Re: Petalifera ramosa with probable eggs [2]

January 12, 2009
From: David and Leanne Atkinson


Hi Bill,
Here is the second part of our message concerning the Petalifera ramosa we found laying eggs on New Year's Eve, one green and one brown in a large patch of Halophila. As we describe in the earlier message [#22135], the brown one was clearly laying eggs, its head moving across the leaf in a zigzag pattern. We didn't look closely initially at the photos of the green one because there was a lot of scatter and out of focus leaves due to the green one being so active. We didn't realise that the green one had also started laying eggs but was disturbed by our approach and started to move off leaving a trail of eggs so tiny that we just thought it was part of the tangle of seaweed and algae. It wasn't until we looked closely at the photos on the computer screen that we realised what we had photographed. In the first photo you can see an orange line underneath the groove running from the parapodial cavity in the groove down to the right hand side of the head and back under the foot to the original Halophila leaf it was laying on. In the second photo we can see the eggs remaining attach at the end to the Halophila leaf and being pulled out of the groove as the Petalifera moves away. In the final shot the eggs have been pulled completely out of the groove and are trailing directly out of the reproductive opening, enlargement of the yellow string shows individual eggs. Hopefully the eggs will survive this unusual laying pattern. You can also see the edge of the groove going down the right hand side of the animal's face. We do have more photos of this Petalifera with egg trail that we can send but felt these three showed the process most clearly and didn't want to overwhelm you. Let us know if you need more.

Locality: The Pipeline, Nelson Bay, Port Stephens, 5 metres, New South Wales, Australia, 31 December 2008, Sandy silty bottom with Halophila surrounded by other seaweeds including kelp. Length: 50 mm. Photographer: David and Leanne Atkinson.

Regards,
Leanne & David Atkinson

atk@hunterlink.net.au

Atkinson, D. & L., 2009 (Jan 12) Re: Petalifera ramosa with probable eggs [2]. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22137

Dear David & Leanne,

Thanks for these photos. I think that even in the uppermost photo the egg string has been pulled, at least partially, out of the sperm groove. What this illustrates though is that calling this groove the 'sperm groove', 'seminal groove' or 'autoseminal groove' - as is the usual practice, is a misnomen. It has the name because it does indeed transport the sperm from the common genital opening in the mantle cavity, down to the penial opening on the right side of the head. However at least in Phyllaplysia - and probably in most aplysiids - it also is the way the egg string passes down to the foot for the deposition of the egg string either in the zigzag pattern of this species or the tangle of most species of Aplysia.

Like many 'discoveries' in science, it is so obvious we have never noticed it before! Unfortunately anatomy is done on preserved specimens and even more unfortunately anatomists are often only interested in structure and tend to have little interest in how the structure functions in the living animal.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Jan 12). Comment on Re: Petalifera ramosa with probable eggs [2] by David and Leanne Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22137

Factsheet

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