Cyclorma Naruse & Ng, 2012, gen. nov.
Creators: name: Naruse, Tohru
name: Ng, Ngan Kee
Publisher: name: Zenodo
Year: 2012
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Cyclorma

description: Cyclorma gen. nov.
Type species. Cyclograpsus lophopus Nobili, 1905, by monotypy.
Diagnosis. Carapace (Fig. 1) sub-quadrate, slightly wider than long, frontal width less than half-width of carapace; frontal margin, anterior margin of eyestalk (when folded) and carapace proper forming smooth arc (Figs. 1, 2). Supraorbital margin laterally directed, J-shaped, entire; inner orbital tooth (Fig. 2 c) triangular, reaching midway to lateral angle of front, leaving wide gape for antenna. Anterolateral, posterolateral margins continuous, entire. Suborbital, pterygostomial, subhepatic regions (Fig. 2 c) covered with reticulated setal pattern, longitudinal groove on pterygostomial region along buccal cavern absent. Antennule set transversely. Antenna not excluded from orbit. Eye (Fig. 2 a, c) short, with trigonal peduncle, dorsal, anterior surfaces compressed (Fig. 2 c). Third maxillipeds (Figs. 2 c, 3a) with rhomboidal gape when closed; ischium trapezoidal in shape, longer than merus, with median groove; merus subcircular, with oblique setose ridge; exopod with long flagellum. Female cheliped (Figs. 1, 2 a, b) short, subequal. Ambulatory legs (Figs. 1, 3 b–d) short, with remarkably flattened, widened meri to propodi; meri distally widened, disto-posterior part foliaceous.
Etymology. The genus name “ Cyclorma ” is derived from an arbitrary combination of the two words of the genera “ Cyclograpsus ” and “ Sesarma ”. Gender neuter.
Remarks. Davie (2002: 207) noted that varunid Cyclograpsus and allied genera differ morphologically from Sesarmidae sensu stricto in the “pattern of development of the grooves that direct respiratory water flow across the pterygostome, and in particular, a more or less clearly defined vertical groove running subparallel along the buccal cavity”, and “a strongly developed, typically stridulatory, sub-orbital crest that is relatively straight, and extends some distance across the lateral branchial region”. This suborbital crest of varunids is usually distinct even in female specimens.
Since the original description by Nobili (1905), and the additional observation by Nobili (1906), no one has reconsidered the systematic position of Cyclograpsus lophopus nor reported on its morphological characters. Recent molecular studies examined several Cyclograpsus species but C. lophopus. Our observation of the type specimens (MNHN-IU-2008-10673, ex- MNHN-B12566; MNHN-IU-2008-20697, ex- MNHN-B32611) have confirmed that C. lophopus lacks a suborbital crest and a vertical groove on the pterygostomial region along the buccal cavern but has an oblique setose ridge (Fig. 2 c). This indicates that C. lophopus should be placed in the family Sesarmidae. The other external morphological characters of C. lophopus are too distinct for the species to be accommodated in any of the existing sesarmid or gapsoid genera. This is especially true for the distinct entire contour of the carapace, including the eye peduncle (Fig. 1), and the short and wide ambulatory legs with foliaceous disto-posterior angles of the meri (Figs. 1, 3 b–d). We thus establish a new genus, Cyclorma n. gen., for this species. Cyclorma n. gen. is a monotypic genus at least for the present.
Lithoselatium Schubart, Liu & Ng, 2009, is morphologically similar to Cyclorma n. gen. as they share a relatively smooth dorsal surface of the carapace (Fig. 2 a), a nearly entire carapace contour (Fig. 1), and proportionally wider ambulatory meri (Figs. 1, 3 b–d). Cyclorma n. gen., however, differs from Lithoselatium by having a convex anterolateral and concave posterolateral margins of the carapace (Fig. 1) (lateral margins of the carapace divergent posteriorly in Lithoselatium; Schubart et al. 2009: figs 9B, 14B); distinctly shorter ambulatory legs (Figs 1, 3 b–d) (proportionally longer in Lithoselatium; Schubart et al. 2009: figs 9B, 13A); and anteriorly and dorsally compressed, trigonal and small eyes (Fig. 2 a, c) (well-developed, bulb-shaped and proportionally larger in Lithoselatium; Schubart et al. 2009: figs 9B, 10C, 13A, 14C).
description: Published as part of Naruse, Tohru & Ng, Ngan Kee, 2012, Establishment of a new genus for Cyclograpsus lophopus Nobili, 1905, within Sesarmidae Dana, 1851 (Crustacea: Decapoda: Brachyura), pp. 63-68 in Zootaxa 3572 on pages 63-67, DOI: 10.5281/zenodo.213204