mesozoa

2

Phylum: Rhombozoa

…Also known as Dicyemida rhombozoa is a phylum of small parasites that live inside the kidneys of cephalopods. Dicyemids exist in two forms, asexual and sexual, juveniles tend to be asexual and adults tend to be sexual. Asexual individuals (called nematogens) produce vermiform larvae within the axial cell. These larvae mature to form more nematogens which will reproduce and fill the kidney. As the larvae age (or the nematogens reach a certain density) they will mature to form rhombogens (the sexual stage). Rhombogens contain gonads (called infusorigens) these infusorigens self-fertilize to produce infusoriform larvae. These larvae are distinct in that they swim around with cilliated rings that look like headlights. These larvae ultimately get released when the host eliminates urine from the kidneys, it is thought that these larvae are both the dispersal and the infectious stage. However the method of infection remains unknown, as are the effects of dicyemids on their hosts.

Phylogeny

Animalia-(mesozoa)-Rhombozoa

Images: Chelsealwood and I.Livingstone

2

Phylum: Orthonectida

…a small (20 spp.) phylum of poorly researched parasites of marine invertebrates. Orthonectids are simply microscopic animals that  consist of a single layer of ciliated cells that surround a mass of sex cells. They swim freely inside their flatworm/polychaete/echinoderm or bivalve hosts and have two separate sexes. Once they are ready to reproduce they will leave their host and will the male’s sperm will penetrate directly into the female’s body. The zygote will develop into a ciliated larva that will escape from its mother to seek out a new host. Once it finds one it will lose its cilia and develops into a plasmodium larva. Which will break up into numerous cells that will become the next generation.

Phylogeny

Animalia-(mesozoa)-Orthonectida

Images: Unknown and Hyman