Planaja, Ng & Forges, 2015

Ng, Peter K. L. & Forges, Bertrand Richer De, 2015, Revision of the spider crab genus Maja Lamarck, 1801 (Crustacea: Brachyura: Majoidea: Majidae), with descriptions of seven new genera and 17 new species from the Atlantic and Indo-West Pacific, Raffles Bulletin of Zoology 63, pp. 110-225 : 178

Planaja n. gen.

Diagnosis. Carapace subovoid; dorsal surface gently inflated, covered by sharp granules or low tubercles; gastric and branchial regions clearly delimited by grooves ( Fig. 34A, B). Intestinal region with small median spine ( Fig. 34A, B). Pseudorostral spines relatively long, slender, diverging ( Figs. 34A, B). Supraorbital eave large, anterior part expanded, foliaceous, margin convex, antorbital spine long, sharp ( Fig. 38A). Intercalated spine distinct, separated from supraorbital eave and postorbital spine by distinct gaps; postorbital spine strong, long, gently recurved; hepatic region with 1 low but distinct spine, much shorter than postorbital spine; 1 or more tubercles below ( Fig. 38A). Lateral carapace margin with 6 or 7 short sharp spines (posterior ones smaller), branchial region with 1 short spine and 1 submedian tubercle ( Fig. 34A, B). Posterior carapace margin with 2 very short median spines ( Fig. 34A, B). Eyes relatively short, slender, with large ovoid cornea ( Fig. 38A). Antennal flagellum short, slender. Basal antennal article longer than broad, rectangular; surface with numerous granules, with 2 spines distally; inner and outer lateral margins granulated; proximal outer angle rounded; antero-external crested rim of antennular fossa touches overlap distal part of basal antennal article by about a third of its width ( Fig. 40N). Epistome wider than long, anterior margin with 2 low granular lobes; posterior margin composed of 4 rectangular plates separated by shallow fissures ( Figs. 40N, 42G). Suborbital margin separated from basal antennal article and margin of postorbital tooth by deep fissures fissures ( Fig. 40N). Outer surface of third maxilliped covered by short setae in adults; ischium subrectangular, just longer than broad; postero-external angle of merus relatively broad, “inserted” into shallower concavity on outer margin of ischium; antero-internal part of ischium rounded, auriculiform ( Fig. 46M, N). Male chelipeds relatively short in adult males, surface of merus and carpus finely granulated; carpus long; propodus of palm elongated, curved, smooth, not inflated, palm as long as fingers; fingers long, slender, gently curved, with distinct basal gape when closed ( Figs. 34A, B, 54N). Ambulatory legs relatively short, slender; merus without dorsal subdistal spine; dactylus elongate, curved, covered with long setae except for corneous tip ( Figs. 34A, B, 56K). Thoracic sternum wide; surfaces of somites 5–8 with numerous prominent rounded tubercles and granules; sternites 3 and 4 depressed; margin between sternites 2 and 3 demarcated by deep notch; anterior margin of sterno-abdominal cavity forming prominent complete rim ( Figs. 51F, G, 52K). Male abdomen subtriangular, with 6 free somites and telson; somites 3 and 4 wider than somite 6 and telson ( Fig. 51F, G). Male press-button abdominal locking mechanism submedian in position on sterno-abdominal cavity ( Fig. 52K). Female abdomen dome-shaped, covering most of thoracic sternum. G1 long, slender, distal part bent approximately 90°, distal part chitinised with rows of short stiff setae, tapering to sharp tip ( Fig. 35A–E).

Type species. Planaja plana n. sp., by present designation.

Etymology. The name is an arbitrary combination of the Latin “ planus ” for flat and Maja . Gender feminine.

Remarks. The main differences between Planaja gen. nov. and the other genera treated here have been discussed under Holthuija and Sakaija . The most diagnostic features of the genus are the relatively flatter carapace in which the dorsal surface is only gently convex, the supraorbital eave is expanded, possessing more spines (six) on the lateral carapace margin, as well as the short and thick ambulatory legs (see key to genera). Another unique character of the type species is that the distal quarter of the G1 is distinctly chitinised and lined with numerous short setae ( Fig. 35A–E), a feature not present in other genera in this study. In this respect, the G1 of Planaja resembles species of Leptomithrax like L. longimanus and L. edwardsii (unpublished data).