Ostracotheres cynthiae Nobili, 1906a

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 544-546

Ostracotheres cynthiae Nobili, 1906a

( Figs. 1 , 4 )

Ostracotheres savignyi . — Adensamer, 1897: 108. — Heller, 1861a: 20, 32. (Not O. savignyi H. Milne Edwards, 1853 ).

Ostracotheres Tridacnae. — Heller, 1861a: 20, 32;1861b: 371. (Not O. tridacnae [ Rüppell, 1830]).

Ostracoteres cynthiae Nobili, 1906a: 409 ; 1906b: 299, 300, 301–302, fig. 9.

Ostracotheres cynthiae . — Laurie, 1915: 465–466, text-fig. 3, pl. 45 fig. 3, 3a, 3b, tab. 3. — Tesch, 1918: 262, 287. — Monod, 1938: 145–146, fig. 25, 26A. — Guinot, 1967: 279. — Schmitt et al., 1973: 6, 28. — Takeda & Konishi, 1989: 1222. — Ng et al., 2008: 250.

NOT Ostracotheres cynthiae . — Tesch, 1918: 263 (= probable undescribed species).

Type material. Lectotype: MNHN-IU-2014-11992 (B10561), female (cl 6.8 mm, cw 8.0 mm), Djibouti, coral reef, from branchial cavity of Cynthia , coll. Gravier, 1904 . Paralectotype: MNHN-IU-2014-11992 (B10561), juvenile female (cl 3.5 mm, cw 4.3 mm), collected with lectotype .

Other material examined. ZRC 2017.0223 , 1 ovigerous female (cl 3.9 mm, cw 4.2 mm), Djibouti, in Herdmania sp. , coll. Coutiere , 1897; ZRC 2017.0227 , 2 spent females (cl 4.0 mm, cw 4.1 mm; cl 5.6 mm, cw 5.7 mm), Gulf of Suez , in ascidian Herdmania momus ( Savigny, 1816) , coll. C. Monniot, March 2001 ; MNHN B10562, 1 ovigerous female (cl 7.8 mm, cw 8.4 mm), Gulf of Suez , 28°36–45′N, 32°52–54′E, 18–30 m, sand and rocks, Sta. XIII, coll. Dollfus, 9 December 1928 ; NHMW 10062 , 1 female (cl 3.8 mm, cw 3.8 mm), Red Sea, coll. G. Frauenfeld , 1855, don. Frauenfeld estate, AN: 1896.XI.39 ; NHMW 10063 , 1 ovigerous female (cl 4.0 mm, cw 4.0 mm), Red Sea , from ascidian, don. Koelbel estate, AN: 1893.III.130 .

Description. Female: Carapace subcircular ( Fig. 4A ), as long as wide or slightly wider than long, surface with short, sparsely scattered setae; strongly vaulted longitudinally, rounded in lateral view ( Fig. 4M ); front slightly produced (more prominent in smaller specimens), convex to subtruncate ( Fig. 4A, N, O ); anterolateral margins defined; dorsal surface smooth, regions weakly indicated, near absent.

Epistome ( Fig. 4C ) with narrow interantennular septum; buccal margin with short triangular median point. Antennular sinus larger than orbit; antennules folded slightly obliquely. Antenna short, free antennal articles not extending dorsally beyond eye; antennal articles 1 and 2 fused to epistome. Eyes filling orbit, cornea pigmented.

Maxilliped 3 ( Fig. 4I, D ) ischiomerus length about 2.2 × width; surface finely and sparsely tomentose; inner margin sinuous, proximal two-thirds weakly concave, almost straight, distomesial margin rounded, produced slightly beyond palp articulation; outer margin strongly convex. Carpus longer than half propodus length. Propodus spatulate, length about twice width, subquadrate, apex rounded. Exopod margins convex; flagellum 1-segmented.

Cheliped (pereopod 1) ( Fig. 4A, B ) surface finely tomentose. Dactylus and pollex curved, apices crossing distally, without gape, irregular, setose distally. Dactylus longer than dorsal margin of propodus palm; with low, irregular occlusal teeth along proximal half. Pollex occlusal margin weakly crenulate, with small, distal tooth and large, triangular proximal tooth; inner ventral margin with row of setae. Propodus palm dorsal margin length about as long as high; outer surface with irregular shallow pits; ventral margin distinctly sinuous, concave at base of pollex. Carpus mesial margin with setal tuft, unarmed; merus unarmed, stout, shorter than propodus. Walking legs (pereopods 2–5) similar ( Fig. 4E–H ), stout; relative lengths: pereopod 3>pereopod 2>pereopod 4>pereopod 5; surfaces finely and sparsely setose; pereopods 2–5 with row of short setae along extensor margins of propodus to merus and short distal row of longer setae on distal flexor meral margin; pereopod 3–4 propodus with row of long natatory setae near extensor margin, extending onto dorsal surface of carpus; each article with row of natatory setae on flexor margin. Meri unarmed, length 3.9–4.2 × height (pereopods 2–4), about 3.2 × height (pereopod 5). Propodi unarmed, length 3.4–3.9 × height (pereopods 2–5). Dactyli (pereopods 2–4) similar, slender, lengths subequal; gently curved, evenly tapering, apices spiniform, corneous; surfaces and extensor margin sparsely setose; one- to twothirds of flexor margin lined with elongated, stiff, simple setae; 0.6–0.7 × propodus length. Pereopod 5 dactylus slender, gently curved, as long as or longer than propodus; proximal three-fourths of flexor margin straight or broadly convex resulting in sinuous flexor margin; apex spiniform, corneous; setation similar to that of pereopod 2–4.

Egg diameter 0.7–0.8 mm (in preservative).

Male: (Based on Laurie, 1915; Monod, 1938). Similar to female but smaller maximum size. Carapace slightly more flattened laterally. Abdomen narrow, distally tapering, widest at somite 3; somite 6 trapezoid, slightly wider than long, shorter than telson; telson slightly longer than wide, apex rounded. G1 apex with short, anterolaterally directed papilla; lateral and mesial margins setose along distal three-fourths ( Fig. 4J ). G2 not known.

Hosts. Ascidians, Pyuridae : Cynthia sp. ( Nobili, 1906a) , Herdmania momus ( Savigny, 1816) . Given taxonomic changes since 1906, the identity of Cynthia sp. reported by Nobili (1906a) is uncertain, although it could apply to Herdmania spp.

Remarks. Ostracotheres cynthiae closely resembles O. tridacnae in carapace shape but is readily distinguished by the morphology of the pereopod 2–5 dactyli and the less pronounced carapace and pereopod setation (relatively sparsely distributed versus finely but densely tomentose in O. tridacnae ). The pereopod 2–5 dactyli are slender and almost linear in O. cynthiae rather than stout and falcate as in O. tridacnae . The pereopod 5 dactylus of O. cynthiae is also distinctly longer (versus subequal) than that of pereopod 4, with a straight to sinuous flexor margin (versus evenly curved) ( Fig. 4A, G, H ). In addition, the setation patterns of the pereopod 2–5 flexor margins differ: O. tridacnae has one or two rows of short, stiff simple setae whereas O. cynthiae always has only a single row and the setae are much longer ( Fig. 2C–F, O , 4A, E–H, K, L ). The two species also differ significantly in maximum known body size ( O. tridacnae to cl 15.4 mm; O. cynthiae to cl 7.8 mm), commensurate with the disparate sizes of their respective hosts.

Nobili’s (1906a) original syntypes of O. cynthiae , a female and a much smaller female (erroneously reported as a male by Nobili), are both extant, of which Schmitt et al. (1973) designated the larger female as lectotype. Although now in delicate condition, the lectotype and paralectotype preserve the diagnostic pereopod and maxilliped 3 features, and rounded carapace, clearly evident also in the other Red Sea material examined here. Nobili’s (1906b) reference to the carapace of the larger female as quadrangular is a misinterpretation of the specimen based on damage; the carapace in all specimens is rounded. No males of O. cynthiae were available for the present study, but based on Laurie’s (1915: text-fig. 3, pl. 45 fig. 3, 3a, 3b) account and stylised figures of a male from the Red Sea, the carapace front is more pronounced and the chelipeds more inflated than in females, as in most other male pinnotherids. The distinctive walking leg dactyli of female O. cynthiae is evident also in males, as figured by Laurie (1915: pl. 45 fig. 3). The G1 of a male O. cynthiae from Djibouti figured by Monod (1938: fig. 25F) ( Fig. 4J ) has the distinctive anterolaterally directed tip present also in O. tridacnae . Monod (1938) referred to the specimen as a juvenile, though the G1 is apparently well developed; unfortunately, the specimen is no longer extant and additional material is required to fully document male morphology. Monod (1938) did not indicate the size of his specimens but Laurie (1915) reported an apparently mature male at 6 mm cl and cw. Females are recorded here to cl 7.8 mm but are ovigerous by cl 4.0 mm.

Ostracotheres cynthiae is known only from ascidians, whereas all confirmed hosts of O. tridacnae are bivalve molluscs ( Tridacna spp. ). As discussed under the account of O. tridacnae , Adensamer’s (1897) Red Sea record of O. savignyi (= O. tridacnae ) from ascidians is based on O. cynthiae .

Tesch (1918) attributed an ovigerous female from the Kai Islands, Indonesia, to O. cynthiae (host Styela pneumonodes Sluiter, 1895 = Polycarpa aurata [Quoy & Gaimard, 1834]: Styelidae ), though described as having a dense dorsal tomentum and “strongly hooked” dactyli of pereopods 2–4, which contrast with the much more “straightened” dactylus of pereopod 5. The pereopod 2–5 dactyli of O. cynthiae sensu stricto, however, are all weakly curved and the dorsal setation short and sparse. Tesch’s (1918) specimen requires restudy and probably represents an undescribed species; it is herein excluded from O. cynthiae . As such, O. cynthiae is confirmed only from the western Indian Ocean: Djibouti and the Gulf of Suez, Red Sea.

Distribution. Western Indian Ocean: vicinity of the Red Sea, from Djibouti to the Gulf of Suez; 18–35 m ( Monod, 1938).

Figures

Fig. 1. Distribution of species of Ostracotheres H. Milne Edwards, 1853. (▲) O. cynthiae Nobili, 1906; (●) O. tridacnae (Rüppell, 1830).

Fig. 4. Ostracotheres cynthiae Nobili, 1906. A–H, ovigerous female, cl 7.8 mm, cw 8.4 mm, Gulf of Suez, MNHN B10562; I, female lectotype, cl 6.8 mm, cw 8.0 mm, Djibouti, MNHN-IU-2014-11992; J, male, Gulf of Suez; K–N, female, cl 3.8 mm, cw 3.7 mm, Red Sea, NHMW 10062; O, ovigerous female, cl 4.0 mm, cw 4.0 mm, Red Sea, NHMW 10063. A, dorsal habitus; B, left chelipid, anterior view; C, cephalothorax, anterior view; D, left maxilliped 3; E–H, right pereopods 2–5; I, right maxilliped 3; J, left G1, sternal view; K, left pereopod 4 dactylus; L, left pereopod 5 dactylus; M, carapace, right lateral view; N–O, carapace front, dorsal view. (D–H, J, after Monod, 1938: fig. 25). Scale: A, B = 2.0 mm; C, D, I, J, = 0.5; E–H, M–O = 1.0 mm; K–L = 0.5 mm.

Fig. 2. Ostracotheres tridacnae (Rüppell, 1830). A–I, female, cl 11.8 mm, cw 11.7 mm, Red Sea, MNHN-IU-2016-10949; J–K, male, cl 8.0 mm, cw 7.6 mm, Red Sea, MNHN-IU-2016-10950; L–O, male, cl 12.1 mm, cw 12.1 mm, Red Sea, NHMD-229248. A, J, dorsal habitus; B, right cheliped, anterior view; C–F, right pereopods 2–5; G, right maxilliped 3; H, carapace, right lateral view; I, cephalothorax, anterior view; K, male abdomen; L, left G1, sternal view; M, left G1, tip, abdominal view; N, left G2, sternal view; O, right pereopod 5 dactylus. Scale: A–F, H, J, K = 4.0 mm; G, I, L, N, O = 1.0 mm; M = 0.5 mm.