Limnognathia

Limnognathia is the only genus in the phylum Micrognathozoa ("small-jawed animal").

Description

Feeding

Limnognathia mainly feeds on bacteria, blue-green algae, and diatoms. It has complex jaws, with fifteen separate elements; these elements are very small, ranging from 4 μm to 14 μm. The animal can extend part of its jaw outside its mouth while eating. It also extends much of its jaw outside its mouth when it is regurgitating indigestible items.

Anatomy

Limnognathia has a large ganglion, or 'brain', in its head, and paired nerve cords extending along the lower side of the body towards the tail. Stiff sensory bristles made up of one to three cilia are scattered about the body. These bristles are similar to ones found on gnathostomulids, but up to three cilia may arise from a single cell in Limnognathia, while gnathostomulids have only one cilium per cell.

Flexible cilia are arranged in a horseshoe-shaped area on the forehead, and in spots on the sides of the head and in two rows on the underside of the body. The cilia on the forehead create a current that moves food particles towards the mouth, while the other cilia move the animal.

Reproduction

All specimens of Limnognathia that have been collected have had female organs. They lay two kinds of eggs: thin-walled eggs that hatch quickly, and thick-walled eggs that are believed to be resistant to freezing, and thus capable of overwintering and hatching in the spring. The same pattern is known from rotifers, where thick-walled eggs only form after fertilization by males. The youngest Limnognathia specimens collected may also have male organs, and it is now hypothesized that the animals hatch as males and later become females, a process called sequential hermaphroditism.