Notonyx A. Milne-Edwards, 1873

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 : 754

Genus Notonyx A. Milne-Edwards, 1873

Notonyx A. Milne-Edwards, 1873: 269 . — Miers 1886: xiv, 235. — Tesch 1918: 200 [in key], 219 [key to species].

TYPE SPECIES. — Notonyx nitidus A. Milne-Edwards,

1873 (by monotypy, gender masculine). SPECIES INCLUDED . — Notonyx gigacarcinicus Clark &

Ng, 2006; N. nitidus A. Milne-Edwards, 1873 ; N. vitreus Alcock, 1900 .

DIAGNOSIS. — Carapace ( Serène & Soh 1976: fig. 16D, E; Clark & Ng 2006: figs 1, 2, 3A, 4, 5A, 7) quadrate, slightly wider than long; widest at rounded anterlolateral angles; front deflected ventrally, with two slight lobes, not marked by median emargination. Notch between front, inner edge of supraorbital border absent; orbits wide, deep, expanded distally ( Clark & Ng 2006: figs 2C, 4C, 5B); supraorbital borders with slightly raised median portion, smooth; suborbital borders with slightly raised median portion, inner tooth absent; lateral borders rounded, without tooth. Dorsal surface of carapace smooth, moderately convex, without clear indication of regions. Outer orbital angle without tooth. Basal antennal article short, distalmost (third) article does not reach front. Eye peduncles ( Clark & Ng 2006: figs 2A, C, 3A, 4A, C, 5A, B, 7) long, much shorter than front (0.3-0.4 front width); cornea small, spherical distal margin, not reniform (not conspicuously dorso-ventrally flattened, not clearly divided into anterior, posterior portions). 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; 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 ( Clark & Ng 2006: fig. 6) short to relatively slender, slightly curved, shorter than propodus; dactylus without dark portion; inner (ventral) margin of propodus smooth; carpus with or without defined tooth on inner margin; merus short. Dorsal margins of ambulatory leg (P2-P5) meri ( Clark & Ng 2006: figs 2, 3E, 4, 5G, 7) unarmed; dactyli of ambulatory legs moderately slender, with carina on each side, with scattered setae. Male abdomen ( Clark & Ng 2006: figs 3F, 5H) with 6 freely-movable somites plus telson, relatively slender, somites 4-6 gradually decreasing in width from somite 3 (widest somite). Telson long, longer than wide. Somite 2 narrower than somite 3; somites 2, 3 leave large portion of thoracic sternite 8 visible. G1 ( Serène & Umali 1972: figs 92, 93; Serène & Soh 1976: figs B, B’; Clark & Ng 2006: figs 3H, I, 5J, K) relatively stout; elongated, bifurcated, or hooked tip; spinules on tip. G2 ( Serène & Umali 1972: figs 94, 95; Serène & Soh 1976: figs C, C’; Clark & Ng 2006: figs 3G, 5I) slender, longer than G1, flagellum longer than proximal part (peduncle); tip variously hooked, slightly enlarged tip without terminal spinule. Penis arising from P5 coxa, moderate size; broad, soft proximal expansion. Female abdomen with 6 freely-movable somites, relatively narrow, with relatively large distal portions of all thoracic sternites visible. Telson wider than long. Somite 2 slightly narrower than somite 3; somites 1, 2 leave large portion of thoracic sternite 8 visible. Vulva relatively large, round, extending from edge of suture 5/6 (displaced, slightly arched) to median portion of thoracic sternite 6, vulvar cover absent.

REMARKS

Notonyx has often, but not always, been included in the Goneplacidae (see review by Clark & Ng 2006). Its carapace is uncharacteristically quadrate and lacks anterolateral teeth, hence its inclusion by Serène (1964) in the Chasmocarcinae Serène, 1964, as a subfamily of the Goneplacidae but now considered an independent family (see Table 1). In contrast to goneplacines, chasmocarcines have abdominal somites 3-5 fused in the male. The genus was nevertheless included in the family Notonycidae of the superfamily Notonycoidea by Števčić (2005). Clark & Ng (2006) placed it in the Goneplacinae .

The cornea of the eyes of Notonyx is much smaller than in goneplacines but the orbits are large (and unusually deep) and the eye peduncles long as in many goneplacines. There are similarities between the general structure of the G1 of Notonyx and those of goneplacines as well. The long G2, longer than the G1, is uncharacteristically curved at the tip, a character it nevertheless shares in part with Goneplacoides marivenae ( Komatsu &Takeda, 2003) (see Komatsu & Takeda 2003: fig. 3e, as Goneplax marivenae , fig. 6e, as G. megalops ). The slender male abdomen is similar to that of most geneplacines. Unlike goneplacines, however, somites 2 and 3 of both the male and female abdomens leave a large portion of thoracic sternite 8 visible. Notonyx appears to be a somewhat aberrant goneplacine, perhaps the result of morphological adaptations (most apparent in the shape of the carapace, the absence of anterolateral teeth, and the reduced corneas) to live in coarse sediments. At least N. gigacarcinicus Clark & Ng, 2006 was collected from intertidal coral rubble.

The genus needs to be revised, a task not undertaken during this investigation. The characters used by Clark & Ng (2006) to differentiate the three known species are not clearly defined and it is clear that there are more species than those listed by them. It is possible therefore that a meticulous revision of the species may prove that Notonyx does not belong to the Goneplacinae but to an independent subfamily within the Goneplacidae .