''Symbion pandora'' is a jug-shaped microscopic aquatic animal that dwells on the mouth-parts of Norway lobsters. The animals are less than ½ mm wide, with sac-like bodies, and three distinctly different forms in different parts of their three-stage life cycle.

Classification and naming

They are so unlike any known animal that its discovery by Danish scientists in 1995 led to the creation of a new

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatu ...

. The phylum Cycliophora, from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

for 'carrying a small wheel', was named after the creature's circular mouth. Two other members of that phylum have since been discovered. ''Symbion'' refers to the animal's symbiotic relationship with its lobster host while the

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''pandora'' refers to the part of the organism's life cycle that reminded Funch and Christensen of the mythical

Pandora's box Pandora's box is an artifact in Greek mythology connected with the myth of Pandora in Hesiod's c. 700 B.C. poem '' Works and Days''. Hesiod reported that curiosity led her to open a container left in the care of her husband, thus releasing phy ...

Description

''Symbion pandora'' has a

bilateral Bilateral may refer to any concept including two sides, in particular: *Bilateria, bilateral animals *Bilateralism, the political and cultural relations between two states *Bilateral, occurring on both sides of an organism ( Anatomical terms of l ...

, sac-like body with no

coelom The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it ...

. There are three basic life stages: *Asexual feeding stage – At this stage, ''S. pandora'' is neither male nor female. It has a length of 347 μm and a width of 113 μm. On the posterior end of the sac-like body is a stalk with an adhesive disc, which attaches itself to the host. On the anterior end is a ciliated funnel (mouth) and an anus. *Sexual stage **Female – ''S. pandora'' has a length of 84 μm and a width of 42 μm during this stage. Its digestive system collapses and reconstitutes itself as a

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. Th ...

. **Male – ''S. pandora'' is the same size as the female in this stage. It has no mouth or anus, which signifies the absence of a digestive system. It also has two reproductive organs.

Reproduction

''Symbion pandora'' can reproduce both asexually by

budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is kno ...

and sexually. The sexual reproductive cycle is triggered when the host crustacean molts its skin in order to grow: a feeding stage buds a male, which attaches to another feeding stage and triggers it to bud a female, which it impregnates. The female is able to swim, and finds another host crustacean, where the larva in her develops. The female dies, and the larva escapes, spawning another feeding stage on the new host.

References

* Costello, M.J. et al. (Ed.) (2001).'' European register of marine species: a check-list of the marine species in Europe and a bibliography of guides to their identification. Collection Patrimoines Naturels, 50: pp. 177 {{Taxonbar, from=Q2714238 Platyzoa Animals described in 1995 Fauna of the Atlantic Ocean