ENZYME ELECTROPHORESIS, GENETIC IDENTITY AND DESCRIPTION OF A NEW GENUS AND SPECIES OF HETERONEMERTEAN (NEMERTEA, ANOPLA) FROM NORTHWESTERNSPAIN AND NORTH WALES

The anoplan order Heteronemertea, particularly the genera Cerebratulus , Lineus and Micrura, contains a very large number of nominate species , many of which are inadequately described. As a consequence, systemat ic difficulties are encountered with the identification of many taxa i n this group, especially those originally established primarily on the basis of their external features. The present paper concerns heterone merteans collected from two locations, the Foz Estuary (north-western Spain) and Llandudno (North Wales). The Spanish collection included sp ecimens identified as Lineus longissimus (Gunnerus), whilst samples fr om Llandudno contained large numbers of Lineus viridis (Muller); sampl es of a third similar but apparently undescribed species were found at both locations. Starch gel electrophoresis showed that samples of the apparent third species were genetically almost identical from each of the two locations, but were clearly different from the two described Lineus species. Histological studies of the unknown specimens revealed anatomical characters, including the unique feature of a proboscis ep ithelium ciliated throughout its length, which exclude it from any kno wn heteronemertean taxon; it is accordingly placed in a new genus and species, for which the name Riseriellus occultus is proposed.