Cyrtomaia micronesica Richer

Komai, Tomoyuki & Tsuchida, Shinji, 2014, Deep-Sea decapod crustaceans (Caridea, Polychelida, Anomura and Brachyura) collected from the Nikko Seamounts, Mariana Arc, using a remotely operated vehicle “ Hyper-Dolphin ”, Zootaxa 3764 (3), pp. 279-316 : 307-308

Cyrtomaia micronesica Richer de Forges & Ng, 2007

( Figs. 22–25 , 26A–E )

Cyrtomaia micronesica Richer de Forges & Ng, 2007: 62, figs. 1–4, 5B, D [type locality: off Haputo, Guam, 270 m].—Ng et al. 2008: 111 (list).

Material examined. RV “Natsushima”, NT10-13 cruise, ROV “Hyper-Dolphin”, dive #1165, Northeast Nikko Seamount, 23°06.748’N, 142°21.554’E, 637 m, 31 July 2010, manipulator, 1 male (39.0 × 43.5 mm), JAMSTEC 081529 -1; same dive, 23°06.709’N, 142°21.873’E, 553 m, 1 male (42.5 × 50.5 mm), JAMSTEC 081529 -2.

Coloration in life. Dorsal side of body and appendages generally tan.

Distribution. Previously known from Guam and Palau, at depths of 210– 600 m. The present specimens extend the geographical range of this rarely collected species to the Nikko Seamount, south of Ogasawara Islands, at depths of 553– 637 m. New records for Japanese marine fauna.

Ecology. We often encountered this species during the dive, though only two specimens were collected. The individuals were found to be slowly wandering on rock substrates.

Remarks. The larger male differs from the smaller male in the more elongate chelipeds with more stout chelae; spines on segments are less strong and/or less acute in the larger specimen than in the smaller specimen. The variation seems to be size-related.

The present specimens agree generally with the original description of Cyrtomaia micronesica in the following diagnostic characters: carapace surfaces finely granular, with small tubercles on branchial regions ( Fig. 23 A); carapace armature including pseudorostral spines distinctly longer than rostrum, very long, smooth, slightly divergent protogastric spines, tiny median gastric spine, strong, acute postocular spines, very small orbital intercalated spines, very small anterior branchial spines, and two cardiac spines reduced to small tubercles; epibranchial and posterior branchial spines reduced to minute tubercles, intestinal spine also reduced to very low protuberance ( Figs. 23 A, B, 24); blunt longitudinal ridge connecting orbital intercalated spine and protogastric spine present ( Fig. 23 B); eyestalk short, only reaching to orbital intercalated spine, with minute tubercle near base of cornea ( Figs. 23 B, 24); second pereopod longer than cheliped, merus bearing slender spines on anteroventral surface arranged in two rows ( Fig. 22 ); third pereopod shorter than second pereopod, though similar in general armature ( Fig. 22 ); fourth and fifth pereopods unarmed except for prominent dorsodistal spine on each merus ( Fig. 22 ); and first abdominal somite with one small median tubercle ( Fig. 23 A). On the other hand, the cheliped of the holotype appears intermediate between the present specimens in the development of spines and the shape of the chela (cf. Richer de Forges & Ng 2007: fig. 4B, C; Figs. 25 A, B); the basal segment of the antennal peduncle is armed with three spines in the present specimens ( Fig. 26A ), rather than four in the type description. Richer de Forges & Ng (2007) cited the length of the cheliped in differentiating C. micronesica and C. cornuta Richer de Forges & Guinot, 1988, but the examination of the present specimens shows that the length of the cheliped increases with growth in C. micronesica .

Although the male first gonopod of the present specimens ( Fig. 26B–E ) agrees well with the figure provided by Richer de Forges & Ng (2007), the original description of the distal part of the male first gonopod may be misleading. The distal part of the male first gonopod of this species is actually flattened, forming a rounded apex in the distal view ( Fig. 26E ); the acuteness of the tip mentioned in the original description actually reflects the strong degree of the compression.

Figures

FIGURE 22. Cyrtomaia micronesica Richer de Forges & Ng, 2007, male (42.5 × 50.5 mm), JAMSTEC 081529 - 2, entire animal in dorsal view (in preservative).

FIGURE 23. Cyrtomaia micronesica Richer de Forges & Ng, 2007, male (42.5 × 50.5 mm), JAMSTEC 081529 - 2. A, carapace and cephalic appendages, dorsal view; B, anterior part of carapace and cephalic appendages, dorsal view.

FIGURE 24. Cyrtomaia micronesica Richer de Forges & Ng, 2007, male (42.5 × 50.5 mm), JAMSTEC 081529 - 2, anterior part of cephalothorax and appendages, anterior view.

FIGURE 25. Cyrtomaia micronesica Richer de Forges & Ng, 2007, left chela. A, male (42.5 × 50.5 mm), JAMSTEC 081529 - 2; B, male (39.0 x 43.5 mm), JAMSTEC 081529 - 1.

FIGURE 26. A – E, Cyrtomaia micronesica Richer de Forges & Ng, 2007, male (42.5 × 50.5 mm), JAMSTEC 081529 - 2; F – I, Progeryon mus Ng & Guinot, 1999, male (27.2 × 34.3 mm), JAMSTEC 018539 - 1. A, basal segment of left antennal peduncle, anterior view; B, left first gonopod, lateral view; C, same, distal part, lateral view; D, same, mesial view; E, same, distal view; F, left first gonopod, ventral view; G, same, distal part, ventral view; H, same, dorsal (inner) view; I, left second gonopod, lateral view. Scale bars: 2 mm for A, B; 1 mm for C, D, F, I; 0.5 mm for E, G, H.