Pedroplax Ng & Komai, 2011, new genus
Creators: name: Ng, Peter K. L.
name: Komai, Tomoyuki
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Goneplacidae
Pedroplax

description: Pedroplax new genus
Diagnosis. Carapace slightly wider than long, with single anterolateral tooth (Figs. 1, 2 A, 3A). Orbit short; eyes large, protruding lateral margin of orbit (Figs. 1, 2 A, 3A). Antennules proportionately large, fossa asymmetrical (Fig. 2 A). Epistome with anterior part triangular; posterior margin sinuous with 3 low median lobes, separated from lateral parts by deep concavity (Fig. 2 A). Endostomial ridges strong. Third maxilliped with merus about as long as broad, anterolateral angle rounded, not auriculiform; ischium subrectangular (Figs. 2 C, 3B). Chelipeds homochelous; chela stout, fingers laterally flattened (Figs. 1, 3 D). Ambulatory legs slender, smooth, unarmed; propodus of fourth leg subfoliaceous; dactylus of fourth leg subspatuliform (Fig. 1 B, C). Thoracic sternites 1, 2 completely fused, forming prominent triangular plate (Figs. 2 C, D); sternites 3, 4 fused, only lateral sutures visible; sutures between sternites 4–8 medially interrupted; longitudinal groove present between sternites 6–8. Press button of abdominal locking mechanism on anterior half of sternite 5 (Figs. 2 D). Coxo-sternal condition, with penis coxal but opening to base of G1 through narrow channel formed by episternite 7, sternite 8 (Fig. 2 E). Male abdomen relatively broadly T-shaped; somite 2 not reaching coxae of fourth pair of ambulatory legs, sternite 8 clearly exposed; somite 3 transversely trapezoidal, almost reaching coxae of fourth ambulatory legs except for narrow part of sternite 8 (Figs. 2 B, 3G). G1 stout, gently curved outwards, distal quarter tapering with 2 stout subdistal spines on outer margin (Fig. 3 H, I); G2 about 1.3 times length of G1, median part dilated with numerous short spines on outer margin, distal part with bifurcated tip, subdistal surface with 4 or 5 spines (Fig. 3 J, K). Vulva prominent, occupying most of anterior half of sternite 6, no visible sternal vulvar cover (Fig. 2 F).
Remarks. Although the carapace is superficially similar to species of Psopheticus Wood-Mason, 1892, and Exopheticus Castro, 2007, it is distinctly less broad proportionately and appears paedomorphic, resembling juveniles of species of those latter genera. This is also true of its disproportionately large eyes. However, there is no doubt Pedroplax megalops is an adult despite its small size; the gonopods are fully developed and three of the females examined are already ovigerous. Although Castro (2007) and Ng et al. (2008) questioned its classification in the Goneplacidae MacLeay, 1838, sensu stricto, there is little doubt it is a goneplacid as currently defined by Castro (2007), Ng & Manuel-Santos (2007) and Castro et al. (2009). The structures of the thoracic sternum (including the arrangement and extent of sutures) and male abdomen as well as the position of the penis and press-button of abdominal locking mechanism of Pedroplax new genus are consistent with other goneplacids.
The most unusual features of Pedroplax new genus are clearly the very peculiar G1 and G2 structures which are unique for the family. In fact, the unusual G1s and G2s were the main reason why its placement in the Goneplacidae was doubted by Castro (2007) and Ng et al. (2008), but as discussed above, all the other key characters argue for its retention in the Goneplacidae. The gonopod structures, together with the atypical carapace features argue for the recognition of a distinct genus for the species. Another key difference of Pedroplax new genus with Psopheticus and Exopheticus is the relative narrowness of male abdominal somite 2 that exposes a large part of thoracic sternite 8 (Figs. 2 B, 3G). In Psopheticus and Exopheticus, the male abdominal somite is broader and only a relatively small part of sternite 8 is exposed, if at all (Castro 2007: fig. 48B).
With regard to the small adult size and disproportionately large eyes and general form of the last ambulatory legs, Pedroplax megalops superficially resembles Guinoplax apheles Castro & Ng, 2010, but the two differ markedly in the characters of the carapace, chela, abdomen, thoracic sternum and gonopods (see Castro & Ng 2010).
Etymology. We take pleasure in naming the genus after Peter Castro, known to his carcinologist friends as “Pedro. The name is used in combination with - plax, a suffix for many goneplacid genera. Gender feminine.
description: Published as part of Ng, Peter K. L. & Komai, Tomoyuki, 2011, A new genus for Psopheticus megalops Takeda, 1989 (Crustacea: Brachyura: Goneplacidae), pp. 61-67 in Zootaxa 2934 on pages 61-62, DOI: 10.5281/zenodo.203270