More sea shells by the sea shore

Nerites

Many algae- and lichen-eating snails hang about in rock pools but are found stranded when the tide goes out. They shut tight their operculums (‘doors’) to protect themselves from dessication and birds. They feed by scraping off algae and lichen on rock surfaces with their radula (mouthparts that have little hooks like Velcro) and are in turn eaten by predatory shells that drill a hole in their thick shells, and birds like oystercatchers. They lay egg capsules on rocks and other shells; the hatchling larvae float about in the water and after a few months settle back on the rocks and continue their development into adults. Nerites comprise one such group.

Black nerite, Nerita atramentosa

Periwinkles

Periwinkles live a similar life to nerites. In the photo below, you can see black nerites (the one on the bottom left has a Nodilittorina pyramidalis on top) and the periwinkles Austrocochlea porcata (with wide stripes) and Austrocochlea concamerata (narrow stripes).

According to Australian Marine Life (Edgar, 1997, Reed Books, p. 245), Nodilittorina unifasciata is the most abundant mollusc  on temperate Australian seashores.

The periwinkle, Nodilittorina unifasciata

Nodilittorina pyramidalis is another common periwinkle.

Nodilittorina pyramidalis

It has obviously read the field guides as it conforms to what Edgar says: ‘ the species is rarely found on flat rock surfaces, preferring sandstone that has weathered into a honeycomb structure’ (p. 246).

N. unifasciata and N. pyramidalis on honeycomb sandstone

Turbans

There are three species of turban shells in the pools at Woody: from largest to smallest, Turbo militaris, Turbo torquatus and Turbo undulatus.

Turbo undulatus - note the shape of the operculum, unique to this species

The operculums on these turbans are all very thick and strong. You can often find them on their own, as they detach from the flesh of the animal after it dies and rots away. A friend thought they were the remains of independent shells themselves. The shape and colour are unique to each species.

Turban operculums

In the photo above, the top row shows the outer surface presented when the turban clams up. The left column is Turbo militaris and the right, Turbo torquatus. The photo below shows the detail of the ‘inside’ of the torquatus operculum. It is quite rough.

Surface texture of operculum of T. torquatus

Turban shells are herbivores and live in the crevices of the rock platform, under the water line. Humans find them edible, as do shorebirds, lobsters, crabs, starfish and predatory marine snails.

Live Turbo militaris with intact operculum

The local Aboriginal people called turbans ‘gugumbal’ and you can find out about how they ate them at www.arrawarraculture.com.au/fact_sheets/pdfs/05_Gugumbal.pdf

The turban is a classic example of a herbivore – a National Parks guide once told me that if the opening of a shell is round, it’s a herbivore. If not, it’s a carnivore. I myself find that whether there is a groove in the shell for its ‘harpoon’ is a more reliable characteristic, but ‘roundness’ is a pretty good start. Moon snails (see The joys of beachcombing) appear to be an exception to the rule – they are round carnivores.

I’ll continue with molluscs in a later post.

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One Response to More sea shells by the sea shore

  1. Cath Clark says:

    Thanks for another Superb Woody posting, O’ Woman of the Sea-Edge, and especially for using my favourite word, Operculum, several times.

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