Semikinetoskias dubia 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 : 48

Semikinetoskias dubia Silén, 1941

( Fig. 24 ; Table 22)

Semikinetoskias dubia Silén, 1941: 114 , figs 168–173.

Material examined. Lectotype (designated here) UPSZTY 191153 D, the best preserved specimens among all the syntypes. Okinose , Sagami, Japan; depth 100–600 m. Leg. Prof. S. Bock 1914 . Paralectotypes: UPSZTY 2472 A–B, UPSZTY 191152 , UPSZTY 191153 E, same details as the lectotype.

Description. Colony erect-flexible with bifurcating unilaminar, biserial branches ( Fig. 24A ).

Autozooids elongate and slender (mean L/ W 3.09), arranged in alternating biserial rows, proximal end tapered, distal end truncated and slightly convex ( Fig. 24B, C ); frontal surface almost entirely occupied by the frontal membrane and the oval opesia, except for a band of smooth gymnocyst, variable in length from 55 to 250 µm; spines absent; opercular region undefined.

A single shortly pedunculate bird’s-head avicularium attached to the external, lateral side of each autozooid at about mid-length close to the opesial margin, placed on a step-like projection ( Fig. 24C ), oriented parallel to the longitudinal axis of the autozooid, 330 µm long (including the peduncle) by 125 µm wide; rostrum ogival, 190 µm long, directed distally and only slightly hooked downward, mandible also ogival ( Fig. 24D ).

Dorsal side smooth with a median shallow sinuous furrow marking zooidal boundaries.

Ovicells not observed.

Remarks. This monospecific genus was introduced by Silén (1941) to allocate S. dubia , a species with features in between two other genera, Bugula Oken, 1815 and Kinetoskias Danielssen, 1868 . Semikinetoskias dubia has Bugula -like autozooids and Kinetoskias -like adventitious, pedunculate avicularia placed on step-like projections. Compared to fig. 173 of Silén (1941), direct observations of the single avicularium preserved attached to the type specimens show that the peduncle is even shorter and can be also positioned parallel to the length of the autozooid (or the longitudinal axis of the branch) ( Fig. 24C, D ) in addition to being placed at a right angle.

Figures

FIGURE 24. Semikinetoskias dubia Silén, 1941. Lectotype (designated here) UPSZTY 191153D, Japan.A. General view of the specimen. B. Close-up of two autozooids lacking pedunculate avicularia because detached. C. Close-up of an autozooid with pedunculate avicularium. D. Close-up of avicularium. E. Dorsal side. Scale bars:A = 1 mm; B = 200 µm; C = 120 µm; D = 100 µm; E = 500 µm.