Chromodoris is a genus of very colourful sea slugs or dorid nudibranchs, marine gastropod molluscs, and the type genus of the family Chromodorididae. Within the genus Chromodoris, there are currently 101 classified species. Species within Chromodoris are commonly found in tropical and subtropical waters, living as members of reef communities and preying primarily on sponges. A molecular phylogeny of the family Chromodorididae resulted in this genus being restricted to a smaller number of species than formerly, most of which have longitudinal black lines on the mantle. Many former members of Chromodoris were transferred to Goniobranchus

Anatomy

Chromodoris species exhibit one of the two major body types found within Nudibranchia. There are a few major bodily features that separate chromodorids from other sea slugs.

Mantle

Dorids have a thick mantle that exists over their foot, and in some species, the mantle can have tubercles (nodules along the surface of an organism that are made of keratin) of different concentrations, shapes, and sizes, providing some rigidity and protection for their soft, shell-less bodies. In most dorid species, the mantle holds toxins that defend the organism that are obtained through their diet.

Respiratory system

Chromodorids breathe oxygen principally through their gills, usually positioned in a featherlike structure located around the anus at their posterior, called the branchial plume.

Phylogeny and taxonomy

The classification of the family Chromodorididae has been the subject of many studies on nudibranches in recent years, most focusing on the phylogeny and its impact on the traditional taxonomies of the genera. Chromodoris was long considered to be the most diverse genus of the Chromodorididae; however, a study published in July 2018 on Indo-pacific species of chromodorid nudibranchs has shown that the genus should be categorized more strictly, and has been narrowed down to 22 species. These species characteristically have black stripes along their bodies and linear spawning.

Chemical defenses

Chromodorid nudibranchs commonly exhibit chemical defenses to protect themselves from predators. Most of the species that exhibit this behavior make use of bioactive compounds like alkaloids, diterpenes, and sesquiterpenes from the sponges they feed on. Nudibranchs can collect these compounds and store them as is, transform them, or be selectively sequestered, although there is no information on how common each mechanism is and which individual species exhibit the individual methods. Chromodorid nudibranchs in particular transport and store their toxic compounds in specialized storage glands located in strategic locations throughout the mantle, called mantle dermal formations (MDFs). These MDFs have been shown to harbor extremely high concentrations of distasteful and potent compounds in comparison to the rest of their body.

Reproduction

All nudibranchs are simultaneous hermaphrodites, with each individual possessing both male and female reproductive structures. During mating, two individuals compete for the position of male by darting their penises at one another until the victor penetrates the body wall of the other and impregnating them, forcing them to act as the female, an act commonly called "penis fencing." From here, the female lays eggs into a substrate, which hatch planktonic vestigial veliger larva, who will further evolve into adults.

Species

Species in the genus Chromodoris include:

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