Anteaeolidiella decorus sp. nov.

(Figs. 3–5)

urn:lsid:zoobank.org:act: E11F5253-9A4F-4031-9D2B-80C0FFAAD79F

Anteaeolidiella takanosimensis: Qi et al. 1989: 139, pl. 1, fig. 13; Zhang et al. 2016: 224, fig. 279. (Not of Baba 1930)

Type material. Holotype: MBM287593, live length 2.5 cm, voucher number: Op-21092901, dissected, 29 September 2021; Paratypes: MBM287594, six specimens, voucher number Op-21100101, live length 2.5 cm, 1 October 2021; voucher number Op-21100102, live length 2.0 cm, 1 October 2021; voucher number Op-21100301, live length 2.0 cm, 3 October 2021; voucher number: Op-21101301, live length 2.5 cm, 13 October 2021; voucher numbers Op-21101302 and Op-21101303, live length 2.0 cm, 13 October 2021.

Type locality. Port Nantun, Qingdao, China, 35°58′ N 120°16′E.

Description. External morphology (Figs 3A–D). Body elongated and slender. Living animals up to 2.5 cm in length. Anterior foot corners are stout and slightly protruded in latero-posterior direction. Background color generally translucent white, with bright orange or pink pigment over the dorsum. Head with a U-shaped orange mark with a darker margin, extending from the rhinophores to the base of oral tentacles. Both lateral sides of the head have a conspicuous pink margin. Rhinophores moderately long and stout, lower part translucent orange in color and the upper part opaque white. Oral tentacles slightly longer than the rhinophores, lower part translucent white and upper half opaque white. Pair of black larval eyes situated underneath the body wall at the posterior side of the rhinophores base. A whitish mid-line extending from the posterior end of the rhinophores to anterior side of the pericardium. An oval opaque white region is present over the pericardium, surrounded by orange or pink pigments. The latter interrupts the connection among white markings and extends almost to the tail. Cerata long and moderately thick, extending from the rear of the rhinophores to the tail and leaving a bare zone over the dorsum. Cerata epithelium diffusely covered with gray, orange, or pink pigments, with a white subapical band, terminating in a white tip. Cnidosacs translucent white. Cerata arranged in 25–28 rows. Each row contains up to seven cerata, decreasing in size towards the foot. Anus located below the second row of cerata on the right side. Gonopore positioned below the first row of the cerata.

Internal anatomy (Figs 4–5). Jaws thin (Figs 4A, B), amber-colored, inner margin (masticatory border) terminates distally in a small pointed process. Masticatory border smooth. Radula (Figs 4C, D) formula 15×0.1.0. Rachidian teeth wide and bilobed, progressively smaller to the posterior region of the radula, bearing 22–25 elongate and acutely pointed denticles to each side of the triangular and elongate central cusp. Oral glands large, fusiform, and conspicuous disposed dorsolaterally to the buccal bulb. Each oral gland comprises rows of giant secretory cells (Fig 5A). Salivary glands absent. Reproductive system is diaulic (Fig 5B). Ampulla wide, long, simply convoluted, and narrows before dividing into the oviduct and the vas deferens. Vas deferens long, wide, forming several loops and ending in a wider proximal portion of the penial sac, which contains an unarmed penial papilla. Oviduct short, connected to a large, rounded receptaculum seminis. The remaining portion of the oviduct departs from the base of the receptaculum and enters the female gland. Vagina opens posterior to the penis.

Etymology. The species name decorus, a Latin adjective, refers to the beautifully colored body of this species.

Distribution and habitat. Known from the Yellow Sea, China, live under intertidal rocks (present study). According to the molecular evidence, this species is also present in Japan (see below in the Discussion).

Biology. This species feeds on the sea anemone Aiptasia sp. Two specimens were found under rock mating and laying eggs (Fig 3E). Its egg mass is a simple spiral consisting of three complete whorls (Fig 3F).

Remarks. Anteaeolidiella decorus sp. nov. is characterized by a translucent white body with bright orange or pink pigment over the dorsum, translucent orange lower parts and opaque white upper parts of rhinophores, and by whitish oral tentacles. The new species is most similar to Anteaeolidiella cacaotica (Stimpson, 1855) from Australia in the coloration of the dorsum and cerata. The latter, however, differs from the new species in having rhinophores and oral tentacles with the same color as the background color (i.e., bright orange), and a lower number of cerata. Internally, Anteaeolidiella decorus sp. nov. shares radular features of Anteaeolidiella cacaotica (Stimpson, 1855). The radular teeth bear 23–24 and 22–25 denticles on each side of the triangular and elongate central cusp in Anteaeolidiella cacaotica and Anteaeolidiella decorus, respectively. The reproductive system of Anteaeolidiella cacaotica has not been studied to date, which prevents us from further comparison.