Itaspiella parana, 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 : 1458-1461

Itaspiella parana n. sp.

( Figure 2 )

Locality

Paraná and Colastiné rivers near Santa Fe´, Argentina. Sublittoral, sandy sediments, October 1989 .

Material Some individuals studied alive and one of them sagittally sectioned (4.5 mm).

Type material

Holotype: one sagittally sectioned specimen deposited in the Museo Nacional de Ciencias Naturales de Madrid (cat. no. MNCN 4.01 /45).

Etymology

The specific name refers to the Paraná river where the specimens were found.

Description

Length about 2 mm. Rapid and extremely spastic movements through the sand grains. Body fusiform, dorsally convex, ventrally flat, cross-section triangular ( Figure 2a ), colourless and transparent. Anterior part of the body with a small cephalic lobe and a row of sensory bristles. Two strong bristles laterally, behind the lobe. Posterior end with numerous adhesive papillae. Pharynx cylindrical, in the middle of body. Encapsulated, characteristically shaped brain communicated with the statocyst through subepidermal muscle fibres. Frontal glands situated behind the brain. Creeping sole extending from the anterior end to the posterior end, sparser behind the genital pore. Epidermis is devoid of dorsal cilia, provided with rod-shaped adenal rhabdites. Epidermal nuclei depressed.

There are three rows of adhesive papillae: two on the lateral margins and one dorsally situated. The papillae consist of one or three cells with connecting subepidermal glands. The posterior end of the body shows a special adhesive area with well-developed papillae. The cylindrical pharynx is situated horizontally, twice as long as wide, with completely ciliated epithelium and the longitudinal muscle layer next to the epithelium. All the pharynx glands are extrapharyngeal and aggregated ventrolaterally. The gut is not extended above the brain. The gastrodermis is thin-walled. The small ovaries at the basis of the pharynx are not divided into follicles and contain only a few oocytes. The two regular rows of testes, with about seven follicles each, are situated below the prepharyngeal gut, separated from each other by a longitudinal fold of the gut. There are two lateral rows of yolk follicles along the body, without a gap along the pharynx. The common oviduct, running on the right side of the atrium, arises by fusion of the two germovitelloducts behind the pharynx. The common genital pore is located near the posterior end. The atrium is funnel-like and receives the bursa stalk from behind, the penis needles dorsally and the shell glands frontally. Cement glands discharge their secretion through the body wall around the gonopore. The male copulatory apparatus consists of a large ovoid seminal vesicle, a caudal diverticulum, a distal tubular prostatic vesicle and a cuticular apparatus. This latter structure comprises 15 needles, each 48.5 mm long, and a medial 54 mm long stylet (‘‘Trichterrohr’’ after Ax 1956). The needles are proximally straight, distally curved, with a short, pointed denticle above the tip. The stylet is dagger-like and pointed distally. The bursa (‘‘primäre Bursalorgan’’ after Ax 1956), with nucleated epithelium and a weak muscular layer, is situated behind the common atrium, and is connected to the latter by a long tubular insemination canal or stalk.

Ecological features. Itaspiella parana was found in the middle Paraná river in sublittoral sediments composed of fine and medium-grained sand. This interstitial habitat, influenced by high water-currents and poor in organic matter, shows generally low biological diversity and abundance. According to the abiotic factors measured in the sample areas ( Table I), the ecological characterization is estimated as follows: stenothermic, mesoeuryionic, rheobiotic, stenobiotic, stenoecious freshwater inhabitant.

Discussion. Itaspiella parana is the first known freshwater representative of genus Itaspiella . At present, only three freshwater species belonging to the Otoplanidae are known: Pseudosyrtis fluviatilis ( Gieysztor, 1938) Ax, 1956 , P. subterranea (Ax, 1951) Ax, 1956 and P. neiswestnovae Riemann, 1965 . Despite its freshwater habitat, I. parana is a typical representative of the subfamily Otoplaninae . It shares the following characters with genus Itaspiella : epidermis with depressed nuclei; two rows of testicular follicles in front of the pharynx; two rows of yolk follicles beside the testes, and beside and behind the pharynx; cuticular apparatus consisting of needles and a stylet; and unpaired bursa behind the common atrium.

The genus Itaspiella is based on I. helgolandica helgolandica (Meixner, 1938) Sopott, 1972 from the North Sea. Other taxa from the Pacific Ocean are included in the genus: I. helgolandica magna ( Ax and Ax, 1967) Sopott, 1972 ; I. bursituba Karling, 1964 ; I. bodegae Karling, 1964 , and I. macrostilifera Tajika, 1984 . The main features and differences between the species are the number of testicular follicles, number of needles and the presence or absence of a precerebral gut diverticulum. Itaspiella h. helgolandica shows 8–10 pairs of testicular follicles and seven to eight needles ( Sopott 1972); I. bursituba 17–22 testicular follicles and 10 needles; I. bodegae 20–30 testicular follicles and 10 needles, and I. macrostilifera seven very strong needles. I. parana is clearly differentiated from its congeners by the presence of a compact bursa, 15 needles and about seven pairs of testicular follicles, and most notably by its habitat, a freshwater environment.

Itaspiella parana is the first record of genus Itaspiella from South America, and the first freshwater record for the Otoplaninae .

Figures

Figure 2. Itaspiella parana. (a) Ventral view of the body (modified from Noreña-Janssen 1995b). (b) Sagittal reconstruction. Ag, adhesive glands; b, bursa; br, brain; cg, cement glands; fg, frontal glands; g, gonopore; i, intestine; m, mouth; mu, muscles; n, needles of the copulatory organ; o, oviduct; ov, ovary; ph, pharynx; sg, shell glands; st, statocyst; t, testes; vi, vitellaria; vs, vesicula seminalis. (c) Needles of the copulatory organ in detail.