Hippopleurifera hirosei, Martino & Rosso & Taylor & Chiu & Fujita & Kitamura & Yasuhara, 2025

Hippopleurifera hirosei sp. nov.

Di Martino, Rosso and Taylor

Figure 27 View FIGURE 27

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Type material. Holotype PMC. B56. 29.7.2024 a, sample 19143 ( Figure 27A–D View FIGURE 27 ); paratype PMC. B56. 29.7.2024 b1, sample 19227 ( Figure 27E View FIGURE 27 ); paratype PMC. B56. 29.7.2024 b2, sample 19135 ( Figure 27F View FIGURE 27 ); paratype PMC. B56. 29.7.2024 b3, sample 19217 ( Figure 27G View FIGURE 27 ); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Etymology. Named in honour of Dr Masato Hirose, recognizing his significant contribution to the study of Japanese bryozoans.

Diagnosis. Hippopleurifera with nodular frontal shield marked by ridges, with 3–4 rows of marginal areolar pores and narrow, elliptical, imperforate central region; orifice keyhole-shaped with downwardly hooked condyles and 6–9 robust, distolateral oral spine bases; adventitious avicularia large and spoon-shaped or small and pear-shaped, placed either laterally to orifice or frontally, single or paired, directed proximally or proximolaterally externally; ooecium seemingly with pitted fenestrae.

Description. Colony encrusting, multiserial, unilaminar. Autozooids distinct, separated by deep furrows, slightly longer than wide (mean ZL/ZW 1.21), rectangular to irregularly polygonal. Frontal shield flat to slightly convex, nodular, marked by faint radial ridges, with 3–4 rows of circular to elliptical marginal areolar pores, 20–45 µm in maximum diameter, and a narrow, elliptical, imperforate central region, 360–515 µm long by 150–240 µm wide. Orifice keyhole-shaped with arched anter separated from a shallow, bowl-shaped poster by two downwardly hooked condyles; 6–9 oral spine bases, 28–45 µm in diameter, arranged in an arch surrounding the anter with the proximalmost pair above or at level with condyles. Avicularia adventitious, single or paired, of two sizes and shapes: type 1, large and spoon-shaped placed laterally to orifice level with the proximalmost spines or laterally on the frontal shield at approximately zooidal mid-length or distal-third; or type 2, small and pear-shaped exclusively observed on the frontal shield; both types directed proximally or proximolaterally externally with complete crossbar. Broken ooecia observed, appearing globular, one measuring approximately 440 µm in length by 570 µm in width, with pitted fenestrae.

Measurements (µm). ZL 868±77, 729–972 (3, 10); ZW 717±102, 583–839 (3, 10); OL 248±28, 188– 287 (3, 9); OW 211±17, 176–231 (3, 9); AvL (type 1) 193±41, 148–294 (4, 10); AvW (type 1) 75±22, 40–123 (4, 10); AvL (type 2) 105±8, 99–111 (2, 2); AvW (type 2) 66±7, 61–71 (2, 2).

Remarks. The definitions of the genera Hippopleurifera and Hippomenella Canu and Bassler, 1917 suffers from ambiguity. Canu and Bassler’s diagnosis of Hippomenella , particularly with reference to the ovicell, included fossil specimens that could potentially be attributed to Hippopleurifera (see Berning, 2013). Our new species is ascribed to Hippopleurifera based on features from both the ovicell and frontal shield, following Berning (2013): the frontal shield is nearly entirely perforated by areolar pores, indicating an extremely reduced umbonuloid part, and the structure of the ooecium, albeit poorly preserved, which seems to possess fenestrae. As noted in an earlier study of the Cenozoic bryozoan fauna of East Kalimantan, certain species exhibit a combination of characters from both genera, showcasing a bifenestrate ooecium typical of Hippopleurifera and an almost imperforate frontal shield characteristic of Hippomenella , thereby constituting an argument for the synonymization of these two genera (Di Martino and Taylor, 2015).

This new species differs from Pacific species assigned to both Hippopleurifera and Hippomenella . Hippopleurifera lateralis (MacGillivray, 1891) has 10 spines and proximomedially directed avicularia. Hippopleurifera? philippinensis Canu and Bassler, 1929 has six spines and avicularia directed distally. Hippopleurifera porosa (Canu and Bassler, 1929) has small, triangular avicularia and only two rows of marginal areolae. Hippopleurifera repugnans (Canu and Bassler, 1929) has 10–12 oral spines and large avicularia placed distally to the orifice and directed distolaterally. Hippomenella avicularis (Livingstone, 1926) has large spatulate avicularia directed distolaterally (see Gordon and d’Hondt, 1997). Hippomenella chepigae Gontar, 1993 has four spines, and paired avicularia located laterally to the orifice. Although described as directed distally, the drawing depicts them as directed proximally (Gontar, 1993, p. 44, figure 6). Hippomenella coronula (Ortmann, 1890) differs in the shape, size and direction of the avicularia, with those placed laterally to the orifice directed distolaterally. Hippomenella rudicula Tilbrook, 2006 has 14 spines. Hippomenella sp. nov. described in the doctoral dissertation of Hirose (2010), and yet to be formalized, has a distinctly elongate orifice and is devoid of spines. The Pleistocene species Hippomenella konnoi Kataoka, 1961 has 11 spines and a distolaterally directed avicularium placed laterally to the orifice.