Imogine mediterranea (Galleni, 1976) Jennings & Newman 1996

Gammoudi, Mehrez, Tekaya, Saïda & Noreña, Carolina, 2009, Contribution to the knowledge of Acotylean Polyclads (Platyhelminthes, Polycladida) from Tunisian Coasts, Zootaxa 2195, pp. 43-60 : 55-58

Imogine mediterranea (Galleni, 1976) Jennings & Newman 1996

( Figures 7–8 )

Syn.: Stylochus (Imogine) mediterraneus Galleni, 1976

Diagnosis (n. emend.): Stylochidae of variable dimensions, but, usually, mature specimens larger than 1 cm in length. Dorsal surface covered by numerous dark brown spots, smaller and denser near the edge of the body. Marginal eyes around the entire body. Male copulatory apparatus with an anchor shaped seminal vesicle. Genital pores separated but very close to each other and opening into the posterior half of the body. Vagina media with a folded epithelium.

Localities: 25 specimens were found among living and dead oysters and mussel shells in the lagoon of Bizerte (37°13 ' 19.29" N; 9°55 ' 49. 94" E).

Other localities: Italy: Galleni (1976), Wenzel et al (1992).

Material examined: 5 mature specimens were sagittally sectioned and mounted on slides. The material examined was deposited in the Museo Nacional de Ciencias Naturales de Madrid ( Spain).

Description: Body is thick and ovoid in shape, up to 30 mm in length. Anterior region with one or two major marginal ruffles. The dorsal side is whitish or brownish covered with dark brown spots except in the median region, where the very large ruffled pharynx can be seen by transparency ( Fig. 7 A). A pair of retractile nuchal tentacles is present ( Fig. 7 C). The eye-spots are distributed along the tentacles ( Figs. 7 C; 8A). The cerebral eyes form two clusters, and frontal eyes are present. Marginal eyes small, arranged in a band all around the body. The ventral side is whitish to cream. The many-folded pharynx is particularly large, with numerous lateral folds ( Fig. 7 B), and lies in the pharyngeal cavity in the second third of the body. The mouth opens onto the exterior at the beginning of the second third of the body. The main digestive trunk extends forwards and backwards over the pharyngeal cavity. Food remains could be observed in the gut of some of the sectioned specimens.

Male copulatory apparatus: The male copulatory organs are located in the distal part of the body. The relatively thick-walled vasa deferentia originate laterally near the middle of the pharynx and run separately ( Fig. 7 B). Close to the seminal vesicle, the wall of the vasa deferentia becomes strongly muscular and is connected with that the muscular lining of the tripartite (anchor-shaped) seminal vesicle ( Fig. 8 C, E), which is elongate and horizontally oriented. The ovoid prostatic vesicle, nearly twice as large as the seminal vesicle, has radial folds, and is lined by a thick musculature ( Fig. 8 E). It is connected distally to an unarmed penis papilla ( Fig. 8 B, E). A tubular male antrum is present which opens to the outside through to a male genital pore situated in the last fifth of the body.

Female copulatory apparatus: The female pore is located just behind the male opening and leads into the antrum femininum or vagina externa, which then leads to the vagina media or shell chamber. In its most distal region, the epithelium of the vagina media appears folded, ( Figs. 8 D; 8E), a feature not described by Galleni (1976). From this area, the vagina interna runs dorsally and posteriorly; then bends ventrally towards the entrance of the oviducts ( Fig. 8 E). Lang’s vesicle is absent. In one specimen, sperm was seen in several areas of the parenchyma, and hypodermic insemination can thus be hypothesized.

Remarks. The genus Imogine was established by Girard in 1853. On the basis of structure (single or tripartite) of the seminal vesicle in mature specimens, Marcus and Marcus (1968) divided the genus Stylochus into two subgenera, Stylochus and Imogine . The same scheme was followed by Faubel (1983) and Prudhoe (1985). Recently, Jenning and Newman (1996) elevated Imogine to the genus level. In the Mediterranean, the only known representative of this genus is Imogine mediterranea (Galleni, 1976) .

The external morphology and characteristics of the copulatory apparatus of our Tunisian specimens is very similar and agrees well with original descriptions of specimens collected by Galleni (1976) from coastal locations near Livorno and Pisa. Some differences, however, occur in the shape of the penis papilla and the antrum masculinum. In Galleni’s diagrammatic reconstruction (Galleni, 1976: Fig 6 ), the penis papilla is vertically oriented, while in our section it is more horizontally oriented. Furthermore, the male antrum in our sections is deeper and narrower ( Fig. 8 E) than in Tuscan specimens.

These differences, however, could be due to muscular contraction during fixation, and we prefer, for the time being, to consider the Tunisian and Tuscan specimens as conspecific.

Specimens of Imogine mediterranea and their egg masses were found in cultures of Mytilus galloprovincialis , among bivalves or inside empty shells.

Figures

FIGURE 6. Theama mediterranea: A: anterior view, B, C: male copulatory apparatus D: detail of the distal portion of the ejaculatory duct, E: sagittal reconstruction of male copulatory apparatus.

FIGURE 7. Imogine mediterranea: A: dorsal view, B: ventral view, C: nuchal tentacles p h: pharynx, v d: vasa deferentia.

FIGURE 8. Imogine mediterranea: A: section showing tentacular eyes, B: penis papilla, C: anchor shaped seminal vesicle, D: folded epithelium in the vagina media, E: sagittal reconstruction of the copulatory apparatus. c: circular muscle, e o: entrance of oviducts, f p: female pore, mp: male pore, pp: penis papilla, p v: prostatic vesicle, s g: shell glands, v: vagina, v e f: vaginal epithelium folds.