Stenostomum amphotum Marcus, 1945

Noreña, Carolina, Damborenea, Cristina & Brusa, Francisco, 2005, A taxonomic revision of South American species of the genus Stenostomum O. Schmidt (Platyhelminthes: Catenulida) based on morphological characters, Zoological Journal of the Linnean Society 144 (1), pp. 37-58 : 41

Stenostomum amphotum Marcus, 1945

( Fig. 1A )

Description: Isolated specimens up to 0.7 mm long. Chains of up to nine zooids, with different degree of development. Elongated body, with dorso-lateral ciliated pits, anterior end slightly tapering. With constriction at the level of the oral pore. Posterior end with intestine-lacking region. Homogeneous ciliated epithelium without longer sensory cilia. Sparse small rhabdites on the ventral surface. Colour in life whitish.

Cerebral ganglia with deeply dentate anterior brain lobes and a pair of internal lobes associated with the posterior ones (trilobate brain after Marcus, 1945a). Two light-refracting bodies, with more than ten spherical corpuscles (type 1), associated with the posterior lobes.

Oral pore oval. Pharynx large (greater than 1/5 of the body length). Two types of pharyngeal glands: (1) antero-ventral rounded glands (type a) and (2) groups of elongated club-shaped glands (type b) laterally in the posterior half of the pharynx. Transition between pharynx and intestine regulated by a muscular sphincter. Intestine with excretophores. Nephridiopore opens at the posterior intestine-lacking region.

Distribution: São Paulo and interior of São Paulo State, Brazil ( Marcus, 1945b). Los Talas, Berisso, Buenos Aires, Argentina, September 1998, December 1998 to January 1999, April 1999 to July 1999, December 1999 to February 2000 and May 2000. This species has not been previously recorded in Argentina.

Stored material: Ten sagittally sectioned specimens in the CHMLP. No. 5303.

Discussion: S. amphotum was synonymized to S. leucops ( de Beauchamp, 1948; Luther, 1960), owing to the difficulty in recognizing differences in the arrangement of the pharyngeal glands. The type and arrangement of the pharyngeal glands and the layout of the rhabdites, the number of brain lobes, and the sphincter between pharynx and intestine, are enough to separate both species. On the other hand, a cladistic analysis (our unpubl. data) confirms the independence of S. amphotum and S. leucops .

Figures

Figure 1. A, Stenostomum amphotum. B, S. arevaloi. C, S. bicaudatum. D, S. ciliatum. E, S. cryptops. Scale bars = 200 Mm.