Crassimarginatella spinifera 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 : 20-21

Crassimarginatella spinifera Silén, 1941

( Fig. 7 ; Table 8)

Crassimarginatella spinifera Silén, 1941: 25 , fig. 20.

Material examined. Holotype by original designation UPSZTY 2466 , Goto Islands , Kyushu, Japan; depth 200–300 m; encrusting a bivalve shell. Leg. Prof. S. Bock 1914.

Description. Colony encrusting, multiserial, unilaminar ( Fig. 7A ).

Autozooids rounded hexagonal to club-shaped ( Fig. 7A ), longer than wide (mean L/ W 1.42), distinct, separated by thin grooves, quincuncially arranged. Gymnocyst extensive proximally (145–250 µm), narrower laterally (25–70 µm), negligible distally, smooth, convex; cryptocyst outlined by a raised beaded rim, surrounding and sloping towards the opesia, evenly extensive proximally and laterally (30–60 µm), minimal distally, coarsely granular with granules 5–10 µm in diameter aligned in radial rows ( Fig. 7B ).

Opesia oval, occupying about half zooidal length (mean OpL/ZL 0.56); opesial spines ranging from 5 to 8 (distributed as follows: 2–4 distolateral, two lateral, 1–5 proximal), most commonly seven, 100–150 µm long, 15–35 µm in diameter (the most robust usually the mid-proximal one), widely spaced, those placed laterally and proximally curved over the aperture but not meeting in the midline, indenting the cryptocyst at the base ( Fig. 7B, D ); orificial opening transversely D-shaped.

Avicularia subvicarious, always smaller than autozooids, placed randomly among autozooids, overall rounded but slightly narrower and constricted at level with the hinge of the mandible ( Fig. 7B, C ), placed on an irregularly polygonal cystid made of smooth, convex gymnocyst; a narrow rim of granular cryptocyst bordering the proximal margin; rostrum and mandible semielliptical, 60–70 × 120–150 µm; pivotal bar or condyles not observed.

Ovicells prominent, globular, resting on the proximal gymnocyst of the distal zooid ( Fig. 7B, D, E ); ectooecium uncalcified except for a narrow, circumferential band of smooth gymnocyst; endooecium extensive, granular; only two distolateral oral spines visible in ovicellate zooids.

Subsequent intramural budding observed in both autozooids and avicularia: in the first case the newly budded polymorph being either an autozooid or an avicularium, in the latter case forming a kenozooid ( Fig. 7E ).

Remarks. Silén (1941) mentioned Crassimarginatella kumatae ( Okada, 1923) has the most similar species to C. spinifera , one of the main similarities being the appearance of the ooecium, rounded and granulated. In describing specimens of C. kumatae from South Korea, Min et al. (2017, p. 473) discussed the definition of the genus Crassimarginatella in relation to the different types of ooecia observed in species currently assigned to this genus. While some species of the genus, such as the type species C. crassimarginata ( Hincks, 1880) , have an ectooecium almost completely calcified, except for a narrow, slit-like window, another group of species, including C. kumatae and C. spinifera , have a mostly membranous ectooecium and an extensively exposed, smooth or granular endooecium. Min et al. (2017) suggested waiting for genetic information before splitting off a new genus. Unfortunately, despite the increasing efforts to build a complete molecular phylogeny for cheilostome bryozoans (e.g. Orr et al. 2021, 2022), sequencing data on Crassimarginatella species are still scarce.

Genus Parellisina Osburn, 1940

Figures

FIGURE 7. Crassimarginatella spinifera Silén, 1941. Holotype UPSZTY 2466, Japan. A. General view of part of the colony. B. Group of zooids. C. Close-up of an avicularium. D. Close-up of ovicellate zooids. E. Examples of intramural budding in both autozooids and avicularia. Scale bars: A, B, D, E = 200 µm; C = 100 µm.