Bugulina kiuschiuensis ( 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 : 42-44

Bugulina kiuschiuensis ( Silén, 1941)

( Fig. 20 ; Table 19)

Bugula pugeti var. kiuschiuensis Silén, 1941: 106 , figs 149–152, pl. 8, figs 29, 30.

Bugulina pugeti kiuschiuensis : Fehlauer-Ale et al., 2015: 8.

Material examined. Holotype by original designation UPSZTY 2458 , Okinoshima (33°51' N; 130°3' E), Japan; depth 40 m; from a gravel sea-bottom consisting of shell fragments. Leg. Prof. S. Bock 1914.

Description. Colony erect-flexible, with bifurcating biserial branches, triserial at bifurcations ( Fig. 20A, C ); each colony frond starting with a single, basal autozooid equipped with a cluster of rhizoids for attachment to the substrate ( Fig. 20B ).

Autozooids rounded rectangular, elongate (mean L/ W 2.01), distinct, separated by deep grooves, arranged in alternating biserial rows, with basal and lateral walls lightly calcified and frontal surface almost completely occupied by the frontal membrane ( Fig. 20A ); the distolateral corners projecting upwards into a blunt, short (30–35 µm long), non-articulated spine ( Fig. 20C, D ) per side, rarely into two.

Opesia U-shaped, occupying almost the entire frontal surface (mean OpL/ZL 0.89) except for a narrow band of smooth gymnocyst ( Fig. 20A ).

A single pedunculate bird’s-head shaped avicularium attached to the external, lateral side of each autozooid at mid-length or slightly more distally, at about two-thirds of zooidal length, close to the opesial margin ( Fig. 20A, C, D ); rostrum directed backwards and beak strongly hooked downward; the triangular mandible also with downward hooked tip ( Fig. 20C, D ), c. 150–160 µm long; crossbar complete; some avicularia slenderer than others.

Ovicells absent.

Remarks. There is some discrepancy between the description of the type specimens in Silén (1941, p. 106) and what has been observed in the present instance. Instead of five colonies attached to the same substrate (a fragment of Thalamoporella lioticha Ortmann, 1890 ), the type specimen consists of 10 fragments without any substrate. However, the original morphological description fits with that observed in the studied specimens.

Silén (1941) described this species as a variety of B. pugeti ( Robertson, 1905) originally described from Puget Sound (Washington State) and Alaska. It mainly differs in having constantly biserial branches instead of multiserial ones with usually 4–7 zooidal rows. Based on this morphological difference and the significant geographic separation between their respective places of origin, the subspecies is here elevated to the status of species. Both Robertson (1905) and Silén (1941) described their species and subspecies as internal brooders, with the embryos sheltered in the distal basal part of the zooidal body cavity. Soule et al. (1995) observed that the distal corners of some zooids in specimens of B. pugeti from British Columbia were curved inward, almost merging over the aperture, and hypothesized that those were the brooding zooids. Similar zooids with infolded distal corners were observed in the present specimens ( Fig. 20A , arrowed, and D). It needs to be determined whether this feature genuinely indicates brooding embryos internally or if the inward rolling of distolateral margins is merely a consequence of drying.

Genus Camptoplites Harmer, 1923

Figures

FIGURE 20. Bugulina kiuschiuensis (Silén, 1941). Holotype UPSZTY 2458, Japan. A. Overview of part of a colony. Arrows indicate putative brooding zooids with folded distolateral margins. B. Close-up of the first basal zooid with rhizoids. C. Close-up of branches at bifurcation. D. Close-up of avicularia and autozooids with folded distolateral margins. Scale bars: A = 400 µm; B, C = 200 µm; D = 120 µm.