Phylladiorhynchus acastus, 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 : 9-12

Phylladiorhynchus acastus n. sp.

( Figs. 2 , 11A , 54A )

Type material. Holotype. Chesterfield Islands , EBISCO Stn CP 2507, 24.7167°S, 159.7167°EE, 286 m, 7 October 2005: ov. F 2.4 mm (MNHN-IU-2014-13796).

Paratypes. Chesterfield Islands . EBISCO Stn CP 2493, 24.7333°S, 159.71667°E, 285–545 m, 6 October 2005: 1 ov. F 3.1 mm (MNHN-IU-2019-2692).—KANADEEP Stn CP 4930, 25.1333°S, 159.9167°E, 300 m, 3 September 2017: 1 M 2.1 mm (MNHN-IU-2017-2521).— Stn CP 4934, 25.0667°S, 159.91667°E, 290–300 m, 3–4 September 2017: 2 M 2.4–3.0 mm, 2 ov. F 2.2–2.9 mm (MNHN-IU-2017-2529).— Stn DW 4940, 25.4833°S, 159.8167°E, 310–320 m, 4 September 2017: 1 M 2.6 mm, 1 F 2.1 mm (MNHN-IU-2017-2634) .

Chesterfield Islands . EBISCO Stn DW 4943, 25.4167°S, 159.8500°E, 300–310 m, 4 September 2017: 3 M 2.4–2.9 mm (MNHN-IU-2017-2646) .

Other material. Philippines. MUSORSTOM 1 Stn 18, 13.9500°N, 120.2833°E, 150–159 m, 21 March 1976: 1 ov. F 2.0 mm (MNHN-IU-2014-13867) .

Papua New Guinea. KAVIENG Stn DW 4412, 02.5500°S, 150.6667°E, 500–600 m, 27 August 2014: 1 M 2.5 mm (MNHN-IU-2014-10017) .

Vanuatu. MUSORSTOM 8 Stn CP 1132, 15.6333°S, 167.0500°E, 161–182 m, 11 October 1994: 1 M 2.0 mm, 2 ov. F 2.0– 2.1 mm (MNHN-IU-2016-424).—MUSORSTOM 8 Stn CP 1133, 15.6500°S, 167.050°E, 174–210 m, 11 October 1994: 1 M 2.9 mm, 1 ov. F 2.4 mm (MNHN-IU-2019-2700) .

Chesterfield Islands . EBISCO Stn CP 4953, 24.1667°S, 159.6833°E, 270–320 m, 5 September 2017: 1 M 1.9 mm, 1 broken (MNHN-IU-2019-2688) .

New Caledonia. LIFOU Stn 1648, 20.9017°S, 167.0550°E, 150–200 m, 7 November 2000: 1 M 1.7 mm (MNHN- IU-2019-2676) .

Etymology. From the name Acastus, an Argonaut, son of Pelias and Anaxibia (Phylomache). 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 iridescent thick long setae. Gastric region flattened, with 4 transverse ridges: epigastric ridge indistinct, with 5 spines (1 median and 2 pairs of spines laterally); anterior protogastric ridge not medially interrupted (interrupted only in the paratype MNHN-IU-2014-10017), nearly extending laterally to carapace margin; anterior mesogastric ridge not medially interrupted, laterally interrupted by anterior branch of cervical groove, and continuing uninterrupted to first branchial spine; anterior metagastric ridge scale-like, sometimes followed by short scattered scales on posterior metagastric region. Mid-transverse ridge not interrupted, slightly medially depressed, preceded by shallow or indistinct cervical groove, followed by 2 not interrupted, or minutely interrupted ridges, interspersed with 1 short lateral ridge and sometimes few, short scattered scales. Lateral margins slightly convex, with 7 spines: first anterolateral spine well-developed, reaching anteriorly to 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 triangular, horizontal, dorsally flattish or slightly concave, 1.8–[2.0] × as long as broad, length 0.4–[0.5] and breadth 0.2–[0.3] that of carapace; lateral margins smooth and straight, with well-developed supraocular basal spines, subapical spines absent. Pterygostomian flap ending in acute tooth, upper margin smooth.

Thoracic sternum: 1.1 as wide as long. Sternite 3 moderately broad, [2.1]2.0–3.0 × as wide as long, anterior margin convex, with or without median feeble excavation. Sternite 4 widely contiguous to sternite 3; surface not depressed in midline, smooth; greatest width [2.7]2.0–3.0 × that of sternite 3, 2.0–[3.0] × as wide as long.

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

Eye: Eyestalk length about 1.0–[1.3] × broader than long, peduncle distally setose, not distinctly expanded proximally; maximum corneal diameter [1.0]1.0 × rostrum width, as wide as eyestalk.

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

Antenna: Article 1 with prominent mesial process, distally falling well short of lateralmost antennular spine. Article 2 with distinct distal spines laterally and mesially. Article 3 often with small distomesial spine. Article 4 unarmed.

Mxp3: Ischium with distinct distal spines on flexor and extensor margins. Merus 0.4–[0.6] × length of ischium, with well-developed distal spine on extensor margin and 2 strong spines on flexor margin.

P1: 3.5–3.6 (males), [2.7]–2.8 (females) × carapace length; subcylindrical, scales with dense short setae and 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]1.1–1.3 length of carapace, 1.7 × as long as carpus. Carpus 2.2–[2.4] × as long as wide. Palm 1.0–[1.1] × carpus length, [1.8]–2.4 × as long as broad. Fingers subequal in length to palm; fixed finger unarmed; movable finger with well-developed basal spine.

P2–4: Slender, subcylindrical, moderately setose and spinose. Meri successively shorter posteriorly: P3 merus 0.7 × length of P2 merus, P4 merus 0.9 × length of P3 merus. P2 merus, 0.8–0.9 × carapace length, 5.5–6.0 × as long as broad, 1.1–1.4 × as long as P2 propodus; P3 merus 5.4–5.5 × as long as broad, 1.4 × as long as P3 propodus; P4 merus [4.9]–5.4 × as long as broad, 1.1–1.4 × 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 distal spine; flexor margins of P2–4 irregular, each with distal spine; P4 lateral surface with median row of 4 small spines, absent in P2– 3. Carpi unarmed on extensor margin on P3–4, distal spine prominent on P2–3, minute on P4; row of small spines below extensor margin on lateral surface of P2–3, unarmed on P4; flexor margin unarmed. Propodi moderately slender, [4.8–5.4]4.8–6.0 × as long as broad; extensor margin irregular, unarmed or with 2–4 proximal spines; flexor margin with 2–4 slender movable spines in addition to distal pair. Dactyli [0.6]–0.7 × length of propodi, ending in incurved, strong, sharp spine; flexor margin with 6–7 movable spines.

Eggs: Ov. F carried approximately 5– 12 eggs of 0.3–0.4 mm diameter.

Live colour. Base colour of carapace and pleon orange. Rostrum light orange. P1 light orange, fingers with reddish strip, distal tips whitish. P2–4 light orange, propodi and dactyli with orange bands.

Genetic data. COI and 16S, Table 1.

Distribution. Philippines, Papua New Guinea, Vanuatu, Chesterfield Islands and New Caledonia, from 150 to 600 m.

Remarks. Phylladiorhynchus acastus belongs to the group of species that has 5 epigastric spines, the rostrum margins are straight and without subapical spines, 3 spines on the anterior branchial margin, and the Mxp3 merus with two prominent spines along the flexor margin. Phylladiorhynchus acastus closely resembles to P. argus , from French Polynesia, New Caledonia and Chesterfield Islands, and P. paula , from the southwestern Indian Ocean (see the differences under the Remarks of P. paula ).

The specimen from Papua New Guinea has the anterior protogastric ridge of the carapace interrupted and a pattern of setae slightly different than specimens from the Phillipines, Vanuatu and New Caledonia. Since there is a single specimen from this population and we were not able to obtain molecular data, we have identified this specimen as P. acastus until additional material can be collected from Papua New Guinea. Furthermore, the specimens from the Chesterfield Islands (KANADEEP, Stn CP4934, Stn DW4943) have the extensor margin of the P2–4 propodi armed with 2–4 proximal spines, whereas this margin is unarmed in the other species, suggesting that this character could be variable.

The genetic divergences between P. acastus and other species were always higher than 12% (COI) and 3% (16S), P. paula was the closest clade. The two sequences of P. acastus from New Caledonia and Chesterfield Islands diverged 0.15% for COI and 0% for 16S. The specimens of P. acastus range in size from 1.7 to 2.9 mm postorbital carapace length.

Figures

FIGURE 2. Phylladiorhynchus acastus n. sp., holotype ovigerous female, 2.4 mm (MNHN-IU-2014-13796): 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, right P1, dorsal view. F, left P2, lateral view. G, left P4, lateral view. H, dactylus of right P2, lateral view. Scale bar: A, E, F, G = 1.0 mm; B–D, H = 0.6 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.

FIGURE 54. Colour in life, dorsal view. A. Phylladiorhynchus acastus n. sp. Papua New Guinea, male 2.5 mm (MNHN-IU- 2014-10017). B, Phylladiorhynhus barbeae n. sp. Papua New Guinea, paratype male 1.6 mm (MNHN-IU-2014-13810). C, Phylladiorhynhus barbeae n. sp. Papua New Guinea, male 2.5 mm (MNHN-IU-2014-13813). D, Phylladiorhynchus gustavi n. sp. French Polynesia, male 2.3 mm (UF16338). E, Phylladiorhynchus janiqueae n. sp. Walter shoal, male 1.8 mm (MNHN-IU- 2014-13840). F, Phylladiorhynchus jeffkinchi n. sp. Papua New Guinea, ovigerous female 2.2 mm (MNHN-IU-2014-2176). G, Phylladiorhynchus joannotae n. sp. French Polynesia, ovigerous female 2.2 mm (UF15544). H, Phylladiorhynchus joannotae n. sp. New Caledonia, female 1.0 mm (MNHN-IU-2014-20147). I, Phylladiorhynchus koumac n. sp. New Caledonia, male 1.5 mm (MNHN-IU-2014-20121).