Hadroplax, Castro, 2007

Castro, Peter, 2007, A reappraisal of the family Goneplacidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) and revision of the subfamily Goneplacinae, with the description of 10 new genera and 18 new species, Zoosystema 29 (4), pp. 609-774 : 696-698

Genus Hadroplax n. gen.

Gonoplax [sic] – Miers 1886: 245 (part).

Goneplax – Tesch 1918: 181 (part). — Balss 1957: 1656 (part). — Serène 1964: 189, 190; 1968: 89 (part). — Guinot 1969b: 520; 1971: 1081 (part). — Dai et al. 1986: 376 (part). — Dai & Yang 1991: 406 (part). — Karasawa & Kato 2003b: 130 [in list], 140 [in list], 141 [in table] (part). — Komatsu & Takeda 2003: 1243 (part).

Teschia Števčić, 2005: 134 (nomen nudum). TYPE SPECIES. — Goneplax sinuatifrons Miers, 1886

(by present designation and by monotypy; gender feminine).

SPECIES INCLUDED . — Hadroplax sinuatifrons ( Miers, 1886) n. comb.

The genus is restricted to the Indo-West Pacific region.

ETYMOLOGY. — From hadros, Greek for “well developed” or “bulky”, in reference to the large basal antennular articles that do not fit into the antennular fossae, a characteristic of the type species, and plax, Greek for “plate” or “tablet”, derived from the generic name Goneplax to denote that the type species of the new genus was formerly included in Goneplax .

DESCRIPTION

Carapace ( Miers 1886: pl. 20, fig. 2, as Gonoplax [sic] sinuatifrons ) transversely rectangular, wider

Revision of Goneplacinae ( Crustacea, Brachyura)

than long; widest at conspicuous outer orbital teeth; front slightly deflected ventrally, sinuous, may be marked by slight median emargination. Notch between front, inner edge of supraorbital border absent. Orbits wide, greatly expanded distally; supraorbital borders conspicuously sinuous; suborbital borders sinuous, with short, wide inner tooth not visible dorsally. Dorsal surface of carapace smooth, moderately convex, without clear indication of regions. Outer orbital angle with conspicuous, anteriorly directed, acute tooth. Nearly straight lateral borders without anterolateral teeth. Basal antennular articles large so they cannot be folded into enlarged fossae ( Serène & Umali 1972: fig. 73). Basal antennal article short, distalmost (third) article nearly reaches front. Eye peduncles ( Miers 1886: pl. 20, fig. 2b, as G. sinuatifrons ) relatively long, only slightly shorter than front (0.8 front width); cornea reniform, dorso-ventrally flattened, nearly divided into anterior, posterior portions. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Third maxillipeds nearly completely close the buccal cavern. No obvious stridulating mechanism other than possible rubbing of proximal portion of cheliped (P1) merus against pterygostomial ridge. Thoracic sternum wide. Median sulcus on thoracic sternite 4 absent; suture 2/3 fused but visible in some specimens, sutures 4/5, 5/6, 7/8 interrupted medially, 6/7 complete. Anterior end of sterno-abdominal cavity anterior to thoracic sternite 4. Cheliped fingers long, slender, shovel-like, curved, shorter than elongated propodus; carpus with conspicuous, acute tooth on inner margin; merus with conspicuous tooth on inner (ventral) margin. Dorsal margins of ambulatory leg (P2-P4) meri with acute distal tooth, P5 unarmed; dactyli of P2-P4 slender, with carina on each side. Male abdomen ( Tesch 1918: pl. 9, fig. 2 a; Serène & Umali 1972: fig. 77, as G. sinuatifrons ) with 6 freely-movable somites plus telson, wide, somites 4-6 gradually decreasing in width from somite 3 (widest somite). Telson wide, wider than long. Somite 3 covers space between P5 coxae, somite 2 narrower than somite 3; somites 1, 2 leave large portion of thoracic sternite 8 visible. G1 ( Serène & Umali 1972: figs 78, 79, as G. sinuatifrons ) long, slender, slightly broadened proximally, bent outwardly at distal end. G2 ( Serène & Umali 1972: figs 80, 81, as G. sinuatifrons ) slender, slightly longer than G1, flagellum slightly longer than proximal part (peduncle), expanded. Penis arising from P5 coxa, moderate size, soft proximal expansion. Female abdomen with 6 freely-movable somites, wide. Telson much wider than long. Somite 3 covers space between P5 coxae, somite 2 slightly narrower than somite 3; somites 1, 2 leave small portion of thoracic sternite 8 visible. Vulva of mature females small, ovoid, extending from 5/6 suture to median portion of thoracic sternite 6, vulvar cover absent, covered by soft membrane.

REMARKS

Teschia Števčić, 2005 , created for Goneplax sinuatifrons Miers, 1886 , was included in a list of “new genera incertae sedis ” ( Števčić 2005: 134) without any indications as to their inclusion in any particular supra-generic taxa. The generic name is unavailable since it was not accompanied by a description or definition to differentiate it from other genera ( ICZN 1999: Article 13.1).

Guinot (1969b: 522) questioned the inclusion of G. sinuatifrons in Goneplax sensu lato, and Serène & Vadon (1981: 126) suggested its elevation as a new genus. Serène & Umali (1972: 82) similarly explained that their new species, Singhaplax ockelmanni ( Serène, 1971) , was not congeneric with G. sinuatifrons on account of the structure of their respective antennules and G1. Apparently unique among the Goneplacidae sensu stricto is the presence of basal antennular articles that are so long that they do not fit into the fossae, even if the fossae are enlarged (see Serène & Umali 1972: fig. 73). Also unique is the shape of the G2, with an enlarged tip (see Serène & Umali 1972: figs 80, 81) and an unusually large portion of thoracic sternite 8 left visible by the male abdomen. The nearly square appearance of the carapace, without anterolateral teeth, is similar to that of Paragoneplax serenei ( Zarenkov, 1972) n. comb., but in the lat- ter the G2 is much shorter than in H. sinuatifrons n. comb. and the G1 is uniquely twisted. The 2/3 thoracic suture was fused but still visible in all eight specimens (including five pre-adults) collected in Indonesia by the Siboga Expedition (largest female, cl 6.1 mm, cw 9.2 mm; ZMA De 241737) but not fused in a small female (cl 4.3 mm, cw 6.4 mm; MNHN-B 10306). The suture was not fused in the female holotype (cl 6.3 mm, cw 9.7 mm; BMNH 18.84.31) and in a large male (cl 7.5 mm, cw 11.2 mm; MNHN-B 10322). Other characters that separate Hadroplax n. gen. from Goneplax sensu stricto and the five Indo-West Pacific genera containing species formerly included in Goneplax sensu lato are summarized in Table 4.

Goneplax nipponensis Yokoya, 1933 could also represent a second species of Hadroplax n. gen. (see Remarks for Singhaplax styrax n. sp. below).