Evidence for Hymenostome Affinities in an Apostome Ciliate

Abstract

The functional mouth of exuviotrophic apostome ciltates appears only after an elaborate metamorphosis that begins at the onset of the molting of their crustacean hosts. In the tomite. a non‐feeding migratory stage, a mid‐ventrai depression at the origin of kineties x, y and z has been misidentified as the cytostome. Studies of fine structure and morphogenesis identify the true but nonfunctional cytostome—the subapiral lateral canal —and the falciform and ogival fields as the adoral ciliature. The anterior row of barren kinetosomes that parallels on the right the anterior third of the lateral canal is actually the infraciliature of a paroral. 2 rows of barren staggered kinetosomes. The canal itself is a narrow tube, its walls partially lined with microtubules. It begins 2–3 μm from the apex of the body and passes between falciform field 9 and the ogival field to end near the end of the ogival field. The fine structure of the infraciliature of the falciform and ogival fields differs markedly from that of the somatic kineties. In the host's early pre‐molt stages, the paroral migrates across the ventral surface of the encysted phoront and is accompanied by the microtubules of the lateral canal. The anterior end of falciform field 9 disorganizes into scattered kinetosomes, the trophont's anterior field of kinetosomes, but the posterior end migrates in an arc across the anterior ventral surface and remains as kinety a located near the angle where kinety 1 sharply par ra continues posteriad ind dorsad to the posterior limit of the extended cytostome. At the end of metamorphosis it sinks into The cytoplasm and disappears. The completion of the extended cytostome, the functional mouth, marks the termination of the microstome‐macrostome transformation. The fine structure of the infraciliature and microtubular elements making up the macrostome and the evocation of the microstome‐macrostome transformation in the presence of specific foods suggest that apostome ciliates any more properly be a suborder of Hymenostomatida rather than a subclass of Oligohymenophorea.

Molecular evolution of Cinetochilum and Sathrophilus (Protozoa, Ciliophora, Oligohymenophorea), two genera of ciliates with morphological affinities to scuticociliates

“…The tomites of these species have somatic monokinetids with an ultrastructural pattern that resembles other oligohymenophoreans. Bradbury (1989) suggested that similarities in the life cycles and the somatic ciliary ultrastructure of hymenostomes and apostomes justified a placement of the apostome ciliates as a suborder within the order Hymenostomatida. Phylogenetic analyses inferred from SSU rRNA gene sequence data supported the monophyly of apostomates and revealed sufficient genetic divergence to other subclasses to maintain this group as a separate subclass of the Oligohymenophorea (Clamp et al.…”

A Redescription of Gymnodinioides caridinae (Miyashita 1933) from Palaemonetes sinensis (Sollaud 1911) in the Songhua River

“…There are other kineties near the cytostome, but whether they are oral kineties in the sense that they aid in feeding and also lack the structure of somatic kineties remains to be determined [3]. A conspicuous kinetal fragment originates subapically, but posterior to the origin of K l .…”

Lynniagrapsolytica n. gen, n. sp. (Ciliophora: Apostomatida: Colliniidae), a Deadly Blood Parasite of Crabs with a Novel Pseudocytopharynx

“…2C, 3). The rosette-associated pore (sometimes erroneously termed the "cytostome"; see Bradbury (1989) for a discussion) is small and often not visible even after silver impregnation. When visible, it appears as a small dark circle at the posterior edge of the rosette, interrupting the ventral "hook" of somatic kineties (described below) (Fig.…”