Catworm

Catworms are very rapid predator worms. They hunt young shellfish and other worms, but also eat organic waste and algae. Catworms are very active. They can quickly stick a kind of tongue in and out. They use it to dig themselves rapidly into the bottom. Catworms are very sensitive to severe winters. After such a winter, they can disappear for years. This worm is also sensitive to pollution from oil or drilling muds containing oil.

The sexes are separate and individuals breed several times over a number of years. Generally, the females breed once each year, beginning in their second year. Breeding takes place between April and June and the larvae are planktonic. N. hombergii is potentially a long-lived species, viz. up to 5 years, as determined from the annual rings in its jaws. N. hombergii is a burrowing predator of juvenile molluscs, crustaceans and other polychaetes. lt also feeds on carrion, diatoms and detritus. Studies in the Wadden Sea have shown this species to be sensitive to low winter temperatures. After cold winters the reduced population showed an increase in production (Clark, 1962; Hartmann-Schröder, 1971; Wolff, 1973; Kirkegaard, 1978; Beukema, 1979; Fauchald & Jumars, 1979; Beukema & Essink, 1986; Sips, 1988; Fish & Fish, 1989; Mathivat-lailier & Cazaux, 1991; Olive & Morgan, 1991; Rainer, 1991).

Large (up to 200 mm) robust free-living bristle worms with a flattened body. The small head features an eversible proboscis with papillae, horny jaws and four short antennae. The dorsal parapodial flaps have a clearly visible papilla-like projection. It is pink to flesh-coloured; the gills are red.

The species is common near the coast, in the Wadden Sea and almost the entire Delta area, with high densities in the Oosterschelde. N. hombergii is furthermore abundant in the southern part of the Dogger Bank.

Although Nephtys hombergii can be found across the entire Belgian part of the North Sea, the species chiefly occurs in the near-coastal zone. In the 1976-1986 period the densities did not exceed 100 ind./m2 whereas densities of more than 300 ind./m2 were observed in the 1994-2001 period.

It is not found in the clean sandy substrates in the Southern Bight, in contrast to N. cirrosa and N. longosetosa. Other studies, however, have reported it from sand, muddy sand, mud and gravel. The species seems to dominate at locations with regularly or permanente low oxygen concentrations (Fallesen & Jorgensen, 1991).

Nephtys hombergii prefers fine sediments: in sediments with a median grain size less than 50 µm the species reaches a relative occurrence of > 90%. The higher the median grain size, the lower the relative occurrence. Nephtys hombergii is no longer found in sediments with a median grain size exceeding 500 µm. Although N. hombergii can be found in sediments with both high and low mud content, the general trend is that the relative occurrence increases as the mud content increases.

A robust nephtyid that is markedly rectangular in cross section. Differences with other the Nephtys species are the combination of lacking dorsal cirri, incised parapodial lobes and distinctly curved gills. The body is maximally 150 mm long with 200 segments. lt is pink to flesh-coloured, with a pearly sheen and red gills (Fish & Fish, 1989; Hartmann-Schröder, 1971; Sips, 1988; Hayward & Ryland, 1990; Rainer, 1991).