STOMATOGENESIS IN KYAROIKEUS-CETARIUS (DYSTERIINA, KYAROIKEIDAE, N-FAM) - CLUES TO ITS SYSTEMATIC PLACEMENT

Morphogenesis in Kyaroikeus cetarius, a large phyllopharyngean parasit e of odontocete Cetacea, begins with the mid ventral proliferation of four short rows of kinetosomes immediately to the left of four pre-exi sting, somatic kinetofragments. The resulting field of eight short kin eties is located within a shallow depression that gradually elongates and deepens to form the oral cavity of the opisthe. The four right-mos t of these kineties sink into the developing oral cavity and divide tr ansversely, producing three distinct sets of kinetofragments. The ante rior and posterior sets each consist of four small fragments and ultim ately produce the mid-ventral, somatic kinetofragments of the proter a nd the opisthe, respectively. In addition, some kinetosomes from the a nterior set give rise to the secretory organelle complex of the proter . The central group consists of two long and one short kinetofragment, which represent anlagen for the opisthe circumoral and preoral kineti es, respectively. These anlagen migrate progressively anteriad while u ndergoing a pronounced counterclockwise rotation that eventually inver ts the developing oral kineties. Simultaneously, two broad sheets of m icrotubules, one beneath each circumoral anlage, extend deep into the cytoplasm and unite to line the cytopharynx of the opisthe. Meanwhile, the remainder of the eight original kinetofragments move laterally ou t of the ventral depression to produce the left ciliary held of the op isthe. Morphogenetic events observed in K. cetarius are typical of cyr tophorid Phyllopharyngia and support inclusion of this genus within su border Dysteriina.