Completion of the Rhizocephalan Life-cycle Joshua Sabey BIOL 4800
Rhizocephalan • Free-living stages Nauplius Cypris
Rhizocephalan • Sacculina externa
Rhizocephalan • Dioecious (most barnacles hermaphroditic). • One host in the life-cycle. • Affects host morphologically, physiologically, and behaviorally. • Infection castrates host. • Crabs (even males) protect externa as if it was their own eggs. • Creates organism with host phenotype and parasite genotype.
Before the Experiment • The nature of the material injected by the Kentrogon has been poorly understood for decades. • Any injection material seen in previous experiments disintegrated into numerous cells. • All experiments performed previously were done in vitro.
Rearing and Infection Experiments • Purpose was to discover the nature of the material injected by the Kentrogon. • Kentrogon injection material was observed in vivo using light and electron microscopy. • Mud crabs, Rhithropanopeus harrisii, were parasitized with the sacculinid rhizocephalan Loxothylacus panopaei.
The Vermigon • A worm-like larva • Consists of a cuticle, epidermis and body of cells that will develop into the ovary. • The cuticle remains intact throughout development to an interna. • Has a distinct internal spiral across the entire length of its body. • The central spiral and actin fibers in the epidermis provide motility.
The Vermigon • The kentrogon injects its vermigon into the blood spaces of the gills. • The vermigon migrates to the heart and then to the posterior region of the crab. • Once in the posterior, the vermigon develops a rootlet system and becomes an interna. • The interna matures and an externa emerges from the rear end of the crab.
Conclusions • It is no longer assumed that the mature rhizocephalan develops from numerous undifferentiated cells in the kentrogon injection material. • The injection material is a whole vermigon consisting of a cuticle, epidermis, and cell bodies that become the uterus. • The vermigon stays as one unit during the maturation process.