PLANARIANS OR FLATWORMS (TURBELLARIA)
S.M. Turk & P.E. Tompsett
The phylum Platyhelminthes, unsegmented, acoelomate, bilaterally symmetrical worms, includes parasitic groups (cestodes, and trematodes) as well as the turbellarians which are mainly free-living and have marine, freshwater and terrestrial representatives. Only the Turbellaria, in part, are considered here (also see Marine Section).
1. Terrestrial species
No fewer than 14 species of land flatworms have been recorded in the British Isles but only three or four are probably native (Jones, 2005). Of the 10 species in the infraorder Terricola, seven have been recorded from Cornwall. Only three of the 10 are considered to be native by Jones (1988): Microplana terrestris (Müller), M. scharffi (von Graff) and M. humicola Vejdovsky; all are small (reaching maximums of 25mm, 90mm and a mere 4mm respectively) and rather scarce although widely distributed in the British Isles and the rest of Europe. M. scharffi has the distinction of being almost endemic”, otherwise being known only from Belgium. The non-native species come from various parts of the world, and two of them, Arthurdendyus triangulatus (Dendy), formerly Artioposthia triangulata (Dendy), the New Zealand Flatworm, and Australoplana sanguinea (Dendy), formerly Geoplana sanguinea (Moseley), the Australian Flatworm (although it also occurs in New Zealand) are spreading throughout the British Isles and Ireland. Both feed on earthworms and the former has become a serious pest especially in Northern Ireland and Scotland, and it is an offence knowingly to distribute this species under the WCA 1981. The first British record of the latter was on Tresco in 1980, and it is now widespread in south-west and north-west England. Another Australian introduction Australopacifica coxii (Fletcher & Hamilton) formerly Geoplana coxii (Fletcher & Hamilton) is known only from the Scillies and Penzance. Kontikia ventrolineata (Dendy) has been found in Cornwall, Guernsey and Merseyside whilst Kontikia andersoni Jones, the native country of which is as yet unknown, is recorded from the Scillies, the Padstow area, Guernsey, the Isle of Man and Northern Ireland. A list of all the species recorded from Britain is given by Turk (1995). The assistance of Dr H. Jones is gratefully acknowledged.
2. Freshwater species
13 species are listed as British by Ball & Reynoldson (1981). Of these, 10 have been found in Cornwall where many sites were examined between 1978 and 1989 by Dr L.S. Bellamy. All are widespread in Britain and relatively common. Dugesia tigrina Girard is native to North America but is now in both northern and southern Britain as a result of the activities of aquarists, according to Ball & Reynoldson (1981); in Cornwall it is known only from Tresowes.