Memoirs: Spolia Bermudiana

Abstract

1. Several stages of a new type of Auricularia (A. bermudensis n.sp.) are described. When fully formed it resembles A. nudibranchiata in the foliation of its ciliated bands and appendages, but is distinguishable by many structural features and in becoming full-grown at less than half the size (<4 mm.). 2. The usual arms are present, adnate to the body, as well as a special ‘strap-shaped process’ with directive functions. They support a system of gutters plainly subservient to food-collection. The terms ‘field’ and ‘sulcus’ (with the diminutive ‘sulculus’) are proposed for the raised and depressed areas of Dipleurulae in general. 3. The so-called ‘larval nervous system’ is claimed to be simply a pair of ciliary organs subservient to the feeding process and comparable to an outer pair of adoral bands (‘oro-lateral bands’). 4. The rectum is in line with the stomach and the anus subterminal, but the ileum is reduced to a dorsal pore, and the part of the rectum adherent to the stomach is a large ventral pouch comparable to that described in A. nudibranchiata by Chun, whose account is confirmed. 5. The author has re-examined the original specimens of A. antarctica and denies the existence of the paired ‘intestinal pouches’ described in this species and in A. nudibranchiata by MacBride. 6. The anterior enterocoel in the younger specimens is unique in possessing two long, tapering, bilaterally symmetrical ‘horns’, functionally dilated. Hydrocoel and water-tube arise from the left horn. Eventually the right horn undergoes self-amputation and is absorbed. At full growth the persistent left horn, still of unusual length, acquires antler-like points and branches, as in A. nudibranchiata. 7. The significance of the new features is discussed in comparison with Tornaria and Planktosphaera.