Prolecithophora

Prolecithophora
File:P vittatum DSCN1397 2.jpg
The Candy-Cane Worm (Plagiostomum vittatum), a common North-East Atlantic species
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Turbellaria
Order:	Prolecithophora Karling, 1940

Prolecithophora comprises an estimated 300 species of small (typically 0.2 - 12 mm, one species up to 50 mm), active, aquatic, flatworms. The group lacks a common English name. Most species are shaped like an elongated stylized droplet, and are opaque white or yellow, frequently with contrasting bands or spots in purple, yellow, red, or brown. They have zero to three, normally two, pairs of pigment-cup eyes, and well developed tactile and chemoreceptor senses. With few exceptions species are protandric hermaphrodites, with internal fertilization. Egg capsules are, according to species, glued to various hard surfaces, and the young hatch as miniature copies of their parents. (Karling, 1940)

Ecology

All prolecithophorans are aquatic, and most live in the sea. Many, especially the freshwater species, are predators and scavengers, but many marine species are associated with colonial animals such as bryozoans or live as symbionts on larger animals such as urchins, and a few species harbor symbiotic algae. Although most are accomplished swimmers, they normally rarely venture far from the bottom, but young specimens are sometimes found in plankton. Many species display positive or negative phototaxis. (Norén, 2002)

Distribution

Although the majority of species live in the sea, there are also brackish and fresh water species, and in Lake Baikal there's been an adaptive radiation resulting in a number of endemic species. Although the order has a cosmopolitan distribution and its representatives often are common, most described species are from temperate waters, while little is known about tropical or deep-sea species. This is a sampling artefact, as prolecithophorans are known to be common in the tropics; when Norén & Jondelius (2004) sampled the shore adjacent to Phuket Marine Biological Center, Phuket, Thailand, they found 14 species of prolecithophorans, all of which were new to science.

Classification

There is no consensus regarding the affinity and classification of Prolecithophora. The classification presented here is after Norén (2002), and is based mainly on molecular data.

• Platyhelminthes - the Flatworms
  • Rhabditophora
    • Neoophora
      • Adiaphanida
        • Fecampiida
        • Tricladida
        • Prolecithophora
          • Protomonotresidae - with one exception exclusively freshwater species from Lake Baikal.
          • Plagiostomidae - mainly marine but with a few freshwater species in e.g. Lake Vänern, Lake Biwa, and Lake Tanganyika.
          • Pseudostomidae - exclusively marine species.

References

1. Karling, T. G. 1940. "Zur Morphologie und Systematik der Alloeocoela Cumulata und Rhabdocoela Lecithophora (Turbellaria)". Acta Zoologica Fennica, 26, 1–260.
2. Noren M. 2002. Phylogeny and classification of prolecithophoran flatworms. Doctoral thesis at Stockholm University. ISBN 917265478-3.
3. Noren M, Jondelius U. 2002. "Phylogenetic position of the Prolecithophora (Rhabditophora, "Platyhelminthes")". Zoologica Scripta. 31:4
4. Noren M, Jondelius U. 2004. "Four new species of the family Plagiostomidae Graff, 1882, (Prolecithophora, "Platyhelminthes") from Phuket, Thailand". Phuket Marine Biological Center Research Bulletin 65:2