Philosyrtis rauli, Noreña & Damborenea & Brusa, 2005

Noreña, Carolina, Damborenea, Cristina & Brusa, Francisco, 2005, New freshwater interstitial Otoplanidae (Platyhelminthes: Proseriata) from the Paraná and Uruguay rivers, South America, Journal of Natural History 39 (18), pp. 1457-1468 : 1462-1466

Philosyrtis rauli n. sp.

( Figure 4 )

Locality

Uruguay river near Las Cañas, Rio Negro Department , Uruguay. Sublittoral , sandy sediments, November 2002, January and February 2003 .

Material

Ten individuals (mature and immature) studied alive, six immature and two mature specimens sagittally sectioned (4 mm).

Type material

Holotype: one sagittally sectioned specimen deposited in the Helminthological Collection , Museo de La Plata, Argentina (cat. no. 5313) . Paratype: one sagittally sectioned specimen deposited in the Museo Nacional de Ciencias Naturales de Madrid (cat. no. MNCN 4.01 /46) .

Etymology

This species is dedicated to Raúl Codina.

Description

The living animals are 0.8–1.1 mm long and about 0.09 mm thick, fast-moving and strongly spastic. Colourless and transparent. The cephalic lobe is not clearly set off, but it is provided with long sensory bristles ( Figure 4a ). Adhesive papillae and bristles on the lateral side of the body at more or less regular distances, more abundant at the posterior end. Numerous needle-like rhabdites grouped behind the encapsulated brain, anterior to the pharynx and between the testes, forming two parallel rows. Isolated rhabdites over the entire body. Epidermis unciliated dorsally, ventrally well developed, ciliated and forming a creeping sole. Pharynx internally ciliated, before the middle of the body. Gut extending from the brain to the posterior end of the body, behind the vesicula seminalis.

Ovaries situated at the basis of the pharynx. Two lateral rows of yolk follicles running from the pharynx to the posterior end. Only one pair of testicular follicles in adult animals, and up to three pairs in juveniles, situated just behind the brain and in front of the ovaries. Male copulatory apparatus consisting of an ovoid vesicula seminalis, the prostatic glands and the cuticular apparatus. The cuticular apparatus consisting of eight needles 23 mm long and 2.73 mm thick. The needles are proximally straight with an elongated, sickle-like terminal end ( Figure 4b ). Bursa absent.

Biology. Philosyrtis rauli was found on a beach with sandy sediment near Las Cañas. According to the abiotic factors measured in the sample areas ( Table I), the ecological characterization is estimated as follows: rheobiotic, thermophilic (it is unquestionably a mesotypical species with thermophilic tendencies that depend on its adaptation to warm environments), stenobiotic (poly-oxibiotic), mesoionic, freshwater inhabitant.

Discussion. Philosyrtis rauli is a typical representative of the subfamily Paratoplaninae ( Ax 1956) and shares the following features with genus Philosyrtis : depressed epithelium in the regions of the creeping sole, dorsally unciliated epithelium; long, finger-like papillae; pharynx in the middle of the body; two rows of testicular follicles and paired ovary in front of the pharynx; two rows of yolk follicles behind the pharynx; cuticular apparatus with needles, but without stylet; absence of a bursa.

The genus Philosyrtis includes eight species, three of them occurring in South America: P. sanjuanensis Ax and Ax, 1974 , P. santacruzensis Ax and Ax, 1974 (Galápagos Islands, Ecuador) and P. eumeca Marcus, 1950 ( Brazil) .

The main difference between Philosyrtis rauli and other South American Philosyrtis species lies in the cuticular apparatus. Whereas P. sanjuanensis and P. santacruzensis bear two groups of needles, one dorsal and one ventral, and P. eumeca has three groups of needles with different structure and localization, P. rauli shows a semicircle with a single type of needle. A similar cuticular apparatus can be found in P. rotundicephala Sopott, 1972 , but this species differs from P. rauli in the number of needles (10 needles in P. rotundicephala , eight needles in P. rauli ) and in the shape of their distal end. Another difference between the two species is the number of testicular follicles, only one pair in P. rauli (character shared with P. eumeca ) and four pairs in P. rotundicephala .

Philosyrtis rotundicephala is a marine species from northern Europe, while P. rauli is the only freshwater species of the genus, from interstitial habitats of the Uruguay river. Within the Paratoplaninae only three species of Pseudosyrtis ( P. subterranea , P. fluviatilis and P. neiswestnovae ) have been recorded for brackish/freshwater habitats.

Figures

Figure 4. Philosyrtis rauli. (a) Ventral view of the body. b, bristles; br, brain; co, copulatory organ, ov, ovary; ph, pharynx; rh, rhabdites; st, statocyst; t, testes; vi, vitellaria; vs, vesicula seminalis. (b) Details of the needles of the copulatory organ.