Emprosthopharynx hartei sp. nov.

Fig. 20

Material examined.

Holotype: Yucatan coast, Mexico • 1; 18 Slides; Dzilam; 21.5°N, 88.9°W; 13 m; 10 May 2018; A. Hernández leg.; CRPPY -0095. Paratypes: Yucatan coast, Mexico • 4; Dzilam; 21.5°N, 88.9°W; 14 m; 9 May 2018; A. Hernández leg.; CRPPY -0092 • 3; Dzilam; 21.5°N, 88.9°W; 14 m; 9 May 2018; A. Hernández leg.; CRPPY -0093.

Distribution.

Dzilam de Bravo, Yucatan, Mexico.

Description.

Body shape elliptical, 10 mm length and 7 mm width. Body constitution solid with a translucent background (Fig. 20 A). Conspicuous whitish intestinal branches extend towards margins. Body periphery with a white dotted line. Nuchal tentacles rounded and prominent, with 20–30 eyes per tentacle. Two small clusters of cerebral eyes close to the tentacles are, 12–20 eyes per cluster (Fig. 20 B). Ruffled pharynx centrally positioned. Oral pore located at pharynx centre. Dorsal pore dorsally in the last body 1 / 3, visible when examined in vivo (Fig. 20 A, E). Reproductive system. Male and female copulatory apparatus situated posterior to the pharynx, in the second 1 / 2 of the body. Male copulatory organ immersed in a muscular bulb: the seminal vesicle, prostatic vesicle, ejaculatory duct, and an elongated penis papilla covered with long cilia with a sclerotised appearance. Elongated seminal vesicle receives the vasa differentia separately at its proximal end. Distally the seminal vesicle connects to the prostatic vesicle through a narrow duct. Prostatic vesicle lined with a thick wavy epithelium and extending into a long duct that surrounds the ejaculatory duct. The ejaculatory duct is ciliated and discharges in the penis papilla. A narrow and shallow male atrium houses the penis papilla (Fig. 20 C, D). Female reproductive system characterised by a short, wide, muscular atrium covered by a well-developed ciliated epithelium. A narrow tubular vagina externa leads from the atrium towards the wider vagina interna, lined with glandular epithelium. At its distal end, the vagina interna divides into two oviducts that turn towards the anterior region. Both sections of the vagina, but especially the vagina interna, are surrounded by dense masses of cement and shell glands. Lang’s vesicle is absent (Fig. 20 C, D).

Etymology.

The species name hartei is dedicated to the conservationist Edward H. Harte, in recognition of his lifelong commitment to environmental conservation and his significant contributions to marine science and the protection of marine ecosystems.

Remarks.

Currently, the genus Emprosthopharynx is composed of nine species: E. gracilis (Heath & McGregor, 1912); E. hancocki (Hyman, 1953); E. heroniensis Beveridge, 2018; E. lysiosquillae Oya, Nakajima & Kajihara, 2022; E. opisthoporus Bock, 1913; E. pallida (Quatrefage, 1845); E. vanhoffeni Bock, 1931; E. onubensis Pérez-García, Gouveia, Calado, Noreña & Cervera, 2024; and E. rasae Prudhoe, 1968. The genus is distributed mainly within the Pacific Ocean, except for E. pallida and E. onubensis, which are native to the Mediterranean, and E. vanhoffeni found in the Cape Verde Islands (Bock 1931) and Morocco (Prudhoe 1985). Emprosthopharynx hartei sp. nov. lacks marginal eyes as do E. pallida, E. onubensis, E. hancocki, E. gracilis, and E. heroniensis. Still, it can be distinguished from the other Emprosthopharynx species by the presence of tentacles, which E. hartei shares only with E. hancocki and E. gracilis (Pérez-García et al. 2024).

Regarding the internal characteristics between Emprosthopharynx hartei and E. hancocki, in both species, the distal region of the papilla peneal is covered by a series of bristles, thickened, or with pseudosclerotised cilia (the styliform development of the basal membrane mentioned by Faubel 1983, 1984). This pseudosclerotised formation differentiates these two species from the other species of Emprosthopharynx, which either present a true stylet (E. vanhoffeni and E. lysiosquillae) or show a naked papilla peneal, without hard structures (E. heronensis, E. gracilis, E. onubensis, E. opisthoporus, E. pallidus, and E. rasae).

The main difference between Emprosthopharynx hancocki and E. hartei is found at the level of the arrangement and shape of the reproductive system. The seminal vesicle and the prostatic vesicle in E. hancocki barely present a small constriction between one organ and another, while in E. hartei the transition between the seminal vesicle and the prostatic vesicle is marked by a tube-like narrowing. In addition, the prostatic vesicle in E. hartei empties through an elongated sinuous extension until the papilla peneal.

The distinction between Emprosthopharynx gracilis and E. hartei lies in the structural and morphological characteristics of the distal region of the male copulatory apparatus. Emprosthopharynx hartei has an elongated prostatic vesicle that leads to a long ejaculatory duct. The duct ends in a papilla peneal surrounded by a flattened atrium. In contrast, E. gracilis is characterised by a rounded prostatic vesicle and a short and robust papilla peneal that opens into a long and deep atrium. Within the female reproductive system, we can observe differences between E. hartei and E. gracilis. For instance, the female atrium in E. hartei is elongated and narrow, whereas in E. gracilis it is short and widened. Additionally, the thickening of the vagina is distinct in the two species: in E. hartei, the thickening is located in the proximal region, while in E. gracilis it is found in the distal region.