Stenostomidae Vejdovsky, 1880

Bharti, Daizy, Brusa, Francisco, Kumar, Santosh & Chandra, Kailash, 2020, First record of Stenostomum sphagnetorum (Platyhelminthes, Catenulida) from India, Zootaxa 4816 (3), pp. 392-396 : 392-393

Family Stenostomidae Vejdovsky, 1880

Genus Stenostomum Schmidt, 1848

Stenostomum sphagnetorum Papi in Luther, 1960

( Figures 1 A–K, 2A–H, 3A–E)

The specimens were extremely contractile but while swimming, the body is spindle-shaped, rounded or pointed anteriorly, tapering posteriorly. The ciliated pits are present between the mouth and the anterior tip, and light refracting bodies (each at posterior-most brain lobe with one refractile sphere each) with a depression in the anterior region were present. The brain comprised of anterior (small and 4-6 in numbers) and posterior lobes (2-4 in numbers). The mouth changes in shape, i.e., rounded, triangular or elongated, probabiy due to contraction of the body. The pharynx is two to three time longer than its width and surrounded by many pharyngeal glands. The dimensions are: body length = 490-690 μm, body maximum width = 65-95 μm, prepharyngeal region width = 40-55 μm, posterior brain lobe length = 20-35 μm, posterior brain lobe

width = 15-25 μm, pharynx length = 55-75 μm, pharynx width = 50-65 μm, trunk width = 55-75 μm (observations based on six specimens from life). The pore of the protonephridium lies at the posterior end. The intestine reaches up to the posterior body end. Invariably, two zooids (observation based on over 15 dividing specimens) were recorded.

The Indian population of Stenostomum sphagnetorum Papi in Luther, 1960 shows similarity with the previously known populations, except for the distribution of excretophores. Stenostomum sphagnetorum is most similar to S. constrictum ( Luther 1960) , however, it can be separated from the former by the rather prominent constriction anterior to the pharynx (vs. less constricted), and round refracting bodies (vs. with depression) ( Luther, 1960). The specimens were present in good abundance in the water sample and were feeding actively on algae and microcrustaceans. It has been reported that some rhabdocoel flatworms feed on the mosquito larvae ( Worna and Koopowitz, 1998; Tranchida et al., 2009). To test if this catenulid feeds on mosquito larvae we inoculated about 100 specimens of Stenostomum sphagnetorum to more or less same number of mosquito ( Culex quinquefasciatus ) larvae. In contrast to above, we observed that the mosquito larvae actively feed on the Stenostomum sphagnetorum specimens and finished them all in about 2 hrs, proving them to be a good food source for mosquito larvae.

Figures

FIGURE 1. Photomicrographs of Stenostomum sphagnetorum Indian population from live. A–K. A specimen, showing the sequences of body shapes during the contraction. Note the specimens were observed under the cover slip, a slight pressure may be present. Arrowhead in (F) points to the nephridiopore; the intestine reaches up to the posterior body end.