Author: Bertsch & S. Johnson, 1982

Order: Nudibranchia  Family:Cadlinidae

Maximum Size: 20 mm

Sightings: Sunshine Coast

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Aldisa pikokai Bertsch & Johnson, 1982

There are many many species of nudibranch possessing projecting tubercles, pustules, spicules, peaking ridges, secondary gills and all manner of other appendages not to mention the cerata of the aeolids. Only a very few however present with distinctive depressions in the notum. One of those that has held a particular fascination for me is Aldisa pikokai.

Aldisa pikokai is an orange/red coloured oval-shaped dorid nudibranch of the Cadlinidae family. Its most distinctive feature is the three crater-like depressions on the midline of the notum; one just anterior to the rhinophores, one just posterior to the rhinophores and the third just anterior to the gills. They are located in the raised midline portion of the notum. These depressions perform a remarkable portrayal of the excurrent oscula of certain sponges. They have a raised lip and numerous small dark spots on the internal base. The rhinophores are orange/red and the gills are dark cream to brown often tipped in white. Other features of this species are irregular transverse patches of cream-white and a reticulated network of ridges. The cream-white pigment varies among specimens in amount and concentration. One of the authors, Scott Johnson, advised me that the presentation of these ridges is variable and may range from prominent to almost smooth. This species is a marvellous example of sponge mimicry. Reported to grow up to 20 mm, the two originally found on the Sunshine Coast, Qld and represented here measured 14 mm and 8 mm.

Described in 1982 from specimens from Hawaii it was subsequently recorded from the Marshall Islands (reported in 1983) and also in 2000 from Okinawa, Japan. This species is reclusive under rocks and coral plates during the day emerging at night to feed upon sponges. This may help to explain the rare sightings and the huge leap in distribution created by the Sunshine Coast, Qld finding. However, this disparity might possibly be explained by just who is looking where. To quote Dr. Bill Rudman of Sea Slug Forum fame: ”I often think that the ‘known distributions’ of many nudibranchs tend to tell us more about the known distributions of opisthobranch workers rather than that of the slugs.”

References:
– Bertsch, H. & Johnson, S. (1982). Three new species of dorid nudibranchs (Gastropoda: Opisthobranchia) from the Hawaiian Islands. Veliger 24: 208-218.

– Johnson, S. & Boucher, L.M. (1983). Notes on Some Opisthobranchia (Mollusca: Gastropoda) from the Marshall Islands, Including 57 New Records. Pacific Science(1983), vol. 37, no. 3

– Millen, S. & Gosliner, T.M. (1985). Four new species of dorid nudibranchs belonging to the genus Aldisa (Mollusca: Opisthobranchia), with a revision of the genus. Zoological Journal of the Linnean Society 84:195–233.

– Yonow, Y., Anderson, R.C., & Buttress, S.G. (2002). Opisthobranch molluscs from the Chagos Archipelago, Central Indian Ocean. Journal of Natural History, 2002, 36, 831–882.

– Tibiriçá, Y., Pola, M., Cervera, J.L. (2017). Two new species of the genus Aldisa Bergh, 1878 (Gastropoda, Heterobranchia, Nudibranchia) from southern Mozambique. Marine Biodiversity. 1-14. 10.1007/s12526-017-0752-x.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #368 (March 2019): 12 by David A. Mullins.

David A. Mullins, July 2019