Notarchus

Notarchus is a genus of sea slugs, specifically marine gastropod mollusks, belonging to the order Nudibranchia. These are shell-less marine snails that are commonly known as nudibranchs. The genus Notarchus is characterized by its sac-like body and the presence of external gills. They are part of the family Umbraculidae, which also includes the genus Umbraculum.

Species within the genus Notarchus are typically found in tropical and subtropical waters worldwide. They are often observed in shallow marine environments, including coral reefs and rocky shores. Their diet consists primarily of sponges, which they consume by grazing on the sponge tissue.

The morphology of Notarchus is distinct. They possess a soft, unsegmented body that can be quite gelatinous. A key feature is the mantle, which is greatly enlarged and forms a dorsal sac covering most of the animal's body. The rhinophores, sensory tentacles found on the head of most nudibranchs, are often short and broad. The external gills are typically arranged in a circlet around the posterior end of the mantle cavity.

Reproduction in Notarchus, as with other nudibranchs, is sexual, and they are hermaphroditic, possessing both male and female reproductive organs. They lay their eggs in gelatinous strings or masses. The larval stage is planktonic before settling to the seafloor to metamorphose into the adult form. Notarchus plays a role in the marine ecosystem as a consumer of sponges.