Fenestrulina undetermined

Fenestrulina sp. Figs 1, 21, 22, 23; Tables 1, 4 Material examined. Italy • 1 living colony on a soft-bodied alga. Mediterranean, Tyrrhenian Sea, NE Sicily, Secca di Ponente, Capo Milazzo Peninsula, sample MI _ SdPn _ G; 38°16'28.2"N, 15°13'22.4"E; 33 m depth; Coralligenous biocoenosis; 6 May 2024; scuba diving; G. Donato leg.; PMC Rosso-Collection I.H.B.159.a. Description. Colony encrusting, multiserial, unilaminar; interzooidal communications via two proximolateral, two distolateral and one distal pore-chambers, visible externally as elongate, elliptical windows (Fig. 21 C). Autozooids ovoidal, distinct, with grooves in-between (Fig. 21 B – D). Upper parts of vertical walls of autozooids gently sloping and exposed, more so at triple junctions (Fig. 21 B, D). Frontal shield moderately convex, more elevated at ascopore level. Gymnocyst developed distal and lateral to orifice. Cryptocystidean area marked by a thin raised rim following autozooidal margins and distally lining the proximal margin of the orifice, widely diverging laterally (Fig. 21 D, E), forming short blunt subtriangular latero-oral extensions (~ 24 μm long, not exceeding 58 μm except for a single case, reaching 83 μm). Frontal shield smooth to gently nodular locally. Pseudopores arranged in a single lateral row, usually restricted to distal half of autozooid, occasionally present proximally (Fig. 21 B, D). One or occasionally two irregular rows of additional pseudopores (2–8) occurring between orifice and ascopore. Pseudopores on a level with frontal surface, subcircular (rarely elliptical) and slightly infundibular, with 2–4 spiny processes fusing in the centre (Figs 21 E, 23 I). Two relatively large (25–76 μm wide), subelliptical, smoothly-rimmed cryptocystidean areas occur distolaterally to the orifice, between spines (Fig. 21 C – E), each bearing one pseudopore with some spiny processes. Primary orifice transversely D-shaped, lined by a thin and smooth rim of calcification; hinge-line straight, distal margin fairly undulating (Fig. 21 E). Four, occasionally three long (up to ~ 180 μm), tubular oral spines, ~ 20 μm in maximum diameter (Fig. 21 B – D), the proximal pair bifurcating (Fig. 21 B – D) at ~ 80 μm from the base, with the distal branch being the longer. Ascopore relatively distal, ~ 74 μm proximal to orifice (Fig. 21 E), the lumen transversely C-shaped, with large distal process and denticulated rim, within a reniform field of smooth gymnocyst, smooth-rimmed, flared and vertically protruding from frontal shield surface (Fig. 21 E). Ovicells, ancestrula, and kenozooids not observed. Remarks. The presence of very long spines, with the two proximalmost ones bifurcated, combined with a smooth frontal shield featuring only a few relatively large pseudopores having spiny processes joining in the centre, distinguishes this species from all others described here. However, we have opted to leave it in open nomenclature because of the absence of ovicells, pending the discovery of fertile colonies. Fenestrulina sp. has been found only once, with a single colony developing small lobes on a green alga, which complicated the identification of ancestrula and periancestrular zooids. The observed lobes are small, and consist of a few autozooids, some of which may represent the zone of astogenetic repetition, but ovicells are absent. Habitat distribution. Fenestrulina sp. has only been found in a coralligenous concretions at 33 m depth, on a green alga. Geographical distribution. Fenestrulina sp. has only been found in the Capo Milazzo area, north-eastern coast of Sicily, south-eastern Tyrrhenian Sea.