Stenostomum arevaloi Gieysztor, 1931

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 : 41-43

Stenostomum arevaloi Gieysztor, 1931

( Fig. 1B )

Stenostomum rachiocaudatum Nuttycombe, 1932

Description: Solitary individuals 0.6–0.8 mm long (minimum 0.35 mm long), diameter 0.13 mm. Chains of two zooids (1–1.5 mm) up to seven zooids (2.5 mm). Body cylindrical, slightly flattened ventrally. With post-pharyngeal constriction. Posterior end tapering, with intestine-lacking region, ending in a very long tail. Its proximal region is adhesive, and the posterior end bends upward ( Nuttycombe & Waters, 1938; Marcus, 1945a). Ciliated pits anterior, long and deep. Epidermal cilia longer than the thickness of the epidermis. Caudal region with long semi-rigid sensory cilia. Rod-shaped rhabdites. The epidermal cells with refractory inclusions (other than rhabdites) of several (up to six) corpuscles. White colour in life.

Anterior brain lobes deeply dentate. Three pairs of subepidermal light-refracting bodies. The first pair, simple and small, located before the anterior brain lobe. The second pair, simple, at the level of the ciliated pits, above the anterior lobes. The third pair at oral pore level, above the posterior lobes; this pair is frequently the largest and formed by two spheres (type 2).

Oral pore rounded, opening between the posterior brain lobes. Muscular pharynx. Pharyngeal glands (type a) opening onto the last two-thirds. A transverse line of cells can be seen ventrally to the pharynx. Conspicuous pharyngeal muscular sphincter. Intestine with a smooth outline ending at the base of the tail. The anterior intestinal region frequently with fine, dark granules. Dorsal excretory pore in the intestinelacking region.

Distribution: Valencia, Spain ( Gieysztor, 1931); Virginia ( Nuttycombe, 1932b; Nuttycombe & Waters, 1938); Georgia ( Nuttycombe & Waters, 1938; Kolasa, 1991), USA; São Paulo and interior of São Paulo State, Brazil ( Marcus, 1945b); Poznan, Poland ( Kolasa, 1973); Kenya ( Young & Kolasa, 1974b); Italy, France and Germany ( Lanfranchi & Papi, 1978).

Discussion: Gieysztor (1931) mentions the occasional presence of a terminal excretory vesicle in the region of the excretory pore. The former has not been observed in the South American specimens.

Marcus (1945b) stated that the pharyngeal glands open only onto the posterior pharyngeal region, while Nuttycombe & Waters (1938) mention that the pharyngeal glands open onto the whole pharyngeal length. The transverse line of cells exhibited ventrally to the pharynx is similar to that described for S. paraguayense ( Martin, 1908) Luther, 1908 .

Figures

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