Prosthiostomum siphunculus (Delle Chiaje, 1822) Lang, 1884

Gammoudi, Mehrez, Ahmed, Raja Ben & Tekaya, Saïda, 2016, Taxonomy of subtidal marine Polyclads from Tabarka (northwest Tunisia) with remarks on their habitat preferences, Ecologica Montenegrina 9, pp. 1-9 : 3-6

Prosthiostomum siphunculus (Delle Chiaje, 1822) Lang, 1884

General features. The worm is of elongated oval shape rounded anteriorly and tiped posteriorly. The dorsal surface is smooth brownish ( Fig. 3a ). Tubular pharynx is located in the second fourth of body. Usually, the animal protrudes its pharynx as a reaction to fixation. Marginal eyes form a semi circle band located in the anterior part of body ( Fig. 3b ). Cerebral eyes are larger than marginal ones and form two clusters included in the semi circle formed by the marginal eyes ( Fig. 3b ). The ventral surface is whitish transparent and shows the tubular muscular pharynx, two genital pores and a well developed sucker located 1mm behind female genital pore.

Ecol. Mont., 9, 2016, 1-9 Reproductive apparatus. Testes are numerous and are scattered mainly in ventral parenchyma more than dorsal one. The ovaries are bigger in size and lie more or less dorsally. The male gonopore leads to a horizontal male antrum housing the pointed strong stylet ( Fig. 3d, e ). The usual eosinophilous granulations indicatives of prostatic secretions are observed in the wall around the stylet supported by small penis papillae ( Fig. 3e ). The latter receive the ejaculatory duct from seminal vesicle and the two prostatic ducts from paired free prostatic vesicles (accessory vesicles) ( Fig. 3c ). The two vesicles are round muscular bodies with narrow lumen and muscularized wall formed by circular fibres ( Fig. 3c ).

The main feature of the female genital apparatus is the presence of cement pouch characteristic of sub-order Cotylea ( Fig. 3 f ). The vagina is oriented vertically and it is connected with two uteri. The sucker is well developed and lies 1 mm behind female genital pore ( Fig. 3e ).

Habitat. The single specimen of Prosthiostomum siphunculus was found creeping on a stone from a depth of 29m. The associated fauna included the sea urchin Paracentrotus lividus , the sea cucumber Holothuria (Roweothuria) polii (Delle Chiaje, 1824) and the polychaete Protula tubularia (Montagu, 1803)

Figures

Figure 3. Prosthiostomum siphunculus a Dorsal view. Scale bar = 1mm. b Anterior region showing the arrangement of eyes. Note the presence of marginal eyes me and two clusters of cerebral eyes ce. Scale bar =10µ. c Ventral view of anterior region showing the paired prostatic vesicles pv. Prostatic canal pc. Scale bar =10µ. d Ventral view of anterior region showing the prominent stylet st. male gonopore mg, prostatic canal pc. Scale bar = 10µ. e section through male apparatus. Prostatic vesicle pv, male atrium ma, male gonopore mg, stylet st, median intestine mi. Scale bar = 10µ. f Section through female genital apparatus, note the presence of cement pouch cp in the vagina. female gonopre fg, main intestine mi. Scale bar =10µ.