Geitodoris planata - population explosion in Holland

August 22, 2001
From: Peter van Bragt

At this moment (summer 2001) we are experiencing a remarkable explosion of Geitodoris planata in the Oosterschelde Bay, in the southwest of the Netherlands. The first specimen recorded from the Netherlands was found in June 1999. Now (July 2001) it is not unusual to find more than 30 adult specimen and over 70 egg ribbons on a single dive. Furthermore they are all of a extraordinary size of up to 12 cm. in length. Picton reports 65 mm. as a maximum size!. They are only found in this single bay and nowhere else at the Dutch coast.

Geitodoris planata is often confused, [also by myself in the past], with Archidoris pseudoargus also called A. tuberculata (citroenslak in Dutch, meaning lemonslug). A. pseudoargus has only been found very rarely at a few locations around the Dutch coast.

I have enclosed some detailed photos of the most characteristic anatomical features of this species in a separate message. Geitodoris planata, also called Discodoris planata and with no common Dutch name yet, can be recognised as belonging to the Doridae and its size of 5-12cm in length for adults. Typical macroscopic features that can be recognised in the field are: The animal has large numbers of tubercles on the outer mantle, in various sizes and rounded in shape. There a small number of typical larger tubercles that are acid glands that most often appear in star shaped light coloured regions. In the present Dutch population the colour of the mantle is most often pink-brownish but can also be much lighter yellowish.

According to Picton Geitodoris planata feeds on sponges such as Hemimycale columella. As can be seen on the slides it feeds here on a Mycale ssp. A yet unidentified species of sponge that commonly grows here encrusting on oysters.

With best regards
Peter H. van Bragt

vanbragt.phjm@hsbrabant.nl

van Bragt , P.H., 2001 (Aug 22) Geitodoris planata - population explosion in Holland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5125

Dear Peter,
Thanks very much for the detailed information in this message and the accompanying one.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Aug 22). Comment on Geitodoris planata - population explosion in Holland by Peter van Bragt . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5125

Factsheet

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