A phylogenetic analysis of Stenostomum and its neotropical congeners, with a description of a new species from the Peruvian Amazon Basin

Abstract

This study reports Peruvian freshwater species of Stenostomum (Catenulida) from the upper Yurúa River of the Amazon Basin. A total of 11 species were found. One of them, Stenostomum ashanika, sp. nov., is described. It can be distinguished by: a pre-pharyngeal constriction; a small cauda; a small, rounded, mobile and ventrally directed pharynx; and a tri-radiate mouth. The remaining 10 species are reviewed and illustrated; eight are first records for Peru. A preliminary phylogenetic analysis of neotropical stenostomid species based on morphological data is undertaken, including all Rhynchoscolex, Stenostomum and Myostenostomum species described for the area. The Rhynchoscolex species are basal and paraphyletic; the species of Myostenostomum are monophyletic, within the Stenostomum clade, supported by the presence of a muscular gizzard in the anterior region of the intestine. Ciliated pits and rhabdoids are synapomorphies of the Stenostomum + Myostenostomum clade. This is the first morphological study of the relationships between stenostomid species. The most relevant characters in the phylogenetic analysis are those related to cerebral brain lobes. The results also show that many of the morphological characteristics of the species under study are poorly known and should be studied in more depth.

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.…”

“…In South America, it has been recorded from Surinam (Van der Land, 1965), Argentina (Noreña et al, 1995), Peru (Damborenea et al, 2011) and the South Brazilian State Rio Grande do Sul (Gamo & Leal-Zanchet 2004, Braccini & Leal-Zanchet, 2013 and in this study). As mentioned previously, the validity of this species has been questioned by Nuttycombe & Waters (1938) and Marcus (1945) who consider the descriptions of this species ambiguous and broad to make its recognition difficult.…”

“…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.…”

“…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.…”

Six freshwater microturbellarian species (Platyhelminthes) in permanent wetlands of the Coastal Plain of southern Brazil: new records, abundance, and distribution

“…This species was represented by a singleton in the summer/autumn survey and was absent in the winter/spring survey (Table 2). It was described from the Holarctic region (Nassonov 1924); in the Neotropical region, it was reported at Belém, northern Brazil (Marcus 1945a) and in the department of Ucayali, Peru (Damborenea et al 2011). The present record increases its known distribution by about 3000 km to the southeast.…”