Steginoporella sp. 1

Steginoporella sp. 1

Figure 2 View FIGURE 2

Figured material. PMC EDM-Collection J.H.B.120a, sample 19210; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony erect, forming cylindrical branches of up to at least 15 longitudinal series of autozooids; maximum diameter of the available branch 3.95 mm. Zooids dimorphic (A- and B-type) with B-zooids on average 1.4 times larger than Azooids and with a more extensive distal oral shelf (distal shelf length 84±15 µm [53–108 µm] in Azooids vs 270±16 µm [240–285 µm] in B-zooids); A-zooids more common than B-zooids (AZ:BZ 3:1). All zooids elongate rectangular (mean AZL/AZW 1.66 and mean BZL/BZW 1.97) with arcuate distal and proximal borders, and finely granular cryptocyst occupying about half length of frontal surface, depressed, flat, pseudoporous (pseudopore diameter 9–14 µm). Opesia semielliptical, longer than wide (mean OpL/OpW 1.25 in both zooid types), delimited proximally by median process (c. 130 µm long by 245 µm wide in A-zooid, 230–275 µm long by 230–270 µm wide in B-zooids) with deep cavity; polypide tube placed centrally and vertically with its distal margin slightly above the level of median process; polypide tube diameter 185 µm in A-zooids and 210 µm in B-zooids. Gymnocyst smooth, reduced distally, forming lateral opercular condyles.

Measurements (µm). AZL 846±72, 706–953 (1, 20); AZW 508±37, 447–573 (1, 20); AZOpL 455±24, 410–504 (1, 14); AZOpW 365±25, 311– 394 (1, 14); BZL 1185±52, 1121–1261 (1, 7); BZW 602±52, 519–675 (1, 7); BZOpL 500±20, 478–530 (1, 6); BZOpW 400±38, 352–437 (1, 6).

Remarks. The widespread Steginoporella magnilabris (Busk, 1854) stands as the sole species within the genus reported from Japan (e.g., Ortmann, 1890; Silén, 1941). It is notable for forming bryozoan thickets in Sagami Bay, spanning depths from 7 to 126 m (Hirose et al., 2013). Among the Steginoporella species characterized by dimorphic zooids and a median process with a deep cavity, S. magnilabris bears the closest resemblance to this specimen from Daidokutsu cave. However, while S. magnilabris is known for its tendency to form large, encrusting uni- to multilaminar sheets ( Tilbrook, 2006) and erect rigid foliaceous colonies (Hirose et al., 2013), it does not typically form erect vincularian colonies with cylindrical branches, as observed in this instance. Steginoporella magnilabris also differs in the general appearance of the cryptocyst, which is more coarsely ornamented, and the shape and surface texture of the median process, which projects less outwards and is more granular than in Steginoporella sp. 1 (see Bock, 2024 https://bryozoa.net/cheilostomata/steginoporellidae/steginoporella _magnilabris .html).