Cribralaria curvirostris Silén, 1941

Martino, Emanuela Di, 2023, Scanning electron microscopy study of Lars Silén’s cheilostome bryozoan type specimens in the historical collections of natural history museums in Sweden, Zootaxa 5379 (1), pp. 1-106 : 37-38

Cribralaria curvirostris Silén, 1941

( Fig. 17 ; Table 16)

Cribralaria curvirostris Silén, 1941: 122 , figs 182, 183.

Material examined. Holotype by original designation UPSZTY 2484 , Bonin Islands (Ogasawara), Japan; depth 100–135 m. Leg. Prof. S. Bock 1914.

Description. Colony encrusting, multiserial, unilaminar ( Fig. 17A ).

Autozooids cribrate, oval with straight distal margin ( Fig. 17A ), almost twice as long as wide (mean L/ W 1.85), distinct, separated by thin furrows; frontal shield convex, smooth, formed by 13–17 partially fused costae, 20–60 µm wide, the distalmost pair the widest, rectangular in the distal half of the zooid, triangular in the proximal half, interdigitated along zooidal midline, separated by 3–4 intercostal pores, 15–40 µm in maximum diameter, circular if single or figure-eight-shaped if double ( Fig. 17A, C, D ). Gymnocyst absent except for a narrow region lateral to the orifice.

Orifice rounded rectangular, longer than wide (mean L/ W 0.60), slightly constricted laterally at about mid-length; distalmost pair of costae forming two short, stout, pointed spines laterally projecting towards the orifice at the same level as the constrictions, and a blunt proximal process centrally at the fusion line ( Fig. 17C–E ).

Avicularia interzooidal, placed distally to most autozooids, lodged on a rectangular cystid, needle-shaped ( Fig. 17B, D ); rostrum acicular, long (110–200 µm), curved, serrated, channelled, accommodated along the margins of two neighbouring autozooids, directed obliquely distally ( Fig. 17B, D ); opening figure-eight-shaped due to a broad immersed opesial shelf with two small, straight condyles ( Fig. 17B–D ).

A single kenozooid observed ( Fig. 17A ), irregularly shaped, 280 × 190 µm, the frontal surface occupied by a circular costate shield with nine costae separated by 1–2 intercostal pores, surrounded by smooth gymnocyst.

Ovicells endozooidal, immersed in the proximal half of the avicularium cystid ( Fig. 17B ); ooecium smooth, cap-like.

Remarks. An SEM micrograph of part of the holotype was previously published in Gordon (1989, pl. 2, fig. B) using the former catalogue number #387. This SEM image was fundamental to clarify that the lacunae were intercostal and not intracostal as might appear from the original drawings of Silén (1941).

Soule et al. (1998, p. 8, table 1) compared measurements and characters of all Cribralaria species described at that time. Measurements reported for C. curvirostris were taken from illustrations and are very different from those obtained from the new SEM images of the holotype and reported in Table 16. In particular, zooid width and avicularium length are much larger in Soule et al. (1998): zooidal size is 658 × 448–492 µm vs 448–629 × 237–361, while avicularium length is 463 µm (palate and opesia, therefore excluding the rostrum) vs 220–300 µm (rostrum included).

Based on the similarities between this genus and Hincksina , including the absence of basal pore chambers and pelmatidia in the spines, and the presence of endozooidal ovicells with cap-shaped ooecia formed by the distal avicularium, Berning et al. (2021) interpreted Cribralaria as a derived flustrid and transferred it from Cribrilinidae to Flustridae .

Figures

FIGURE 17. Cribralaria curvirostris Silén, 1941. Holotype UPSZTY 2484, Bonin Islands, Japan. A. Group of zooids, one ovicellate, interzooidal avicularia and a kenozooid. B. Close-up of the ooecium immersed in the distal avicularium. C. Tilted view of two autozooids showing the latero-oral, prominent spines. D. Close-up of interzooidal avicularia with curved, serrated rostrum. E. Close-up of the orifice. Scale bars: A = 200 µm; B, C = 120 µm; D = 100 µm; E = 40 µm.