Seiitaoides mirabilis Forges & Lee & Ng 2021, n. sp.
Creators: name: Forges, Bertrand Richer De
name: Lee, Bee Yan
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Majidae
Seiitaoides
Seiitaoides mirabilis

description: Seiitaoides mirabilis n. sp.
(Figures 8, 9, 13I–K)
Eurynome stimpsoni — Griffin & Tranter, 1974: 166, fig. 1a–c (not Eurynome stimpsoni Miers 1884).
Material examined. Holotype: 1 male (cl 13.2 mm, pcl 11.2 mm, cw 7.3 mm, bcw 6.4 mm) (MNHN-IU-2010- 1301A), stn CP3288, in front of Narendry Bay, Madagascar, 1431.9’S 4726.54’E, 46–54 m, coll. MIRIKY, 14 July 2009. Paratypes: 1 ovigerous female (cl 11.7 mm, pcl 10.2 mm, cw 6.4 mm, bcw 5.6 mm) (MNHN-IU-2010- 1301B), 1 female (cl 13.0 mm, pcl 11.3 mm, cw 7.1 mm, bcw 6.4 mm), 1 ovigerous female (cl 12.9 mm, pcl 11.2 mm, cw 7.1 mm, bcw 6.5 mm), 1 female (with Sacculina) (cl 10.0 mm, pcl 8.8 mm, cw 6.0 mm, bcw 5.1 mm) (ZRC 2020.379, ex MNHN-IU-2010-1035), 3 ovigerous females (cl 13.3 mm, pcl 11.7 mm, cw 7.4 mm, bcw 6.5 mm; cl 10.4 mm, pcl 9.0 mm, cw 6.0 mm, bcw 5.2 mm; cl 10.4 mm, pcl 8.8 mm, cw 5.6 mm, bcw 5.1 mm) (MNHN-IU-2010-1035), same locality and collection data as holotype.— 1 male (badly damaged) cl 9.2 mm, pcl 8.2 mm, cw 5.2 mm, bcw 4.6 mm (ZRC 2020.376, ex MNHN-IU-2010-1186), stn DW3235, Madagascar, 1432.56’S 4727.71’E, 46–54 m, coll. MIRIKY, 6 July 2009.
Comparative material. Seiitaoides orientalis (Sakai, 1961): 2 males (cl 8.5 mm, pcl 7.3 mm, cw 5.1 mm, bcw 4.1 mm; cl 5.5 mm, pcl 4.8 mm, cw 3.2 mm, bcw 2.8 mm), 2 females (cl 7.5 mm, pcl 6.6 mm, cw 5.0 mm, bcw 3.6 mm; cl 7.3 mm, pcl 6.6 mm cw 4.8 mm, bcw 3.6 mm) (ZRC 2020.374), stn T36, Cervera Shoal, west Pamilacan island, Bohol, Visayas, Philippines, sand on echinoderm bed, 929.3’N 12351.5’E, 95–128 m, coll. PANGLAO 2004, 4 July 2004.
Diagnosis. Pseudorostral spines cylindrical in cross section, gently diverging; outer margin with small accessory spinules (Fig. 8A–C). Supraorbital eave broad, margin spinulated, with proximal angle enlarged, forming blunt tooth; postocular tooth slender, longer than preocular, separated by narrow gap, intercalated spine short, tightly appressed against long curved postocular spine; 3 ocular teeth totally surround eye (Figs. 8B, C, 9A). Hepatic spine short, flattened, with prominent boletiform tubercle dorsal to it, separated from postocular tooth by wide gap (Figs. 8B, 9B). Gastric region with 1 median cardiform plate; protogastric area with 2 tubercles; cardiac region covered by large raised ovoid plate; branchial region with 2 large rounded plates; lateral margin with 3 large boletiform tubercles; surfaces between plates with small sharp granules Fig. 8B, C, E). Intestinal region and posterior carapace margin raised, with granuliform, adjoining low plate-like granuliform plates on posterolateral margin. Basal antennal article fused with carapace, with 2 blunt distal teeth and 2 or 3 medially (Fig. 9A, B); flagellum subequal in length to pseudorostral spines. Anterolateral flange of buccal cavity gently serrated (Fig. 9A, B). Third maxilliped with 2 sharp granules on ischium (Fig. 9A, B). Adult male cheliped very long; merus long, with short spines; carpus short with 2 spines on outer surface; chela wider distally with 2 sharp spines on outer face, fingers short, with serrulate cutting margins (Figs. 8A, 9C). Ambulatory legs short, setose, merus slightly carinate on dorsal margin, unarmed (Fig. 9D). Anterior part of thoracic sternum depressed; distal part of sternopleonal cavity with distinct smooth rim surrounding telson (Fig. 9A). Male and female pleon with 6 free somites; male and female somite 1 with large subtruncate rounded tubercle (Fig. 8A, B, D); lateral margins of male somite 3 swollen; male telson much longer than wide with concave lateral margins (Fig. 9A, B). G1 gently sinuous, elongate, with slightly flattened extremity (Fig. 13I–K).
Type locality. Narendry Bay, Madagascar.
Etymology. The term mirabilis is a Latin term for beautiful, alluding to the appearance of the species.
Remarks. The species closest to Seiitaoides mirabilis n. sp. is S. orientalis (Sakai, 1961), described from Japan but has also been reported from the Indonesian Moluccas and Western Australia (cf. Sakai 1961: 140, text-fig. 1c, d, pl. 4 fig. 2; Griffin 1970: 7, fig. 1; Griffin & Tranter 1986: 251, fig. 69b, e–f). Several specimens of S. orientalis were on hand from the Philippines and they agree with the descriptions and figures by these authors. The differences with S. mirabilis n. sp. are as follow: in S. orientalis, the branchial plate has a sharp spine pointing outwards (versus without spine in S. mirabilis n. sp.; Fig. 8A, B, D); on the posterior carapace margin, there are two granulated raised plates (versus with three in S. mirabilis n. sp.; Fig. 8A, B, D); the meri of the ambulatory legs are spiny (versus carinate in S. mirabilis n. sp.; Fig. 8A, D); the intercalated spine is large and sharp (versus reduced, blunt and tightly appressed against the postocular tooth in S. mirabilis n. sp.; Fig. 8A, B); the supraocular eave is narrow with 4 or 5 teeth on its margin (versus broad with the border serrulated, and enlarged on the posterior angle as a tooth in S. mirabilis n. sp.; Fig. 8B); the anterolateral flange of the buccal cavity is lined with long sharp spines (Fig. 12E) (versus gently serrated in S. mirabilis n. sp.; Fig. 9A, B); the distal part of the sternopleonal cavity has 3 sharp spines on the rim surrounding telson (Fig. 12E) (versus distal part of sternopleonal cavity with smooth rim in S. mirabilis n. sp.; Fig. 9A); and the merus of the chela is inflated in adult males (versus chela slender in S. mirabilis n. sp.; Fig. 8A) (cf. Fig. 12C–E; Griffin 1970: fig. 1; Sakai 1961: pl. 4 fig. 2; 1965: pl. 37 fig. 5; 1976: text-fig. 119, pl. 76 fig. 1). The G1 structures are very different; in S. mirabilis, it is distinctly sinuous and long (Fig. 13I, J) but it is almost straight and proportionately shorter short and straight in S. orientalis (cf. Sakai 1961: fig. 1c, d).
Griffin & Tranter (1974: 166, fig. 1a–c) described and figured a female (cl 12.5 mm) he identified as Eurynome stimpsoni from the Gulf of Eilat in the Red Sea but in almost all aspects, it matches S. mirabilis n. sp. The only difference is that the pseudorostrum is relatively short (Griffin & Tranter 1974: 166, fig. 1a) but this is within the range for females of this species (e.g., Fig. 8D). Eurynome stimpsoni was described by Miers (1884: 523, pl. 47 fig. A, a; Fig. 12A) from one male and three females (largest 11.0 × 6.0 mm) from Providence Reef near the Seychelles and has not been reliably reported since. While S. mirabilis n. sp. superficially resembles S. orientalis, it differs markedly in that the carapace is distinctly pyriform in carapace shape with the posterior part much wider than the anterior part (Fig. 8A, B, D) (versus carapace slender with the posterior half of the carapace only slightly wider than the anterior part in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig.A); the pseudorostrum is slender and elongate (Fig. 8A, B, D) (versus prominently flattened dorsoventrally and lobiform in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig. A); the supraorbital eave slopes towards the front with the margin spinulate, the postorbital spine is slender, long and directed obliquely anteriorly (Fig. 8B) (versus supraorbital eave subparallel, entire and resembles a lobiform tooth directed laterally in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig. A); the hepatic lobe is armed with a dorsal plate and a prominent spine ventral to it (Fig. 8A, B, D) (versus with only one plate in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig. A); the intestinal plate is in three distinct parts (Fig. 8A, B, D) (versus one continuous plate in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig. A); and the ambulatory legs, especially the meri, are distinctly longer (Fig. 8A, D) (versus distinctly shorter in S. orientalis; Fig. 12A; Miers 1884: pl. 47 fig. A).
description: Published as part of Forges, Bertrand Richer De, Lee, Bee Yan & Ng, Peter K. L., 2021, The taxonomy of spider crabs of the genera Eurynome, Choniognathus, Seiitaiodes and Kasagia (Crustacea: Brachyura: Majidae) from southwest Indian Ocean, pp. 301-333 in Zootaxa 5048 (3) on pages 314-317, DOI: 10.11646/zootaxa.5048.3.1, http://zenodo.org/record/5556341