[8][9] The multiciliated epidermis displays unique interconnected ciliary rootlets and mode of withdrawal and resorption of worn epidermal cells.

[14] Research on the species Xenoturbella bocki has shown it to have external fertilization, with eggs and sperm being released from new openings in the body wall.

[20] This refers to the enigmatic, unusual taxonomic status of the animal, initially considered as related to turbellarians, a group of flatworms whose aquatic species stir microscopic particles close to their ciliated epidermis.

The two smaller species, X. bocki and X. hollandorum, which are up to 4 centimetres (1.6 in) long, are found in shallower waters less than 650 metres (2,130 ft) deep.

[27] Three larger species, X. monstrosa, X. churro, and X. profunda, which were 10 centimetres (3.9 in) or greater long and lived in deeper waters 1,700–3,700 metres (5,600–12,100 ft), form another clade.

[3] Acoelomorpha X. japonica X. bocki X. hollandorum X. monstrosa X. churro X. profunda The systematic and phylogenetic position of Xenoturbella among animals has been considered enigmatic since its discovery.

[30] A subsequent study suggested a placement of the genus in its own phylum, Xenoturbellida, as a deuterostome clade and sister group to the Ambulacraria.

[17] Molecular studies based on the concatenation of hundreds of proteins revealed indeed a monophyletic group composed by Xenoturbella and Acoelomorpha.