Trapezionida macilenta, 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 macilenta sp. nov.

Figs 6 , 9A

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

Material.

Holotype: Papua-New Guinea. Papua Niugini Stn PT 05, 3 December 2012, 05°12.4'S, 145°49.3'E, 80 m: male, 5.7 mm (MNHN-IU-2013-1094).

Description.

Carapace: 1.2 × as long as broad, feebly convex, with a few secondary striae and scales between main transverse ridges. Ridges with very short plumose setae and a few scattered long iridescent setae. Intestinal region without scales. Gastric region with five pairs of epigastric spines, longest pair behind supraocular spines, one pair between longest pair; one median protogastric spine. One parahepatic, one anterior branchial, and one postcervical spine on each side. Frontal margins oblique. Lateral margins slightly convex and convergent posteriorly. First lateral spine at anterolateral angle, well-developed, not reaching level of sinus between rostrum and supraocular spines; two or three small spines in front of anterior branch of cervical groove. Branchial margins slightly convex, with five spines. Rostrum spiniform, ~ 0.8 × length of remaining carapace, slightly upwards directed, not dorsally carinated. Supraocular spines reaching midlength of rostrum and not reaching end of cornea, subparallel, slightly upwards directed. Pterygostomian region unarmed, ending in round tip.

Thoracic sternum: 0.7 × as long as broad. Surface of thoracic sternites IV-VI smooth, only a few short scales on sternite IV. Sternite III 3.7 × as wide as long. Sternite IV trapezoidal, anterior margin contiguous to sternite III along ¾ of its length; 2.5 × as wide as long, and 2.0 × as wide as sternite III.

Pleon: Ridges of pleomeres unarmed; somites II and III each with three uninterrupted transverse ridges on tergite behind anterior ridge: pleomeres IV and V with anterior ridge only; posteromedian margin of pleomere VI straight.

Eye: Ocular peduncle longer than broad. Cornea moderately dilated, maximum corneal diameter 0.3 distance between bases of anterolateral spines.

Antennule: Article 1 (distal spines excluded) very long, ~ 0.5 × carapace length, 3.0 × as long as wide (excluding spines), clearly overreaching end of cornea, with two distal spines, mesial spine longer than lateral; two spines on lateral margin, proximal one short, located at midlength of segment, distal one long, not reaching end of distal spines.

Antenna: Article 1 with distomesial spine not exceeding article 2. Article 2 with distomesial spine, exceeding article 3, distolateral spine shorter than distomesial, slightly exceeding article 3. Articles 3 and 4 unarmed.

Mxp3: Ischium with well-developed spine on flexor distal margin. Merus slightly shorter than ischium; flexor margin with two spines, median slightly stronger than distal spine; extensor margin with minute distal spine. Carpus unarmed.

P1: 4 × carapace length, with scattered long plumose setae, and some long iridescent setae; some short setae on spines and scales. Merus 1.5 length of carapace, 2.2 × as long as carpus, with some dorsal and mesial spines; distal spines strong, distomesial spine barely reaching proximal fourth of carpus. Carpus 0.6 × length of palm, 3.2 × as long as broad, with spines along mesial and dorsal sides. Palm 4.4 × as long as broad, with row of dorsal spines; one row of spines along mesial and lateral margins, continuing along movable and lateral fingers, respectively. Fingers 0.7 × length of palm.

P2-P3 (P4 lost): Long and slender, with some short setae and some scattered iridescent setae along extensor margins of all articles. P2 2.8 carapace length. Meri shorter posteriorly (P3 merus 0.9 × length of P2 merus); P2 merus as long as carapace, 7.2 × as long as broad, 1.2 × as long as P2 propodus; P3 merus 6.2 × as long as broad, 1.1 × as long as P3 propodus. Extensor margins of meri with row of six-eight proximally diminishing spines on P2-P3; flexor margins with three or four spines followed proximally by several eminences; lateral sides unarmed. Carpi with three or four spines on extensor margin; lateral surface with several granules sub-paralleling extensor margin; flexor margin with well-developed distal spine. Propodi 9.0-9.5 × as long as broad; extensor margin unarmed; flexor margin with nine or ten slender movable spines, one fixed distal spine. Dactyli slender, length 0.8 × that of propodi; flexor margin with ten movable spinules along entire border, with ultimate spinule at base of unguis; P2 dactylus 8.0 × as long as wide.

Colour in life.

Ground colour of the carapace, pleon and appendages orange with large reddish patches. P1-P4 with reddish and whitish transverse bands. Distal P1 palm reddish (Fig. 9A ).

Genetic data.

COI, 16S.

Etymology.

From the Latin, macilentus, thin, in reference to the long and slender antennular peduncle.

Remarks.

Trapezionida macilenta belongs to the group of species having one median protogastric spine, anterior ridge of the pleomere II tergite unarmed, thoracic sternites smooth and the antennular article 1 very slender, with the distomesial spine longer than the distolateral spine.

The new species is closely related to T. diluta sp. nov. from New Caledonia (see above). However, both species are easily distinguished by several characters:

The branchial lateral margin of the carapace has four spines in T. diluta and five in T. macilenta . The pleomeres II and III tergites each with two or three uninterrupted transverse ridges behind the anterior ridge T. macilenta , whereas there is only one transverse ridge in T. diluta .

The extensor margin of the Mxp3 merus has one minute distal spine in T. macilenta , absent in T. diluta .

Genetically both species are different. T. macilenta showed high divergence values compared with T. diluta (6.42% COI, 4.6% 16S).

Distribution.

Papua-New Guinea, 80 m depth.

Figures

Figure 6. Trapezionida macilenta sp. nov., male holotype, 5.7 mm (MNHN-IU- 2013 - 1094), Papua-New Guinea 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, merus and carpus, dorsal view F right P 1, palm and fingers, dorsal view G right P 2, lateral view H dactylus of right P 2, lateral view I right P 3, lateral view. Scale bars: 1.0 mm (A, E, F, G, I); 0.5 mm (B, C, D, H).

Figure 9. Colour in life A Trapezionida macilenta sp. nov., male holotype, 5.7 mm (MNHN-IU- 2013 - 1094), Papua-New Guinea B Trapezionida pulex sp. nov., ovigerous female paratype, 4.4 mm (MNHN-IU- 2013 - 1882), New Caledonia.