Parapinnixidae Števčić, 2005

Tsang, Ling Ming & Naruse, Tohru, 2023, Recognition of Parapinnixidae Števčić, 2005, and Tetriasidae fam. nov. in Pinnotheroidea De Haan, 1833 (Crustacea: Brachyura: Thoracotremata), Zootaxa 5249 (5), pp. 540-558 : 548-549

Family Parapinnixidae Števčić, 2005

Parapinnixini Števčić, 2005: 118.

Diagnosis. Carapace rounded-trapezoidal to ovoid, wider than long in both sexes, female wider than male; dorsally convex longitudinally and transversely; regions not well defined; front and buccal cavern proportionally narrow ( Figs. 5 , 6 ). Epistome narrow transversely, buccal cavern subtriangular, small ( Figs. 5A , 6 ). Antennal article 1 oval, separated from buccal cavern by lateral end of epistome and anteromesial angle of pterygostomial region ( Fig 6 ). Mxp3 ( Fig. 5 ) completely filling buccal cavern when closed ( Fig. 5A ); ischium and merus completely fused to form ischiomerus; ischiomerus triangular, produced mesioproximally, palp 2- or 3-segmented, small, dactylus, if present, attached to distal end of propodus; exopod short, stout. Ambulatory legs bilaterally symmetrical, stout, length P2>P3>P4>>P5. Male pleonal somites and telson all free, strongly narrowed from somite 3 to 4, somites 5 and 6 narrow; telson much longer than combined length of somites 4–6, almost distally reaching imaginary line joining anterior angles of cheliped coxae. G1 long, slender, strongly bent mesially at proximal one-third to one-quarter, tapering distally. G2 small. Female pleonal somites and telson free, lateral margins converging distally from somite 3 to telson, forming triangular outline, leaving wide space between margins of pleon and thoracic sternum, telson distally reaching far short from buccal cavern.

Type genus. Parapinnixa Holmes, 1895 , by original designation.

Genera included. Parapinnixa Holmes, 1895 ; Sakaina Serène, 1964 .

Remarks. The Parapinnixidae Števčić, 2005 (originally established as a tribe in Pinnotheridae ) currently contains 10 species of Parapinnixa Holmes, 1895 from the western Atlantic and the eastern Pacific oceans ( Schmitt et al. 1973; Werding & Müller 1990; Campos 1994; Thoma et al. 2005), with a questionable record of P. affinis Holmes, 1900 , from Siberia ( Kobjakova 1967), seven species of Sakaina Serène, 1964 , from eastern coast of Eurasia ( Kim & Sakai 1972; Schmitt et al. 1973; Jiang & Liu 2011). They have a characteristic appearance with a roundedtrapezoidal to ovoid carapace contour and the ambulatory legs decreasing in length posteriorly. The most distinctive feature of Parapinnixidae is the very small mxp3 with triangular ischiomerus that is completely fused and produced mesioproximally. The mxp3 palp is also small and 2- or 3-segmented, and the distal article inserts at the tip of the preceding article. The buccal cavern is also small ( Fig. 5A ), for example, Parapinnixa nitida (Lockington, 1876) ( Holmes 1895: pl. 20, figs. 8, 9), Parapinnixa hendersoni Rathbun, 1918 ( Rathbun 1918: fig. 59, pl. 26, fig. 1, 3, 4), Sakaina japonica Serène, 1964 ( Serène 1964: fig. 22A; Jiang & Liu 2011: fig. 7B). In Pinnotheridae , the mxp3 is generally large, the palp is distinct, and the ischiomerus or merus are proportionally larger, and usually produced mesiosubdistally, forming a somewhat hatchet-shape, or subrhomboidal to subrectangular and distally wider or at least not distinctly narrower than the proximal part. The buccal cavern is large and semicircular, for example, the pinnotherine Pinnotheres pisum ( Linnaeus, 1767) (Becker & Türkay 2010: figs. 1C, 5C), the pinnixine Pinnixa cylindrica (Say, 1818) ( Rathbun 1918: 160 fig. 99a, pl. 35, fig.8), and the pinnixulaline Pinnixuala valerii ( Rathbun, 1931) ( Palacios Theil et al. 2016: fig. 9d).

Another diagnostic character of Parapinnixidae is the very slender G1 that is markedly bent mesially at the proximal one-third to one-quarter ( P. cubana Campos, 1994 ( Campos 1994: fig. 2F); P. magdalenensis Werding & Müller, 1990 ( Werding & Müller 1990: fig. 1e); S. japonica ( Serène 1964: fig. 22C; Jiang & Liu 2011: fig. 7E); S. yokoyai ( Takeda et al. 1991: fig. 4E)). The G1 of Pinnotheridae and Tetriasidae fam. nov. is generally simple and straight to broadly curved, but not marked bent at the subproximal part, for example, the pinnotherine Pinnotheres pisum ( Linnaeus, 1767) (Becker & Türkay 2010: fig. 4C, D), the pinnixine Pinnixa cylindrica (Say, 1818) ( Heard & Manning 1997: fig. 1e), and the pinnixulaline Pinnixuala valerii ( Rathbun, 1931) ( Palacios Theil et al. 2016: fig. 9a).

Figures

FIGURE 5. Cephalothorax and third maxilliped (mxp3) of Sakaina yokoyai (Glassell, 1933), RUMF-ZC-5827, female, 6.5 × 10.2 mm, Oshoro, Hokkaido. A, cephalothorax, anteroventral view; B, mxp 3, left, outer view (setae partially trimmed); C, mxp 3, left, inner view. c, carpus; d, dactylus; e, exopod; epm, epistome posterior margin; im, ischiomerus; p, propodus; pm, pterygostomial margin.

FIGURE 6. Anterior part of cephalothorax and appendages of Sakaina yokoyai (Glassell, 1933). RUMF-ZC-5827, left side, female, 6.5 × 10.2 mm, Oshoro, Hokkaido.A, anterior view; B, anteroventral view. a1, antennal article 1; epm, epistome posterior margin; pm, pterygostomial margin. Arrowhead, possible opening for nephridiopore.