Purple Nudibranch - Hypselodoris bullocki/apolegma

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Purple Sea Slugs (Hypselodoris bullocki and H. apolegma) are easy to spot with bright purple or fuchsia bodies adorned with an opaque white edge on the mantle and yellow to orange gills and rhinophores typically. Some variation to these colors may be observed from specimen to specimen.

These two species are very similar and have only recently been reclassified as two "sister species" rather than regional variations of H. bullocki. The primary difference is the white margin which is sharp on H. bullocki and diffuses into the base color on H. apolegma.

The term "nudibranch" means "naked gill" and refers to the fringy, tassel-like gills visible on many species. This group include animals that we commonly refer to as "sea slugs" as well as the sea hares popular for algae control. As a group, there is not much known about many species of nudibranch and more are being discovered and reclassified continuously. While some like the sea hares are well studied and we know enough about their life cycles and diets for them to be maintained, the diet and requirements of most nudibranchs is largely unknown. Most are thought to feed on sponges, polyps, tunicates. Some of the most colorful nudibranchs are actively collected and sold for aquariums but many more come as "hitchhikers" on rock and corals, for better or for worse.

Use caution when placing any nudibranch in your reef system if its diet is an unknown. Nudibranchs in aquariums are generally shortlived, both due to their natural short lifespans as well as the difficulty of meeting their dietary requirements.