Cranosina transversa ( 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 : 18-20

Cranosina transversa ( Silén, 1941)

( Fig. 6 ; Table 7)

Copidozoum transversum Silén, 1941: 41 , figs 52–55, pl. 2, fig. 6.

Cranosina transversa : Osburn, 1950: 49.

Material examined. Holotype by monotypy UPSZTY 2465 , Okinose , Sagami, Japan; depth 600 m; colony fragment detached from the substrate. Leg. Prof. S. Bock 1914.

Description. Colony encrusting, multiserial, unilaminar.

Autozooids rounded polygonal ( Fig. 6A ), hexagonal, pentagonal or lozenge-shaped, slightly longer than wide (mean L/ W 1.12), distinct, separated by thin grooves and a raised rim of beaded cryptocyst, irregularly arranged. Gymnocyst absent; cryptocyst outlined by a raised beaded rim, immersed, more extensive proximally (140–230 µm), narrower laterally and distally (50–110 µm), finely granular with granules 5–12 µm in diameter aligned radially all around the opesia, the innermost ring of granules projecting inwards, giving the opesia a denticulate appearance ( Fig. 6A, B ).

Opesia seemingly oval and extended for most of the zooidal frontal length; orificial opening transversely Dshaped, 220–230 × 300–310 µm.

Avicularia interzooidal, spoon-shaped, situated at the distal end of each zooid ( Fig. 6A ) on an irregularly rectangular cystid; rostrum raised and channelled, directed laterally or proximolaterally to either side ( Fig. 6B ), the length of the avicularium sometimes exceeding the length of the cystid hence the rostrum tip reaches the margins of the adjacent zooid; mandible acicular, about 250–400 µm long ( Fig. 6A ) pivoting on two robust condyles ( Fig. 6B ).

Ovicells not observed.

Remarks. Osburn (1950, p. 49) was the first to suggest Cranosina as a better fit for Copidozoum transversum when comparing his new species, Cranosina colombiana , with similar taxa. However, Chimonides & Cook (1994, p. 44) put on standby Osburn’s recommendation, awaiting the discovery of specimens to ascertain the method of brooding and type of ovicell. The type specimen lacks ovicells but the general appearances of autozooids and avicularia (including their placement distal to each autozooid) corresponds well with the type specimen of the genus, C. coronata ( Hincks, 1881) .

The inability to bleach the specimen (due to its type status and fragility) and to see the limit of the cryptocyst below the frontal membrane prevented observation and measurement of the opesia.

Genus Crassimarginatella Canu, 1900

Figures

FIGURE 6. Cranosina transversa (Silén, 1941). Holotype UPSZTY 2465, Japan.A. Close-up of two autozooids and associated interzooidal avicularia distally placed. B. Close-up of an interzooidal avicularium showing the two robust condyles. Scale bars: A = 200 µm; B = 60 µm.