Phylladiorhynchus pollux, Rodríguez-Flores & Macpherson & Machordom, 2021

Rodríguez-Flores, Paula C., Macpherson, Enrique & Machordom, Annie, 2021, Revision of the squat lobsters of the genus Phylladiorhynchus Baba, 1969 (Crustacea, Decapoda, Galatheidae) with the description of 41 new species, Zootaxa 5008 (1), pp. 1-159 : 116-118

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Phylladiorhynchus pollux

n. sp.

Phylladiorhynchus pollux n. sp.

( Figs. 44 View FIGURE 44 , 50C View FIGURE 50 )

Type material. Holotype. New Caledonia. LIFOU Stn 1451, 20.7883°S, 167.1133°E, 10–21 m, 19 November 2000: ov. F 3.5 mm (MNHN- IU-2014-13797) GoogleMaps

Paratype. New Caledonia, Recif Mbere , 22.3316°S, 166.2200°E, 10 m, 5 May 1993: 1 M 3.8 mm (MNHN-IU- 2019-2698) GoogleMaps .

Etymology. From the name Pollux, an Argonaut, son of Zeus and Leda. The name is considered a substantive in apposition.

Description. Carapace: As long as or slightly longer than broad; transverse ridges with dense short setae, and few scattered short and thick setae. Gastric region slightly convex, with some transverse ridges:epigastric ridge armed with 4 epigastric spines; anterior protogastric ridge not medially interrupted, nearly extending laterally to carapace margin, followed by a posterior protogastric ridge not medially interrupted; anterior mesogastric ridge not medially interrupted, laterally continuing to first branchial spine, posterior mesogastric ridge absent or scale like; anterior metagastric ridge not medially interrupted, laterally continuing to second branchial spine, followed by posterior median metagastric scale; secondary scales can be present between ridges. Mid-transverse ridge not interrupted, medially depressed, preceeded by distinct cervical groove, followed by 2 uninterrupted or minutely interrupted ridge, interspersed with 2 scale-like ridges. Lateral margins slightly convex, with 5 spines: first anterolateral spine well-developed, overreaching level of lateral orbital spine, second spine (hepatic) well-developed, slightly dorsomesial from lateral margin, and followed by 3 branchial spines (2 anterior and 1 posterior). Rostrum leaf-like, horizontal, dorsally flattish, narrow [1.7]–1.9 × as long as broad, length 0.4 and breadth 0.2 that of carapace; lateral margins smooth and convex, with well-developed supraocular basal supraocular spines, subapical spines minutes. Pterygostomian flap ending in blunt tooth, upper margin slightly irregular.

Thoracic sternum: As wide as long. Sternite 3 moderately broad, 2.0–[3.0] × as wide as long, anterior margin nearly straight. Sternite 4 widely contiguous to sternite 3; surface depressed in midline, smooth; greatest width [3.5]–4.6 × that of sternite 3, 2.6–[2.7] × as wide as long.

Pleon: Elevated ridges with with short setae and a few scattered thick setae. Tergite 2–3 with anterior and posterior transverse elevated ridges; tergite 4 with anterior transverse ridge; tergites 5–6 smooth.

Eye: Eyestalk length about 0.9–[1.0] × broader than long, peduncle distally setose, not distinctly expanded proximally; maximum corneal diameter [1.1]–1.2 × rostrum width, as wide as eyestalk.

Antennule: Article 1 slightly longer than wide, with 4–5 well-developed distal spines: distomesial spine welldeveloped; proximal lateral spine absent or minute.

Antenna: Article 1 with prominent mesial process, distally falling well short of lateral antennular spine. Article 2 with small distomesial and distolateral spines. Articles 3 and 4 unarmed.

Mxp3: Ischium with distinct distal spines on flexor and extensor margins. Merus and ischium subequal in size, with well-developed distal spine on extensor and flexor margins.

P1: 3.4 (male), [2.1] (female) × carapace length; subcylindrical, spiny and densely covered with plumose setae and scattered long stiff setae; merus, carpus and palm with spines along mesial, dorsal and lateral surfaces, distal and mesial spines usually stronger than others. Merus 1.2–1.3 length of carapace, twice as long as carpus. Carpus twice as long as wide. Palm 1.3 × carpus length, 2.8 × as long as broad. Fingers 0.7 × palm length; fixed finger unarmed; movable finger with small basal spine.

P2–3 (P4 lost in both specimens): Moderately stout, subcylindrical, highly setose and spinose, densely covered with plumose setae: P3 merus 0.6–[0.9] × length of P2 merus. P2 merus, 0.8 × carapace length, 4.4–[4.7] × as long as broad, 1.2–[1.4] × as long as P2 propodus; P3 merus [4.3]–4.6 × as long as broad, [1.1]–1.2 × as long as P3 propodus; extensor margin of P2 and P3 with row of spines, proximally diminishing, with prominent distal spine; flexor margin irregular,with distal spine on P2–3. Carpi with 3–4 spines on extensor margin on P2–3; distal spine prominent; row of small spines below extensor margin on lateral surface of P2–3; flexor margin unarmed or with small distal spine. Propodi moderately stout, 5.0–6.5 × as long as broad; extensor margin irregular, armed proximally with 2–4 small spines on P2–3; flexor margin with 3–4 slender movable spines in addition to distal pair. Dactyli 0.5–0.6 × length of propodi, ending in incurved, strong, sharp spine; flexor margin with 5–6 movable spines.

Eggs. No data. The holotype carried one egg of 0.5 mm diameter.

Live colour. Unknown.

Genetic data. COI and 16S, Table 1.

Distribution. New Caledonia, between 10 and 21 m.

Remarks. Phylladiorhynchus pollux belongs to the group of species having 4 epigastric spines and Mxp3 merus with one prominent spine along the flexor margin. The group of species includes P. australis , from New Zealand and Southern Australia, P. integrus from Japan to Chesterfield Islands, P. lenzi from Chile, P. nui from southeastern Australia, Tasmania and New Zealand, P. poeas , from French Polynesia, P. porteri , from Chile, and P. pusillus from the southwestern Pacific. However, the new species is easily distinguished from these species by the number of spines on the anterior branchial margin: 2 spines in P. pollux and 3 spines in the other species. Furthermore, the posterior protogastric ridge is present and entire in P. pollux , being absent or scale-like in the other species.

The sequences of P. pollux were more than 22% (COI) and 11% (16S) divergent from all other species.

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