Parasmittina cf. delicatula (Busk, 1884)

Parasmittina cf. delicatula (Busk, 1884) View in CoL

Figure 31 View FIGURE 31

cf. 1884 Mucronella delicatula Busk , p. 156, pl.

18, fig. 2.

cf. 1973 Parasmittina delicatula (Busk) ; Soule and Soule, p. 401, fig. 6D–F.

Figured material. PMC EDM-Collection J.H.B.133a, sample 19210; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony encrusting, multiserial, multilaminar. Autozooids distinct, separated by shallow grooves, slightly longer than wide (mean ZL/ZW 1.13), oval to irregularly polygonal, chaotically arranged due to frontal budding. Frontal shield flat to slightly convex, coarsely granular, imperforate except for a single row of typically more than 20 circular to elliptical marginal areolar pores, 15–45 µm in maximum diameter; additional smaller pores, about 10 µm in diameter, flanking the avicularium. Primary orifice orbicular, with rectangular lyrula occupying approximately one-third of its width (mean LyW/OW 0.32), and robust triangular condyles, medially directed, 10–12 µm long by 11–13 µm wide; orifice encircled by a rim of smooth calcification, sometimes extending laterally as open flaps; oral spine bases numbering one or absent, distal, medial, 14–20 µm in diameter. Avicularia adventitious, located lateral to orifice, usually single, sometimes paired, proximally directed, of three types: type 1, small-sized rounded triangular; type 2, medium-sized elliptical to slightly spatulate; type 3, large, almost as long as an autozooid, broadly spatulate; complete crossbar not observed. When observed paired, one of the avicularia is small and the other medium-sized. Ovicells not seen.

Measurements (µm). ZL 437±31, 409–483 (1, 6); ZW 386±38, 325–435 (1, 6); OL 132±6, 124–142 (1, 9); OW 134±9, 122–150 (1, 9); AvL (type 1) 77±10, 66–87 (1, 5); AvW (type 1) 65±10, 48–71 (1, 5); AvL (type 2) 124±6, 119–132 (1, 4); AvW (type 2) 63±6, 58–72 (1, 4); AvL (type 3) 371 (1, 1); AvW (type 3) 191 (1, 1).

Remarks. Parasmittina delicatula was originally described from Hawaii and has since been reported widely across the Pacific, including Japan. Hayward and Parker (1994), who designated a lectotype, noted that this species is highly variable. Despite this variability, there are two traits that seem to remain constant: 1) the orbicular shape of the primary orifice, which is also equipped with a lyrula having a straight distal edge and gently concave sides, along with thin, pointed condyles slightly curving downward, and distal border bearing a single median spine, absent in some autozooids; 2) the enlarged spatulate avicularia that can be as long as an autozooid and have a slender complete crossbar.

In our specimen, the condyles are more robust and are not downwardly curved but are instead directed medially. Avicularian crossbars were not observed, likely due to their delicate structure, and no ovicells were found, hindering further comparisons. Compared to the description and illustration of P. delicatula by Hirose (2010), our specimen differs again in having more robust condyles not downwardly curved. In addition, in the Recent specimen from Sagami Bay, the medium-sized avicularia may also point distally, while the small triangular avicularia were not observed.