Paromalostomum scilliensis, Faubel & Warwick, 2005

Faubel, A. & Warwick, R. M., 2005, The marine flora and fauna of the Isles of Scilly: Free-living Plathelminthes (‘ Turbellaria’), Journal of Natural History 39 (1), pp. 1-45 : 18-20

Paromalostomum scilliensis sp. nov.

( Figure 4 )

Material examined

HOLOTYPE: Site 3: few specimens, in squash preparation, stored on CD-ROM: 2003.5.22.1, WM: 2003.5.22.1.

Etymology

The specific epithet refers to the Isles of Scilly where it was found.

Description

Length of body of living sexually mature specimen up to 2.9 mm, when squashed under a cover glass. Body ends rounded but rear body end somewhat pointed. Colour greyish with darkly contrasting gut and ovary. Intestine taking on yellowish brown coloration when diatoms ingested. Eyes, rhabdites, adhesive glands and tactile cilia absent around margin of body. Rhammite tracks running from anterior tip of body to the level of pharynx bilaterally. The species feeds on small nematodes, nauplii of harpacticoids, diatoms and detritus particles.

Reproductiυe system. Single testis and ovary on the left side of body. Testis anterior to ovary. Seminal vesicle small, joined via a short intervesicular duct with the oval prostatic vesicle (198 M m long). Male stylet apparatus ( Figure 4B,C ) consisting of penis stylet and glandular stylet. Penis stylet (m. HT) 172 M m long, the twisted proximal part of which is 85 M m long and distal straight tube 87 M m long; the glandular stylet is 182 M m long (m. HT). The glandular stylet is joined with a single accessory gland; the penis stylet joins the 198 M m long prostatic vesicle. The bursal sclerotized organ ( Figure 4B,C ) consists of a midpiece (42 M m long, m. HT) and a mouthpiece (56 M m long, m. HT). The midpiece looks like a clog; the mouthpiece bears distally a disc-shaped terminal thickening ( Figure 4C ). Sperm tubes absent. A pyriform vesicle containing sperm opens into the proximal part of the mouthpiece.

Discussion

To date the genus Paromalostomum contains nine valid species. With the exception of P. subflaυum Sopott-Ehlers and Schmidt, 1974, all of them have been recorded from the North Atlantic and its marginal seas. Based on the sclerotized elements of the male organs (penis stylet, glandular tube) and female organs (mouth piece, midpiece), P. scilliensis proves to be a member of the genus Paromalostomum Meixner in Ax, 1951. According to the arrangement of details of the sclerotized elements, P. scilliensis displays closer relationships to P. dubium (de Beauchamp 1927) . Main differences from P. dubium are the absence of sperm tubes, much longer mouthpiece and diverging construction of the clog-shaped midpiece. With respect to the penial stylets, differences lie mainly in the greater length of the stylets of P. scilliensis . The male stylet looks more or less identical with that of P. dubium but the glandular tube is S-shaped ( Figure 4B ). In contrast to P. dubium , P. scilliensis lacks rhabdites, tactile cilia at anterior and posterior body end, and the characteristic adhesive glands at the rear body end.

Figures

Figure 4. Paromalostomum scilliensis sp. nov. (A) Dorsal view in squash preparation; (B) genital complex in squash preparation; (C) male sclerotized stylet and glandular stylet (latter not drawn in full length); (D) sclerotized bursal organs. Scale bars: 500 Mm (A); 100 Mm (B); 50 Mm (C, D).