Hydatina physis from Japan

December 20, 2003
From: Yukari Sato

Hello Dr. Rudman,

Here are images of an egg-laying and mating in Hydatina physis.

Date: 11 Nov 2003
Depth: 14m
Length: approx.40mm
Location: Zushi (near Hayama), Sagami Bay, Japan

Best regards,
Yukari Sato

yukarisss@hotmail.com

Sato, Y., 2003 (Dec 20) Hydatina physis from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11551

Thanks Yukari,
Hydatina and the related animals in the superfamily Acteonoidea are considered very primitive opisthobranchs. Apart from obvious primitive signs such as having an external shell, these animals all have a large external penis. In all other opisthobranchs the penis is internal and only everts during mating.

From your photos, and others I have seen, the egg ribbon of Hydatina also interesting in the way it is formed. It seems as though the whole ribbon is completely produced before it is attached to the substrate. The egg ribbon of Hydatina is attached by a mucus thread or string which is anchored in the sediment. It seems that anchoring the ribbon is the last stage in the process and only occurs after all the ribbon is exuded from the genital opening. A quite different process than that of nudibranchs and other opisthobranchs which gradually attach the ribbon as it is being exuded from the genital pore.
Best wishges
Bill Rudman

Rudman, W.B., 2003 (Dec 20). Comment on Hydatina physis from Japan by Yukari Sato. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11551

Factsheet

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