Reussirella indica

Reussirella indica (Cook, 1965) (Fig. 4.1–6) Cupuladria indica Cook, 1965: 169, pl. 2, figs 1, 2; Menon & Nair 1975: 570, fig. 3h–j; Symphonia & Nathan 2022: fig. 4.6–7. Cupularia umbellata: Hincks 1887b: 125, non Lunulites umbellata Defrance, 1823. Cupuladria guineensis: partim Silén 1942: 8 (part), non pl. IV, figs 13, 14; Amui & Kaselowsky 2006: 9, figs 1–2, non Cupularia guineensis Busk, 1854. Material examined. SMF 1802 (St. 236 KD), SMF 1824 (St. 283 KU), SMF 5608A (St. 283 KU), SMF 40783 (St. 283 KU; Fig. 4.4, 4.6), SMF 40807 (St. 236 KD; Fig. 4.3, 4.5), SMF 40808 (St. 283 KU; Fig. 4.1–2). Description. Colony discoidal, cup-shaped, convex frontally, concave on the basal side, multiserial, unilamellar (Fig. 4.1–2). Autozooids arranged in alternating rows radiating from the centrally located ancestrula, opening on the convex surface. Basal side divided into radial sectors, tuberculate (Fig. 4.3). Ancestrula located in colony centre, autozooidal, surrounded by 7–8 autozooids (Fig. 4.4). Autozooids rounded rhomboidal, separated by thin furrows, 314–440 μm (ẋ = 385 ± 30 µm; CV = 8; N = 45 on 3 specimens) long by 244–450 μm (ẋ = 331 ± 55 µm; CV = 17; N = 45 on 3 specimens) wide. Gymnocyst not visible. Cryptocyst granular; in autozooids from early astogeny (up to fifth or sixth generation) sunken centrally, pierced by ellipse of pores; in older autozooids circumopesial, steeply sloping into opesia or serrated at the margins (Fig. 4.5–6). Opesia rectangular, not developed in autozooids from the early astogeny, 205–279 μm (ẋ = 243 ± 20 µm; CV = 8; N = 30 on 2 specimens) long by 135–237 μm (ẋ = 181 ± 29 µm; CV = 16; N = 30 on 2 specimens) wide. Operculum terminal, semielliptical. Spine bases and ovicells not observed. Vibracula monomorphic, interzooidal, proximal to each autozooid, triangular, with dextral or sinistral denticle, asymmetrical, 89–167 μm (ẋ = 123 ± 18 µm; CV = 15; N = 45 on 3 specimens) long by 99–168 μm (ẋ = 130 ± 16 µm; CV = 13; N = 45 on 3 specimens) wide, having flagelliform setae (Fig. 4.1). Vibracularian opesia, occupying almost whole frontal surface, triangular. Kenozooids not observed. Remarks. Amui & Kaselowsky (2006) misidentified specimens from R.V. Meteor expeditions to the Gulf of Aden and the Red Sea as Cupuladria guineensis (Busk, 1854). Although the frontal surface of these colonies resembles that of Cupuladria guineensis, several key morphological differences indicate that they represent a different species. Notably, autozooids from the early astogeny exhibit a porous, calcified frontal area (Fig. 4.4), and, more importantly, the basal surface structure diverges significantly (Fig. 4.3). Whereas species of Cupuladria Canu & Bassler, 1919 possess a basal side divided into polygonal sectors, the specimens in question display radial sectors with tuberculate calcification (Fig. 4.2–3), which is a defining feature of Reussirella. These features support the reassignment of all Gulf of Aden material previously identified as Cupuladria guineensis to Reussirella indica. Consequently, the presence of Cupuladria guineensis in the Gulf of Aden and the Red Sea must be regarded as a misidentification. Cupuladria indica Cook, 1965 was first transferred to Reussirella by Bałuk & Radwański (1984) in their original description of the genus. However, Cook & Chimonides (1994a) later questioned this assignment, noting that Reussirella indica lacks the denticulate cryptocyst typical of other Reussirella species. Nevertheless, as these authors also observed, the close morphological similarity among many cupuladriid species complicates generic delineation. Despite its superficial resemblance to Cupuladria guineensis, the distinct basal wall calcification in Reussirella indica provides strong justification for maintaining the two species in separate genera. Reussirella indica was originally described by Cook (1965) from the Andaman Sea, the Gulf of Oman, the Red Sea, and the Gulf of Aden. Its distribution was subsequently extended to the southwest coast of India by Menon & Nair (1975), indicating a broad distribution across the northern Indian Ocean. It remains the only extant representative of Reussirella known from this region.