Two new acoels (Acoelomorpha) of the genus Haplogonaria from the northwest Atlantic.

Two previously unknown species of Haplogonaria (Acoela), H. schillingi sp. nov.

How the worm got its pharynx: phylogeny, classification and Bayesian assessment of character evolution in Acoela.

Acoela are marine microscopic worms currently thought to be the sister taxon of all other bilaterians. Acoels have long been used as models in evolutionary scenarios, and generalized conclusions about acoel and bilaterian ancestral features are frequently drawn from studies of single acoel species. There is no extensive phylogenetic study of Acoela and the taxonomy of the 380 species is chaotic.

To be or not to be a flatworm: the acoel controversy.

Since first described, acoels were considered members of the flatworms (Platyhelminthes). However, no clear synapomorphies among the three large flatworm taxa -- the Catenulida, the Acoelomorpha and the Rhabditophora -- have been characterized to date. Molecular phylogenies, on the other hand, commonly positioned acoels separate from other flatworms.

Concordance of molecular and morphological data: The example of the Acoela.

Morphological features of the Acoela appear to be quite plastic, including those of the copulatory organs, which provide the principle characteristics used for the systematics of this group. Consequently, classification schemes of the Acoela comprise numerous polyphyletic groupings. In this review, we detail recent revisions of acoel systematics using molecular sequence data and new and reevaluated morphological characteristics.

Comparative morphology of the bursal nozzles in acoels (Acoela, Acoelomorpha).

Systematics of the Acoela is particularly difficult because of the paucity of readily discernible morphological features. In other soft-bodied worms, sclerotized structures, such as copulatory stylets, provide important characters that can be seen in whole mounts, but acoels generally lack such features. Among the few sclerotized structures in acoels are bursal nozzles-tubiform outlets on the seminal bursae that are believed to be conduits (spermatic ducts) through which allosperm are transported to the oocytes.

Molecular systematics of the Acoela (Acoelomorpha, Platyhelminthes) and its concordance with morphology.

The phylogenetic relationships of the lower worm group Acoela were investigated using newly obtained nuclear 18S rDNA sequences from 16 acoels in combination with 16 acoel sequences available on GenBank from other laboratories. Parsimony and maximum likelihood analyses of the molecular data supported the concept that the Acoela is monophyletic; however, the gene tree produced by these analyses conflicts with the current taxonomic system for the Acoela in several family-level groupings. Most notable is the apparent polyphyly of the largest family of acoels, the Convolutidae.