Chaceon alcocki Ghosh and Manning, 1993

Chaceon alcocki Ghosh and Manning, 1993 View in CoL

( Fig. 8 View Figure 8 )

Chaceon alcocki Ghosh and Manning, 1993: 714 View in CoL , figs. 1–3 (type locality: off Travancore coast, 8°37’N 75°37’30”E). — Ng et al., 2008: 147 (list). — Jose et al., 2019: 749, figs. 1–3.

Geryon affinis View in CoL — Alcock, 1899a: 85 [not Geryon affinis Milne Edwards and Bouvier, 1894 View in CoL ].

Material examined. 1 male (CL 146.4 mm, CW 161.1 mm) ( IO /SS/BRC/00300), off Alleppey (Kerala), Arabian Sea , FORVSS stn. 32121, 9.25°N 76.17°E, 55 m, coll. Dr. Vinu Jacob, HSDT ( CV), 13 December 2013 GoogleMaps .

Remarks. Alcock (1899a) erroneously reported a female geryonid (110.5 × 126.5 mm) from off Travancore (Kerala) coast at 410–520 m as Geryon affinis . Ghosh and Manning’s re-examination of this specimen(1993)resulted in the establishment of a new species, Chaceon alcocki , characterized by short frontal and anterolateral spines, the absence of distal spines dorsally on the P2–P5 meri, and laterally compressed pereopod dactyli. Jose et al. (2019) reported another female specimen (146 × 156 mm) collected from a commercial trawl landing along Kerala coast, and was reportedly caught at 260–300 m depth.

The present specimen is the first male and the largest specimen reported for this species. The G1 is stout, curved, tapering distally; inner margin is covered with a row of short setae along proximal half, distal quarter with a short spinulose patch terminating sub-distally; outer margin with spinulose patch on distal one-third terminating sub-distally, followed by a small patch of long setae appearing like a spinose projection ( Fig. 8J View Figure 8 ). G2 shorter than G 1 in length,slender, tapering distally, with spinose process subdistally on inner margin ( Fig. 8J View Figure 8 ). Among the closely related congeners, published descriptions of only two species, Chaceon macphersoni Manning and Holthuis, 1988 and Chaceon goreni Galil and Manning, 2001 were supplemented with illustrations of the gonopods. Chaceon alcocki differs from C. macphersoni and C. goreni in the presence of setae on both inner and outer margins (vs. row of setae on inner margin in C. goreni (see Galil and Manning, 2001: fig. 3C–E); absence of setae on either margin in C. macphersoni (see Manning and Holthuis, 1988: fig. 4G, H)).

Distribution. Known only from the southeastern Arabian Sea off Kerala at 50–520 m depths ( Ghosh and Manning, 1993; Jose et al., 2019; present study).