Description & Behavior

Blue dorid nudibranchs (sea slugs), Hypselodoris bullockii (Collingwood, 1881), aka Bullock’s Hypselodoris, range in color from a pale straw, or even white background to a deep purplish pink. There is usually a thin opaque white line at the mantle border, but some have a reddish purple border. Typically the gills and rhinophores are yellow or orange with a basal pink or purplish band.

Nudibranchs in the Order Nudibranchia are the true sea slugs (adults have no shells and externally exposed gills) and are classified as:

  • Order Nudibranchia
    • Suborder Dexiarchia
      • Infraorder [unassigned] Dexiarchia
        • Family Charcotiidae
        • Family Dironidae
        • Family Dotidae
        • Family Embletoniidae
        • Family Goniaeolididae
        • Family Heroidae
        • Family Madrellidae
        • Family Pinufiidae
        • Family Proctonotidae
      • Infraorder Aeolidida (aeolid nudibranchs)
        • Superfamily Aeolidioidea
          • Family Aeolidiidae
          • Family Facelinidae
          • Family Glaucidae
          • Family Piseinotecidae
          • Family Unidentiidae
        • Superfamily Fionoidea
          • Family Calmidae
          • Family Eubranchidae
          • Family Fionidae
          • Family Pseudovermidae
          • Family Tergipedidae
        • Superfamily Flabellinoidea
          • Family Flabellinidae
          • Family Notaeolidiidae
      • Infraorder Dendronotida
        • Superfamily Tritonioidea
          • Family Aranucidae
          • Family Bornellidae
          • Family Dendronotidae
          • Family Hancockiidae
          • Family Lomanotidae
          • Family Phylliroidae
          • Family Scyllaeidae
          • Family Tethydidae
          • Family Tritoniidae
    • Infraorder Euarminida
      • Superfamily Arminoidea
        • Family Arminidae
        • Family Doridomorphidae
    • Infraorder Pseudoeuctenidiacea
      • Superfamily Doridoxoidea
        • Family Doridoxidae
  • Suborder Euctenidiacea
    • Infraorder Doridacea (dorid nudibranchs)
      • Superfamily Doridoidea
        • Family Actinocyclidae
        • Family Cadlinidae
        • Family Chromodorididae « Blue dorid nudibranchs, Hypselodoris bullocki
        • Family Discodorididae
        • Family Dorididae
      • Superfamily Onchidoridoidea
        • Family Akiodorididae
        • Family Goniodorididae
        • Family Onchidorididae
      • Superfamily Phyllidioidea
        • Family Dendrodorididae
        • Family Mandeliidae
        • Family Phyllidiidae
      • Superfamily Polyceroidea
        • Family Aegiridae
        • Family Gymnodorididae
        • Family Hexabranchidae
        • Family Okadaiidae
        • Family Polyceridae
    • Infraorder Gnathodoridacea
      • Superfamily Bathydoridoidea
        • Family Bathydorididae

Infraorders Doridoidea (dorid nudibranchs) and Aeolidoidea (aeolid nudibranchs) are the two largest groups of nudibranchs.

Characteristics of dorid nudibranchs include a broad, flat foot, a thick, fleshy mantle, and a circle of gills on the posterior end of the dorsal surface. The gill surrounds the anus. These nudibranchs are also generally the larger species.

Aeolid nudibranchs have long, narrow bodies, lack gills, and have a number of projections on the dorsum called cerata. These slugs are generally smaller in size.

Dendronotida nudibranchs characteristics include rhinophoral sheaths, mid-lateral anus, but resemble aeolids.

Euarminida nudibranchs are a motley group of species. The species in this infraorder differ greatly amongst themselves which makes very few externally consistent characteristics. Some features that many of the species in this infraorder share are lack of rhinophoral sheaths and, often, oral tentacles, and the anus is far forward on the body. These broad characteristics of the suborders are helpful in determining which suborder an individual belongs to so that it may be identified further.

Nudibranchs move by muscular action or by ciliary action which causes the slug to move quite slowly. In a slug that moves via muscular action, contraction and expansion of the muscles move the slug forward. In ciliary motion, cilia in the foot beat against the substrate causing the slug to move forward.

World Range & Habitat


Originally described from the South China Sea, this species is found in the western Pacific as far south as southern Queensland. They are also found off north western Australia, Indonesia, Thailand, in the tropical western Pacific and the central to eastern Indian Ocean.

Feeding Behavior (Ecology)

All nudibranchs are carnivorous feeding on sessile or sedentary organisms. Each suborder of nudibranch has a major food source. For dorids, most food comes from preying on bryozoans and sponges (Dysidea and Aplysilla) while aeolids and dendronotideans prey upon cnidarian species. Just as the suborder Euctenidiacea is diverse, so is the food they consume. It is important to remember that the substrate a nudibranch is found on may not necessarily be its food source.

Life History

All nudibranchs are hermaphroditic, but rarely will they fertilize themselves. Normally nudibranchs will copulate and each individual will lay an egg mass, called a nidosome. Egg masses of a number of nudibranchs are quite distinctive and can be found on substrates where nudibranchs feed or are often found. When the eggs hatch, a veliger larva (larva with a protective shell and a ciliated flap-shaped foot used for swimming and feeding) is usually released. The veliger has a shell, but once the larvae has settled out of the plankton, the shell is released and they enter a juvenile stage.

Conservation Status & Comments

Very delicate and fussy feeders. Not recommended for aquaria. Nudibranchs are a diverse group of species and are found throughout the world. Little is known about them due to their short life span and the fact that they often appear in one place and disappear shortly after making it difficult to study the ecology and life history of the organisms. The Pacific Coast, and particularly Monterey Bay, has a large number of species of nudibranchs compared to other areas of the world where these animals are found.

References & Further Research

Sea Slug Forum: Hypselodoris bullockii (Collingwood, 1881)
The Slug Site
Jeff’s Nudibranch Site and Coral Reef Gallery
Opisthobranch of the Week

Research Hypselodoris bullockii @
Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS

Search for Blue Dorid Nudibranchs @
Flickr ~ Google ~ Picsearch ~ Wikipedia ~ YouTube