Risbecia pulchella - Stretching ?

June 6, 2008
From: Kamal El Tawil


Concerning message #21047:

Dear Bill,

This beautiful Risbecia pulchella was "standing up fully streched" on a coral tip. I have seen other species do the same and I now wonder if there is a reason for this behaviour. After a few minutes it crawled on the reef.

Locality: Elphinstone Reef, 15 metres, Egypt, Red Sea, 27 May 2008. Length: 60 mm. Photographer: Kamal El Tawil.

Kindest regards,
Kamal
www.coralworld.net

kamal@coralworld.net

El Tawil, K., 2008 (Jun 6) Risbecia pulchella - Stretching ?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21625

Dear Kamal,

In your earlier message I hesitated to give a reason for that other characteristic Risbecia behaviour - trailing. There is a whole field of research, called ethology, which studies animal behaviour. This 'stretching behaviour' is often seen, but like 'trailing', no scientific research has been done on it.  However there seems to be a perfectly reasonable explanation for stretching - but remember it is just an hypothesis. Stretching and waving the head and neck around is seen in many snails and slugs both in the sea and on the land. These animals are essentially blind, so they rely on other senses such as touch and smell to discover where they are. When they are crawling along and reach the top of a rock or the edge of a leaf, they can't see the gap in front of them, but they can certainly feel that they are running out of something to crawl on. So I presume the first aim of stretching is to see if their is something solid nearby which they can move to. In water, stretching and waving the head around also waves the rhinophores, or other chemosensory organs on the head, so they can 'look' for interesting smells, which could mean food or a mate. As you illustrate in your photos, after stretching for awhile and finding nowhere to go, or no smells to investigate, they just settle down and blindly crawl away.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Jun 6). Comment on Risbecia pulchella - Stretching ? by Kamal El Tawil. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/21625

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Risbecia pulchella

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