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Auckland Shell Club |
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Auckland Shell Club |
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February Meeting
Members brought in a variety of items of interest, as well as shells for display, shells for sale, and shells for free.
Peter showed three battered specimens of Nautilus macromphalus from Ninety Mile Beach. This distinctive species occasionally floats to our shores from the waters off New Caledonia. An extra surprise inside one of them was a perfect specimen of Pinctada sugillata, kindly identified on the spot by Dr. Richard Willan. Amongst the other items of interest Peter brought in were a distorted Semicassis pyrum, and a large Linatella caudata which Richard also managed to quickly identify.
Dr. Richard Willan is the Senior Curator of Molluscs at the Museum and Art Gallery of the Northern Territory (MAGNT) in Darwin, Australia. Richard has been a member of our club since he was 12 years old. He has been studying opisthobranchs for almost 40 years, and has published four books and numerous scientific papers on nudibranchs. We were privileged to have such a world renowned speaker, and the room was filled to capacity. His presentation was titled "The Private Lives of Nudibranchs".
Nudibranchs are a group of soft-bodied marine gastropod molluscs that shed their shell after their larval stage. Richard describes them as the "Orchid animals of the sea". Their colours are bewildering, their shapes are bizzare, and their behavior is peculiar.
Currently there are about 4000 species of nudibranch species known worldwide, but only about 1500 of these have so far been named. They are classified into 40 families. New Zealand has representatives of most of these families, Australia has more, but the Coral Triangle (see May/2011 newsletter) contains the most species.
Nudibranchs are divided into two main types - Dorid and Aeolid. Dorids have clusters of gills on their posterior part of the body, while Aeolids have venomous appendages spread across their back or sides. All have two pairs of tentacles. They use blood pressure to push out their body parts, and use muscles to pull them back in. The majority of nudibranch species are subtidal in shallow seas, but some species live as deep as 2000m. Some species live intertidally, some swim freely in the water column, and one floats on the surface of the sea.
Knowledge of nudibranchs has expanded over the last few decades due to underwater photography and scuba diving, however we still know very little about their behaviour and biology.
Richards study of nudibranchs have led him to two conclusions ...
1. Nudibranchs are rare in time and space. EG. for many species, only a small number of sightings have been recorded over the last 50 years. Other species have a very specific habitat, occuring for example on just one sponge in a large area.
2. The "why" questions are the hardest to answer. This question crops up continually in the study of their locomotion, feeding, reproduction, and behaviour.
Locomotion: The "Spanish dancer" is a large (up to 600mm) brilliant red nudibranch which usually crawls on the sea floor using its muscular foot. But if provoked it unrolls its mantle and swims away with undulating body and mantle movement. Richard gave us an entertaining demonstration of this movement (in the style of the late Prof. Morton). This primitive species which is relatively common in the tropics, but not found in NZ, is wonderful to observe in motion. More advanced nudibranchs use drugs to escape predators. Others defend themselves with stinging cells at the tips of the processes on their backs. These nudibranchs obtain the stinging cells by eating stinging hydroids.
Feeding: Richard showed an amazing photo of a nudibranch feeding on a translucent sea-squirt. The nudibranchs feeding tube can clearly be seen inside the sea-squirt, vacuming up its soft internal organs. Nudibranchs have a wide range of food and will even eat other nudibranchs of the same species.
Reproduction: Nudibranchs are hermaphrodites, with complicated reproductive organs that allow them to mate both ways at the same time. They lay characteristic egg ribbons, and from one spawning can produce 10 egg masses - each containing millions of eggs. Sometimes they indulge in spawning orgies. The most notable examples of this are the aggregations of thousands of Omnidoris depressa in the Scottish sea lochs. Nudibranchs live for a maximum of one year, and usually die after spawning. Blue dragon nudibranchs display maternal care by wrapping themselves around their eggs. They can incubate their eggs for about one month, not needing to eat because they are solar powered. Another species carries its young internally in a pouch, like a marsupial.
Behaviour: The Imperial Nudibranch has peculiar globes on its back which emit flashes of bright light when the animal is provoked. Richard showed us videos of "trailing" behavior, where two animals travel head to tail. Also photos of a vigorous and prolonged fight between two of the same species, a behaviour never seen before. But strangest of all was the photograph of two different species mating!
The following websites and books are recommended for further information, and images of nudibranchs ...
. http://www.nudipixel.net/
. http://www.seaslugforum.net/
. "Undersea Jewels: A Colour Guide to Nudibranchs", by Dr. Richard Willan and Gary Cobb.
. "Philippine Marine Mollusks, Volume III", by ConchBooks (www.conchology.be).
Next Meeting – Tuesday 12th March – Auckland Museum
We will meet at the Auckland Museum for a talk by the Marine Invertebrates Curator, Dr. Wilma Blom.
Wilma will give us an update on what is happening now with the mollusc collections, as well as the future plans.
Attendees should be at the southern (Atrium) entrance of the Museum by 7:15pm.
Subscriptions for 2013
A reminder that subscriptions are now due for everyone who received an invoice with the last newsletter.
Contact our Treasurer Michael Barlow on (09) 623 3231 if you have any queries.
New Zealand Shell Show 2013 – Pakuranga, 3-5/May
Exhibitors please ensure that your entry forms are sent to Peter before the end of March.
Volunteers are required for duties during the weekend. Please contact Margaret Morley (09 576 8323 or mmorley@aucklandmuseum.com) if you can spare some time on the weekend 4th - 5th of May.
The Shell Show Schedule is available here, or contact Peter Poortman (petermwp@gmail.com or 09 817 1397) for more information.
Poirieria Magazine
We welcome contributions to our club magazine "Poirieria".
Anything related to shells or collecting would be greatly appreciated - Eg. shelling trips/finds, personal observations/tips, scientific research, historic anecdotes, a notable washup, etc.
Please email articles to Peter Poortman at petermwp@gmail.com, or post to 26 Pendlebury Street, Green Bay, Auckland 0604.
Club Library
We have an extensive collection of books, magazines, and scientific publications available, as well as a biological microscope.
Other Club News
. Our annual Shell Auction will be held on Saturday 26th October (Labour weekend) at the Albany Hall.
. Wanted: Australasian Shell News, vol 112 (2001). Contact Margaret Morley on 09 576 8323 or mmorley@aucklandmuseum.com.
. Wanted: Shell Show display cases. Contact Peter Poortman at petermwp@gmail.com or 09 817 1397.
. Items of interest for the monthly newsletter are always welcome - email to petermwp@gmail.com, or post to Peter Poortman, 26 Pendlebury Street, Green Bay, Auckland 0604.
