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Related FAQs: Nudibranchs, Nudibranchs 2, Nudibranch Identification, Nudi ID 2, Nudi ID 3, Nudi ID 4, & Nudibranch Behavior, Nudibranch Compatibility, Nudibranch Selection, Nudibranch Systems, Nudibranch Feeding, Nudibranch Disease, Nudibranch Reproduction, Berghia Nudibranchs, Marine Snails 1, Marine Snails 2, Marine Snails 3Marine Snails 4, Sea SlugsSeaslugs 2, Snail ID 1, Snail ID 2, Snail ID 3

Related Articles: Dorid et al. Nudibranchs pt. 2, Aeolid Nudibranchs pt. 3, Sea Slugs, Gastropods, Mollusks, Aiptasia/Glass Anemones

/The Conscientious Marine Aquarist

Nudibranchs, The Naked-Gill Sea Slugs, pt. 1, Dorids

To: Pt. 2, Pt. 3, Pt. 4, Pt. 5, Pt. 6, Pt. 7, Pt. 8, Pt. 9, Pt. 10, Pt. 11, Pt. 12, Pt. 13, Pt. 14, Pt. 15, Pt. 16

By Bob Fenner

Phyllidia arabica

Order Nudibranchia- Naked-gill sea slugs. Largest of the five Orders of Opisthobranch gastropods. Lack shells, are carnivorous (feed on sessile invertebrates like sponges, sea fans, hydroids, corals... some are predaceous on other nudibranchs.). Lack predators by and large themselves due to unpalatability, toxicity, venom... mainly from recycled molecules via their prey. 

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Considering their small size, often bizarre body shapes and dazzling coloration, it's no wonder nudibranchs are often unidentified by divers, aquarists and tide-poolers for what they are; marine snails that lack shells, just like their lowly terrestrial cousins found sliming around under rotting wood and vegetation.

But most of us emote "oohs" and "aahhs" rather than "yecch" when we view these "butterflies of the sea". Unfortunately, few efforts at keeping them in captivity have been successful. Many failures, as you'll see, are aquarist-originated; chemical poisoning, unstable conditions, and most importantly, starvation.


Nudibranchs are mollusks (Phylum Mollusca, = "Soft-bodied" animals a group including squids, octopi, abalones, Chitons, tusk shells, mussels, scallops, oysters... Further sub classified, they belong to the Class Gastropoda, the "stomach-footed" mollusks (snails and their relatives); which are still further divvied up into the Subclass Prosobranchia- with a mantle cavity and organs located anteriorly in their classically twisted (or torted) shells. Our group is the other Subclass, the Opisthobranchia, shows a reduction of shell and mantle cavity; many are de-torted, that is, secondarily bilaterally symmetrical.

The Order Nudibranchia is one of nine extant Orders in the Subclass; they lack shells and mantle cavities. To review:

Phylum Mollusca

Class Bivalvia, et al.

Class Gastropoda

Subclass Prosobranchia ("ahead gills")

Subclass Opisthobranchia ("behind gills"). Have Rhinophores; sensory organs for chemicals, currents. Below: Rhinophores anteriorly, anal gills posteriorly.

Rhinophores and gills...

Order Aplysiacea, et al. (sea-hares)

Order Nudibranchia- Naked-gill sea slugs, 

    Suborder Doridacea- Dorids

    Suborder Aeolidacea- Aeolids

    Suborder Dendronotidacea- Usually have an oral hood and series of cerata running down their backs. 

    Suborder Arminacea

The nudibranchs comprise four sub-orders, about seventy families and one thousand-plus valid species. Two of the sub-orders are rarely seen in the hobby, the Dendronotacea and Arminacea, but the following information concerning the other two groups applies to them.

Suborder Doridacea, Dorids:

('Door-idz'), (Suborder Doridacea) dwell in rocky intertidal zones worldwide, sometimes in good numbers. Their mantles cover their entire dorsal surface and hang over their foot. Their gill plumes are arranged around a rear anal vent area and are capable of retraction into a specialized pocket. The chemosensory tentacles, or rhinophores at the head end can likewise be retracted. 

Family Chromodorididae: More than 360 species in the Indo-Pacific, Caribbean, Mediterranean... the genus Chromodoris alone with 165... colorful generally. Typified by oval mantles that cover their foot entirely. Their posterior located secondary anal gills are pinnate, one pair of tentacles, rhinophores lamellate.

Genus Anisodoris

Anisodoris nobilis Bergh, 1898, Sea Lemon, Pacific sea lemon, Noble pacific doris. E. Pacific; Alaska to Baja California; low intertidal to 35 m. To more than 8 inches in length. This one at the SIO Birch Aq., San Diego, CA. 

Genus Cadlinella

Cadlinella ornatissima (Risbec 1928). Red Sea, Indo-Pacific; Malaysia to Australia. To 2 cm. N. Sulawesi (Lembeh Strait) pic. 

Genus Ceratosoma: Long-bodied, tailed, highly branched gills. Mantles with prominent lateral extensions.  

Ceratosoma alleni Gosliner 1996. A mimic and found on shallow reefs dominated by Xeniid colonies. To 50 mm. Indo-Pacific. Northern Sulawesi.

Ceratosoma gracillimum Semper in Bergh, 1876. Tropical east to west Pacific.. To 2 cm./.75" Note absece of marginal lateral lobes connecting the heads with the "arms". N. Sulawesi image. 

Ceratosoma tenue. Two pair of flat, lateral body lobes, and a spotted marginal purple edging. Red Sea to Hawai'i. To 11 cm. N. Sulawesi images. 


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Ceratosoma trilobatum
(J.E. Gray 1827). Distinguished from the similar appearing and overlapping distributed C. tenue by the possession of three lobes on the forward body, and a continuous marginal purple line. N. Sulawesi pix. 


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Genus Chromodoris: Largest genus of Nudibranchs. 

Chromodoris annae Bergh 1877. Indo-Malaysian Peninsula. To 2 cm. N. Sulawesi pic. Sponge eaters. http://www.seaslugforum.net/search.cfm?searchstring=Chromodoris+annae

Chromodoris bullocki Collingwood 1881. Variable in color... sometimes almost all white or pink with a white margin. Gills and rhinophores with red tips. Western Pacific; Taiwan, Philippines, Indonesia.  N. Sulawesi pic. 

Chromodoris coi Risbec 1956. Western Pacific; Vietnam, PNG, Marshall Islands. N. Sulawesi pic. Do a distinctive from the center out movement when approached. http://www.seaslugforum.net/search.cfm?searchstring=Chromodoris+coi+

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Chromodoris collingwoodi. West Pacific. To 4.5 cm/1.75". Bali 2014

Chromodoris fidelis. Red Sea to the Marshall Islands. To 4 cm. Said to feed exclusively on the Purple Sponge, Aplysilla violacea. N. Sulawesi pic. 

Chromodoris kempfi Purple-Crowned Sea Goddess. To 3/4". Bonaire 2016, Di Pic.

Chromodoris kuniei Pruvol-Fol 1930. Found in the central Indian Ocean to the southwestern Pacific. One in N. Sulawesi.  http://www.seaslugforum.net/search.cfm?searchstring=Chromodoris+kuniei

Verticals (Full/Cover Page Sizes Available

To: Pt. 2, Pt. 3, Pt. 4, Pt. 5, Pt. 6, Pt. 7, Pt. 8, Pt. 9, Pt. 10, Pt. 11, Pt. 12, Pt. 13, Pt. 14, Pt. 15, Pt. 16

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