Steginoporella sp. 2

Steginoporella sp. 2

Figure 3 View FIGURE 3

Figured material. PMC EDM-Collection J.H.B.121a, sample 19210; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony erect, forming cylindrical branches of up to at least eight longitudinal series of autozooids; maximum diameter of the available branch 1.63 mm. Zooids dimorphic (A- and B-type) with B-zooids on average 1.3 times longer than Azooids, with a more extensive distal oral shelf (distal shelf length 93±11 µm [68–115 µm] in A-zooids vs 241±16 µm [219–268 µm] in B-zooids); Azooids more common than B-zooids (AZ:BZ 3:1). All zooids elongate rectangular (mean AZL/AZW 1.69 and mean BZL/BZW 2.02) with arcuate proximal border; distal border arcuate in A-zooids, straight in B-zooids; cryptocyst finely granular occupying about half length of frontal surface, depressed, flat, pseudoporous (pseudopore diameter 8–12 µm). Opesia semielliptical, longer than wide (mean OpL/OpW 1.28 in A-zooids, OpL/OpW 1.36 in B-zooids), delimited proximally by a median process (c. 142–145 µm long by 176–196 µm wide in A-zooids, 168–175 µm long by 179–190 µm wide in B-zooids) with moderately deep cavity; polypide tube placed centrally and vertically not visible in frontal view, its distal margin slightly below the level of median process; polypide tube diameter c. 130 µm in A-zooids and c. 160 µm in Bzooids. Gymnocyst smooth, reduced distally, forming lateral opercular condyles.

Measurements (µm). AZL 801±69, 674–873 (1, 18); AZW 474±33, 412–570 (1, 18); AZOpL 397±43, 353–478 (1, 6); AZOpW 311±28, 263–348 (1, 6); BZL 1052±37, 1002–1120 (1, 7); BZW 521±44, 462–594 (1, 7); BZOpL 440±9, 426–448 (1, 5); BZOpW 323±33, 282–370 (1, 5).

Remarks. Based on the available evidence, this species seems to differ from its Daidokutsu congener in having narrower branches made of fewer longitudinal series, and in the squared distal end of the B-zooids. Among the Steginoporella species characterized by dimorphic zooids, a median process with a moderately deep cavity, and straight distal margins of B-zooids, S. haddoni Harmer, 1900 is the most similar in the general zooidal appearance, as depicted in both Harmer (1900, figure 11) and Pouyet and David (1979, figure 2). Nevertheless, S. haddoni differs in having encrusting colonies and B-zooids twice the size of the Azooids.