Labioporella aviculifera (Silén, 1941) n. comb.

(Fig. 1; Table 2)

Siphonoporella aviculifera Silén, 1941: 62, figs 73–75.

Material examined. Holotype by monotypy SMNH-Type-3082 (Fig. 1A–E) North Pacific, Yokohama Bay, Tokyo, Japan; depth 115 m. Leg. Vega Expedition 1878–1880, Station 1083 . Other material: SMHN-132263 (Fig. 1F–J); North Pacific, Tokyo Bay, Japan; depth 119 m.

Description. Colony encrusting, multiserial, uni- to multilaminar due to self-overgrowth; interzooidal communication through transversely elliptical uniporous septula (Fig. 1J), c. 60 × 30 µm, observed on the lateral vertical walls at about mid-length; septular pore also elliptical, c. 15 × 5 µm.

Autozooids arranged in alternating rows, distinct with narrow grooves and a raised rim of smooth calcification, variable in shape from oval to club-shaped to rounded polygonal, almost twice as long as wide (mean L/ W 1.86) (Fig. 1A, C, D); vertical wall thickness 140–250 µm (Fig. 1J). Gymnocyst absent; cryptocyst extensive, occupying three-fourths of zooidal length, flat proximally and centrally, rising and becoming more convex distally below the opesia at level with the polypide tube, forming a raised, striated rope-like rim distally and laterally to the opesia and sloping steeply inwards; granular, with granules 10–15 µm in diameter, and those of the rope-like opesial rim aligned in radial rows; pseudoporous, with 20–35 circular pseudopores scattered centrally, about 7–10 µm in diameter (Fig. 1E, G). Two circular opesiules at the sides of the polypide tube, c. 20–30 µm in diameter (Fig. 1B).

Opesia immersed, eye-shaped to semi-circular; polypide tube generally placed centrally and symmetrically (Fig. 1B, J), short, circular (175–200 µm in diameter); operculum semi-circular (Fig. 1H, I), roughly corresponding in size to the diameter of the polypide tube (155–175 × 170–185 µm); two communication pores visible through the opesia in the inner distolateral corners of some autozooids (Fig. 1D).

Avicularia infrequent, placed at bifurcation of zooidal rows (Fig. 1A, C, D), about one-third to one-fourth of autozooidal length; cystid rectangular (Fig. 1G), rostrum slightly raised, rounded, symmetrical and distally directed (Fig. 1F), cryptocyst granular and imperforate, opesia occupying half to two-thirds of frontal surface, semi-elliptical to bell-shaped (Fig. 1A, C, D, F); mandibles not observed.

Intramural, reparative budding common in autozooids (Fig. 1C, F, J).

Remarks. Species of the genus Siphonoporella, including the type species S. nodosa Hincks, 1880 (see Cook et al. 2018, fig. 3.31), are characterized by a lightly calcified skeleton, a small nodular proximal gymnocyst, a smooth imperforate cryptocyst, a long eccentrically placed polypide tube, and the absence of B-zooids and avicularia. Conversely, in Silén’s species the skeleton is robust, the gymnocyst is absent, the cryptocyst is granular and pseudoporous, and avicularia are present although infrequent. The main reason that led Silén (1941) to place his species in Siphonoporella was the position of the polypide tube. However, in frontal view the polypide tube seems to be placed centrally in the majority of autozooids (Fig. 1A–D), while only in a few cases seems to lean more towards one side (e.g. Fig. 1F). The view from the top of a broken zooid at colony edge (Fig. 1J) also confirms its central position. Similar variability is also seen in other Labioporella species [e.g. L. bimamillata (MacGillivray, 1885) see Bock (2023) http://bryozoa.net/cheilostomata/steginoporellidae/labioporella _bimamillata .html]. Based on all the above reasons, the genus Labioporella seems to be the best fit for this species and the new combination L. aviculifera is hereby proposed.

Although avicularium size is one-third to one-fourth that of an autozooid, Silén (1941) described the avicularia as vicarious based on their position at the bifurcation of zooidal rows in which they occupy the site of one of the two daughter zooids (Fig. 1D). In other species of Labioporella with avicularia [e.g. L. crenulata (Levinsen, 1909) see Cook et al. 2018, fig. 3.30)], these are usually the same size as autozooids, fitting more properly into the definition of vicarious.