Cytotaxonomy in Some Species of the Genus Leiobunum (Opiliones, Arachnida)

Abstract

The genus Leiobunum (Leiobunidae) includes a number of species. Some of them are easily distinguished, but others are very difficult to classify morphologically. The usefulness of chromosomal study in the classification of such difficult species was first indicated by Suzuki (1957). The present study further supports this indication. Namely, it has been known that Leiobunum kohyai shows a unique karyotype and that the two populations of L. montanum differ entirely in karyo-types. The species used as materials for this study were L. kohyai collected from Mt. Odaigahara and L. montanum coming from two localities ; Mt. Ishizuchi and Mt. Hokidaisen. The chromosome slides were made by the temporary squash and the sectioned methods using testes. For the former, acetic-orcein was employed. Results. 1) Leiobunum kohyai. A large number of spermato-gonial metaphase plates were obtained. However, due to the small size of the chromosomes, counting was rather difficult. The number was determined as 2n=20, which consisted of 4 acrocentrics and 16 metacentrics. In the metaphase plate of the first division 10 bivalents were clearly seen (Figs. 1, 2). No sex-chromosome or chromosomes showing special behavior or structure could be observed. 2) Leiobunum montanum. Ishizuchi population. The spermato-gonial chromosomes were clearly counted as 24. The complement consisted of 12 acrocentrics and 12 metacentrics (Fig. 6). At the metaphase of both first and second divisions 12 bivalents (Fig. 3) and 12 dyads, respectively, were observed. In this case, as in the above species, the presence of any heterochromosomes could not be recognized throughout the entire spermatogenetic cycle. 3) Leiobunum montanum. Hokidaisen population. An excellent spermatogonial metaphase plate showed 2n=18. All the chromosomes were represented by metacentrics (Fig. 7). The metaphase plates of the first and second divisions showed 9 bivalents and 9 dyads,