Author: Undescribed

Order: Pleurobranchoidea  Family: Pleurobranchidae

Maximum Size: 18 mm

Sightings: Sunshine Coast

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Pleurobranchaea sp. 01 Undescribed

This is the first species of the Pleurobranchaea genus to be found here. It looks similar to Pleurobranchaea maculata (Quoy & Gaimard, 1832) but following a discussion with Bob Burn we are calling it Pleurobranchaea sp. 01. Bob Burn is of the opinion that this species could possibly be Pleurobranchaea dorsalis Allan, 1933 that is listed as taxon inquirendum on WoRMS. The specimens described by Allan were collected from Botany Bay and Sydney Harbour. Both Pleurobranchaea maculata and Pleurobranchaea novaezealandiae Cheeseman, 1878 were considered in arriving at the identification.

Species of Pleurobranchaea have much more widely separated rhinophores than those of the Pleurobranchus genus that we find quite regularly here.

Pleurobranchaea sp. 01 is elongate oval in shape. The mantle is reduced, being smaller than the foot, the foot being revealed on each side and as a large rounded tail portion protruding beyond the posterior edge of the mantle. The mantle is wavy along the lateral margins. Anteriorly there is a large and broad forward-projecting trapezoidal oral veil or velum, as wide as the animal’s foot. The anterior edge of the oral veil appears to be finely serrated. Rhinophores are rolled, slit vertically, widely spaced out at the edges of the mantle and jut laterally at 45 degrees. At times the gill can be seen protruding out from under the right margin of the mantle.

The dorsum of the mantle has a background colour of creamy-brown with a dark brown/purplish reticulation. There is some white speckling to the margins. The reticulation extends on to the oral veil and onto the anterior face of the rhinophores. White speckling is distributed across the surface of the oral veil and is very fine upon the posterior face of the rhinophores. The reticulation also extends across the broad tail as does the white speckling that is also quite obvious on the foot margins.

Species of Pleurobranchaea are opportunistic carnivorous feeders and are known to consume a range of soft-bodied invertebrates.

David A. Mullins – October 2020

References:
– Allan, J. K., (1933). Opisthobranchs from Australia. Records of the Australian Museum 18(9): 443-450, plate lvi

– Willan, R. C. (1984). A review of diets in the Notaspidea (Mollusca: Opisthobranchia), Journal of the Malacological Society of Australia, 6:3-4, 125-142

– Willan, R. C. (1998). Order Notaspidea Pp. 977-980 in Beesley, P. L., Ross, G. J. B. & Wells, A. (Eds) Mollusca: The Southern Synthesis. Fauna of Australia. Vol.5 CSIRO Publishing, Melbourne, Part B 565-1234 pp

– Burn, R. (2015). Nudibranchs and related molluscs. Museum Victoria.

– MolluscaBase eds. (2020). MolluscaBase. Pleurobranchaea dorsalis Allan, 1933. Accessed through: World Register of Marine Species (WoRMS) at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=535701