Parellisina sileni Osburn, 1949

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 : 21-23

Parellisina sileni Osburn, 1949

( Fig. 8 ; Table 9)

Ellisina latirostris Silén, 1941: 36 , figs 41, 42.

Parellisina sileni Osburn, 1949: 5 , fig. 10.

Material examined. Holotype by original designation SMNH-Type-3081, North Pacific , Yokohama Bay, Tokyo, Japan; depth 115 m. Leg. Vega Expedition 1878–1880, Station 1083.

Description. Colony encrusting a flat rocky substrate, 2.5 × 4.5 cm in size; colony size 3.523 × 2.648 mm ( Fig. 8A ); one distal pore-chamber window visible on zooids at colony growing edge, elliptical, 60 × 28–38 µm ( Fig. 8H ). Ancestrula seemingly tatiform and elliptical, about 300 µm long by 215 µm wide, with at least seven spines encircling the opesia ( Fig. 8B , arrowed).

Autozooids oval, longer than wide (mean L/ W 1.37). Gymnocyst mostly not visible but in some zooids extensive proximally (85–145 µm), narrow (20–50 µm) to minimal laterally, smooth, convex ( Fig. 8C–E ); cryptocyst raised, beaded, narrow proximally (50–90 µm), tapering (30–55 µm) and steeply sloping inwards the opesia laterally, disappearing distally ( Fig. 8C, D ). Interzooidal communication through uniporous septula, elliptical, about 20 µm long by 15 µm wide, visible on lateral walls at zooidal mid-length ( Fig. 8I , arrowed).

Opesia oval, occupying almost the entire length of the frontal surface ( Fig. 8D ); operculum semicircular ( Fig. 8F ). Pair of delicate spines placed distolaterally on the gymnocyst, the basal diameter 5–7 µm, visible also in ovicellate zooids; an additional spine placed at about zooidal mid-length visible in some autozooids ( Fig. 8C, D ).

Avicularia vicarious, falciform, placed on a polygonal or often rectangular cystid with the gymnocyst always well developed laterally and sometimes extensive distally ( Fig. 8C, F ); proximal cryptocyst narrow, beaded as in autozooids ( Fig. 8F ); rostrum asymmetrical, curved to either side, rounded, jagged, raised and distally directed; opesia small, elliptical to subcircular, 78–116 long by 54–68 µm wide; condyles triangular and robust; mandible shape similar to that of the rostrum ( Fig. 8F ). Kenozooids distal to avicularium asymmetrically triangular with a central, rounded triangular to subcircular opening, 40–70 µm long by 50–70 µm wide ( Fig. 8G, H ).

Ovicells globular, not closed by the operculum, resting on the proximal gymnocyst of the distal zooid, indenting and modifying the outline of its cryptocyst ( Fig. 8C ); ectooecium uncalcified except for a narrow smooth band of calcification visible distally ( Fig. 8E ), endooecium coarsely granular ( Fig. 8C–E ).

Remarks. Silén (1941) described this species as Ellisina latirostris before being aware of the description of the new genus Parellisina , and the species P. latirostris , by Osburn (1940). The new genus was introduced for membraniporid/calloporid taxa having interzooidal avicularia associated with a kenozooid, as is the case in Silén’s species. When Osborn (1949) transferred Silén’s species to Parellisina the specific name was preoccupied and he renamed it as P. sileni in honour of its original author. Parellisina sileni differs from Parellisina latirostris in the shape of the avicularian rostrum, falciform in the former species and spatulate in the latter, and of the associated kenozooid, triangular and spade-shaped, respectively (see Fig. 8G and Osburn 1940, pl. 4, figs 33, 34).

Figures

FIGURE 8. Parellisina sileni Osburn, 1949. Holotype SMNH-Type-3081, Japan. A. General view of the colony encrusting a rock. B. Ancestrula, seemingly tatiform with at least seven countable spine bases (see white arrows) and early astogeny. Two distolateral spine bases usually visible on periancestrular autozooids (see black arrows). C. Group of ovicellate zooids with complete or incomplete ooecia and an avicularium. Arrows point to preserved circumopesial spine bases. D. Close-up of an ooecium and an autozooid without the frontal membrane showing the beaded cryptocyst, the opesia and spine bases, one placed proximolaterally and the other distolaterally (see arrows). E. Close-up of an ovicellate zooid with frontal membrane and distolateral spine bases flanking the ooecium. F. Close-up of an autozooid with the frontal membrane and open operculum showing the outline of the orifice, and two avicularia with the falciform mandibles mirroring the shape of the rostrum. G. Closeup of an avicularium with the associated kenozooid. H. Avicularia with open mandibles showing the elliptical opesia and robust, triangular condyles almost touching, and the autozooids at colony edge showing the distal pore-chamber window and a broken ooecium. I. Broken autozooids showing the lateral uniporous septula (see arrows) for autozooidal communication. Scale bars: A = 1 mm; B, C, D = 200 µm; E, F, G = 150 µm; H, I = 250 µm.