Background Entoprocta affinities within Lophotrochozoa remain unclear. In different studies, entoprocts are considered to be related to different groups, including Cycliophora, Bryozoa, Annelida, and Mollusca. The use of modern methods to study the neuroanatomy of Entoprocta should provide new information that may be useful for phylogenetic analysis. Results The anatomy of the nervous system in the colonial Barentsia discreta was studied using immunocytochemistry and transmission electron microscopy. The ganglion gives rise to several main nerves: paired lateral, aboral, and arcuate nerves, and three pairs of tentacular cords that branch out into tentacular nerves. The serotonergic nervous system includes paired esophageal perikarya and two large peripheral perikarya, each with a complex net of neurites. Each tentacle is innervated by one abfrontal and two laterofrontal neurite bundles. Sensory cells occur regularly along the abfrontal side of each tentacle. Star-like nerve cells are scattered in the epidermis of the calyx. The stalk is innervated by paired stalk nerves. Conclusions The neuroanatomy of the colonial Barentsia discreta is generally similar to that of solitary entoprocts but differs in the anatomy and ultrastructure of the ganglion, the number of neurite bundles in the calyx, and the distribution of serotonin in the nerve elements. A comparison of the organization of the nervous system in the Entoprocta and Bryozoa reveals many differences in tentacle innervations, which may indicate that these groups may not be closely related. Our results can not support with any certainty the homology of nervous system elements in adult entoprocts and adult “basal mollusks”.

A new genus and species of solitary entoproct, Emschermannia ramificata, is described from the Kara Sea. It is an epibiont of the nephtyid polychaete Aglaophamus malmgreni, collected from 25-472 m depth. The species is about 250-300 μm long, with 8-10 tentacles, and buds are formed from a frontal area of the calyx. The calyx and stalk are not separated from each other by a cuticular septum, and a star-cell complex is absent. Emschermannia ramificata attaches to a substratum via a basal plate from which pseudostolons grow. Zooidal morphology conforms to that of the Loxosomatidae, but the attachment structure is unique among solitary entoprocts; it resembles basal plates and stolons of colonial entoprocts, but pseudostolons of Emschermannia serve only for attachment, not for budding. Overall, the morphology of Emschermannia may be considered intermediate between that of solitary and colonial forms, with relevance to evolutionary development within Entoprocta.

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Here we describe a new species of colonial entoproct Coriella chernyshevi n. sp. from the Sea of Okhotsk, western Pacific Ocean, found at depths of 305-624 m. This is the first record of an entoproct species for the Sea of Okhotsk. Coriella chernyshevi is a large species with a zooid length of 6-7 mm. The calyx bears 32-34 tentacles. Zooids extend from a central stem formed by closely adjoined stolons. Only one other species of Coriella has been described previously, Coriella stolonata Kluge, 1946, from the Arctic Ocean, found at a depth of 45 m. Coriella chernyshevi and C. stolonata share a same rigid stem structure, but they differ in zooid size and tentacle number. The only other barentsiid that has been described as having a rigid central stem is Pedicellinopsis fruticosa Hincks, 1884. Based on the presence of a central stem in colonies, and similarities in structure of zooids and colonies, we suggest a close relationship between Coriella and Pedicellinopsis. Finally, an overview of both genera and all three species is given.

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