Product Code Database
Catenulida is an order of Platyhelminthes in the classical classification, or a class of flatworms in a phylogenetic approach. They are relatively small free-living flatworms, inhabiting freshwater and marine environments. There are about 100 species described worldwide, but the simple anatomy makes species distinction problematic.
The are unpaired. Unusually, the male gonopore opens on the dorsal surface of the animal, above the pharynx, while the female reproductive system lacks any of the usual ducts and related structures found in other flatworms. The sperm is nonmobile and lacks flagella or cilia. Asexual reproduction by paratomy is common, and it usually leads to a chain of organisms (), hence the name, from Latin catenula, small chain.
Members of the symbiosis genus Paracatenula lack a Digestive system, and instead harbor intracellular Chemotroph bacterial symbionts that are assumed to provide their nutrition.
The diet of most catenulids consists of small invertebrates and algae that they capture from the water column. Others, such as those of the genus Paracatenula use chemoautotrophic bacterial symbionts that live inside their cells as a food source.
Although there are no known synapomorphies connecting Catenulida to other flatworms (Rhabditophora), molecular studies indicate that they are sister-groups. All characters common to both clades, such as the internal fertilization and the simple gut with a single opening, are found in other groups as well.
|
|
