Leptoplana tremellaris (Müller, 1774) Örsted 1843

Gammoudi, Mehrez, Garbouj, Myriam, Egger, Bernhard & Tekaya, Saïda, 2017, Updated inventory and distribution of free-living flatworms from Tunisian waters, Zootaxa 4263 (1), pp. 120-138 : 124-125

Leptoplana tremellaris (Müller, 1774) Örsted 1843

( Fig. 2 b, Fig. 3 a–i)

We report this species for the first time from the Mediterranean sea, so we give its description below.

Habitat. 5 specimens were found under stones.

Locality. Errimel beach (36° 52' 25.87"N; 10° 39' 57.06" E).

Other localities in the world. The North Sea (Müller 1773; Bock 1913); Scotland ( Fleming 1823) ; Belgium (van Beneden 1860); Saint Malo , France ( Keferstein 1868); the Irish Sea ( Gamble 1893a); the Isles of Scilly ( Faubel & Warwick 2005); Atlantic Spanish coasts ( Marquina et al. 2014b).

Description. The body is oval in shape. It measures 15 mm in length by 4 mm in width, the anterior end being broader than the posterior. Dorsal surface is beige ( Fig. 2 b). Digestive ramifications could be easily seen. Tentacles are lacking. Two clusters of cerebral and tentacular eyes are present ( Fig. 3 a,b). Ventral surface shows a ruffled pharynx located at the second third of body, two vasa deferentia filled with sperm and two uteri filled with eggs ( Fig. 3 b,e). A genital pit is located between male and female gonopore and closer to the latter ( Fig. 3 c). The epidermis is provided with several rhabdites ( Fig. 3 d). The pharynx is provided with 12 pairs of lateral folds. The mouth is situated at the hind end of the third fifth of the body and in the third fourth of the pharyngeal cavity. Immediately behind the posterior end of the pharyngeal chamber lies the male copulatory apparatus. The male genital pore opens to a narrow extended male atrium and is provided with a diverticulum oriented dorsally ( Fig. 3 f). The ejaculatory duct leads to a narrow tubular prostatic vesicle. The latter vesicle is of interpolated type and was observed to contain some eosinophilous secretions ( Fig. 3 f,g,h). Its internal glandular lining is smooth and is connected to a seminal vesicle, usually filled with sperm ( Fig. 3 g,h). Before entering the seminal vesicle, the tubular prostatic vesicle gives birth to a diverticle lying below the seminal vesicle ( Fig. 3 g,h). A muscular tissue is separating the two organs. The female genital pore, situated behind the male one, leads to a short external vagina directed dorsally followed by a large median vagina oriented fronto-dorsally ( Fig. 3 i). Before reaching the dorsal body wall, the vagina curves posteriorly to form an internal horizontal portion corresponding to the internal vagina. Anteriorly, this part does not exceed the level of projection of the female genital pore.

Remark. The genus Leptoplana Ehrenberg was thoroughly revised by Gammoudi et al. (2012b). The authors deduced and supported the idea that the unique representative of the genus Leptoplana in Mediterranean area is Leptoplana mediterranea ( Bock 1913) . This was confirmed by Marquina et al. (2014a).

Leptoplana mediterranea shows clear similarity with Leptoplana tremellaris . Externally both species are almost impossible to separate ( Gammoudi et al. 2012b). The study of sections of specimens from Tunisia and sections of Leptoplana tremellaris from Scilly Islands (English channel) made by Faubel (1983) and also sections of specimens of L. mediterranea from Tunisia, allowed us to find some features distinguishing L. mediterranea from L. tremellaris . In L. mediterranea we found 1) The presence of a genital pit nearer to the male pore and not to the female one. 2) The seminal vesicle is of oval shape. 3) The ventral diverticulum of the prostatic vesicle presents a common dividing wall with the seminal vesicle. 4) The hatched juvenile is provided with twelve eyes.

In contrast, in L. tremellaris of Faubel (1983) and new material from Tunisia we found: 1) The genital pit is closer to the female pore than to the male one ( Fig. 3 c). 2) The seminal vesicle is pear shaped ( Fig. 3 g, h). 3) Muscle and mesenchyme are surrounding the prostatic vesicle ( Fig. 3 g, h). 4) The hatched juvenile is provided with two pairs of eyes ( Fig. 2 n,o).

Based in these data, we considered the similarity of our new specimens with those of Faubel and also the difference between our specimens and specimens of Leptoplana mediterranea to be substantial enough to determine Leptoplana tremellaris from Tunisian waters and thus to report this species for the first time from the Mediterranean sea, since L. tremellaris was considered to be missing in the Mediterranean by Gammoudi et al. (2012b).

Figures

FIGURE 2. Polyclads from Tunisian waters. Dorsal view in all panels, anterior to the left. a Leptoplana mediterranea. b Leptoplana tremellaris. c Echinoplana celerrima. d Theama mediterranea; the depicted specimen was collected in Calvi, Corse. e Imogine mediterranea. f Discocelis tigrina. g Cestoplana rubrocinta. h Comoplana agilis. i Prosthiostomum siphunculus. j Prostheceraeus moseleyi. k Thysanozoon brocchii. l Pseudoceros maximus. m Yungia aurantiaca n hatching in Leptoplana tremellaris. o hatched four-eyed juvenile of Leptoplana tremellaris. Scale bars: 2 a – c, 2 e – m: 5 mm; 2 d, 2 n – o: 100 microns.

FIGURE 3. Leptoplana tremellaris. a Dorsal view of anterior region showing the arrangement of eyes. Note the presence of two clusters of tentacular eyes te located posteriorly to two clusters of cerebral eyes ce. b Ventral view of anterior region showing confluent uteri ut filled with eggs. Tentacular eyes te, cerebral eyes ce. c Ventral view of posterior region showing male gonopore mg, genital pit gp and female gonopore fg. d Sagittal section of body wall. Note the presence of rhabdites rh among epithelial cells supported by basal lamina bl. The musculature is developed and organized in different layers, circular layer cl, oblique layer ol and longitudinal layer ll. e Section through uteri and ovaries showing uterine eggs ue and ovarian egg oe. f Section through male gonopore mg. The male atrium is provided with diverticulum d. Prostatic vesicle pv. g Section through seminal vesicle sv and ventral diverticulum of the prostatic vesicle dpv. Note the presence of mesenchyme separating seminal vesicle and prostatic vesicle. h Section through the entrance of vas deferens vd into the seminal vesicle. Note the presence of mesenchyme separating seminal vesicle sv and prostatic vesicle pv. i Section through female genital apparatus, the vagina is formed by vagina externa ve, vagina media vm and vagina interna vi. Female gonopore fg. Scale bars: 3 a – b: 0.5 mm; 3 c: 100 microns; 3 d: 10 microns; 3 e – i: 100 microns.