Exechonella coronida, Martino & Rosso & Taylor & Chiu & Fujita & Kitamura & Yasuhara, 2025

Exechonella coronida sp. nov.

Di Martino, Rosso and Taylor

Figure 22 View FIGURE 22

zoobank.org/ A0297EDF-09F0-4B12-A0C4-AD5C572DCF8B

Type material. Holotype PMC. B53. 29.7.2024 a, sample 19010 ( Figure 22A–C View FIGURE 22 ); paratype PMC. B53. 29.7.2024 b1, sample 19007 ( Figure 22D View FIGURE 22 ); paratype PMC. B53. 29.7.2024 b2, sample 19035 (not figured); Core 19, Daidokutsu cave, Okinawa, Japan, Holocene.

Etymology. Greek ‘koronída’, meaning coronis, i.e., a curved punctuation mark similar to a small apostrophe or a curved line used in ancient Greek to show a crasis (the contraction of two vowels into one), referring to the coronis-like shape of its avicularia.

Diagnosis. Exechonella of the magna -complex with numerous, medium-sized, rounded, and spaced foramina with narrow rims, single or paired curved avicularia with rounded triangular rostrum proximally directed having a complete crossbar, and a few small marginal pores between avicularia and zooidal margins.

Description. Colony encrusting, multiserial, uni- to multilaminar due to self-overgrowth. Autozooids distinct, separated by deep grooves and thin raised sutures, lozenge-shaped, longer than wide (mean ZL/ZW 1.21). Frontal shield slightly convex, nodular, evenly and densely perforated by 20–42 medium-sized, regularly spaced, rounded foramina with a slightly raised, narrow rim; no frontal projections. Primary orifice concealed by a collar-like peristome; condyles not seen. Peristome pustulose, imperforate; secondary orifice semicircular to elliptical to eye-shaped. Avicularia adventitious, sporadic; if present, single or paired, placed approximately at zooidal mid-length, laterally, adjacent to zooidal lateral corners deriving from a marginal areolar pore and associated with a foramen. Foramina associated with avicularia having modified shape compared to foramina elsewhere on frontal shield, appearing more elongate elliptical or resembling a fissure; a raised rim outlines both the avicularium and the associated foramen, with the total diameter outlined by this rim, occupied by the avicularium for two-thirds, and by the foramen itself for one-third. Avicularia curved, rostrum rounded triangular, proximally directed, external lateral edge raised; crossbar complete; 3–5 small (14–28 µm in diameter), circular marginal areolar pores present between the external lateral edge of the avicularium and the margin of the zooid. Clusters of up to five circular marginal areolar pores often developing in the same position, even in the absence of an avicularium.

Measurements (µm). ZL 913±115, 687–1144 (3, 20); ZW 752±80, 614–940 (3, 20); OL (secondary) 185±15, 169–198 (1, 3); OW (secondary) 235±15, 222–251 (1, 3); PeL 117±35, 61–161 (3, 8); FoN 30±5, 20–42 (3, 20); FoD 45±9, 32–59 (3, 20); AvL 151±18, 118–173 (3, 20); AvW 93±14, 78–122 (3, 20).

Remarks. This species belongs to the Exechonella magna -complex, which is characterized by lozenge-shaped zooids, low collar-like peristomes, numerous large foramina with free space in between, and proximally directed triangular avicularia equipped with a complete crossbar (Cook and Bock, 2004; Cáceres-Chamizo et al., 2017). Although efforts have been made to disentangle other Exechonella species-complexes such as the E. ampullacea -complex, E. antillea -complex, E. brasiliensis -complex and E. verrucosa -complex (see Cáceres-Chamizo et al., 2017), the E. magna - complex remains unresolved. Exechonella coronida sp. nov. is easily distinguished from all other specimens currently identified as E. magna (McGillivray, 1895) because of the curved shape of its avicularia. In specimens of E. magna from the Miocene of Muddy Creek ( Australia), avicularia are either lozenge-shaped (Cook and Bock, 2004, figure 2A) or drop-shaped (Cook and Bock, 2004, figure 3A), consistently with an acutely triangular rostrum. Recent specimens attributed to E. magna from the Solomon Islands also have drop-shaped avicularia ( Tilbrook, 2006, pl. 18E), while avicularia are described as triangular for the Philippines’ specimens of Canu and Bassler (1929).

The general shape and distribution of foramina in E. coronida sp. nov. are reminiscent of species in the E. brasiliensis -complex. However, avicularia in this group lack a crossbar and have a central nipple-like structure (Cáceres-Chamizo et al., 2017).