Caulibugula bocki 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 : 47-48

Caulibugula bocki Silén, 1941

( Fig. 23 ; Table 21)

Caulibugula bocki Silén, 1941: 109 , figs 153–157.

Material examined. Holotype by original designation UPSZTY 2461 ( Fig. 23A ), Bonin Islands (Ogasawara), west from Chichijima, Japan; depth 100–110 m; sea-bottom made of shell rubble and sand . Paratype UPSZTY 191151 ( Fig. 23B–F ), Bonin Islands (Ogasawara), east from Higashijima, depth 135 m. Leg. Prof. S. Bock 1914 .

Description. Colony erect-flexible with bifurcating unilaminar, biserial branches ( Fig. 23B, C ); the creeping basal part of the colony formed by tubular kenozooids strongly calcified, and with a slit-like membranous central area ( Fig. 23A ).

Autozooids elongate and slender (mean L/ W 4.07), shorter at bifurcations, arranged in alternating biserial rows, proximal end tapered, distal end truncated straight or slightly convex ( Fig. 23D, E ); frontal surface almost entirely occupied by the frontal membrane and opesia, except for a short band of smooth gymnocyst, 75–100 µm long; spines absent; opercular region well-defined, transversely D-shaped, 50–70 × 90–115 µm ( Fig. 23C, D ). A single, incomplete zooid, with a more tubular shape and distal end evenly rounded, observed ( Fig. 23E, F ).

Avicularia and ovicells seemingly absent.

Remarks. The holotype specimen consists only of the creeping basal part of the colony formed by tubular, strongly calcified kenozooids ( Fig. 23A ). The two branches emanating from the kenozooidal stalk, one consisting of two kenozooids and the other of three autozooids and four kenozooids as described in Silén (1941, p. 109), were not found. The studied holotype material is from locality 32 as indicated by Silén (1941). However, this initial indication conflicts with the figure caption, in which the specimen drawn is referred to locality 31. No material labeled as C. bocki has been found from locality 31 in the collection, suggesting that it might be a typological error. The other specimen available, the paratype from locality 37 ( Fig. 23B–G ), lacked the distal kenozooids described and figured in Silén (1941, figs 155, 156), while included the tubular zooid ( Fig. 23F ) interpreted by Silén (1941) as transitional between a distal kenozooid and a ‘true’ autozooid. It is worth noting that the numerical identifiers assigned to localities by Silén (1941) lack any direct correlation with sampling station numbers; they were simply part of an ordinal sequence.

The large volume of unsorted material deposited at MEUU from Prof. S. Bock’s 1914 expedition might provide better preserved specimens showing all the described characters, an ideal condition for the selection of a neotype in the future .

Genus Semikinetoskias Silén, 1941

Figures

FIGURE 23. Caulibugula bocki Silén, 1941. A. Holotype UPSZTY 2461, Bonin Islands, Japan. A. Stem of strongly calcified kenozooids and chitinous tubes. B–F. Paratype UPSZTY 191151, Bonin Islands, Japan. B. Branch bifurcation. C. Close-up of zooids at bifurcation. D. Close-up of autozooids along the branch. E. Branch with a partially preserved tubular autozooid. F. Close-up of the tubular autozooid in (E). Scale bars: A, C = 300 µm; B = 500 µm; D, E = 200 µm; F = 100 µm.