Glossodoris dalli
Dorids are the largest group of nudibranchs. Their representatives include animals of many sizes. Thir anus is smartly placed in the center of their circle of gills. This interesting placement of the anus is a price that many molluscs have had to pay for once having a shell. Because if you have a shell, and it only has one opening, your butt is invariably going to end up close to your mouth, gills, eyes, whatever. So, eventhough nudibranchs don't have shells anymore, this condition is probably one inherited from their evolutionary ancestors.
The dorids are divided into three large groups: the cryptobranch dorids, the phanerobranch dorids, and the porostome dorids. The cyrptobranchs can withdraw their gills into the body, while the phanerobranchs cannot. The porostomes can also withdraw their gills; however, they have a reduced head and no tentacles on it.
An important feature in dorids is that they are holohepatic. That is to say, the digestive gland is a single mass in them as opposed to being branched as in Aeolids and some other nudibranchs.
Chomodoridae is a large family with many colorful and beautifuly patterned species.
Many Chromodorids feed on sponges, and as with other sea slugs, they are often found sitting on top of their favorite prey species. Many of these nudibranchs specialize in only one species of sponge. Finicky eating habits like these are what make keeping nudibranchs in aquaria often so difficult. Sometimes it is a challenge just to figure out what the critters want to eat, let alone keeping a supply of prey alive and well in the tank. So, it is much better to leave the animals in peace and enjoy looking at them while scuba diving.
Getting back to the sponges that these guys eat. Sponges secrete toxic chemical which are abosrbed by the dorids and stored in the mantle glands on their backs so as to repel potential predators.
