Arthropoma semipunctata, Martino & Rosso & Taylor & Chiu & Fujita & Kitamura & Yasuhara, 2025

Arthropoma semipunctata sp. nov. Di Martino, Rosso and Taylor

Figure 49 View FIGURE 49

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Type material. Holotype PMC. B66. 29.7.2024 a, sample 19048 ( Figure 49A–D View FIGURE 49 ); paratype PMC. B66. 29.7.2024 b1, sample 19025 ( Figure 49E–F View FIGURE 49 ); paratype PMC. B66. 29.7.2024 b2, sample 19041 ( Figure 49G–H View FIGURE 49 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Etymology. Latin, meaning half-dotted, referring to the partially visible pseudoporous endooecium.

Diagnosis. Arthropoma with four distal spines in non-ovicellate autozooids but lacking in ovicellate autozooids, frontal shield pierced by slit-like pseudopores arranged in concentric ellipses leaving a slender imperforate strip beneath the orifice; orifice with deep, narrow sinus bordered by a flared, slim, proximal rim; ovicell kenozooidal; ooecium with exposed pseudoporous endooecium in its distal half, and smooth calcified ectooecium covering its proximal half.

Description. Colony encrusting, multiserial, unilaminar. Autozooids distinct, delineated by deep furrows, quincuncially or irregularly arranged, rounded hexagonal to irregularly polygonal, longer than wide (mean ZL/ZW 1.34). Frontal shield convex, pierced by pseudopores except for a narrow, central, rectangular strip below the orifice, 45–65 µm wide by 200–230 µm long, indistinct in some zooids; pseudopores slit-like, c. 15–25 µm long, arranged in concentric ellipses encircling the zooidal perimeter, with 4–5 rows distal to the orifice. Orifice placed at about 100–150 µm from distal zooidal margin, semicircular, wider than long, with a narrow, deep U-shaped sinus, flanked by two rectangular (10–15 µm wide by 50–65 µm long), crenulated condyles, slightly surpassing the length of the proximal margin on each side of the sinus and forming a distal constriction; a narrow (10–25 µm wide), flared rim surrounding the orifice (and sinus) proximally and laterally; four non-articulated distal oral spines present, short (20–35 µm long), tapering to a point with a small apical pore, the proximalmost pair positioned slightly above the distal half of the orifice, regularly and largely spaced, with pseudopores between pairs of spines, spine diameter at the base 18–26 µm; no spines visible in ovicellate zooids. Ovicell hyperstomial, globular, kenozooidal; endooecium partially exposed distally, with orange-peel texture, densely pierced by minute (2–3 µm in diameter), circular pseudopores; ectooecium partially calcified, covering the proximal half of the ooecium, the outline undulately rounded and W-shaped, smooth surface. Kenozooids associated with ovicells, irregularly polygonal, the portion exposed pseudoporous as zooidal frontal without further openings.

Measurements (µm). ZL 718±64, 647–834 (4, 12); ZW 537±54, 482–655 (4, 12); OL 135±5, 127–141 (4, 11); OW 170±6, 162–179 (4, 11); SinL 63±5, 52–71 (4, 12); OvL 313±32, 290–335 (2, 2); OvW 358±6, 353–362 (2, 2).

Remarks. Among Arthropoma species, only two others have autozooids with oral spines: A. subarensis Jain, Gordon, Huang, Kuklinski and Liow, 2022 and A. occidua Winston and Jackson, 2021 . These species differ from A. semipunctata sp. nov. in features of the ooecium. Arthropoma subarensis is characterized by a reticulate dimpled patterning of the endooecium with minute perforations at the bottom of each dimple (Jain et al., 2022), while A. occidua features a helmet-shaped ooecium, longer than wide, with slightly granular calcification and a few small pseudopores ( Winston and Jackson, 2021).