Glabrilaria biavicularia (Kataoka, 1961)

Glabrilaria biavicularia (Kataoka, 1961) View in CoL

Figure 19 View FIGURE 19

v. 1961 Cribrilaria biavicularia Kataoka , p. 242, pl. 27, fig. 5.

Figured material. PMC EDM-Collection J.H.B.130a, sample 19025; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Description. Colony encrusting, multiserial, unilaminar. Autozooids distinct, separated by shallow grooves, oval to rhomboidal or rarely polygonal, longer than wide (mean ZL/ZW 1.37). Frontal shield flat, consisting of 12–15 (mean 14) narrow costae including suboral pair, maximum basal width 20–37 µm, tapering towards the centre, converging along an irregular midline, adorned with a prominent, pointed pelmatidium at the base. Costae connected by intercostal bridges creating 5–7 slit-like to reniform intercostal lacunae, 8–18 µm in length. Suboral pair of costae extremely reduced, originating within the length of orifice proximal margin not laterally relative to the orifice, extending proximally (almost longitudinally to the zooid elongation) and creating a distinctive suboral area with a large, rounded to upside-down triangular suboral pore, measuring 23–32 × 27–34 µm. Gymnocyst exposed along zooidal margins, typically wider proximally (proximal axial length 50–104 µm). Orifice semicircular with straight proximal margin; five, regularly spaced oral spine bases, 10–15 µm in diameter, the proximalmost pair placed slightly above the proximal oral margin. Avicularia teardrop-shaped, mostly paired and of different sizes, occasionally single, emerging from basal pore chambers lateral to the orifice, positioned either at the same level as the proximal margin of the orifice or slightly above aligned with the proximalmost pair of spines; rostrum slender and needle-like, oriented distomedially around distal edge of orifice, resting beside oral spines; small mandibular pivots present. A single kenozooid observed, polygonal, with reduced costate shield of six radial costae, 116 × 114 µm. Pore-chamber windows visible along lateral walls of zooids at colony periphery, rounded to elliptical, 9–26 µm long by 5–10 µm wide. Ovicells not observed.

Measurements (µm). ZL 348±41, 298–415 (1, 11); ZW 254±11, 239–269 (1, 11); OL 60±2, 58–63 (1, 10); OW 65±3, 60–70 (1, 10); AvL 98±16, 77–142 (1, 16); AvW 41±4, 36–49 (1, 16); KzL 189 (1, 1); KzW 192 (1, 1).

Remarks. The characteristics observed, including the number of oral spines, costae, and avicularia, as well as the position and orientation of the avicularia, and size measurements fall within the documented variability range for this species as described by Kataoka (1961). In the single fragment recovered, the number of spines consistently remains at five, while Kataoka (1961) noted a range of 4–6 spines in his Pleistocene specimens. Additionally, there is also a slight discrepancy in the variability of coastal number: 12–15 in the Holocene fragment compared to 11–14 in the Pleistocene specimens. It is possible that the vestigial suboral costae were not accounted for by Kataoka (1961). Furthermore, upon examination of the holotype image, albeit with caution due to its poor quality, there appears to be a potential difference in the development of the gymnocyst, which seems less extensive than in our material. Kataoka (1961) did not mention the presence of pointed pelmatidia, which may be due to preservational issues, as observed also in some zooids within our fragment.