Xanthias joanneae Mendoza, 2013

Padate, Vinay P., Cubelio, Sherine Sonia & Takeda, Masatsune, 2024, First records of some coral reef-associated brachyuran crabs from the Nicobar archipelago, India, Zootaxa 5486 (4), pp. 476-498 : 491-494

Xanthias joanneae Mendoza, 2013

( Figs. 2G , 9A–B , 10S–V )

Xanthias joanneae Mendoza 2013: 375 , figs. 1–4 (type locality: Panglao Island, Philippines, 4 m depth).— Poupin et al. 2018: 65

(remarks), 82.— Takeda & Komatsu 2018: 171, 172 (remarks), 183 (discussion).—Takeda et al. 2018: 121 (discussion). Xanthias maculatus — Takeda & Komatsu 2005: 282, fig. 5A [Not Xanthias maculatus Sakai, 1961 ].

Material examined. 1 male (6.4 × 4.2 mm) (IO/SS/BRC/00197), FORVSS stn. 38818, south of Great Nicobar Island , Nicobars, India, 6.65°N, 93.83°E, 56 m depth, chain bag dredge, coll. V.P. Padate, 16 August 2019 .

Description. Carapace transversely ovate, subhexagonal, 1.5 times as long as wide, dorsal surface smooth, glabrous, only orbital region and anterior portions of 2M, 3M regions indistinctly demarcated ( Figs. 2G , 9A ). Frontal margin slightly deflexed, divided into 2 gently convex lobes by wide V-shaped notch. Anterolateral margin convex, divided into 4 lobiform teeth separated by V-shaped notches. Posterolateral margin longer than anterolateral margin, nearly straight, distinctly converging posteriorly. Posterior margin slightly concave medially ( Fig. 9A ).

Antennules folding transversely; mxp3 merus subquadrate, half as long as ischium, anterolateral angle rounded ( Fig. 9B ).

Chelipeds massive, subequal, 1.4 times as long as CL, surfaces smooth, dactylus robust, longer than palm ( Fig. 9B ). Pereopods 2–5 shorter than chelipeds, P4 longest, dactyli nearly as long as propodi ( Fig. 9B ).

Male pleon subtriangular, somites 3–5 fused; telson subtriangular, 0.7 times as long as wide ( Fig. 9B ). G1 stout, distal half curving laterally; distal tip with narrow apical lobe, subdistal portion with patch of spinules and several subterminal setae ( Fig. 10S–V ).

Colouration. Fresh specimen: Carapace, chelipeds and pereopods light yellowish orange with randomly arranged ocelli or bluish-white spots fringed with dark orange. Carapace with 48 ocelli ( Fig. 2G ). Lower distal half of cheliped palm with saddle-shaped dark olive patch extending to proximal four-fifths of fingers, finger tips whitish ( Figs. 2G , 9B ). Pereopods with 2–4 ocelli on the dorsal surfaces of meri, carpi and propodi and white bands at the articulation ( Figs. 2G , 9B ).

Biology. The present specimen was collected from rocky substrate in the vicinity of crinoids, at 56 m depth. Known to occur in coral rubble on sand and gravel, subtidal coral platform, reef slopes and deep waters from 3–290 m depths ( Mendoza 2013; Takeda & Komatsu 2018).

Remarks. Mendoza (2013) described Xanthias joanneae from 6 males and 8 females collected from coral reef microhabitats at 2–110 m depths in the Bohol Sea, Philippines. Xanthias joanneae closely resembles Xanthias maculatus Sakai, 1961 and Xanthias claudiae Mendoza, 2023 in the smooth texture of the carapace and pereopods, basal width of male telson exceeding that of anterior margin of pleonal somite 6, and the presence of ocelli on the body and appendages. However, it differs from the other two species in the higher number of small ocelli (> 40) on the carapace ( Figs. 2G , 9A ) (versus 10–13 large ocelli in X. claudiae ( Mendoza 2023: fig. 26A, B); 14–20 moderately large ocelli in X. maculatus ( Takeda & Komatsu 2018: fig. 5B)); ill-defined 2M, 3M regions on the carapace ( Fig. 9A ) (versus feebly indicated in X. claudiae ( Mendoza 2023: figs. 27A, 28A); discernible regions in X. maculatus ( Mendoza 2013: fig. 5A)); moderately lobiform anterolateral teeth separated by narrow V-shaped notches ( Fig. 9A ) (versus indistinctly lobiform teeth in X. claudiae ( Mendoza 2023: figs. 27A, 28A); distinct acute teeth separated by wide troughs in X. maculatus ( Mendoza 2013: fig. 5A)); a relatively narrow thoracic sternite 4 with straight lateral margins ( Fig. 9B ) (versus relatively wider sternite 4 with convex lateral margins in X. maculatus ( Mendoza 2013: fig. 5B)); smooth external surface of the cheliped palm ( Fig. 9B ) (versus palm with 2 longitudinal ridges on lower outer surface in X. claudiae ( Mendoza 2023: fig. 28I, J) and X. maculatus ( Mendoza 2013: fig. 5B)); relatively broader pereopod meri ( Fig. 2G ) (versus relatively narrower pereopod meri in X. claudiae ( Mendoza 2023: fig. 27G) and X. maculatus ( Mendoza 2013: fig. 5A)); and a relatively stouter G1 with a wider apical lobe ( Fig. 10S–V ) (versus a relatively slender G1 with a narrower apical lobe in X. claudiae ( Mendoza 2023: fig. 29A–C) and X. maculatus ( Sakai 1961: fig. 1f, g)). The Indian specimen conforms to the description and illustrations of the holotype provided by Mendoza (2013), however differs in having a long patch of spinules ( Fig. 10T–U ) (versus few spiniform granules; Mendoza 2013: fig. 4I–J) immediately proximal to the apical lobe.

Geographical distribution. Bohol Sea, Philippines ( Mendoza 2013), Amami-Oshima Island, Japan ( Takeda & Komatsu 2018), and Nicobars, India (present study). The present observation is the first record from Indian Ocean indicating westward extension of the known geographical range.

Figures

FIGURE 2. Dorsal habitus photographs (A–C, E–G: fresh specimens; D: ethanol-preserved specimen): (A) Singhaplax ockelmanni (Serène, 1971), male (IO/SS/BRC/00360, 4.8 × 2.5 mm); (B) Urnalana angulata (Rathbun, 1911), undetermined sex (IO/SS/BRC/00184, 6.9 × 7.0 mm); (C) Pseudolambrus confragosus (Calman, 1900), male (IO/SS/BRC/00323, 22.2 × 18.0 mm; (D) Cavoportunus dubius (Laurie, 1906), male (IO/SS/BRC/00191, 26.9 × 20.4 mm); (E) Cyrtocarcinus truncatus (Rathbun, 1906), male (IO/SS/BRC/00193, 8.6 × 6.1 mm); (F) Visayax osteodictyon Mendoza & Ng, 2008, male (IO/SS/ BRC/00194, 5.2 × 3.6 mm); (G) Xanthias joanneae Mendoza, 2013, male (IO/SS/BRC/00197, 6.4 × 4.2 mm). Scale bars: A–B, E, G, 2 mm, C, 10 mm, D, F, 5 mm.

FIGURE 9. Xanthias joanneae Mendoza, 2013, male (IO/SS/BRC/00197, 6.4 × 4.2 mm), Andaman Sea, India: colour photographs: (A) carapace, dorsal view; (B) mxp3, chelipeds, pereopods, sternum and pleon, ventral view. Scale bars: A–B, 2 mm.

FIGURE 10. First and second gonopods: Singhaplax ockelmanni (Serène, 1971), male (IO/SS/BRC/00360, 4.8 × 2.5 mm): (A) entire G1, pleonal view; (B) entire G1, sternal view; (C) entire G2, pleonal view. Pseudolambrus confragosus (Calman, 1900), male (IO/SS/BRC/00323, 22.2 × 18.0 mm): (D) entire G1, pleonal view; (E) G1 distal portion, pleonal view; (F) G1 distal portion, sternal view; (G) entire G1, sternal view; (H) entire G2, pleonal view. Cavoportunus dubius (Laurie, 1906), male (IO/SS/BRC/00191, 26.9 × 20.4 mm): (I) entire G1, pleonal view; (J) entire G1, lateral view; (K) entire G1, mesial view; (L) entire G2, pleonal view. Cyrtocarcinus truncatus (Rathbun, 1906), male (IO/SS/BRC/00193, 8.6 × 6.1 mm): (M) entire G1, pleonal view; (N) entire G1, sternal view; (O) entire G2, sternal view. Visayax osteodictyon Mendoza & Ng, 2008, male (IO/ SS/BRC/00194, 5.2 × 3.6 mm): (P) entire G1, pleonal view; (Q) G1 distal portion, pleonal view; (R) entire G1, sternal view. Xanthias joanneae Mendoza, 2013, male (IO/SS/BRC/00197, 6.4 × 4.2 mm). (S) entire G1, pleonal view; (T) G1 distal portion, pleonal view; (U) G1 distal portion, sternal view; (V) entire G1, sternal view. Scale bars: A–C, P–V, 0.2 mm, D, G–N, 1 mm, E, F, O, 0.5 mm.