Tetriasidae Tsang & Naruse 2023, fam. nov.
Creators: name: Tsang, Ling Ming
name: Naruse, Tohru
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Tetriasidae

description: Family Tetriasidae fam. nov.
Diagnosis. Carapace (Fig. 2) rectangular to subtriangular, wider than long in both sexes, female carapace wider than that of male, dorsally convex longitudinally and transversely; regions clearly defined by grooves; front and buccal cavern proportionally wide, especially species with wider carapace (Figs. 2, 3A, 4A). Epistome wide transversely, buccal cavern semicircular, large (Figs. 3A, B, 4). Antennal article 1 oval, placed anterior to lateral part of epistome, posteromesial part of article 1 minutely protruding onto epistome posterior margin (Fig 4). Mxp3 (Fig. 3) longitudinally placed in buccal cavern (Fig. 3A, B). Maxilliped 3 ischium and merus fused but demarcated by superficial suture, merus produced mesio-subdistally; palp 3-segmented, each article about two-thirds length of merus; carpus length as long as distal width of merus, semi-triangular, attached to distolateral corner of merus; propodus widened distally; dactylus inserted at distolateral corner (in situ) of propodus, subrectangular. Exopod wide, subrectangular, distolateral corner concave, flagellum distinct. Ambulatory legs (Fig. 2) bilaterally symmetrical, stout to slender, length P3>P2>P4>>P5. Male pleonal somite and telson free, pleonal somites narrow horizontally, especially somites 4–6, telson (Fig. 3B) much wider, distally reaching suture between mxp3 ischium and merus when closed. G1 simple, slender, slightly curved distally. G2 small. Female pleon and telson free, covering most of thoracic sternum and distally entering buccal cavern in large female.
Type genus. Tetrias Rathbun, 1898, by present designation and monotypy.
Etymology. Rathbun (1898) did not provide an etymology of the type genus Tetrias. It is probably derived from the Latin word “Tetris”, an adjective derived from the word “teter”, which means ugly and not beautiful. It may also be from the Greek word “ Tetrix ”, which refers to a grouse (a compact dull-brown well camouflaged bird), and the name is used for a genus of family Tetrigidae (grasshopper). Considering ICZN Articles 29.3.3, 29.6 and Recommendation 29A, the entire genus name “ Tetrias ” is used as the stem of the family name Tetriasidae.
Remarks. Members of Tetriasidae fam. nov. are characterized by their setose appearance, rectangular to subtriangular and high carapace, and dorsal surface regions of the carapace being clearly demarcated by grooves in both sexes (Fig. 2; A. Milne-Edwards 1873: pl. 18, fig. 3; Rathbun 1898: pl. 43, fig. 12). Tetriasidae fam. nov. is distinct from other pinnotheroid families in its large mxp3 palp articles: the dactylus is enlarged, the carpus, propodus and dactylus are each about two-thirds length of the merus, and the dactylus is inserted at the distolateral corner of the propodus (in situ) (Fig. 3; Rathbun 1898: pl. 43, fig. 13). Most members of Pinnotheridae sensu stricto with 3-segmented mxp3 palps have the dactylus slender to narrowly spatulate and inserted subdistally on the lower margin of the propodus, for example, the pinnotherine Pinnotheres pisum (Linnaeus, 1767) (Becker & Türkay 2010: fig. 5C), the pinnixine Pinnixa cylindrica (Say, 1818) (Rathbun 1918: 160 fig. 99a), and the pinnixulaline Pinnixuala valerii (Rathbun, 1931) (Palacios Theil et al. 2016: fig. 9d) (also see Manning 1993; Ahyong & Ng 2007; Ahyong 2018; Ng & Ahyong 2022). The mxp3 dactylus of some pinnotherid species is either inserted at the distal end of the propodus or relatively enlarged (Table 1), but none of them simultaneously possess both character states. The pinnotherine Pinnaxoides chilensis (H. Milne Edwards, 1837) has a superficially similar mxp3 condition to tetriasids but is still markedly different because the distomesial corner of the propodus is produced (Rathbun 1898: pl. 43, fig. 10, as P. hirtipes; Garth 1957: fig. 9D; Takeda & Prince Masahito 2000: fig. 2C; Ng & Manning 2003: fig. 7A, B; Campos 2017: fig. 3d–f).
Tetriasidae fam. nov. also differs from the two pinnotheroid families in its unique combination of characters: the presence of a superficial suture between mxp3 ischium and merus (Fig. 3D; Rathbun 1898: pl. 43, fig. 13) (versus absent in pinnotherine pinnotherids, except for some species of Pinnaxodes, such as P. chilensis (H. Milne Edwards, 1837) (Campos 2017), P. floridensis Wells & Wells, 1961 (Wells & Wells 1961: fig. 2F, G), and P. gigas Green, 1992 (Green 1992: fig. 3F)); and the proportionally wider front, hence horizontally wider buccal cavern and widely separated eyes (Fig. 3A; A. Milne-Edwards 1873: pl. 18, fig. 3; Rathbun 1898: pl. 43, fig. 12; 1918: pl. 39, fig. 4, 5) (versus narrow in Parapinnixidae (Fig. 5A, also see remarks of Parapinnixidae) and pinnotherine pinnixines, such as Pinnixa cylindrica (Say, 1818) (Rathbun 1918: pl. 35, figs. 5–8)).
Tetriasidae fam. nov. is currently known by one genus and two species: Tetrias fischerii (A. Milne-Edwards, 1867) and T. scabripes Rathbun, 1898 (Ng et al. 2008). An ongoing revision of the genus will recognise more species of Tetrias from the Indo-West Pacific (T. Naruse, T. Komai and P. K. L. Ng, in preparation).
description: Published as part of Tsang, Ling Ming & Naruse, Tohru, 2023, Recognition of Parapinnixidae Števčić, 2005, and Tetriasidae fam. nov. in Pinnotheroidea De Haan, 1833 (Crustacea: Brachyura: Thoracotremata), pp. 540-558 in Zootaxa 5249 (5) on pages 545-548, DOI: 10.11646/zootaxa.5249.5.2, http://zenodo.org/record/7701343