Phylladiorhynchus cepheus, 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 : 32-34

Phylladiorhynchus cepheus n. sp.

( Figs. 10 , 11K )

Type material. Holotype. French Polynesia. BENTHAUS Stn DW 2009, 22.5333°S, 151.3333°W, 320–450 m, 24 November 2002: ov. F 3.4 mm (MNHN-IU-2014-13860).

Paratypes. French Polynesia. BENTHAUS Stn DW 1945, 23.8167°S, 147.7000°W, 120–500 m, 17 November 2002: 1 M 2.4 mm (MNHN-IU-2014-13858) .

Other material. French Polynesia. BENTHAUS Stn DW 2006, 22.4500°S, 151.3167°W, 350–450 m, 24 November 2002: 1 M 2.7 mm, 1 ov. F 2.2 mm (MNHN-IU-2014-13882).— Stn DW 2009, 22.5333°S, 151.3333°W, 320–450 m, 24 November 2002: 1 ov. F 2.5 mm (MNHN-IU-2019-2686), 1 ov. F 3.1 (MNHN-IU-2014-13732) .

Etymology. From the name Cepheus, an Argonaut, son of Coronus. The name is considered a substantive in apposition.

Description. Carapace: [1.1]–1.2 × as long as broad, transverse ridges with dense short setae. Gastric region flattened, with 3–4 transverse ridges: epigastric ridge indistinct, with a few plumose setae, and 4–5 spines (rarely 1 median spine, usually 1 median produced process or scale with thick setae, and 2 pairs of spines laterally); anterior protogastric ridge not medially interrupted; anterior mesogastric ridge not medially interrupted, laterally interrupted by cervical groove; anterior metagastric ridge scale-like, otherwise absent, with short scattered scales in anterior metagastric area. Mid-transverse ridge not interrupted, preceded by shallow or undistinct cervical groove, followed by 2 uninterrupted or minutely interrupted ridges, interspersed with 1–2 short lateral ridges and few, short scattered scales. Lateral margins straight, with 7 spines: first anterolateral spine well-developed, reaching or exceeding level of lateral orbital spine, second spine (hepatic) small, slightly dorsomesially from lateral margin, and followed by 5 branchial spines (3 anterior and 2 posterior). Rostrum leaf-like to sub-triangular, horizontal, dorsally flattish or slightly concave [1.5]–1.9 × as long as broad, length [0.4]–0.5 and breadth 0.2–[0.3] that of carapace; lateral margins smooth and slightly convex, with well-developed supraocular basal spines and minute subapical spines. Pterygostomian flap ending in sharp tooth; upper margin smooth.

Thoracic sternum: As wide as long. Sternite 3 moderately broad [2.3]2.0–2.5 × as wide as long, anterior margin convex. Sternite 4 widely contiguous to sternite 3; surface depressed in midline, smooth; greatest width 2.4–[2.8] × that of sternite 3, 3.0 × as wide as long.

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

Eye: Eyestalk length about 1.0–[1.1] × broader than long, peduncle distally setose, not distinctly expanded proximally; maximum corneal diameter [0.8]–0.9 × rostrum width, as wide as eyestalk.

Antennule: Article 1.4 × longer than wide, with 5 distal spines: distomesial spine well-developed; proximal lateral spine small, always present.

Antenna: Article 1 with prominent mesial process, nearly reaching end of lateralmost antennular spine. Article 2 unarmed, sometimes with minute distolateral spine or granule. Articles 3 and 4 unarmed.

Mxp3: Ischium with distinct distal spines on flexor and extensor margins. Merus 0.5–[0.6]× length of ischium at midlength, extensor margin with well-developed distal spine, flexor margin with 2 strong spines.

P1: slender 4.5–5.0 × carapace length (males), [3.7]3.5–3.9 (females); subcylindrical, spiny and with scattered long stiff setae and dense plumose thick setae; merus, carpus and palm with spines along mesial, dorsal and lateral surfaces, mesial spines usually stronger than others. Merus [1.4]1.3–1.9 length of carapace, [2.1]–2.5 × as long as carpus. Carpus [3.3]2.4–3.3 × as long as wide. Palm [1.3]–1.4 × carpus length, [3.9]3.3–4.6 × as long as broad. Fingers [0.7]0.6–0.8 × palm length; fixed and movable fingers each with basal spine.

P2–4: Slender, subcylindrical, moderately setose and spinose. Meri successively shorter posteriorly: P3 merus [0.5]–0.6 × length of P2 merus, P4 merus 0.9–[1.0] × length of P3 merus. P2 merus, [0.8]–1.0 × carapace length, [5.4]–6.3 × as long as broad, [1.1]–1.3 × as long as P2 propodus; P3 merus [5.1]–5.3 × as long as broad, 1.2 × as long as P3 propodus; P4 merus 5.5–[5.9] × as long as broad, 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, distal spine absent; flexor margins with distal spine in P2–3, absent in P4; P4 lateral surface with 3 small spines, absent in P2–3. Carpi with 8–9 small spines on extensor margin on P2–3 (serrated), with 2 small spines on P4; distal spine prominent on P2, smaller or absent in P3–4; flexor margin unarmed. Propodi slender, [7.5–8.0]7.8–8.0 × as long as broad; extensor margin irregular, usually unarmed; flexor margin with 2–3 slender movable spines in addition to distal pair. Dactyli0.4–0.5 × length of propodi, ending in incurved, strong, sharp spine; flexor margin with 6–7 movable spines.

Eggs: Ov. F carried approximately 30– 40 eggs of 0.3–0.4 mm diameter.

Live colour. Unknown.

Genetic data. COI and 16S, Table 1.

Distribution. French Polynesia, from 230 to 500 m.

Remarks. Phylladiorhynchus cepheus belongs to the group that present the epigastric ridge with 4 spines and often one median process or scale with thick plumose setae (rarely with 5 spines), 3 spines on the anterior branchial margin of the carapace and the Mxp3 merus with two prominent spines along the flexor margin. The specimens range from 2.4 to 3.4 mm postorbital carapace length. Phylladiorhynchus cepheus closely resembles to P. butes , from New Caledonia, Chesterfield Islands, Indonesia and French Polynesia, and P. maestratii , from New Caledonia (see the differences under the Remarks of P. maestratii ).

Figures

FIGURE 10. Phylladiorhynchus cepheus n. sp., A–D, G–I, holotype ovigerous female 3.4 mm (MNHN-IU-2014-13860): A, carapace and pleon, dorsal view. B, thoracic sternites 3 and 4. C, right cephalic region, showing antennular and antennal peduncles, ventral view. D, right Mxp3, lateral view. E, right P1, merus and carpus, dorsal view. F, right P1, propodus and dactylus, dorsal view right. G, left P2, lateral view. H, left P3, lateral view. I, left P4, lateral view. J, dactylus of right P2, lateral view. Scale bars: 1.0 mm.

FIGURE 11. Rostrum, dorsal view. A, Phylladiorhynchus acastus n. sp., paratype male 2.6 mm (MNHN-IU-2017-2646). B, P. amphion n. sp., holotype male 2.4 mm (WAM C55691). C, P. amphion n. sp., paratype female 2.6 mm (WAM C53887). D, P. argus n. sp., paratype ovigerous female 3.5 mm (MNHN-IU-2014-23836). E, P. asclepius n. sp., paratype ovigerous female 2.1 mm (UF22401). F, P. australis Schnabel & Ahyong, 2019, female 4.0 mm (MNHN-IU-2019-2596). G, P. bahamut n. sp., holotype male 2.5 mm (UF40205). H, P. barbeae n. sp., paratype male 2.2 mm (MNHN-IU-2019-2643). I, P. boucheti n. sp., paratype ovigerous female 2.5 mm (MNHN-IU-2017-3830). J, P. butes n. sp., paratype female 2.1 mm (MNHN-IU-2016-449). K, P. cepheus n. sp., paratype male 2.4 mm (MNHN-IU-2014-13858). L, P. eneus n. sp., paratype male 2.1 mm (MNHN-IU- 2014-13801). Scale bars = 1 mm.