Nudibranchs – enough said?

I don’t scuba dive any more, but every now and then I am in the right place at the right time to see a nudibranch in a rock pool. These little creatures are molluscs, but ones that lose their shells early on in life. They are spectacularly coloured, thought to advertise what zoologists call ‘distastefulness’ – ‘I taste yucky so don’t waste your time attacking me’. A friend, Peter, took this photo of a chromodoris at Woody Head last year.

A species of chromodoris in a rock pool at Woody Head, photo by Peter Scharf

‘Nudibranch’ means ‘naked gill’, and you can see the pink gills at the rear (right) of the chromodoris above. The two pink things at the front (left) are called rhinopores, and scent or taste the environment.

Nudibranchs feed on a variety of animals (they are carnivores), including hydroids, sponges, bryozoans, tunicates, barnacles and anemones.

Last weekend I found this one at the water’s edge, but had to move it to photograph it or risk both of us being washed away. It’s about 2 cm long. Neville Coleman, in his Nudibranchs Encyclopedia, calls it the scribbled doriopsilla (Doriopsilla miniata).

Scribbled doriopsilla

Aeolids like Spirulla neopolitana below are also nudibranchs, but don’t have an obvious ‘naked gill’ like the ones above. The frondy bits are called ‘cerata’, and, according to Wells and Bryce’s Sea Slugs of Western Australia,  are ‘digestive gland extensions with thin walls allowing the ready exchange of gases’ – in other words, they have the same function as gills.

Spirulla neopolitana, photo by Peter Scharf

There are supposed to be about 3000 species of nudibranchs – and that’s just the scientifically known ones –  so you could spend a lifetime or more getting to know these fabulous jewels.

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4 Responses to Nudibranchs – enough said?

  1. Cath Clark says:

    Wonderful pictures ~ I didn’t know nudies started out with shells.

    • Nudis generally lay gelatinous spirals with eggs in the matrix. The eggs hatch into a larval stage (with shells) – the larvae float around with the rest of the plankton in the sea. At some point they settle out of the plankton and metamorphose into tiny adults. According to http://www.seaslugforum.net/showall/larvcult:

      ‘Basically the time between egg-laying and hatching differs in different species and can range from a few hours to 3 weeks or more. In most cases (we think) the egg develops in its capsule into a microscopic shelled veliger larva which hatches out into the sea where it lives and feeds, again for a variable period of time depending on the species. Some larvae don’t feed and spend only a short period in the plankton.

      ‘In some cases the eggs develop directly into a little crawling slug which hatches out of the egg capsule which is usually laid on the preferred food of the species.’

      Also check out http://divocean.blogspot.com/2007/06/nudibranch-larvae.html for pics of the larvae.

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