The taxonomy, zoogeography and biology of Bipalium kewense Moseley, 1878 (Tricladida, Terricola)
Knowledge of this cosmopolitan land planarian is briefly reviewed. The external morphology and anatomy of the copulatory organs are considered with emphasis on the variation of taxonomic characters. This species can be distinguished from similar planarians by differences in markings, particularly those of the head and neck; positions of body apertures and structure of the copulatory organs.
Karyological studies on neoblasts of B. kewense reveal a diploid chromosome complement of 16; one subtelocentric, three submetacentric and four metacentric pairs of chromosomes.
The present distribution of the species is mapped. Its natural range extends through Vietnam to Kampuchea. Elsewhere it has been introduced by man. Outside its normal range Bipalium is always confined to habitats in man-modified environments. Its natural habitat is probably tropical rainforest in the uplands of Indochina. Temperatures in these regions are more representative of a subtropical than tropical-humid type climate. This may explain the occurence of the species in low temperature hothouses and its tolerance to low outdoor temperatures.
Man has apparently passively dispersed B. kewense together with rooted plants. A sequential spread of the species from country to country worldwide cannot be ascertained. In Australia and North America B. kewense shows an immature disjunct distribution typical of an introduced species. Generally, older records in each centre are from hothouses in coastal cities; more recent records from outdoors further inland.
Asexual reproduction by architomy in B. kewense appears to be largely influenced by environmental temperature and the availability of earthworms, its sole food-source. Sexual specimens of the species have been found mainly in regions with tropical or subtropical climates. Sexual reproduction may be seasonal. Sexual Bipalium can reproduce asexually by architomy. This probably does not occur during periods of cocoon production. Factors influencing sexual reproduction are not clear.
Outdoors the species is usually prevalent in spring and autumn, less common in summer and winter. Mortality and ‘aestivation’ may account for reduced numbers of specimens observed during these periods. B. kewense also exhibits seasonality in hothouses where it reaches maximum numbers in winter months and is scarce in summer.
B. kewense is of marginal medical and veterinary importance because of its implication in cases of pseudoparasitism in humans and domestic animals. It is of minor commercial importance as a pest on earthworm farms in the southern United States.