Author: (Risbec, 1928)

Order: Nudibranchia  Family: Aeolidiidae

Maximum Size: 18 mm

Sightings: Sunshine Coast

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Bulbaeolidia alba (Risbec, 1928)

Most nudibranchs either just seem to sit there or glide along smoothly. Nothing much seems to be happening. It all appears so effortless and then, ….. you spy your first specimen of Bulbaeolidia alba. What is going on here? This small aeolid nudibranch moves forward with a movement that can only be described as jerky or head rocking. It’s almost mesmerising to watch the rhinophores moving rhythmically backwards and forwards in unison with the rear-most cerata and ensures it is easy to track through the substrate growth.

Bulbaeolidia alba is a small species, recorded as large as 18 mm in length but most commonly sighted in the 5 – 12 mm range. The body is flattened but wide, there being no pericardial swelling of note. The cerata are crowded down each side and are mostly carried laid flat along the dorsum but curve towards the dorsal midline. The last row may curve upwards. Both body and cerata are translucent but covered with varying amounts of white pigment. The translucent brown rhinophores also carry white pigment but more sparsely so than the cerata. They are long, distinctive and sturdy being closely set at the base but then separating and normally carried in a V shape. There are two prominent bulbous swellings along their length. The rhinophore bases are marked in red that may present just as a simple transverse line posteriorly, or as a complete circling thereof. The base of the rhinophores and the dorsum immediately posterior exhibit a brown reticulation created by the presence of symbiotic zooxanthellae, obtained from their prey and farmed within for nutritional benefit. The oral tentacles are stout with a midpoint constriction and bulbous end. The translucent tail protrudes past the trailing cerata but is not always obvious.

It is thought to hunt and feed upon small sea anemones like the majority of its fellow members of the Aeolidiidae family. Bulbaeolidia alba is a wide-spread species across the Indo-Pacific. Until recently it was also thought to be much more wide-spread globally but those are now known to be different species through molecular sequencing in 2017. These others have restricted ranges (endemic) and are: Hawaii = Bulbaeolidia paulae, Brazil = Bulbaeolidia oasis, Eastern Pacific = Bulbaeolidia sulphurea, and confirms that Japan = Bulbaeolidia japonica.

The Bulbaeolidia genus was raised in 2013 following molecular sequencing that resulted in species being moved from Aeolidiella. The prominent bulbous swellings on the rhinophores of all those species is reflected in the name given to this new genus.

Other synonyms include: Spurilla alba.

Originally described as Aeolidiella alba.

Above: The aeolid nudibranch Bulbaeolidia alba moving across the substrate with the characteristic rhinophore rocking action clearly evident as it searches for its anemone prey.

David A. Mullins, July 2019

References:
– Gosliner, T.M. (1985). The aeolid nudibranchs family Aeolidiidae (Gastropoda, Opisthobranchia) from tropical southern Africa. Annals of the South African Museum, 95: 233–267.

– Carmona L, Pola M, Gosliner TM, Cervera JL. (2013) A Tale That Morphology Fails to Tell: A Molecular Phylogeny of Aeolidiidae (Aeolidida, Nudibranchia, Gastropoda). Plos One. 2013; 8(5), e63000.

– Carmona L, Pola M, Gosliner TM, Cervera JL. (2017) Integrative taxonomy and biogeography of the genus Bulbaeolidia (Nudibranchia: Aeolidida). Journal of Molluscan Studies (2017): 1–11.

– This Species Profile has been modified from a previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #365 (December 2018):12-13 by David A. Mullins