Hemismittoidea dicki, Martino & Rosso & Taylor & Chiu & Fujita & Kitamura & Yasuhara, 2025

Hemismittoidea dicki sp. nov.

Di Martino, Rosso and Taylor

Figure 28 View FIGURE 28

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Type material. Holotype PMC. B57. 29.7.2024 a, sample 19061 ( Figure 28A–C View FIGURE 28 ); paratype PMC. B57. 29.7.2024 b, sample 19210 ( Figure 28D View FIGURE 28 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Etymology. Named in honour of Prof. Matthew Dick, recognizing his significant contribution to the study of Japanese bryozoans.

Diagnosis. Hemismittoidea with rounded hexagonal to lozenge-shaped autozooids, each showing a single row of 18–25 closely spaced, marginal areolae within funnel-like depressions separated by distinct ridges; orifice with anvil-shaped lyrula occupying more than half its width; presence of oral spines uncertain; peristome with lateral flaps and sharp constrictions; avicularium positioned asymmetrically between two peristomial pores, needle-like, with acutely triangular, serrated rostrum pointing proximolaterally; ooecium striated and pseudoporous, except for a proximal imperforate portion, with a narrow distal band of secondary calcification.

Description. Colony encrusting, multiserial, unilaminar. Autozooids distinct, separated by shallow grooves, slightly longer than wide (mean ZL/ZW 1.23), rounded hexagonal to lozenge-shaped, quincuncially or irregularly arranged. Frontal shield flat or slightly convex, coarsely granular, imperforate except for a single row of 18–25 (with an average of 20) circular to elliptical marginal areolar pores, 19–43 µm in maximum diameter, closely spaced and located within funnel-like depressions separated by distinct ridges; an additional pair of pores of different sizes positioned on each side of distal margin of avicularium, the smallest measuring 12–14 µm in diameter, the largest 22–30 µm in diameter, in a few instances two pores on one side and only one on the other. Primary orifice elliptical, wider than long, with anvil-shaped lyrula occupying more than half of its width (LyW/OW 0.56), and acutely triangular condyles medially directed; short peristome surrounding and hiding primary orifice, more developed laterally, forming two flaps; secondary orifice keyhole-shaped, 160–185 µm long by 150–180 µm wide, with acutely triangular proximal constrictions defining a U-shaped pseudosinus; presence of oral spines uncertain; single, putative spine base rarely observed. Avicularium adventitious, single, needle-like, suboral, asymmetrically positioned, 30–50 µm from peristomial pseudosinus; rostrum raised, elongate, acutely triangular, with roughly serrated edges, directed proximolaterally on either side, with the tip sometimes resting on the marginal areolae; crossbar complete, thicker laterally, thin and fragile centrally, without ligula, creating a small, circular opening distally and a larger upside-down triangular to trapezoidal opening proximally. Ovicell hyperstomial, globular, formed by the distal zooid, not closed by zooidal operculum; ooecium smooth, radially striated, pierced by 40 circular to elliptical pseudopores arranged radially, maximum diameter of 5– 30 µm, the proximal rectangular portion flat and imperforate, with a narrow, 30–35 µm wide, peripheral band of secondary calcification spreading from adjacent zooids.

Measurements (µm). ZL 626±78, 512–721 (2, 9); ZW 507±80, 427–678 (2, 9); OL 130 (1, 1); OW 165 (1, 1); AvL 235±52, 143–300 (2, 14); AvW 55±7, 40–66 (2, 14); OvL 256 (1, 1); OvW 310 (1, 1).

Remarks. This new species is attributed to Hemismittoidea because of its asymmetrically developed submedial avicularium, which appears to bud from a distolateral areola and a median peristomial pore. This feature is a key differentiator between Hemismittoidea and Smittoidea Osburn, 1952 ( Soule and Soule, 1973; Gordon, 1984).

Hemismittoidea dicki sp. nov. stands out from other known species of Hemismittoidea because of the lack of obvious oral spines. In two instances, a small, circular pore (12 µm in diameter) has been observed on the distal margin of the peristome (see arrows in Figure 28A, D View FIGURE 28 ) that could potentially be the base of an ephemeral peristomial spine. Although the original diagnosis of the genus specifies, 2–6 oral spines as a typical character, we believe that the absence of oral spines is a less critical feature when compared to the distinctive submedial avicularium.

The only other Hemismittoidea species from the Northwest Pacific, H. taiwanensis Gluhak, Lewis and Popijak, 2007 , described from the southeastern coast of Taiwan, differs in having a convex frontal shield, less conspicuous marginal areolae, and rounded peristomial constrictions, in addition to 4–6 robust oral spines (Gluhak et al., 2007).