Boninia corolla Liu & He sp. nov.

Etymology.

The species name corolla is a Latin noun meaning “flower crown”, referring to the radially arranged prostatoid organs around the male atrium that look like a flower.

Material examined.

Holotype: • MBM 288498, Da’ao Village Beach (22°33.50'N, 114°53.33'E), Huidong, Guangdong Province, China; coarse-grained sand, 28 April 2024, coll. Hai-Long Liu; sagittal sections on five slides, deposited at MBMCAS; GenBank accession: PX 511324 (COI), PX 511553 (16 S), PX 511556 (18 S), and PX 511559 (28 S). Paratypes: • MBM 288499, sagittal sections on 4 slides, same data as for holotype; GenBank accession: PX 511554 (16 S), PX 511557 (18 S), and PX 511560 (28 S). MBM 288500, sagittal sections on four slides, same data as for holotype; GenBank accession: PX 511555 (16 S), PX 511558 (18 S), and PX 511561 (28 S).

Description.

The worm is flat and slender, translucent milky-white, and with tapering posterior end (Fig. 1 A). Anesthetized specimens are 14–26 mm long and 0.8–1.2 mm wide. A pair of fine, flexible tentacles (approximately 0.5 mm long) is present on either side of head (Fig. 1 B).

The tentacular eyes are absent. A pair of cerebral eyespots is symmetrically located at the anterior margin of the brain, with the two eyespots in each pair lying closely together (Fig. 1 B). Marginal eyespots, 28–48 in number, are evenly distributed along the base of the tentacles, extending to the posterior margin of the brain (Fig. 1 B).

The intestine is highly branched and darkened by gut contents. A ruffled pharynx is 7–11 mm long and is located at or slightly posterior to the center of the body (Fig. 1 A). The mouth opens slightly anterior to the center of the pharynx. The male pore lies approximately 1 mm behind the posterior end of the pharynx (Fig. 1 D). The female pore opens 1.5–2.0 mm posterior to the male pore (Figs 1 D, 2 F). An adhesive organ is located at the posterior end of body on ventral side.

The male copulatory apparatus is comprised of a seminal vesicle, an interpolated prostatoid, a penis papilla, and 9–15 prostatoid organs. A pair of sperm ducts extends along each side of the midline, curves at the posterior region of the pharynx, and enters the seminal vesicle separately (Fig. 1 D). The seminal vesicle is somewhat ovoid (Fig. 2 A, F), with both ends elongated, and the distal end opening into the prostatic vesicle (Fig. 2 A, F). The seminal vesicle is lined with a flat, ciliated epithelium and surrounded by a layer of very strong circular muscle fibers, especially near the distal part; a few longitudinal muscle layers lie external to the circular fibers (Fig. 2 A, F). The prostatic vesicle is nearly heart-shaped (50 μm in its long axis, 25 μm in its short axis), lined with high epithelium, and connects to penis papilla (Fig. 2 A, F). The penis papilla is unarmed and projects into the male atrium (Fig. 2 A, F). The inner wall of the male atrium is ciliated. The individual ducts of 9–15 prostatoid organs are radially arranged into a single girdle around the male atrium (Figs 1 C, 2 C) and open into inner area of the male atrium (Fig. 2 A, F). Each pyriform prostatoid organ bears a sclerotized stylet (approximately 60 μm in length) (Figs 1 C, 2 D). Extracapsular glands produce glandular secretion into each prostatoid organ (Fig. 2 C, D, F).

The ovaries are dorsally arranged in two rows, one on each side of the body, extending from behind the brain to almost the posterior end of the body. A pair of uterine canals, posterior to the male copulatory organ, are connected through short lateral branches to multiple uterine vesicles (approximately 10–17 in number on each side) (Fig. 1 D, E). Each uterine canal widens distally to form a large posterior dilation filled with eggs (Fig. 1 D, E). The uterine canals connect to the vagina immediately anterior to the entrance of Lang’s vesicle (Figs 1 D, 2 B, E, F). The Lang’s vesicle is elongated (240 μm in its long axis; 150 μm in its short axis) and is lined with ciliated epithelium (Fig. 2 B, E). The ciliated vagina extends anteriorly for a short distance, then turns ventrally to dilate and form a shell chamber, which is surrounded by numerous cement glands (Fig. 2 B, E). The vagina continues its course to open externally through the female genital pore.

Distribution.

The species is known from the type locality, Huidong, Guangdong, China.

Habitat.

Intertidal, coarse-grained sand.

Molecular phylogeny, DNA taxonomy, and genetic distances.

Our BI and ML trees are almost identical to each other in topology. All Boninia species form a clade with high support values (BP = 100 %, PP = 1) (Fig. 3). Boninia corolla sp. nov. is sister to a clade composed of all other species of the genus except B. yambarensis and B. neotethydis, with support values (BP = 72 %, PP = 0.96). For species delimitation, the bPTP analysis results in 8 entities for the concatenated dataset, and ABGD results in 6 entities for COI (Fig. 3, Suppl. material 1: fig. S 1). Notably, both delimitation approaches consistently supported Boninia corolla sp. nov. as a distinct species (Fig. 3). The uncorrected p-distances for the COI, 16 S, and 28 S in Boninia are shown in Tables 2 – 4, respectively. Intraspecific genetic distances ranged from 0.00–0.42 % for COI, 0.24–0.47 % for 16 S, and 0.00–0.13 % for 28 S. Interspecific genetic distances ranged from 10.72–22.14 % for COI, 2.58–21.02 % for 16 S, and 0.50–4.01 % for 28 S, with the exception of B. uru and B. cf. uru, which showed no divergence, 0.00 %.