from French Polynesia. However, the three species differ from each other in some characters.

The differences between T. brevitas and T. fornacis are as follows:

The dorsal carapace surface has two branchial dorsal spines in T. brevitas , and only one in T. fornacis .

The pleomeres II and III tergites each with one uninterrupted transverse ridge on tergite behind anterior ridge in the new species, these ridges are interrupted or scale-like in T. fornacis .

The distal spines of the antennular article 1 are subequal or slightly different in the new species, whereas the distomesial spine is clearly longer than the distolateral in T. fornacis .

The distomesial spine of the antennal article 1 is very long, reaching the end of the antennal peduncle in T. fornacis , whereas this spine only slightly exceeds the antennal article 2.

The dorsal surface of P1 palm is unarmed in T. fornacis , whereas it has numerous spines in T. brevitas .

Genetically both species are different. T. brevitas showed high divergence values with T. fornacis (15.9% COI).

The differences between T. brevitas and T. descensa are as follows:

The dorsal carapace surface has two branchial dorsal spines in T. brevitas , and only one in T. descensa .

P2-P4 are more slender in T. descensa (P2 merus and dactylus, 6 and 5 × as long as wide, respectively) than in T. brevitas (P2 merus and dactylus, 4 and 4 × as long as wide, respectively).

Genetically both species are different. T. brevitas showed divergence values with T. descensa of ~ 4.3% for COI).

Distribution.

New Caledonia, at 310-460 m.

Figures

Figure 4. Trapezionida brevitas sp. nov., male holotype, 4.1 mm (MNHN-IU- 2017 - 1336), New Caledonia A carapace and pleon, dorsal view B sternal plastron C cephalic region, showing antennular and antennal peduncles, ventral view D right Mxp 3 ischium and merus, lateral view E right P 1, dorsal view F right P 2, lateral view G dactylus of right P 2, lateral view H right P 4, lateral view. Scale bars: 1.0 mm (A, E, F, H); 0.5 mm (B, C, D, G).