Author: (Cuvier, 1804)

Order: Nudibranchia  Family: Hexabranchidae

Maximum Size: 250 mm

Sightings: Sunshine Coast

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Hexabranchus lacer, recently resurrected from nomen oblitum, and after many years being considered Hexabranchus sanguineus, presents with three distinct morphotypes somewhat related to location but with some overlapping of range. The paper identifying the morphotypes treats them all as the same species but raises the question are they “….evolving as separate evolutionary units……”? No genetic difference was determined from the sequencing undertaken, nor from examination of internal morphology, however the three morphotypes are based on an extensive review of colour images and ontogeny.

Morphotype 1 – French Polynesia, central Pacific and western Pacific.
Morphotype 2 – western Pacific to Marshall Islands
Morphotype 3 – west Indian Ocean

On the Sunshine Coast of south-east Queensland, Australia morphotypes 1 & 2 can be identified across their range of development from juveniles through transition phases to mature forms. The images are all posted individually but also as two composites, one for each morphotype as an aid to comparison and showing their ontogeny – the various stages in development.

Hexabranchus lacer appears to be much more commonly found on the Sunshine Coast than Hexabranchus sanguineus, the only other species of the five Indo-Pacific Hexabranchus recently identified (see reference below).

David A. Mullins – June 2023

References:
Tibiriçá, Y., Pola, M., Pittman, C., Gosliner, T. M., Malaquias, M. A. & Cervera, J. L. (2023). A Spanish dancer? No! A troupe of dancers: a review of the family Hexabranchidae Bergh, 1891 (Gastropoda, Heterobranchia, Nudibranchia). Organisms Diversity & Evolution. Published online: 20 June 2023, https://doi.org/10.1007/s13127-023-00611-0