Phylladiorhynchus amphion, 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 : 12-13

Phylladiorhynchus amphion n. sp.

( Figs. 3 , 11B–C )

Type material. Holotype. Western Australia , S end Ashmore Reef, Stn 134/K13, 12.2960°S, 123.0272°E, 12 m, 30 September 2013: M 2.4 mm ( WAM C55691).

Paratypes. Western Australia, Vulcan Shoal, Stn 146/K13, 12.7993°S, 124.2667°E, 19 m, 6 October 2013: 1 ov. F 2.2 mm ( WAM C55694) .— Eugene McDermont Shoal, Stn 147/K13, 13.0769°S, 124.5835°E, 22 m, 6 October 2013: 1 M 2.8 mm ( WAM C55695) .— Imperieuse Reef. Stn 157/K14-T2, 17.5070°S, 118.9658°E, 12–15 m, 5 October 2014: 1 M 1.8 mm, 2 ov. F 2.1–2.2 mm ( WAM C53891) .— Rowley Shoals, Clerke Reef, Stn 154/K14, 17.2799°S, 119.3766°E, no depth, 4 October 2014: 1 M 2.4 mm, 1 F 2.6 mm ( WAM C53887) .

Other material. Western Australia , W Point Ashmore, Stn 135/K13, 12.2437°S, 122.2437°E, no depth, 1 October 2013: 1 M 2.2 mm, 1 ov. F 2.4 mm ( WAM C53888).—Rowley Shoals, Clerke Reef, Stn 151/K14, 17.2519°S, 119.3590°E, 12–20 m, 2 October 2014: 1 M 2.4 mm, 1 F 2.1 mm ( WAM C56280) .

Etymology. From the name Amphion, an Argonaut, son of Hyperasius and Hypso. The name is considered a substantive in apposition.

Description. Carapace: as long as or slightly broader than long, sexually dimorphic (wider on females) 0.9–1.0 (males), [0.8]–0.9 (females) × as long as broad; transverse ridges with dense short setae and few scattered thick setae. Gastric region slightly convex with 4 transverse ridges: epigastric ridge distinct with 2 median spines and some lateral short scales, often followed by small scattered scales; anterior protogastric ridge not medially interrupted, nearly extending laterally to carapace margin, often followed by small scattered scales; anterior mesogastric ridge not medially interrupted, continuing to first branchial spine; anterior metagastric often medially interrupted, sometimes followed by short scattered scales on posterior metagastric region. Mid-transverse ridge not interrupted, slightly medially depressed, cervical groove indistinct, followed by 2 not interrupted or minutely interrupted ridges, interspersed with 2 short lateral ridges and sometimes few, short scattered scales. Lateral margins convex, with 6–7 distinct spines: first anterolateral spine well-developed, reaching anteriorly to level of lateral orbital spine, second spine (hepatic) well-developed, slightly dorsomesially from lateral margin, and followed by 4–5 branchial spines (3 anterior and 1–2 posterior). Rostrum leaf-like, horizontal, dorsally flattish or slightly concave, sexually dimorphic (shorter and wider in females) [1.6]–1.8 (males), 1.2–1.4 (females) × as long as broad, length [0.4]0.3–0.5 and breadth 0.2–[0.3] that of carapace; lateral margins smooth and convex, with well-developed supraocular basal spines and small subapical spines. Pterygostomian flap ending in blunt tooth, upper margin smooth.

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

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

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

Antennule: Article 1 slightly longer than wide, with 5 distal 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 well-developed distomesial and distolateral spines. Article 3 with distomesial spine. Article 4 unarmed.

Mxp3: Ischium with distinct distal spines on flexor and extensor margins. Merus 0.8 × length of ischium, with well-developed distal spine on extensor and flexor margins.

P1: 3.0–[3.2] (males), 2.0–2.2 (females) × carapace length; subcylindrical, spiny and 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 0.8–[1.2] length of carapace, [1.6]1.5–1.8 × as long as carpus. Carpus 1.7–[2.2] × as long as wide. Palm [1.1]–1.2 × carpus length, 1.4–[2.0] × as long as broad. Fingers 0.8 × palm length; fixed finger with 1–2 basal spines; movable finger with 3 spines.

P2–4: stout, setose and spinose. Meri successively shorter posteriorly: P3 merus 0.8–[0.9] × length of P2 merus, P4 merus [0.9]0.9 × length of P3 merus. P2 merus, 0.6 × carapace length, [3.0]–3.8 × as long as broad, 1.1–[1.2] × as long as P2 propodus; P3 merus 2.8–[3.2] × as long as broad, 1.0–[1.2] × as long as P3 propodus; P4 merus 3.5 × as long as broad, 1.1 × 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, unarmed; flexor margin irregular, with distal spine on P2–3, absent or small on P4. Carpi with 2–4 spines on extensor margin on P2–3, unarmed on P4; distal spine prominent on P2–3, absent on P4; row of granules below extensor margin on lateral surface of P2–4; flexor margin unarmed. Propodi stout, [4.0–4.3]3.9–4.6 × as long as broad; extensor margin irregular; flexor margin with 3–4 slender movable spines in addition to distal pair. Dactyli [0.5–0.7]0.5–0.6 × length of propodi, ending in incurved, strong, sharp spine; flexor margin with dactylar spines at basis of 5–6 movable spines.

Eggs: Ov. F carried approximately 10– 25 eggs of 0.3–0.5 mm diameter.

Live colour. Unknown.

Genetic data. COI and 16S, Table 1.

Distribution. Western Australia, from 12 to 22 m.

Remarks. Phylladiorhynchus amphion belongs to the group of species having 2 epigastric spines, 1 hepatic spine, 3 spines on anterior branchial margin of the carapace and dactylar spines along the flexor margin of P2–4 dactyli. The specimens range from 1.8 to 2.8 mm postorbital carapace length. The closest relative is P. joannotae from French Polynesia, Guam Island, Papua New Guinea, Vanuatu and New Caledonia (see the differences under the Remarks of this species). The two sequences of P. amphion from Western Australia diverged 1.8% for COI and 1.2% for 16S.

Figures

FIGURE 3. Phylladiorhynchus amphion n. sp., A, C–J, holotype male 2.4 mm (WAM C55691); B, paratype ovigerous female 2.1 mm (WAM C53891): A, B, carapace and pleon, dorsal view. C, thoracic sternites 3 and 4. D, left cephalic region, showing antennular and antennal peduncles, ventral view. E, right Mxp3, lateral view. F, left P1, dorsal view. G, right P2, lateral view. H, right P3, lateral view. I, right P4, lateral view. J, dactylus of right P2, lateral view. Scale bar: A, B, F–I = 1.0 mm; C–E, J = 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.