Onychocella subsymmetrica Canu & Bassler 1929

Onychocella subsymmetrica Canu & Bassler, 1929 (Fig. 5.1–4) Onychocella subsymmetrica Canu & Bassler, 1929: 124, text-fig. 30, pl. 12, figs 7, 8; Yang et al. 2018: 498, figs 8, 9. Onychocella angulosa: Harmer 1926: 256, pl. XVI, figs 8, 9;? Mawatari 1965: fig. 59a–d; non Cellepora angulosa Reuss, 1848. Smittipora sp.: Martha et al., 2015: fig. 4g. Material examined. SMF 10692 (St. 236 KD; Fig. 5.2–4), SMF 10697 (St. 236 KD; Fig. 5.1). Description. Colonies encrusting, multiserial, unilamellar (Fig. 5.1–2). Zooids arranged quincuncially, separated by medial groove. Pore chambers not observed.Ancestrula autozooidal, budding three autozooids distally (Fig. 5.1). Autozooids subhexagonal, 343–544 μm (ẋ = 439 ± 55 µm; CV = 13; N = 30 on 2 specimens) long by 280–429 μm (ẋ = 346 ± 40 µm; CV = 11; N = 30 on 2 specimens) wide. Gymnocyst not visible. Cryptocyst sunken centrally, raised around the rims, surrounding opesia from all sides, granular. Opesia subterminal, D-shaped, occasionally with opesiular indentations at proximolateral corners, 122–194 μm (ẋ = 145 ± 15 µm; CV = 10; N = 30 on 2 specimens) long by 124–217 μm (ẋ = 148 ± 18 µm; CV = 12; N = 30 on 2 specimens) wide (Fig. 5.3). Spine bases lacking. Ovicells not observed. Avicularia monomorphic, vicarious, irregularly interspersed among autozooids, lanceolate, asymmetrical, oriented dextrally or sinistrally, 348–640 μm (ẋ = 541 ± 92 µm; CV = 17; N = 12 on 2 specimens) long by 198–280 μm (ẋ = 234 ± 27 µm; CV = 12; N = 12 on 2 specimens) wide (Fig. 5.4). Avicularian aperture centrally located, longitudinally elliptical, 150–227 μm (ẋ = 180 ± 25 µm; CV = 14; N = 12 on 2 specimens) long by 74–130 μm (ẋ = 97 ± 18 µm; CV = 15; N = 12 on 2 specimens) wide; crossbar not observed. Avicularian cryptocyst sunken, surrounding aperture from all sides, granular. Rostrum acutely triangular, sometimes slightly curved, directed distally, neither overlapping nor indenting proximal cryptocyst of distal autozooid. Intramural reparative budding of avicularia inside avicularia common, manifold. Kenozooids not observed. Remarks. The specimen illustrated by Harmer (1926) as Onychocella angulosa (Reuss, 1848), collected from shallow waters in the Sulu Sea south of North-Ubian Island, Philippines, is identical to our specimens from Djibouti. Canu & Bassler (1929) later described Onychocella subsymmetrica as a new species from other localities in the Sulu Sea. However, this name was not widely accepted by several subsequent authors and was often considered a junior synonym of Onychocella angulosa (e.g., Mawatari 1965). Following Yang et al. (2018), who recognised Onychocella subsymmetrica as a valid species, we apply this name to the specimens from the Gulf of Aden. In the synonymy list provided above, only recent occurrences are considered. The taxonomic validity of several species comparable to Onychocella angulosa remains a subject of debate (see also Taylor et al. 2018). Onychocella angulosa is the type species of the genus Onychocella, and was originally described from the Miocene of Austria by Reuss (1848). However, the original illustration is of poor quality, contributing to ongoing uncertainty regarding its identity. Di Martino et al. (2022) re-examined the type material and designated a lectotype from Nussdorf, Vienna, Austria. Onychocella angulosa differs from Onychocella subsymmetrica by having larger opesiae that are typically at least half the size of the autozooid, and in consistently lacking proximolateral opesiular indentations. Another species frequently considered a junior synonym of Onychocella angulosa is Onychocella marioni Jullien, 1882, which is a common species from the Mediterranean Sea. Similar to Onychocella angulosa, this species also lacks proximolateral opesiular indentations and has larger opesiae (see Rosso et al. 2020) compared to Onychocella subsymmetrica.Additionally, Onychocella antiqua (Busk, 1858) from Madeira, Portugal, was illustrated by Taylor et al. (2018) as Onychocella angulosa (their fig. 1a–c), but differs in having trifoliate opesiae that are consistently terminal. A comprehensive revision of the type material for Onychocella subsymmetrica, Onychocella marioni, and Onychocella antiqua, alongside comparative analysis of Onychocella angulosa, is necessary to clarify their taxonomic status and to prevent further misidentifications.