Stomatogenesis in Kyaroikeus cetarius (Dysteriina, Kyaroikeidae, N. Fam.): Clues to Its Systematic Placement

Morphogenesis in Kyaroikeus cetarius, a large phyllopharyngean parasite of odontocete Cetacea, begins with the midventral proliferation of four short rows of kinetosomes immediately to the left of four pre-existing, somatic kinetofragments. The resulting field of eight short kineties is located within a shallow depression that gradually elongates and deepens to form the oral cavity of the opisthe. The four right-most of these kineties sink into the developing oral cavity and divide transversely, producing three distinct sets of kinetofragments. The anterior and posterior sets each consist of four small fragments and ultimately produce the mid-ventral, somatic kinetofragments of the proter and the opisthe, respectively. In addition, some kinetosomes from the anterior 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 kineties, respectively. These anlagen migrate progressively anteriad while undergoing a pronounced counterclockwise rotation that eventually inverts the developing oral kineties. Simultaneously, two broad sheets of microtubules, 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 out of the ventral depression to produce the left ciliary field of the opisthe. Morphogenetic events observed in K. cetarius are typical of cyrtophorid Phyllopharyngia and support inclusion of this genus within suborder Dysteriina.