Auricellina biserialis, Martino & Rosso & Taylor & Chiu & Fujita & Kitamura & Yasuhara, 2025

Auricellina biserialis sp. nov.

Di Martino, Rosso and Taylor

Figure 21 View FIGURE 21

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Type material. Holotype PMC. B52. 29.7.2024 a, sample 19132; Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Etymology. Latin, meaning two rows, referring to the arrangement of autozooids in two alternating series within the internode.

Diagnosis. Catenicellid with multizooidal, biserial internodes. Autozooids claviform, arranged in alternating series. Frontal shield smooth, with symmetrical pore areas (vittae) adjacent to the orifice extending proximally beyond it, and minute pores scattered along the margin. Orifice transversely Dshaped with shallowly concave proximal margin interrupted medially by a short suture. Ovicell elongate, flat frontally, with a horizontal median slit-like fissure or two uncalcified areas on each lateral half; sometimes with a longitudinal carena. Avicularia seemingly absent. Dorsal side smooth with a small drop-shaped or narrowly elliptical pore area, with a few pores, placed at the distolateral corner of autozooids or distal margin of the ooecium.

Description. Colony erect, likely jointed and branching; branching pattern unknown. Internodes multizooidal and biserial. Autozooid distinct, separated by deep grooves, claviform, tapering proximally forming a tubular cauda 180–220 µm long and c. 65 µm wide, much longer than wide (mean ZL/ZW 3 including cauda), arranged in alternating series. Frontal shield convex, smooth, largely gymnocystal except for two symmetrical, cryptocystal pore areas (vittae) adjacent to the orifice, extending proximally beyond it, slightly depressed in relation to their rim and the surrounding gymnocyst, 80–105 µm long by 40–75 µm wide, with minute pores scattered along the margin; pores circular, 1–2 µm in diameter; costae and foramina absent. Orifice monomorphic, transversely D-shaped, with proximal margin starting with straight corners sloping towards the centre forming a shallowly concave median proximal part, interrupted medially by a short, vertical suture, 8–12 µm long. Ovicell subimmersed, elongate (mean OvL/OvW 1.55), occupying the cauda and one-third of the proximal portion of the distal zooid; ooecium flat frontally, with an ectooecial slit-like fenestra (45–100 µm long by 5– 10 µm wide) on its proximal third, placed medially, extending horizontally, slightly arched, sometimes separated into two openings of different size and shape, obliquely oriented sometimes developing a median longitudinal carena; ooecial opening quadrangular, c. 45 µm long by 65–80 µm wide, likely not closed by zooidal operculum. Dorsal side smooth, entirely gymnocystal except for a drop-shaped or narrowly elliptical (c. 70 µm long) cryptocystal pore area smaller than those on the frontal (40–45 µm long by 20–25 µm wide); cryptocystal pore area placed at the dorsal distolateral corner of autozooids or if ovicellate at the dorsal distolateral margin of ooecium, with 1–2 circular pores, 3 µm in diameter; a pronounced suture between the back of the ooecium and the margin of the cauda visible proximally, distally the dorsal side of the ooecium seemingly fusing with the surface of the cauda. Avicularia seemingly absent.

Measurements (µm). ZL 531±28, 507–561 (1, 3); ZW 186±7, 179–194 (1, 3); OL 62±7, 57–67 (1, 2); OW 79.5±1, 79–80 (1, 2); OvL 255±10, 248–262 (1, 2); OvW 163.5±11, 156–171 (1, 2).

Remarks. This species differs from the only other species assigned to the genus in the arrangement of internodes. In Auricellina nuda (Gordon, 1993) comb. nov., internodes consist of 1–2 autozooids, while in A. biserialis gen. et sp. nov. there are at least five, but probably more, autozooids per internode. Another difference is in the presence of pore areas on the sides of the cauda in A. nuda comb. nov., absent in A. biserialis sp. nov., and in the number of pores in the vittae, which are more abundant in A. nuda comb. nov. than in A. biserialis sp. nov.