In this article we will discuss about the structure of Sacculina with the help of a diagram.
1. This is a specimen of sacculina—“the sucking root barnacle” an ectoparasite on crab.
2. It is in the form of a flat, fleshy and sac-like structure having only the gonad. It is found attached to the ventral surface of crabs between thorax and abdomen.
3. The various body divisions (segmentation), almost all appendages, eyes, mouth, anus & alimentary canal etc. are degenerate in adult as a result of parasitic mode of life.
4. There is present a small peduncle below, which sends five highly branched and anastomosing filaments into the body of host to absorb nourishment.
5. It is hermaphrodite and its development is completed through a “nauplius larva” which changes to cypris larva which alone is capable of infesting new hosts.
Note:
To begin with, a cypris larva of sacculina attaches to a normal crab, discards its shell, penetrates inside and gets converted into a mass of cells and is attached to the intestine of host It remains there till the crab molts next, whence a part of it protrudes out as sac-like structure containing an ovary. The remaining internal parts get branched, filamentous and penetrate into different organs of the host.