Leptoplana tremellaris (O.F. Muller, 1774)

Gammoudi, Mehrez, Tekaya, Saïda & Noreña, Carolina, 2009, Contribution to the knowledge of Acotylean Polyclads (Platyhelminthes, Polycladida) from Tunisian Coasts, Zootaxa 2195, pp. 43-60 : 49-52

Leptoplana tremellaris (O.F. Muller, 1774)

( Figures 4–5 )

Distribution in Tunisia: 15 specimens were collected from under rocks in the lagoon of Tunis (36°49 ' 06.61" N; 10°17 ' 23.37" E).

Other localities: United Kingdom: Fleming (1823), Gamble (1893), Faubel (1983), Faubel & Warwick (2005). France: Keferstein (1868). Belgium: Beneden (1860). Egypt: Palombi A (1928). Italy: Steinböck (1933). Croatia: Steinböck (1933).

c v d: common vas deferens, f p: female pore, o v: oviduct, p h: pharynx, v: vagina, v d: vasa deferentia.

c: circular muscle, c v d: common vas deferens, d: diagonal muscle, f p: female pore, l: longitudinal muscle, mp: male pore, o v: oviduct, p v: prostatic vesicle, s g: shell glands, s v: seminal vesicle, v: vagina.

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

Description: Externally very similar to Echinoplana celerrima . Length up to about 30 mm, body shape broadly oval. Dorsal surface yellowish-brown with a dark band in the median line ( Fig. 4 A). Tentacles lacking. With about 36 cerebral eyes arranged in two clusters, and about 60 lateral tentacular eyes. The cerebral eyes are smaller and more anterior than the tentacular eyes ( Fig. 4 B). The ruffled pharynx is situated in the anterior half of body ( Fig. 4 C). It opens onto the outside by a mouth located in the posterior third of the pharyngeal cavity.

The two genital pores are well separated and situated in the last third of the body. Between them and closer to the male pore, a fold of the ventral wall, lined by a thickening of the body musculature is present. It corresponds to the so-called “sucker” present in some species of the genus Leptoplana ( Figs. 4 F; 5A).

Male copulatory apparatus: The male copulatory apparatus is directed backwards. The coiled vasa deferentia appear on either side of the posterior end of the pharynx, continue anteriorly near the posterior quarter of the pharynx, then diverge laterally and run posteriorly to converge into the proximal end of the seminal vesicle. The anterior, frontally oriented branches of vasa deferentia may anastomose with the caudally oriented ducts ( Fig. 4 C). The muscular seminal vesicle is located dorsally and very close to the pharynx. The prostatic organ is interpolated and tubular in shape ( Fig. 5 c). It is subdivided into three compartments characterized by different epithelium lining. The whole size of the prostatic vesicle is relative to the volume of seminal vesicle.

From the distal end of the prostatic vesicle, a narrow canal oriented obliquely and anteriorly acts as an eversible unarmed cirrus, provided distally with a penis papilla. This opens into a relatively large penial cavity. The male copulatory complex is enclosed within a thick muscular bulb, which can be seen by transparency in gently squashed living animals.

Female copulatory apparatus: The female genital pore leads into a shallow antrum feminum or vagina externa, which extends dorsally to open into the widened vagina media. The vagina media runs dorsally and turns posteriorly to form the vagina interna, which receives the common oviduct ( Figs. 4 E; 5B). Large amounts of eosinophilous mucous secretion of glandular origin were observed inside the vagina. In two specimens fixed just after copulation, the vagina was expanded and filled with a mass of sperm ( Fig. 5 B).

Remarks. Leptoplana tremellaris , the type species of the genus Leptoplana , has a worldwide distribution, and was extensively re-described by Bock (1913) and Faubel (1983). The latter author placed the species within the family Leptoplanidae Stimpson, 1857 . Prudhoe (1985) accepted the taxonomic position within the Leptoplanidae , in the subfamily Leptoplaninae Marcus, 1947 .

L. tremellaris is usually confused with E. celerrima and also with species of the genus Notoplana to which it is similar in shape and color. Living specimens of E. celerrima and L. tremellaris can nonetheless be easily distinguished, as in the ventral face of E. celerrima the cirrus and the “H” shaped vasa deferentia can be seen by transparency ( Fig. 1 C). On the contrary, in L. tremellaris the cirrus is missing and the vasa deferentia are “M” shaped ( Fig. 4 C).

The majority of sectioned specimens of L. tremellaris showed an invagination between the male and female pore, known as “sucker” ( Figs. 4 F; 5A), distinct from the true sucker of the Cotylea, located behind the female pore and clearly evaginated. One specimen was seen to be without this structure. This specimen showed nonetheless a well developed seminal vesicle and was fully sexually mature ( Fig. 5 C).

It has to be noted that some species of the genus Leptoplana were described as being without a sucker ( Boone, 1929; Hyman, 1953). Based on observations above, we suppose that the presence of a sucker between genital pores in Leptoplanidae , being subject to intrapopulational variation, possibly linked to maturity/ copulation stages, could not be used for systematic purposes.

Figures

FIGURE 1. Echinoplana celerrima: A: dorsal view, B: cerebral and tentacular eyes, C: ventral view, D: distal part of the cirrus in a living animal, E: connection of proximal part of cirrus and prostatic vesicle, F: everted cirrus.

FIGURE 4. Leptoplana tremellaris: A: dorsal view, B: cerebral and tentacular eyes, C: ventral view, D: connection of vasa deferentia and seminal vesicle, E: vagina and oviducts, F: sucker.

FIGURE 5. Leptoplana tremellaris: A: section showing the sucker, B: vagina just after copulation, C: reconstruction of the specimen not provided with a sucker.