Sunday, 20 April 2008

Nerita textilis

Although the beaches of northern Australia are home to a large number of nerite species, this is not among them. Nerita textilis occurs mostly along rocky shores of the western Indian Ocean. This specimen is from Natal in South Africa.

Nerita textilis is at the big end of the neritid size scale. Shells may reach 40 mm or more. The surface is sculptured with spiral cords that follow the line of coiling crossed with radial ridges. In small snails, the black and white markings are like a newly-printed chequerboard. In this larger one, only the pattern on the lip gives an idea of how the shell once looked.



Classification of Nerita depends mainly on characters of the operculum and aperture. Apart from the sculpture, this species differs from N. polita (featured in a recent post) in three ways:
  • The operculum is covered with small granules and is not differentiated into an inner and outer region.
  • The callus (the shelf on the whorl side of the aperture) is concave and also textured with granules.
  • The teeth along the outer edge of the aperture are well-defined.



Vermeij's table of characters by subgenus indicates that it is allied with N. albicilla in Nerita (Theliostyla). I'm slowly coming to terms with this classification. (Hey, I'm a slow learner!) I might even test myself on it later.

Reference
Vermeij, G.J. (1984). The systematic position of the neritid prosobranch gastropod Nerita polita and related species. Proceedings of the Biological Society of Washington 97: 688 – 692.

2 comments:

Mel said...

I'm a slow learner too! There are SO MANY things to learn and as I don't want to forget, I take my time ;)

Snail said...

You're not the only one, Mel!

Have you joined the Nature Blog Network yet?