Stylochus mediterraneus Galleni, 1976

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 mediterraneus Galleni, 1976

Fig. 3

Stylochus (Imogine) mediterraneus Galleni, 1976 .

Imogine mediterranea ( Galleni, 1976) Jennings & Newman, 1996 .

Material examined.

• MNCN 4.01/3448 to 3463, Station 11 , 29 April 2014, 14 mm long, sagittal sectioned into 16 slides ; • MNCN 4.01/3521 to 3560, Station 11 , 19 April 2015, 30 mm long, sagittal sectioned into 40 slides (all the measurements from the description refer to this last specimen) ; • MNCN 4.01/3957 , Station 11 , 30 November 2017, 12 mm long ; • MNCN 4.01/3959 , Station 11 , 19 May 2016, 32 mm long ; • MNCN 4.01/3960 , Station 11 , 2 February 2018, 28 mm long ; • MNCN 4.01/3561 to 3630, Station 12 , 2 March 2014, live and fixed specimen, no histological processed ; Station 13 , 15 June 2015, 42 mm long, sagittal sectioned into 70 slides .

Description.

Thick worm with oval shape and variable length, 42 mm long (26.33 ± 11.41 mm). Dorsal side brownish with brown pale spots scattered along the whole surface (Fig. 3 A ). A few dark spots are also present, more numerous in the body margin. Margins white, with dark spots. Ventral side pale or cream (Fig. 3 B ). Nuchal retractile tentacles present. Tentacular eyes present at the base and on the tips of the tentacles (Fig. 3 C ). Cerebral eyes arranged in two clusters between the tentacles. Frontal eyes present, scattering to the anterior margin. Marginal eyes around the entire body edge. Pharynx ruffled, anterior located with numerous lateral branches (Fig. 3 B ). Oral pore anteriorly positioned in the central part of the pharynx. Gonopores separated but close together (0.2 mm), located in the last third of the body.

Reproductive system.

Male system with spermiducal bulbs, anchor-shaped seminal vesicle, polyglandular prostatic vesicle, and short penis papilla (Fig. 3 G ). Spermiducal bulbs enter separately into the tripartite seminal vesicle. Seminal vesicle horizontal (Fig. 3 D ), located just behind the prostatic vesicle. Prostatic vesicle elongated (0.74 mm long), with a well-developed muscular wall (0.05 mm) and crossed by numerous extravesicular glands (Fig. 3 E, G ). In the middle section, the prostatic and seminal ducts together form the ejaculatory duct (Fig. 3 G ). Penis papilla short-housed in a ciliated male atrium (Fig. 3 E ).

Female pore close to the male pore, leading to a slightly folded external vagina (Fig. 3 F, G ). Distal part of the external vagina internally folded (Fig. 3 F, G ). Smooth internal vagina, in which the paired oviducts are received. Lang’s vesicle absent.

Remarks.

The features of the specimens studied herein match Galleni’s (1976) description for specimens found on the Tuscany coast ( Italy), except for the structure of the female complex, in which the presence of folds within the vagina externa is not mentioned. However, Gammoudi et al. (2009) also noted the horizontal orientation of the penis papilla, the ciliated or non-ciliated atrium, and the dilatations in the external vagina in specimens from Tunisia and not for the populations from Tuscany ( Galleni 1976).

Biology.

The specimens were observed under rocks in the intertidal zone and among brown algae Halopteris scoparia (Ochrophyta). In other studies, this species and its egg masses were found in cultures of Mytilus galloprovincialis (Mollusca, Bivalvia) ( Gammoudi et al. 2009).

Distribution.

This species was reported in several localities of the Mediterranean Sea, such as Croatia ( Bytinski-Salz 1935, as Stylochus pilidium ); Livorno, Marina di Pisa, and Punta Bianca, Italy ( Galleni 1976); Liguria, Italy ( Wenzel et al. 1992); Temara, Morocco, the Atlantic Ocean ( Prudhoe 1989); Tunisia ( Gammoudi et al. 2009); and Murcia ( Marquina et al. 2014 a). Our record is the first for this species on the Atlantic coasts of the Iberian Peninsula and in Andalusia.

Figures

Figure 3. Stylochus mediterraneus (MNCN 4.01 / 3521 to 3560). Histological sections are antero-posteriorly oriented: A. Dorsal view of a living specimen; B. Ventral view; C. Detail of the tentacles and cerebral eyes; D. Histological section of the seminal vesicle and part of the prostatic vesicle; E. Histological section of the male copulatory organs; F. Histological section of the female apparatus; G. Sagittal reconstruction of the reproductive system. Abbreviations: c. cilia; cg, cemental glands; eg, extravesicular glands; ev, external vagina; 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.