Phylladiorhynchus hylas, 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 : 45-48

Phylladiorhynchus hylas n. sp.

( Figs. 16 , 21D )

Records requiring verification:

Galathea pusilla . — Tirmizi, 1966: 175, figs 1A–C (Red Sea).

Type material. Holotype. Reunion Island, MD32 Stn CP 43, 21.3450°S, 55.4483°E, 73–77 m, 18 August 1982: M 1.9 mm (MNHN-IU-2016-496).

Paratypes. Reunion Island. MD32 Stn CP 43, 21.3450°S, 55.4483°E, 73–77 m, 18 August 1982: 1 M 1.7 mm, 1 ov. F 1.6 mm (MNHN-IU-2016-495) .

Etymology. From the name Hylas, an Argonaut, son of Theiodamas and Menodice. The name is considered a substantive in apposition.

Description. Carapace: 0.9 × as long as broad; transverse ridges with some short setae, and few scattered iridescent thick long setae. Gastric region slightly convex with some transverse ridges: epigastric ridge indistinct, with 3 spines (1 median and 2 spines laterally) and some outer granules, continuing with few scales; anterior protogastric ridge not medially interrupted, laterally interrupted with few scales to carapace margin, posterior protogastric ridge scale-like; anterior mesogastric ridge scale-like, laterally interrupted by anterior branch of cervical groove, laterally continuing with few scales, posterior mesogastric area with few scales; anterior metagastric not medially interrupted, followed by small scales on posterior metagastric region. Mid-transverse ridge not interrupted, medially depressed, preceded by a shallow or indistinct cervical groove, followed by 2 not interrupted or minutely interrupted ridges, interspersed with 3 short lateral ridges. Lateral margins slighly convex, with 7 spines: first anterolateral spine welldeveloped, reaching end of lateral orbital spine, second spine (hepatic) minute, and followed by 5 branchial spines (3 anterior and 2 posterior). Rostrum leaf-like, horizontal, dorsally flattish, 1.1–[1.2] × as long as broad, length 0.4 and breadth 0.3 that of carapace; lateral margins serrated and convex, with well-developed supraocular spines, lateral margins of supraocular spines serrated, subapical spines distinct. Orbit sharply excavated. Pterygostomian flap ending in anterior spine, upper margin serrated.

Thoracic sternum: As wide as long. Sternite 3 moderately broad, 2.0–[2.6] × as wide as long, anterior margin convex, and with median feeble excavation. Sternite 4 widely contiguous to sternite 3; surface depressed in midline, smooth; greatest width 2.7–[2.9] × that of sternite 3, 2.3–[2.8] × as wide as long.

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

Eye: Eyestalk length about 1.1 × broader than long, peduncle distally setose, not distinctly expanded proximally; maximum corneal diameter 0.8 × rostrum width, as wide as eyestalk.

Antennule: Article 1 1.3 × longer than wide, with 5 spines: distomesial spine well-developed; proximal lateral spine minute.

Antenna: Article 1 with prominent mesial process, distally clearly not reaching lateralmost antennular spine. Article 2 with small distomesial and distolateral spines. Article 3 sometimes with small distomesial spine. Article 4 unarmed.

Mxp3: Ischium with distinct distal spines on flexor and extensor margins. Merus [0.7]–0.8 × length of ischium, with 1 median and 1 distal spine on extensor margin, 1–3 much larger spines on flexor margin.

P1: [2.3] (male) × carapace length; subcylindrical, spiny, with scattered long stiff setae and few thick setae; merus, carpus and palm with spines along mesial, dorsal and lateral surfaces, distal and mesial spines usually stronger than others. Merus [0.9] length of carapace, [2.0] × as long as carpus. Carpus [2.1] × as long as wide. Palm [1.1] × carpus length, [1.9] × as long as broad. Fingers [0.9] × palm length; unarmed.

P2–4: Subcylindrical, moderately setose and spinose. Meri successively shorter posteriorly: P3 merus [0.8] × length of P2 merus, P4 merus [0.7] × length of P3 merus. P2 merus, [0.7]–0.8 × carapace length, [4.9]–5.7 × as long as broad, [1.2] – 1.4 × as long as P2 propodus; P3 merus [4.4] × as long as broad, [1.3] × as long as P3 propodus; P4 merus [3.3] × as long as broad, [1.0] × as long as P4 propodus; extensor margin of P2 and P3 with row of spines, proximally diminishing, with prominent distal spine; P4 extensor margin irregular, with small distal spine; flexor margins of P2–4 serrated, each with distal spine; P4 lateral surface with median row of 3 small spines. Carpi with 2 or 3 spines on extensor margin on P2–3, unarmed on P4; distal spine prominent on P2–3, smaller on P4; row of small spines below extensor margin on lateral surface of P2–3, unarmed on P4; flexor margins P2–4 irregular, each with distal spine. Propodi stout, [4.4–4.8]4.0–5.0 × as long as broad; extensor margin serrated, unarmed; flexor margin with 2–4 slender movable spines in addition to distal pair. Dactyli 0.7–0.8 × length of propodi, ending in incurved, strong, sharp spine; flexor margin with 5 movable spines.

Eggs. Ov. F (MNHN-IU-2016-495) carried 5 eggs of 0.3 mm diameter.

Live colour. Unknown.

Genetic data. No data.

Distribution. Indian Ocean, Reunion Island, probably Red Sea, at 73– 77 m.

Remarks. The specimens identified and illustrated by Tirmizi (1966) as P. pusillus are very similar to the new species, P. hylas , although they are different from P. pusillus (see also Lewinshon 1969; Schnabel & Ahyong 2019). Unfortunately, we have not examined this material and the status of these specimens should be resolved in future studies. Phylladiorhynchus hylas has 3 spines on the epigastric ridge and closely resembles P. koumac , from New Caledonia, and P. pulchrus , from French Polynesia, Phillipines, and Vanuatu based on the 3 spines on the anterior branchial margin, gastric region strongly convex, the leaf-like rostrum (margins clearly convex and subapical spines present), and elevated ridges upraised dorsally. However, they can be easily differentiated by the number of epigastric spines, 3 spines in P. hylas and 5 spines in the other species. The specimens of P. hylas range from 1.6 to 1.9 mm postorbital carapace length.

Figures

FIGURE 16. Phylladiorhynchus hylas n. sp., holotype male 1.9 mm (MNHN-IU-2016-496): A, carapace and pleon, dorsal view. B, thoracic sternites 3 and 4. C, left cephalic region, showing antennular and antennal peduncles, ventral view. D, right Mxp3, lateral view. E, left P1, dorsal view. F, left P2, lateral view. G, left P3, lateral view. H, right P4, lateral view. I, dactylus of left P2, lateral view. Scale bar: A, E–H = 1.0 mm; B–D, I = 0.6 mm.

FIGURE 21. Rostrum, dorsal view. A, Phylladiorhynchus euryalus n. sp., paratype male 1.8 mm (UF34732). B, P. gustavi n. sp., paratype male 1.7 mm (UF9756). C, P. heptacanthus n. sp., holotype female 2.1 mm (MNHN-IU-2017-2534). D, P. hylas n. sp., paratype female 1.6 mm (MNHN-IU-2016-495). E, P. integrirostris (Dana, 1852), male 1.6 mm (UF15285). F, P. integrus (Benedict, 1902), ovigerous female 3.2 mm (MNHN-IU-2014-13853). G, P. iphiclus n. sp., holotype ovigerous female 2.3 mm (MNHN-IU-2019-2662). H, P. janiqueae n. sp., paratype male 1.8 mm (MNHN-IU-2016-482). I, P. jeffkinchi n. sp., paratype male 2.7 mm (MNHN-IU-2014-13565). J, P. joannotae n. sp., paratype male 2.1 mm (MNHN-IU-2014-20055). K, P. joannotae n. sp., holotype ovigerous female 2.1 mm (MNHN-IU-2014-13805). L, P. koumac n. sp., paratype male 1.5 mm (MNHN-IU- 2014-20121). Scale bars: 1 mm.