The developmental stages of Lernaeocera Branchialis (Linn.)

Abstract

The morphology of a complete series of developmental stages of Lernaeocera branchialis is described. Seven stages are passed through before reaching the gadoid (final) host.The structure of the mouth tube and appendages is discussed in detail and compared with those of related genera in which the resemblances are close.The free single nauplius and copepodid stages are immediately followed by four chalimus stages on Pleuronectes flesus; these show some dedifferentiation though segmentation is not lost. An explanation is given for the peculiar suspensory mechanism of the chalimus.A second dedifferentiation follows the second well-developed pelagic phase in which the adult form is attained and copulation takes place. Some irregularity is noted in the details of the retrogressive metamorphosis of the maturing female on the gadoid host.The rate of increase in body length in Lernaeocera decreases regularly up to the assumption of the adult form (stage VII). In this respect it is similar to the free-living copepods Diaptomus, Eurytemora and Calanus, but is in strong contrast to Caligus centrodonti which has an increasing growth rate up to the fourth chalimus stage. In the latter at this stage there is a marked acceleration in the growth rate unaccompanied by any change in shape or any other discontinuity, whereas in Lernaeocera there are early discontinuities in development, yet the growth rate is continuous when expressed graphically: it is a straight line rather than a logarithmic curve as would be expected from our knowledge of the higher Crustacea.The size of the female is greater than that of the male: that of the female overlapping the male of the succeeding stage. Variations in size of the larvae in a stage group are not seasonal, and an explanation is offered for giant larvae.Similar lernaeocerid larvae and males to those of Lernaeocera branchialis on Pleuronectes flesus were found on Solea solea and Cyclopterus lumpus. No characters of generic or specific significance could be found which would serve o t separate them from Lernaeocera branchialis so that their identity is not determined.