Austrotheres, Ahyong, 2018

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 546-547

Austrotheres new genus

Diagnosis. Female: Carapace subcircular to sub-hexagonal, as long as or slightly longer than wide, posterior margin rounded, slightly projecting; sclerotised, hard; longitudinally vaulted, with weak to distinct epigastric ridge; front slightly produced anteriorly, subtruncate; anterolateral margins well defined, lateral surfaces near vertical; dorsal surface smooth or granulated, regions poorly to moderately defined, glabrous. Eyes visible in dorsal view. Antennal flagellum reaching beyond mid-height of eye but not dorsal margin of orbit. Maxilliped 3 ischiomerus completely fused, without trace of suture; palp 2-segmented; carpus shorter than propodus; propodus spatuliform, widened distally; exopod flagellum 2-segmented, distally setose. Chelipeds equal, stout, robust, dactylus and pollex with simple, pointed tips. Pereopods 2–5 symmetrical from left to right, slightly compressed, ovate in cross-section; dactyli with simple, spiniform apices, subequal or pereopod 5 dactylus longer. Pereopod 5 articulating with body at same level as pereopod 4. Abdomen with 6 free somites and telson; in adults, widest at somites 4 and 5, covering bases of walking legs. Gonopore simple, ovate, on sternite 5 near mesial end of sternite 5/6 suture. Male: similar to female, though smaller, carapace posterior margin flattened; G1 straight, flattened, distinctly narrowing at distal 1/4, with distinct step followed by lanceolate tip oriented along main axis; G2 without exopod.

Type species. Austrotheres pregenzeri new species, by present designation.

Etymology. An arbitrary combination of of the Latin, australis , southern, and the suffix - theres, alluding to the southern distribution of the species of the genus. Gender: masculine.

Composition. Austrotheres holothuriensis ( Baker, 1907) new combination, A. pregenzeri new species.

Remarks. Austrotheres closely resembles Ostracotheres in overall carapace shape (rounded to ovate, as long as wide or slightly longer than wide, with well-defined anterolateral margins and near vertical lateral surfaces), the 2-segmental maxilliped 3 flagellum, and similar, left–right symmetrical walking legs, but differs in having a relatively hard (versus firm but poorly sclerotised) carapace with an epigastric ridge, glabrous (versus finely setose) carapace surface, and the form of the G1. Whereas the G1 apex in Ostracotheres is blunt with a short, sharp, anterolaterally directed papilla ( Fig. 2L, M , 4J ), the G 1 in Austrotheres is distally lanceolate, and approximately in line with the G1 axis ( Fig. 6O, P , 7O, P ). Austrotheres also similar to the monotypic ascidian associate, Tunicotheres Campos, 1996 (type species: T. moseri ( Rathbun, 1918) from the western Atlantic. Species of both genera have natatory setae on pereopods 3–4 and a somewhat polygonal carapace, but Tunicotheres is readily separated by having pereopod 5 articulating above the level of pereopod 4, rather than at the same level as in Austrotheres .

Unlike most other pinnotherids, in which females rarely or never leave the host and have weakly sclerotised exoskeletons, both sexes in Austrotheres have a comparatively hard carapace, natatory setae on the walking legs, and apparently frequently venture outside judging from the provenance of material reported below. Such morphology and behaviour in Austrotheres is consistent with reproductive strategies exhibited by a number of other pinnotherids, such as Tumidotheres Campos, 1989 and Fabia subquadrata Dana, 1851 from the eastern Pacific, which temporarily leave their host for copulatory swarming ( Campos, 1989, 2016). Species of Austrotheres may also have similar reproductive strategies, but too little is presently known of their biology to make reliable inferences about behaviour. Both species of Austrotheres occur in the southern half of Australia ( Fig. 5 ).

Figures

Fig. 2. Ostracotheres tridacnae (Rüppell, 1830). A–I, female, cl 11.8 mm, cw 11.7 mm, Red Sea, MNHN-IU-2016-10949; J–K, male, cl 8.0 mm, cw 7.6 mm, Red Sea, MNHN-IU-2016-10950; L–O, male, cl 12.1 mm, cw 12.1 mm, Red Sea, NHMD-229248. A, J, dorsal habitus; B, right cheliped, anterior view; C–F, right pereopods 2–5; G, right maxilliped 3; H, carapace, right lateral view; I, cephalothorax, anterior view; K, male abdomen; L, left G1, sternal view; M, left G1, tip, abdominal view; N, left G2, sternal view; O, right pereopod 5 dactylus. Scale: A–F, H, J, K = 4.0 mm; G, I, L, N, O = 1.0 mm; M = 0.5 mm.

Fig. 4. Ostracotheres cynthiae Nobili, 1906. A–H, ovigerous female, cl 7.8 mm, cw 8.4 mm, Gulf of Suez, MNHN B10562; I, female lectotype, cl 6.8 mm, cw 8.0 mm, Djibouti, MNHN-IU-2014-11992; J, male, Gulf of Suez; K–N, female, cl 3.8 mm, cw 3.7 mm, Red Sea, NHMW 10062; O, ovigerous female, cl 4.0 mm, cw 4.0 mm, Red Sea, NHMW 10063. A, dorsal habitus; B, left chelipid, anterior view; C, cephalothorax, anterior view; D, left maxilliped 3; E–H, right pereopods 2–5; I, right maxilliped 3; J, left G1, sternal view; K, left pereopod 4 dactylus; L, left pereopod 5 dactylus; M, carapace, right lateral view; N–O, carapace front, dorsal view. (D–H, J, after Monod, 1938: fig. 25). Scale: A, B = 2.0 mm; C, D, I, J, = 0.5; E–H, M–O = 1.0 mm; K–L = 0.5 mm.

Fig. 6. Austrotheres pregenzeri new species. A–J: female holotype, cl 10.5 mm, cw 10.2 mm, Port Stephens, AM P72226. K–Q: male paratype, cl 4.9 mm, cw 4.6 mm, Botany Bay, AM P63040. A, K, dorsal habitus; B, carapace, right lateral view; C, cephalothorax, anterior view; D, M, right maxilliped 3; E, right cheliped, anterior view; F–I, right pereopods 2–5; J, female abdomen; L, left cheliped, anterior view; N, male abdomen; O, right G1, sternal view; P, right G1 tip, mesial view; Q, right G2, sternal view. Scale: A–B, J = 2.0 mm; C–I, K, L, N = 1.0 mm; M = 0.5 mm; O–Q = 0.25 mm.

Fig. 7. Austrotheres holothuriensis (Baker, 1907) new combination. A–G, female lectotype, cl 8.3 mm, cw 7.2 mm, Gulf St. Vincent, SAM C1389; H–N, male paralectotype, cl 6.2 mm, cw 6.5 mm, Gulf St. Vincent, SAM C1389; O–Q, male, cl 5.5 mm, cw 5.2 mm, Shoreham, AM G5724; R–S, female, cl 13.6 mm, cw 12.6 mm, Tasmania, AM P4047. A, H, carapace, dorsal view; B, I, left maxilliped 3; C, J, right cheliped, anterior view; D, right pereopod 2; E, K, right pereopod 3; F, L, right pereopod 4; G, M, right pereopod 5; N, male abdomen; O, right G1, sternal view; P, right G1 tip, mesial view; Q, right G2, sternal view; R, carapace, right lateral view; S, cephalothorax, anterior view. A, C–H, J–M = 2.0 mm; B, I, N = 1.0 mm; O–Q = 0.5; R = 2.8 mm; S = 1.4 mm.

Fig. 5. Distribution of species of Austrotheres new genus. (■) A. holothuriensis (Baker, 1907) new combination; (●) A. pregenzeri new species.