Morphologic.al studies of eleven new species in the family permitted reconstruction of progressive evolutionary lines. and this strongly implies progressive evolutionary lines for other acoela.Solenofiloniorphn funiliq n. sp.. Myopea crassula n. g. n. sp., M . latafnucium n. sp., E'usanlruwz rhammiphorum n. g. n. sp. and Endocincta punctata n. g. n. sp. are described from the coast of Sorth Carolina, U.S.A., and S. guuymensis n. sp. is described froni the Gulf of California. Five additional unnamed species from the r.9. Pacific Coast, Sweden and Tunisia are briefly described.TI!-o species groupings were based on correlation between two different arrangements of pharyns muscles and trio arrangements of antrum niuscles and further correlations with lesser chardcter 8. The membership of the two groupings in a single family make it clear that evolution proceeded by dddition of structures to a less complex common ancestor. Functional and behavioral considerations support the evolutionary path drawn from morphology. Distinctive statocyst structure, ciliary interconnections and sperm morphology shared by acoels showthem to have a coninion ancwtrg, but clearly different pharynges and male structures cannot be consistent with evolution by reductions. A common ancestor of low complexity has probably given rise to several partly Iiartillel evolutionary lines which together form the structurally diverse hoela. The hie tor^ of acoel systematics is also briefl) summarized.

Crezée, M. (University of Florida Marine Laboratory, Gainesville, FL 32611, USA) and Tyler, S. Hesiolicium gen.n. (Turbellaria Acoela) and observations on its ultrastructure. Zool. Scr. 5 (5): 207–216, 1976. —Hesiolicium inops gen.n., sp.n. is a thin and elongate protandric hermaphrodite from the marine interstitial environment. The male pore, with no accessory organs, lies just posterior to the mouth, with no pharynx. The dorsal ovary, lateral testes, adhesive papillae and a caudal organ are other features. The posterior and midventral adhesive papillae are bundles of haptocilia up to 22 μm long. In a crook near their base these adhesive cilia have three microtubule doublets displaced from the rest of the axoneme, giving the crook region a figure‐eight cross section. The caudal organ is a complex of cilium‐bearing sensory cells, large gland cells and modified muscle and epidermal cells. The rootlets of epidermal cilia and the two axial units of the sperm are as described for other acoels. Principally because of the haptocilia, Hesiolicium is provisionally placed in the Paratomellidae.