Sea Slugs

The term sea slug refers to a group of marine mollusks that are related to snails. Sea slugs have small or, more typically, no shells. They are members of the scientific order Opisthobranchia, and include families such as the nudibranch, which is entirely shell-less, and the bubble shells, which have a lightweight external shell.The Sea Slug Forum: What is a Slug?

• Cephalapsidea
• Sacogloss
• Anaspidea
• Notaspidea
• Thecosomata
• Gymnosomata
• Pleurobranchomorpha
• Nudibranchia

The nudibranch is a common sea slug. It is generally oblong in shape with feathery gills.National Geographic: Nudibranch It has a jelly-like body and no mantle cavity.Aquatic Community: Nudibranch There are 3000 species of nudibranch that are classified into four main groups, based on appearance. The Harlequin nudibranch has a pair of tentacles on the top of its head and is the most numerous of the nudibranchs. The Tubercular nudibranch is covered with fingerlike appendages and is second most common. The Black Gilled nudibranch has a cuplike sheath on its head, and the Veiled nudibranch has ridges on its back with a fleshy lobe on its head.Nudibranch.com: About Nudibranches - Opisthobranchs