Anisakis simplex (Rudolphi, 1809, det. Krabbe, 1878) (Nematoda: Ascaridoidea): morphology and morphometry of larvae from euphausiids and fish, and a review of the life-history and ecology.

Larval Anisakis 7.7 to 23.6 mm long from euphausiids, and larvae 18.0 to 21.9 mm long from a teleost fish were morphologically and morphometrically alike and fitted the description by Beverley-Burton, Nyman & Pippy (1977) of A. simplex L3. Three small larvae, 4.2 to 5.9 mm long, from euphasiids resembled L3 in anterior but not in posterior morphology; their tails lacked a mucron but, in two of them, cuticular separation at the posterior extremity revealed clearly the mucron characteristic of L3 within. These small larvae are identified as L2 of A. simplex in the process of moulting to L3. Japanese reports of typical L3 from 6.9 to 32.7 mm long in euphausiids, the occurrence in teleosts of typical L3 from only 8.8 to over 30 mm long, and the present observations strongly suggest that the moult from L2 to L3 occurs in euphausiids and begins when the larvae are about 4-6 mm long. Although it appears, therefore, that only one moult occurs in the egg of A. simplex (i.e. ensheathed L2 hatches), two moults there have been reported for various terrestrial and certain aquatic ascaridoids (i.e. ensheathed L3 hatches). The morphology and homology of the lips and associated sense organs of A simplex L3 are discussed relative to that of a 'typical' adult ascaridoid. A main conclusion is that euphausiids in the North-East Atlantic and northern North Sea, and perhaps universally, are major intermediate hosts of A simplex. The status as hosts of squid and teleosts harbouring L3 is discussed. An extensive literature is reviewed in relation to the present observations.