Sea Louse - Morphology

Morphology

Lepeophtheirus salmonis tends to be approximately twice the size of most Caligus spp. (e.g. C. elongatus, C. clemensi, etc.). The body consists of 4 regions: cephalothorax, fourth leg-bearing segment, genital complex, and abdomen. The cephalothorax forms a broad shield that includes all of the body segments up to the third-leg bearing segment. It acts like a suction cup in holding the louse on the fish. All species have mouth parts shaped as a siphon or oral cone (characteristic of the Siphonostomatoida). The second antennae and oral appendages are modified to assist in holding the parasite on the fish. The second antenna is also used by males to grasp the female during copulation. The adult females are always much larger than males and develop a very large genital complex which in many species makes up the majority of the body mass. Two egg strings of 500 to 1000 eggs (L. salmonis) that darken with maturation are approximately the same length as the female’s body. One female can produce 6-11 pairs of egg strings in a lifetime of approximately 7 months.