A taxonomic revision of South American species of the genus Stenostomum O. Schmidt (Platyhelminthes: Catenulida) based on morphological characters

Abstract

This paper revises the genus Stenostomum based on a rich collection of species from Argentina and on a review of bibliographical resources of all known South American species. The description of South American species is standardized. The new genus Anokkostenostomum is established and several species of Stenostomum are transferred to it based on the absence of light-refracting bodies and the presence of a metameric anterior brain lobe. We report five Stenostomum species and three Anokkostenostomum species new to Argentina and present an identification key for South American species. Finally, all the world species are compiled, with an overview of their distribution.

Stenostomum Leucops Dugès, 1828 (Platyhelminthes, Catenulida): A Putative Species Complex With Phenotypic Plasticity

“…The morphological characteristics of S. leucops here studied correspond to those described by Noreña et al (2005) and Damborenea et al (2011). The same occurs for S. grande.…”

“…The small number of cells observed in Stenostomum may also be important to the usefulness of these worms as models for biological studies. Although the number of zooids is not a diagnostic characteristic for Stenostomum species identification, this characteristic is always cited in the descriptions of species of this genus (Van Cleave, 1929;Nuttycombe & Waters 1938;Noreña et al, 2005;Damborenea et al, 2011;Gamo & Leal-Zanchet, 2004). Van Der Land (1965), Gamo & Leal-Zanchet (2004) and Noreña et al (2005) describe S. leucops as having only two zooids.…”

“…Although the number of zooids is not a diagnostic characteristic for Stenostomum species identification, this characteristic is always cited in the descriptions of species of this genus (Van Cleave, 1929;Nuttycombe & Waters 1938;Noreña et al, 2005;Damborenea et al, 2011;Gamo & Leal-Zanchet, 2004). Van Der Land (1965), Gamo & Leal-Zanchet (2004) and Noreña et al (2005) describe S. leucops as having only two zooids. On the other hand, Van Claeve (1929) and Palmberg (1990) report that the worms they studied showed multiple zooids (up to five), but do not described the conditions under which these animals were cultivated.…”

“…Stenostomum leucops was collected in March of 2009 and S. grande Child, 1902, in November of 2012. These specimens were identified following Noreña et al (2005) and Damborenea et al (2011). The diagnostic characteristics of S. leucops are the light-refracting bodies with disc shaped, pharyngeal glands rounded shape, without a sphincter between pharynx and intestine, and the pharyngeal glands are on the entire surface of the pharynx.…”

“…However, further studies by Noreña et al (2005) have validated this species. More recently, Larsson et al (2008) used DNA sequences of 18 S rDNA and COI to show that S. leucops constitutes a monophyletic group.…”