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.

The Life-Cycle

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.

Results: The Vermigon

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 Life-Cycle

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.