Larval Anisakis simplex (Rudolphi, 1809, det. Krabbe, 1878) and larval Hysterothylacium sp. (Nematoda: Ascaridoidea) in euphausiids (Crustacea: Malacostraca) in the North-East Atlantic and northern North Sea

Abstract

ABSTRACTOver 26000 specimens representing five euphausiid species collected, mostly in 1969, in the North-East Atlantic and northern North Sea were examined for parasites. Hysterothylacium sp. larvae were rare, occurring in only two euphausiid samples from inshore localities; the 9 larvae found (3.8 to 12.3 mm long) are described and illustrated. Infection with larval Anisakis simplex was virtually restricted to Thysanoessa spp. and appeared to be discontinuous. Infection was absent to the west of Scotland, and rare to the north of Scotland and at the Faroes. Larval A. simplex was not uncommon in offshore regions of the northern North Sea at depths between 100 and 200 m; the prevalence rate there for individual euphausiid species in individual samples was mostly 0 to 40% but an exceptionally high rate of 78.0% was recorded. Larvae in euphausiids do not become encapsulated but appear to remain active. Experimental observations on the sedimentation rate of A. simplex eggs and hatched larvae in sea water at 10°C are discussed in relation to embryonation and hatching at different temperatures, and depth of the sea. New host records are claimed for larval A. simplex in Nyctiplutnes couchii, and for larval Hysterothylacium sp. in Thysanoessa inermis. No individual euphausiid harboured more than one parasite, either larval nematode or ellobiopsid (see also SMITH, 1981). Morphological and morphometric observations on larval A. simplex from euphausiids are reported elsewhere (SMITH, 1983).