Stylochus marimarensis, Pérez-García & Gouveia & Calado & Noreña & Cervera, 2024

Pérez-García, Patricia, Gouveia, Filipa, Calado, Gonçalo, Noreña, Carolina & Cervera, Juan Lucas, 2024, Acotylea (Platyhelminthes, Polycladida) from the southern and western Iberian Peninsula, with the description of five new species, Zoosystematics and Evolution 100 (4), pp. 1487-1513 : 1487-1513

Stylochus marimarensis sp. nov.

Fig. 5

Holotype.

• MNCN 4.01/2820 to 3058, Station 12 , 2 March 2014, 55 mm long, sagittally sectioned into 237 slides.

Diagnosis.

Oval-shaped worm with flattened anterior and tapered posterior ends. Pinkish colouration and pale pink spots scattered on the dorsal surface; black spots dispersed along the margins and at the base of the tentacles; margins whitish; ventral body pale pink; gonopores separated in last body third; with spermiducal bulbs; opening of the ejaculatory duct medially within the penis papilla; penis papilla elongated; male and female atrium ciliated.

Description.

Oval shaped Stylochidae with flattened anterior and tapered posterior ends. Firm corporal thickness. Dorsal pigmentation pinkish, with scattered pale pink spots (Fig. 5 A ). Whitish margins with some folds and black mottling. Ventral surface pale pink (Fig. 5 B ). Transparent, conical nuchal tentacles (Fig. 5 C ) on either side of the cerebral lobes. Tentacular eyes situated at the base and tips of the tentacles. Two elongated clusters of cerebral eyes between the tentacles. Marginal eyes along the body margin, more numerous anteriorly. Pharynx ruffled along central body region. Oral pore medial. Gonopores separated (0.82 mm), reddish pigmented, and near the posterior end.

Reproductive system.

Male system with an anchor-shaped seminal vesicle, a polyglandular prostatic vesicle (“ djiboutiensis ” type), and an elongated penis papilla (Fig. 5 F ). Spermiducal bulbs well-developed (Fig. 5 D ). Seminal vesicle tripartite (0.55 mm length, 0.65 mm width). Prostatic vesicle elongated, oval-shaped (1 mm long), surrounded by numerous extravesicular glands. Penis papilla elongated (0.22 mm) opening in a ciliated atrium. Seminal and prostatic ducts join medially to form the ejaculatory duct (Fig. 5 F ).

The female reproductive system is a simple tube divided into the external and internal vagina. Without Lang’s vesicle. The oviducts open together in the proximal region of the internal vagina. Abundant shell and cement glands empty into both vaginas. Female atrium shallow and ciliated.

Type locality.

Santa Maria del Mar Beach, Cadiz ( Spain).

Etymology.

The name of the new species refers to the type locality, Santa María del Mar.

Biology.

Collected under rocks in the intertidal zone. The species was found on a stony bottom interspersed with rocky pools.

Distribution.

The only locality where this species was collected is Santa Maria del Mar Beach, Cadiz ( Spain).

General discussion of the newly described species of Stylochus .

Sixty-two accepted Stylochus species are distributed worldwide ( Tyler et al. 2006–2024) and are distinguished mainly by their colour pattern, eye arrangement, and colour and shape of the tentacles ( Jennings and Newman 1996; Bulnes 2010). Nevertheless, additional features allow distinction among these species, such as the opening of the gonopores, together or separately, the junction of the seminal duct with the prostatic duct in the penis papilla, the shape and size of the penis papilla, and the inner outline of the external vagina. All of these characteristics are compared in Table 2 for Stylochus spp. distributed in the eastern Atlantic, Mediterranean, and Black Seas.

Stylochus marimarensis sp. nov. differs from other known species of the genus by its pinkish pigmentation with pale pink spots on the dorsal side, bordering whitish margins, and black mottling. The known species in the Mediterranean and eastern Atlantic vary in colour from brown, orange, and white to yellow, but none of them display a continuous white edge, as in S. marimarensis sp. nov.

Stylochus spp. distributed out of these territories that share similar pigmentation with S. marimarensis sp. nov. are S. qeshmensis Maghsoudlou & Momtazi, 2014 and S. kimae Jennings & Newman, 1996 . S. qeshmensis has a rosy brown colour with dark brown spots scattering dorsally except along the margins, white tentacles, and a short penis papilla. Black spots of S. marimarensis sp. nov. are distributed within the margins only, and few of them are under the tentacles. This latter presents transparent tentacles and long penis papilla. S. kimae has a bright orange-pink colour and several light brown dots, features which are lacking in S. marimarensis sp. nov. Both S. qeshmensis and S. kimae lack spermiducal bulbs, a very prominent character in S. marimarensis sp. nov.

Stylochus erytheius sp. nov. has remarkable orange, dark pigmentation and lacks a whitish margin. S. fafai also shares an orange colour, displays close but separated gonopores, a reduced penis papilla, and a female system without dilatations. The mottling of S. mediterraneus is darker than that of S. marimarensis sp. nov., and the latter has a more elongated penis papilla than the one observed in S. mediterraneus . S. neapolitanus presents a bold orange band in the margins, a dark brown background and greenish mottling on the dorsal side, and a reduced penis papilla. All of these features differ from those of the new species. The same occurs with S. plessisii since the colour pattern is different, with a whitish colour and black and orange spots. S. pilidium bears a yellowish, pale colour and a reduced penis papilla. Finally, S. stellae has a brown colour with dark brown spots, with separated gonopores close to each other and a proximal junction of the prostatic and seminal ducts, while S. marimarensis sp. nov. displays well-separated gonopores and a medial junction of the ducts.

On the other hand, the species that most resemble S. erytheius sp. nov. are S. fafai and S. pilidium . S. fafai shows a similar body shape and pigmentation, but the gonopores are located close together, the penis papilla is reduced, and the external vagina lacks dilatation. The background colour of S. pilidium is quite different, showing pale-yellow pigmentation, and the junction of the prostatic and seminal ducts is proximally located; the penis papilla is shorter than that observed in S. erytheius sp. nov., and the external vagina lacks dilatation.

Other species that share some similarities with S. erytheius are S. kimae and S. rutilis Yeri and Kaburaki 1918 . The most pronounced differences between S. kimae and S. erytheius are the dorsal pigmentation. This one is brighter and pinkish with light brown mottling in S. kimae and orangish with darker brown mottling and white dots in S. erytheius sp. nov. Additionally, the junction between the seminal and prostatic ducts occurs proximally in S. kimae and distally in S. erytheius sp. nov. Conversely, S. rutilis displays a reddish orange dorsal colour, with also reddish spots and a red median line. This type of pattern is lacking in S. erytheius sp. nov. The marginal eyes are distributed along the anterior margins of S. rutilis but encircle the entire body of S. erytheius sp. nov. Finally, the gonopores are very close together in S. rutilis but distinctly separated in S. erytheius sp. nov.

Figures

Figure 5. Stylochus marimarensis sp. nov. (MNCN 4.01 / 2820 to 3058). Histological sections are postero-anteriorly oriented: A. Dorsal view of a living specimen; B. Ventral view; C. Detail of the tentacles and cerebral eyes; D. Histological section of the male copulatory apparatus; E. Histological section of the female copulatory organs; F. Sagittal reconstruction of the reproductive system. Abbreviations: c, cilia; cg, cement glands; eg, extravesicular glands; ev, external vagina; fa, female atrium; fp, female pore; i, intestine; iv, internal vagina; ma, male atrium; mp, male pore; ov, oviduct; pp, penis papilla; pv, prostatic vesicle; sb, spermiducal bulbs; sv, seminal vesicle.