Conescharellina brevirostris Silén, 1947

Conescharellina brevirostris Silén, 1947 View in CoL

Figure 63 View FIGURE 63

v. 1947 Conescharellina brevirostris Silén , p. 39, text-fig. 24, pl. 1, figs. 4–6.

Figured material. PMC EDM-Collection J.H.B.150a, sample 19053 ( Figure 63A–B View FIGURE 63 ), sample 19095 ( Figure 63C–D View FIGURE 63 ), and sample 19081 ( Figure 63E–F View FIGURE 63 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony small, conical, height (H) 0.765 –1.200 mm and basal diameter (BD) 1.125 – 1.535 mm in our specimens (mean H/BD 0.75), with 12–18 slightly prominent, narrow, radial costules corresponding with the raised peristomes of the autozooids, alternating with intercostular valleys occupied by rows of interzooidal avicularia. Autozooids arranged in radial rows corresponding to the prominent costules, with 3–4 autozooids per row; orifices of autozooids in the same costule vertically aligned but alternating with orifices of autozooids in neighbouring costules; autozooids observed on the antapical surface distinct, separated by sloping vertical walls, outlined by a lateral row of circular, widely spaced marginal pores (10– 15 µm in diameter) on each side, elliptical to oval, elongate (mean ZL/ZW 1.73); interzooidal communication through small, circular, uniporous pore-chamber windows, 3–5 along each lateral margin of the zooids, 8–18 µm in diameter. Frontal shield convex around the orifice, flat centrally, smooth, nodular, imperforate except for one or two elliptical marginal areolar pores (10–15 µm in maximum diameter) placed laterally. Primary orifice with semielliptical anter and rounded triangular condyles, 8–10 µm long, pointing mediodistally and defining a shallow U-shaped sinus, longer than wide (mean OL/OW 1.22); apical pore generally absent unless there is an adjacent avicularium; peristome collar-like, well developed laterally and proximally, forming a proximal concave shelf about 25–30 µm wide, absent or little developed distally. Interzooidal avicularia circular, arranged in radial, sinuous or linear rows along the furrows between costules, with 6–8 avicularia per row, rostrum slightly raised, randomly directed, either distolaterally or proximolaterally, crossbar complete. An additional adventitious avicularium only in some autozooids, placed distolaterally to the orifice, lying on the peristome, elliptical, with blunt triangular rostrum directed proximolaterally, and with complete crossbar. Apical surface coarsely tubercular, occupied by kenozooids and avicularia; antapical surface with kenozooidal pits and avicularia in radial rows, continuous with those of the lateral surface of the colony, and centrally. Ovicell hyperstomial, globular, placed obliquely on the frontal of distal zooid to avoid obstructing its orifice, extending to the adjacent avicularian valley; ectooecium mostly uncalcified, forming a smooth, slightly raised peripheral rim, endooecium rugose and finely granular, with granules roughly arranged in radial rows, nearly disappearing in the medial distal area.

Measurements (µm). ZL (measured on the antapical surface) 549±84, 438–587 (2, 11); ZW (measured on the antapical surface) 317±49, 246–371 (2, 11); OL 112±9, 101–122 (2, 5); OW 92±4, 86– 97 (2, 5); AvL (frontal) 50±5, 39–62 (3, 20); AvW (frontal) 47±5, 38–56 (3, 20); AvL (base) 29±2, 28– 33 (2, 4); AvW (base) 32±2, 30–35 (2, 4); OvL 206 (1, 1); OvW 267 (1, 1).

Remarks. We have observed and described for the first time a complete ovicell in C. brevirostris . Silén (1947) noted a wide and shallow excavation emanating from the right distolateral margin of an autozooid peristome and extending into the neighbouring valley, which he interpreted as a broken ooecium (see Silén, 1947, text-figure 24). However, this structure was not observed in the syntype colonies re-examined by Di Martino (2023) using SEM. The discrepancy may be because Silén had access to more colonies than are currently available in the type collection at the Swedish Museum of Natural History in Stockholm. Silén (1947) also suggested that the ectooecium was delicate and prone to breaking. This assumption is supported by our observations, as the ectooecium is largely uncalcified. Additionally, Silén (1947) anticipated that the ooecium would develop obliquely to the right, as seen in another species of the genus, C. striata Silén, 1947 , and this inference has also been confirmed.

Although slightly larger than the subsequently described Conescharellina sp. 1 , this colony is still regarded as relatively young based on its size and the number of autozooids per row.