117 — Sea hare, Aplysia keraudreni

Aplysia keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.

Sea hares are large sea slugs which can reach sizes of up to half a metre in length. They get their name from a superficial appearance to actual hares. There are several species of sea hare found in New Zealand and although they are not considered to be rare, they tend to be what known as locally common. What this means is that if conditions are right you can get loads of them, but otherwise you won't see them at all.

Aplysia keraudreni Rang, 1928, is found in northern New Zealand and there is a similar species found in Australia. From what I can gather, sea hares (and particularly this species) are not that well-described, so it may turn out that this is a different species than previously thought. A. keraudreni has also been recorded from Chile and it is considered to have a south Pacific distribution (Medina et al., 2005; Uribe et al., 2013).

Aplysia keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.

Egg mass of A. keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.,

Aplysia keraudreni, expelling ink.

Once they reach adult size, sea hares don't appear to have many natural predators—but when they're disturbed can release clouds of toxic liquid. The colour of these inky clouds can go some way to helping identify the species: Aplysia keraudreni releases a purply-coloured ink, while the ink of A. dactylomela is wine-red coloured, and A. juliana doesn't release ink of any kind. The video below shows A. keraudreni expelling ink.

The sea hare pictured here (~25cm in length) was part of a mating pair and sea hares are known for forming-up into long chains of mating pairs. They then lay eggs in long gelatinous noodle-like structures, which can look a lot like a pile of instant noodles. However, if you look closely you can see the individual eggs.

The eggs hatch to release a tiny planktonic veliger larvae, which then live in the plankton for some time and then settle. This would also appear to be one part of sea hare biology that is not that well-known for many species.


More info

Sea slug forum: What are sea hares?

Medina, M., Collins, T., & Walsh, P. J. 2005. Phylogeny of sea hares in the Aplysia clade based on mitochondrial sequence DNA data. Bulletin of Marine Science 76(3), 691–698.

Uribe, R. A., Nakamura, K., Indacochea, A., Pacheco, A. S., Hooker, Y., & Schrödl, M. 2013. A review on the diversity and distribution of opisthobranch gastropods from Peru, with the addition of three new records. Spixiana, 36(1), 43–60. 

Willan, R. C., Morton, J. E. 1984. Marine molluscs part 2: Opisthobranchia. University of Auckland, Leigh Marine Laboratory, Leigh, New Zealand. 106 pp.