White Catworm

Breeding occurs in March and August. The species presumably has planktonic larvae. Analyses of its gut contents has shown this species to be a predator of small invertebrates (Clark, 1962; Hartmann-Schröder, 1971; Wolff, 1973; Fauchald & Jumars, 1979; Olive & Morgan, 1991).

Medium-sized (up to 100 mm) free-living bristle worms with a flattened body. The small head bears an eversible proboscis with papillae, horny jaws and four short antennae. The species distinguishes itself from other Nephtys species by typical parapodial flaps and a branchial cirrus that, on the last parapodia, is as long as the gill.

N. cirrosa is a dominant species in the Southern Bight with high densities at the Brown Bank and near the coast. lt is furthermore common at the Dogger Bank. Only few individuals are found in the Oyster Ground. Low densities are furthermore reported from the Delta area and the western Wadden Sea.

In both periods Nephtys cirrosa was widely spread on the Belgian part of the North Sea, where the species was observed from the coastal zone to the open sea in rather large quantities and with a high frequency of occurrence. Maximum density of N. cirrosa in the 1976-1986 period was 100 ind./m2 whereas densities up to 1,000 ind./m2 were recorded in the 1994-2001 period.

The distribution of N. cirrosa appears to be strongly related to the grain size of the sediment, i.e. it prefers clean, coarse to fine sandy sediments as found in the Southern Bight (Rainer, 1991).

Nephtys cirrosa is found in sediments with a median grain size of 250 to 550 µm and reaches a very high relative occurrence (> 80%). However, N. cirrosa can also be found in finer and coarser sediments. The species is observed in mud-poor sediments as well as in mud-rich sediments, but nevertheless displays a slight preference for low mud content levels (< 10%).

A relatively slender nephtyid polychaete of a few centimetres long and about 95 segrnents. Apart from its dimensions, N. cirrosa differs from the other Nephtys species by the absence of dorsal cirri, the serrated sculpture of the chaetae and the small size and shape of the gills. lt is yellowish white with red gills (Wolff, 1973; Sips, 1988; Hayward & Ryland, 1990; Olive & Morgan, 1991).