A Lobster's Microscopic Friend
Symbion pandora - a new life form and a new phylum

 
Just before Christmas 1995, a new life form discovered by Danish biologists on the lips of the Norway lobster attracted world-wide media attention. Why? This topical article by Dave Walker describes and illustrates this "zoological highlight of the decade" using the biologists' published material and includes an exclusive photograph kindly supplied by the original researchers.
 
 

Image right reproduced with the permission of 'Nature' magazine
(MacMillan Publishers).
 
 
 
 

Why the excitement about the discovery of a new animal species and phylum?
It is not that difficult to find a new species. Place an experienced botanist and zoologist in a poorly investigated area of the world such as virgin rainforest and leave them there for a while to study the fauna and flora. It is quite likely that a tiny beetle, fly or plant such as a moss may be found which is unidentifiable and is declared a new species. In fact it is believed that millions of species remain undiscovered. What other marine life forms remain undiscovered?

 So why did the discovery of S.pandora excite not just the scientific community but attract media attention world-wide? For two main reasons.

 Firstly, the organism was not discovered in the depths of a rain forest or an oceanic trench, but on the bristles surrounding the mouth of the Norway lobster Nephrops norvegicus which can be caught in the Kattegat Straits, a busy shipping lane between Sweden and Denmark. You've probably eaten the Norway lobster - as scampi and chips!

 Secondly, when a new animal species is discovered, no matter how unusual, it can normally be classified into a known group of creatures with the same body plan or phylum. Although there are 1.5 million plus known species in the world, they can all be classified into 35 or so phyla. These include the chordates (eg the vertebrates such as man), molluscs (snails) and arthropods (jointed limbed e.g. insects).

 However, S.pandora was so unusual that it could not be classified into any of the existing phyla, and a new one was suggested called Cycliophora. How was it's name derived?

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The structure and life cycle of Symbion pandora
The organism has a very complex life cycle, with a number of well-defined sessile and free swimming stages with different morphologies. The largest and most illustrated phase is the feeding stage. The key features of this stage are as follows.

 - typically 350 µm long
- attached by an adhesive disc to the lips of the lobster
- feeds using a mouth surrounded by a ring of cilia
- excretes via an anus next to the mouth ring
- the feeding stage continually produces inner buds which replace the feeding structures
- both asexual and sexual reproduction can occur

 View a beautiful annotated diagram of Pandora's feeding stage showing it's cellular structure.

Pandora's sex life is so peculiar that scientists at the Natural History Museum, UK were left puzzled! A museum scientist was quoted as saying 'it is unlike anything we have seen before'. There was a debate whether Pandora had one penis or two, a fact eagerly announced by the popular press!

Pandora's sexual and asexual reproductive cycle is explained and illustrated in Reference 1. The essential features of the sexual cycles are as follows.

 As well as sessile (stationary) stages there are three free-swimming stages i.e..
- a larva containing a new feeding stage
- dwarf males (size typically 84 um) which settle on feeding stages
- females which attach to the lobster, and subsequently degenerate producing larva which disperse.

 All the free-swimming stages do not feed and are short-lived.

Sexual reproduction is initiated when the lobster is near the end of its moult cycle. At this stage sexually mature feeding stages are found attached to the lobster's lips.

 The asexual aspect of the life cycle explains why large populations of feeding stages with no mature sexual stages have been found on lobsters.

 Cycliophora, in which S.pandora has been placed, is thought to have affinities to the phyla Entoprocta and Ectoprocta. The Ectoprocta are also known as the bryozoans or moss animals. Bryozoans are microscopic invertebrates that can form beautiful colonies which are often attached to rocks and plants in both fresh and seawater. The bryozoans reproduce asexually by a budding process similar to that of Pandora.

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Why was it called Symbion pandora?
The observation of a feeding stage which contains both an inner bud and a Pandora larva with a miniature feeding stage inside, gave rise to the pandora species name i.e. a reference to Pandora's box of Greek mythology.

 Symbion is derived from the Greek syn '(together) with' and bios 'living', which refers to the close association the organism has with it's host. The phylum name Cycliophora is a Greek derivative referring to the circular mouth ring.

What other marine life remains undiscovered?
Reinhardt Kristensen, one of the co-discoverers of Pandora, has stated that the minutiae of marine life have been overlooked for too long. 'This is only the beginning. When we have finished, the zoological system will be turned upside down'. He can speak with authority, the last phylum to be discovered, the Loricifera, was discovered in Brittany in 1983.... by Kristensen! The Loricifera are minute organisms which live between sand grains.

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Key:
1 - adhesive disc attached to bristle surrounding lobster's mouth
2 - dwarf male
3 - anus
4 - ring of cilia around mouth funnel

SEM image kindly supplied by Peter Funch, University of Copenhagen.

 Annotation by D Walker.
 

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Acknowledgements

The author sincerely thanks Peter Funch for sending Micscape an SEM image for this article, and congratulate him, his co-worker Reinhardt Moebjerg Kristensen and colleagues on their discovery and reporting of Symbion pandora. (The original discovery of the organism is credited in Reference 1 to T. Fenchel of the Marine Biological Laboratory, Elsinore, Denmark.)

 The author and Micscape Editor would also like to thank 'Nature' magazine (Macmillan Publishers) for permission to reproduce the line drawings in or linked to this article, which were originally published in Reference 1 below.

References and Further Reading

 1) "Cycliophora is a new phylum with affinities to Entoprocta and Ectoprocta" by Peter Funch and Reinhardt M Kristensen. Nature, vol 378, p711-714, 1995. This is the letter to Nature that triggered the media attention and is illustrated by superb annotated diagrams and SEM photographs.

 2) "New phylum from the lobster's lips" by Simon Conway Morris. Nature, vol 378, p661-662, 1995. An interesting overview of the new discovery published in the same December 14th 1995 edition with an additional beautiful drawing. The author of this article stated that the discovery was "the zoological highlight of the decade".

 3) Other magazines published summaries of the above two references. e.g. New Scientist, December 16th 1995, page 17.

 Taxonomy can be a difficult subject to get to grips with, particularly because there is no definitive classification, and taxonomic groups are occasionally renamed. A good introduction to the classification of organisms is given below.

 4) Encyclopaedia Britannica, 1993, vol 14, page 1088-1095. 15th Edition, 1993.

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This article is based on the above references and has been written by Comments to the author sent via our contacts page quoting page url plus : ('dwalker','')">Dave Walker an amateur microscopist and naturalist for the on-line magazine Micscape; a magazine which encourages an interest in the microscopic world. Comments on the text by Peter Funch, the co-discoverer of Symbion pandora, are appreciated but any errors are the author's i.e. Dave Walker!

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