Morphogenetic Pattern in Laurentiella acuminata (Ciliophora, Hypotrichida): Its Significance for the Comprehension of Ontogeny and Phylogeny of Hypotrichous Ciliates

Abstract

Morphogenetic events during division, physiological reorganization, and postraumatical regeneration, the last being induced both chemically and microsurgically, were studied by light microscopy on protargol‐impregnated specimens of the hypotrichous ciliate, Laurentiella acuminata. Parakinetal stomatogenesis, from transverse cirrus‐1 during division and reorganization, changes during regeneration to a parakinetal one which characterizes more primitive members of Hypotrichida in the S. O. Stichotrichina, but solely when the AZM is damaged. These morphogenetic events a) confirm the previous inclusion of L. acuminata among the Oxytrichidae on the basis of its morphological characters and indicate that it is a primitive species of this family related with the Stichotrichina through genera Pleurotricha and Paraurostyla; b) suggest a synthetic model that explains both the positioning and timing of cortical morphogenesis in the cell cycle. The key point of this model is the attribution to the AZM of a repressive capacity on the stomatogenic area, the last one being positioned according to the system of gradients of morphogenetic activity proposed by Jerka‐Dziadosz to explain location of primordia in urostylids. This repression is manifested not as a gradient, as indicated by De Terra, but as a long‐term repression limited to a certain distance. Simultaneous repression and stimulation occurring in a growing cortex with the AZM remaining constant in size could explain the critical ratio, buccal cortex/somatic cortex, at which stomatogenesis is triggered as indicated by De Terra.

Developmental Heterochrony in Ciliated Protozoa: Overlap of Asexual and Sexual Cycles During Conjugation

“…Conversely, if a relatively bigger AZM exists, then it will prevent the emergence of a new AZM primordium, or even cause a developing AZM primordium to regress. This rule can accommodate the observations on post-traumatic regeneration in hypotrichs like Oxytricha (Hashimoto, 1961), Laurentiella (Martin et al, 1983), and probably also the urostylids (Jerka-Dziadosz, I 967). 7).…”

Morphology and Morphogenesis of Onychodromus quadricornutus n. sp. (Ciliophora, Hypotrichida), an Extraordinarily Large Ciliate with Dorsal Horns1

“…These rows are produced by splitting of some of the rightmost FVT anlagen, in both the proter and the opisthe (Figs. 16,18,23).…”

Morphogenesis in the Heterotrich Ciliate Climacostomum virens. II. Oral Development During Regeneration1

“…Generally, the range of urea concentrations employed extends from 2% for Stentor (25) to 6% for C. virens. The duration of the treatment varies from 30 sec for L. acuminata (21) to 2 min for C. virens, and the ciliates are treated 1-3 days following the last feeding. Among all these studies, however, little information exists concerning the effects of such factors as temperature, urea concentration, or duration of the urea treatment.…”

“…In the medium shedding type (Figs. 15,[19][20][21][22], the AM and all the anterior ADM are removed, but the posterior ADM remain attached to the buccal tube; in vivo, these cells often show a typical rostrum (Figs. 9, 10).…”