Rastrognathia macrostoma gen. et sp.n. is described as belonging to Rastrognathiidae fam.n. The ultrastructure is described, especially the nervous and digestive systems and the epidermal specializations. In the epidermis the single cilia belong to the choanocyte‐like cell type. An epidermal sensory cell with several cilia is described. The intraepithelial nervous system shows an orthogon pattern. Two ventral nerve trunks unite into a buccal ganglion. The jaws are secreted by the buccal epidermis. The endoderm consists of a single cell type. The food consists of bacteria. The mesodermal elements consist of six main longitudinal muscles.

Psammodrilus aedificator sp.n. is described from an arctic subtidal sandy habitat at 2–3 m depth. The new species represents a link between the two genera Psammodrilus and Psammodriloides, but it has a distinct warty collar shared only with Psammodrilus balanoglossoides. This unique structure was investigated by transmission electron microscopy. Each wart consists of one large cell with microvilli arranged in a hexagonal pattern. The collar epidermis is devoid of cilia. The head consists of prostomium and peristomium, the thorax consists of 7(8) segments, both tagmata totally ciliated. Each of the six pairs of cirri have an aciculum. The abdomen consists of 20 segments and is ciliated except for the dorsal sulcus. Psammodrilus aedifcator sp.n. is sessile and forms a “house” of agglutinated sand grains. Only females (8 mm) and a few juveniles (4 mm) were found in July‐August. Mature eggs are extremely large (310 μm), evidently an adaptation to arctic conditions. Throughout the year the interstitial fauna at the type locality was rich, both in species and individuals. Some of the associated fauna included coelenterates, many turbellarians, nemerteans, chaetonotid gastrotrichs, archiannelids and polychaetes and, less abundantly, a few gnathostomulids, macrodasyid gastrotrichs, nematodes, eutardigrades, halacarids, harpacticoid copepods and ostracods.

No abstract

The postlarval phase is an essential period in the life history of marine invertebrates; vulnerable to high mortality, it ultimately influences the distribution and abundance of adult populations. In the deep NE Atlantic, a large number of postlarval ophiuroids have been found during certain times of the year, but their identification is difficult. The present work describes the ontogenesis of 12 post-metamorphic shallow-water or deep-sea ophiuroids from samples collected during the Biofar and Rockall Trough Programmes in the NE Atlantic Ocean. Analysis of the postlarval development reveals that species can be identified from a very early post-metamorphic phase using particular morphological characters. The ontogeny of homologous structures reveals similarities within related groups. However, at the same time, these structures give rise to different adult structures in different taxa. Data on the postlarval development of Ophiura ajinis suggest that this species is more closely related to the genus Ophiocten and a change in generic status is proposed. 0 1998 The Linnean Society of London ADDITIONAL KEY WORDS:-postlarvaemorphologygrowth series -SEM ontogenesis.