Cauloramphus costatus 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 : 13-14

Cauloramphus costatus Silén, 1941

( Fig. 3 ; Table 4)

Cauloramphus costatus Silén, 1941: 31 , figs 31–33.

Material examined. Holotype by original designation UPSZTY 2462 , Okinose , Sagami, Japan; depth 600 m. Leg. Prof. S. Bock 1914.

Description. Colony encrusting, multiserial, unilaminar.

Autozooids pear-shaped with a tapering proximal gymnocyst ( Fig. 3A, B ), longer than wide (mean L/ W 1.56), distinct, separated by deep grooves, quincuncially arranged. Gymnocyst extensive proximally (100–255 µm), narrower laterally (50–65 µm), smooth; cryptocyst steeply sloping towards the opesia, narrow, 50–65 µm wide, completely obscured by spines, granular with granules c. 8 µm in diameter ( Fig. 3E ).

Opesia pear-shaped, occupying most of the zooidal length (mean OpL/ZL 0.66) ( Fig. 3E ); opesial spines varying in number from 22 to 33 (more commonly 28), 20–30 µm in maximum width, 185–300 µm long, acuminate, very closely set with little space between them, meeting and often overlapping in the midline, forming a slightly convex, costate frontal shield; opesial spine bases 20–25 µm in diameter; four short (60–80 µm long) spines, 18–25 µm in diameter placed distal to the orifice ( Fig. 3B ); orificial opening bell-shaped, 200–220 × 300–310 µm.

Avicularia adventitious, budding from pore chambers placed on the lateral gymnocyst ( Fig. 3D, E ), a very short peduncle expanding into the avicularian chamber; two latero-oral avicularia constantly placed between the distal orifice spines and the first pair of opesial spines, often two additional avicularia placed laterally at zooidal mid-length, sometimes one more (rarely two) avicularium placed proximolaterally; all avicularia tear-drop shaped with triangular rostrum directed distally or distolaterally to left or right and with two small condyles ( Fig. 3D ); the distalmost pair of avicularia slightly larger than the others.

Ovicells globular, resting on the proximal gymnocyst of the distal zooid ( Fig. 3A, C, D ); ooecium smooth with a triangular proximal opening (45–60 µm high by 115–120 µm wide at the base); only two distolateral oral spines, tightly against the lateral proximal margin of the ooecium, visible in ovicellate zooids ( Fig. 3C, D ).

Kenozooids observed as intramural buds in place of autozooids ( Fig. 3F ), pear-shaped, with smooth gymnocyst and central, oval opesia (260–285 × 190–210 µm) surrounded by a beaded rim of cryptocyst c. 20 µm wide.

Remarks. In addition to Cauloramphus costatus , eight other species of this genus have been reported in Japanese waters: C. cryptoarmatus Grischenko, Dick & Mawatari, 2007 ; C. disjunctus Canu & Bassler, 1929 ; C. japonicus Silén, 1941 ; C. magnus Dick & Ross, 1988 ; C. multispinosus Grischenko, Dick & Mawatari, 2007 ; C. niger Grischenko, Dick & Mawatari, 2007 ; C. pseudospinifer Androsova, 1958 ; C. spinifer ( Johnston, 1832) . These species are all easily distinguishable from C. costatus : C. cryptoarmatus is characterised by an extensive coarsely granular cryptocyst ( Grischenko et al. 2007, fig. 9); C. disjunctus has zooids interconnected by tubular chambers separated by lacunae (e.g. Dick et al. 2011, fig. 3); in C. japonicus , opesial spines do not meet in the midline (see description below and Fig. 4 ); avicularia are rare but single and with a longer peduncle if present in C. magnus ( Grischenko et al. 2007, fig. 10), C. pseudospinifer ( Dick et al. 2005, fig. 3G, H), and C. spinifer ( Grischenko et al. 2007, fig. 13), and apparently absent in C. multispinosus ( Grischenko et al. 2007, fig. 11); finally, the ooecium is cap-like and granulose in C. niger ( Grischenko et al. 2007, fig. 12).

The delicate striations in the ooecium as described and drawn in Silén (1941, p. 33, fig. 31) were not observed.

Figures

FIGURE 3. Cauloramphus costatus Silén, 1941. Holotype UPSZTY 2462, Japan. A. Group of zooids. B. Close-up of an autozooid. C. Close-up of an ovicellate zooid. D. Close-up of ovicells and avicularia. E. Close-up of an autozooid deprived of spines, showing the granular cryptocyst and the budding sites of avicularia. F. Intramurally budded kenozooids. Scale bars: A = 400 µm; B, C, E, F = 200 µm; D = 100 µm.

FIGURE 4. Cauloramphus japonicus Silén, 1941. Holotype UPSZTY 2463, Japan. A. Group of zooids. B. Close-up of two autozooids lacking stalked avicularia. The arrow indicates the only proximolateral avicularium observed in the specimen. C. Close-up of two autozooids with a single stalked avicularium. D. Intramural budding in autozooids. E. Ovicellate zooids with paired stalked avicularia. F. Close-up of an ovicell flanked by two stalked avicularia. Scale bars: A–E = 200 µm; F = 100 µm.