Selective mirror-image reversal of ciliary patterns inTetrahymena thermophila homozygous for ajanus mutation

Summary The development of the oral apparatus (OA) and of neighboring ciliary structures ofTetrahymena thermophila was analyzed in cells homozygous for ajanus (jan A) mutation plus a recessiveenhancer of janA (eja). Such cells frequently possess two OAs located on opposite sides of the cell, a primary (1°) OA previously reported to be normal, and a secondary (2°) OA previously reported to express a mirror-reversal of right-left asymmetry. This study confirms the reality of a reversal in the gross orientation of membranelles in most developing 2° OAs. It also shows that there is a reversal of asymmetry in the pattern of resorption of basal bodies of ciliary rows adjacent to the 2° OA, and in the arrangement of basal-body couplets making up the portion of the apical crown of the cell situated close to the 2° OA. However, the locations at which membranelles of the 2° OA become modified during late phases of oral development remain normal, so that membranelles of 2° OAs are superimposable on those of 1° OAs. In addition, the membranelles of 2° OAs frequently undergo a rotation during the final phases of oral development, so that even their spatial orientation becomes normal. This mixture of reversed and normal features can be accounted for by postulating a superimposition of a reversed largescale asymmetry on a normal local asymmetry of ciliary units. This postulate predicts that no single mutation can bring about a complete mirror-image reversal of ciliary patterns.1° OAs appear normal by light microscopy. However, detailed analysis of SEM, preparations of isolated 1° OAs indicate subtle abnormalities of basal body arrangement in some of these OAs.     

Positional reorganization in compound janus cells of Tetrahymena thermophila

The janus mutations of Tetrahymena thermophila convert the large-scale organization of the dorsal surface of the cell into a mirror-image of the ventral surface, which is characterized by a second, abnormal, oral apparatus and by contractile vacuole pores to the left of the second oral area rather than the usual right. This conversion could be due either to a local change in the response to an unaltered positional system or to a more global reorganization of the system itself. janus homopolar doublets were used to distinguish between these two alternatives. Homopolar doublets can be made by fusing two similarly oriented cells in side-by-side parabiosis. Non-janus homopolar doublets typically possess two sets of normal oral structures with contractile vacuole pores to the right of each of them. In janus doublets, there are up to four sets of oral structures, with the abnormal oral structures located between the two sets of normal oral structures; contractile vacuole pores are situated to the right of the normal oral areas and to the left of the abnormal oral structures. Non-janus homopolar doublets are known to propagate their compound condition for a number of cell divisions, but also to regulate toward the singlet state through a progressive reduction in number of ciliary rows followed by loss of one of the two sets of major cell surface structures. janus homopolar doublets go through a corresponding regulation. As a consequence, the location of the abnormal oral structures relative to the normal ones is more variable in janus doublets than in janus singlets. Sometimes the abnormal oral structures shift to a position close to their normal counterparts and then the intervening CVP sets disappear. There is evidence for occasional fusion of an abnormal oral area with an adjacent normal oral apparatus, a condition that may be transitional to the singlet state. These observations are inconsistent with the idea of a fixed positional system and strongly suggest a global reorganization of the surface pattern in a manner consistent with predictions of an intercalation model that was first proposed to explain the regulation of non-janus doublets to singlets.     

A genically determined abnormality in the number and arrangement of basal bodies in a ciliate

When an F₁ of a cross between clones K₇ and VF₁₇ of Euplotes minuta was backcrossed to the K₇ parent, 6 of the 30 progeny clones displayed a syndrome of abnormalities in cortical pattern, which included (1) substantial reduction in number of dorsal cilia, (2) a lesser reduction in number of ciliary rows, (3) absence of one or both right caudal cirri, (4) appearance of incomplete and abnormally oriented membranelle bases, (5) irregularities in form of ventral cirri. The length of cilia and arrangement of subpellicular fiber bundles were fully normal in these 6 clones, as were cell size and division rate. A test cross of one of these abnormal clones with the F₁ parent yielded a 1:1 segregation of normal and abnormal progeny clones, with no intermediate clones, suggesting a single-gene basis for the abnormal condition. Comparison of development in normal and abnormal clones suggested that the abnormal clones were defective in the formation of basal bodies; new basal bodies often failed to form at the expected sites, and occasionally appeared in atypical spatial relations to old basal bodies. As a probable consequence of this defect, the fidelity of cytoplasmic inheritance of preexisting ciliary row number, which was demonstrated to be considerable in normal clones, was reduced in the abnormal clones.     

Structural deficiency of 180°-rotated ciliary rows in Tetrahymena: Implications on the inheritance and development of a non-genically acquired cortical trait during vegetative propagation

The present study reveals a deficiency in the number of ciliated basal bodies along 180° rotated ciliary rows (IRs) in Tetrahymena. This feature is common to IRs recently generated in young clones with stable corticotypes (total number of ciliary rows per cell), irrespective of the number of IRs present per cell or their cellular location, and is found before the cell loses any of the IRs. In cells bearing three IRs, the IRs on the two sides of the inversion immediately next to normal ciliary rows (junctures) exhibit an even greater deficiency in ciliated basal bodies, compared to the IR located internally between two other IRs; the normal ciliary rows flanking the inversion are also somewhat deficient. These observations show that the IRs of Tetrahymena are structurally deficient, hence developmentally defective, and suggest that they are intrinsically unstable. We propose that basal body development along IRs tends to be truncated before the stage of ciliation; such basal bodies would fail to acquire the potential to serve as nucleating centers for new basal body development in the next round of basal body proliferation, leading to the eventual loss of the IRs. © 1992 Wiley-Liss, Inc.     

How the mirror-image pattern specified by a janus mutation of Tetrahymena thermophila comes to expression

The initial changes of cell-surface organization that occurred as the recessive janAl (janus) mutation of Tetrahymena thermophila first became expressed were elucidated in a special mating scheme in which old macronuclei homozygous for janA⁺ were synchronously replaced by new macronuclei homozygous for janAl. During this period of onset of expression, the number, regularity, and asymmetry of the ciliary rows remained unchanged. New normal (primary) oral apparatuses (OAs) continued to be formed posterior to old OAs, as in normal cells. At about four fissions after conjugation, abnormal (secondary) OAs with a partial reversal of asymmetry began to appear nearly opposite to the primary OAs, close to but not at the eventual circumferential position of janAl secondary OAs. The array of contractile vacuole pores (CVPs), normally located adjacent to two ciliary rows centered near 22% of the cell circumference to the righ of the primary oral meridian, underwent a two-step transformation: first, the number of adjacent ciliary rows bearing CVPs increased to 3, 4, and sometimes 5, then “skipped” rows appeared within this broadened CVP-arc to split the single set of CVPs into two separated subsets. The CVP transformations occurred gradually and progressively. They began prior to the expression of secondary OAs but accelerated as secondary OAs appeared. As the CVP are became broader, its midpoint shifted somewhat to the right, away from the primary oral meridian, but ended up close to halfway between the primary and secondary oral meridians. The data provide a better fit to an intercalation model than to an alternative double gradient model, suggesting that the janAl mutation alters the large-scale organization of positional values by preventing the expression of a subset of these values and thus provoking reverse-intercalation of the remainder.     

Development of the ciliature of Tetrahymena thermophila: II. Spatial subdivision prior to cytokinesis

The cell surface of Tetrahymena thermophila is made up of an anterior region in which virtually all basal bodies of ciliary rows are ciliated, and the remainder in which ciliated and unciliated basal bodies are fairly irregularly interspersed. This pattern persists through interfission development until the stage of appearance of the equatorial ring of gaps in the ciliary rows that marks the fission zone. The ciliation pattern then becomes subdivided, in large part through the rapid ciliation of contiguous basal bodies located posterior to the fission zone. We interpret this process as a wave of ciliation of preexisting basal bodies that propagates posteriorly from the site of the fission zone. The location, extent, and timing of the ciliation process are the same in inverted as in normally oriented ciliary rows, in spite of the fact that in inverted rows the visible fission zone gap is tardily formed and the local configuration of ciliature around this gap is abnormal. The putative ciliation wave thus does not depend directly upon the local manifestations of the fission zone. However, in a cell-division-arrest mutant, cdaA1, analyzed under conditions in which formation of fission-zone gaps is permanently prevented in some ciliary rows but not in all, it is found that the ciliation pattern becomes subdivided in those ciliary rows that express fission-zone gaps and fails to become subdivided in neighboring rows that fail to manifest gaps. We interpret this combination of findings to indicate that a signal localized at the cell equator initiates a set of polarized developmental events that simultaneously create and demarcate two cellular fields within what was previously one. We further suggest that the characteristic tandem cell division pattern of ciliates is fundamentally a process of segmentation, which might involve mechanisms of gradient subdivision analogous to those taking place during segmentation of insects and other multicellular organisms.     

The Regulation of Homopolar Doublets to Singlets in Glaucoma

ABSTRACT. In the ciliate Glaucoma scintillans , the process of transformation of unbalanced homopolar doublets to singlets was investigated. Cells were fixed 1–3 days after inoculation and impregnated with silver according to the Chatton-Lwoff technique. The two oral apparatuses (OAs) approached each other partly due to a loss of ciliary rows in one of the two components (semicells) consisting of a doublet. The contractile vacuole pore (CVP) in the narrow semicell (sc1) was lost at an early stage of regulation, while the position of CVP in the broad semicell (sc2) shifted toward the right after the loss of sc1. The sc1 of 20 row-intervals in breadth was a transition point above which the sc1 was able to persist for awhile, and beneath which it was actively lost. There was no evidence for an independent effect of sc2 on the transformation of doublets to singlets. In cell division, an additional reversed oral primordium (sOP) was formed in unbalanced doublets, usually within a narrow sc1 of 11–20 row-intervals. The position of the sOP was generally 4–6 row-intervals distant from the right side of the oral meridian (OM1) with the cell's left OA. Most of the doublets with an sOP lacked an oral primordium in the OM1. No mature triplet with 2 normal OAs and an abnormal OA was found in these preparations. The pathway of regulation, the movement of the CVP, and the formation of an sOP are discussed.     

bcd: A mutation affecting the width of organelle domains in the cortex of Tetrahymena thermophila

Summary A single-gene recessive mutation, bcd (broadened cortical domains), of Tetrahymena thermophila is characterized by a variable broadening of the spatial domains within which cortical organelles, including both the contractile vacuole pores (CVP) and oral apparatus (OA), are formed. The phenotype is not temperature-sensitive. During the development of the organelles of the mutant prior to cell division, extra CVPs and extra oral primordia (OP) appear near ciliary rows adjacent to the rows at which these structures normally form. In the later stages of development, some, but not all, of these extra structures are resorbed, or in the case of the oral domain, multiple adjacent OPs may be completely or partially integrated into a single enlarged OA. When multiple OAs persist, one or more of these may display a reversed orientation reminiscent of those encountered in janus mutants. However, unlike janus, bcd cells do not express any sign of a mirror-image global organization.Our results can best be accounted for by postulating that the bcd mutation affects some common determinant of the widths of both CVP and OA domains. Studies are in progress which explore the relationship between this width-determining mechanism(s) and the mechanism(s) determining the location of cortical organelles around the cell circumference.     

Pattern Formation in Mirror-Image Doublets of the Ciliate Stylonychia pustulata

ABSTRACT. Mirror-image symmetry doublets of the ciliate Stylonychia pustulata were obtained from the progenies of dividing cells in which cell division was inhibited by heat-shocks. In two components consisting of the doublet, the left (cell's) component possessed ciliary organelles arranged in almost the same pattern as in normal singlets, while the right one had surface organelles located in a mirror-image symmetry of those of the left component. In cell division of the doublet, two sets of ciliary primordia that were arranged in a mirror-image symmetry developed synchronously in both components. In about 80% of oral primordia (OP) of the right components, the arrangement of the membranellar bands became abnormal. In some cases, OP of the right component were occasionally separated into two longitudinal halves, each consisting of normal membranelles and inverted membranelles. A set of primordia of the paroral membranelles and fronto-ventro-transverse cirri was rarely derived from the basal bodies of the right half with a band of normal membranelles. As a result, a third component with the ciliary organelles normally arranged emerged on the right side of the original right component. The differentiation of membranelles and segmentation of the primordial streaks into cim proceeded from anterior to posterior. A cytoplasmic bulge with multiple right marginal cirral rows was frequently formed at the right margin of the doublet. The behavior in the separation of third and fourth streaks from a primordial streak of dorsal cirri was not mirror-image symmetrical in each component.     

Cytogeometrical determination of ciliary pattern formation in the hypotrich ciliate Stylonychia mytilus

Specification of polar and lateral axes has been investigated in several metazoan developmental systems. In order to analyze this phenomenon in unicellular organisms, singlet cells of the ciliate, Stylonychia mytilus, were cut along their longitudinal axis and the regenerative morphogenetic sequence was analyzed. Morphogenesis in right fragments, which folded such that the posterior and anterior ends were juxtaposed and fused, leads to formation of two partially mirror-imaged incomplete ventral ciliary patterns. Regenerative morphogenesis in singlet hypotrich ciliates typically produces only one complete set of ciliary organelles. These data demonstrate that cytoplasmic orientation (cytogeometry) plays a major role in the determination of ciliary pattern and that polar and lateral axes are determined independently in this species.     

The Structure and Development of the Dorsal Bristle Complex of Oxytricha fallax and Stylonychia pustulata*

SYNOPSIS. Oxytricha fallax and Stylonychia pustulata possess 6 rows of dorsal bristle units. Each dorsal bristle unit consists of a pair of kinetosomes; the anterior kinetosome has a cilium and the posterior kinetosome a ciliary stub. The kinetosome pair, located at the bottom of a cortical pit surrounding the cilium and ciliary stub, is surrounded by an asymmetrical fibrillar mass. Future rows 1-4 are formed from 2 sets of primordia originating within mature dorsal rows 1-3. Rows 5 and 6 originate from the anterior regions of both right marginal cirral primordia. Old dorsal bristle units utilized in formation of primordia are presumably maintained in the new rows of the proter and opisthe; those outside the primordia are resorbed. The morphogenetic pattern of the Oxytrichidae is similar to those of the Urostylidae and Holostichidae, but quite different from that of the Euplotidae.     

The Positioning of Ciliary Organelles in Hypotrich Ciliates*†

It is commonly observed in hypotrichs that new ciliary rudiments arise directly from or in close juxtaposition to certain pre-existing ciliary elements. Oral primordia often are initiated near specific cirri, cirral rudiments frequently arise as a result of the disaggregation of certain old cirri, and new dorsal ciliature is formed within pre-existing ciliary rows. In the first 2 situations it has been demonstrated experimentally that neither the old ciliature in question nor the specific cortical site marked by that ciliature is essential for the appearance of the new cirral rudiment. The experimental analysis done thus far suggests that the positions of oral and cirral primordia are determined by interacting gradients established in relation to certain reference points. The nature of the reference points is not fully elucidated; in some cases at least these points appear to be more closely related to topographic features of the cell than to specific pre-existing cortical structures. In the dorsal ciliary rows of Euplotes new ciliary units are formed usually and perhaps invariably in close proximity to old ones, and are generally oriented along the axis of the pre-existing row. The result is a tendency to perpetuate the preexisting row number across cell generations. Changes in row number, however, can occur as a result of occasional formation of new units at right angles to the row, a process that is much enhanced in certain homozygous segregants (basal body deficient). The optimal row number (stability range) as well as the number of ciliary units are under genic control. In addition, the spatial pattern of distribution of ciliary units among rows is invariant in all of the material examined. This pattern is presumed to result from an underlying field whose geometry is independent of both the number of units and the number of rows.     

Scanning Electron Microscopy of the Adoral Ciliary Zone of Cycloposthium Bundle (Ciliophora,Entodiniomorphida)1

The adoral ciliary zone of Cycloposthium spp., inhabiting the large intestine of the horse, was studied by scanning electron microscopy. It could be divided into four parts: outer, inner, left, and right zones. The outer zone, extending on the anterior periphery of the apical cone of the body, had 20 tuft-like syncilia arranged radially around the longitudinal axis. Each ciliary tuft consisted of about 170 cilia, and in cross section it had a rectangular shape. The cilia of the inner zone, situated at the top of the apical cone, were aggregated irregularly to form shorter bundles than the tufts of the outer zone. The innermost cilia of this zone were shorter than the outermost. There was a distinct non-ciliated border between the outer and inner zones. A horseshoe-like operculum having no cilia was present at the center of the adoral ciliary zone, and the opening of the vestibulum was situated as a cleft crossing from the center to the right periphery of this zone. No cilia extended onto the vestibular wall. The left ciliary zone was situated beneath the outer zone and consisted of five short rows of barren kinetosomes of which only the central row possessed very short cilia. The right ciliary zone, consisting of a few rows of cilia situated at the bottom of the inner adoral lip, was also easily distinguished from the other ciliary zones. This zone was interpreted as an extension of the outer adoral zone passing along the right side of the apical cone. These ciliary zones were considered to be highly differentiated and useful for both movement of and ingestion of food.     

How the mirror-image pattern specified by a janus mutation of Tetrahymena thermophila comes to expression

The initial changes of cell-surface organization that occurred as the recessive janA1 (janus) mutation of Tetrahymena thermophila first became expressed were elucidated in a special mating scheme in which old macronuclei homozygous for janA+ were synchronously replaced by new macronuclei homozygous for janA1. During this period of onset of expression, the number, regularity, and asymmetry of the ciliary rows remained unchanged. New normal (primary) oral apparatuses (OAs) continued to be formed posterior to old OAs, as in normal cells. At about four fissions after conjugation, abnormal (secondary) OAs with a partial reversal of asymmetry began to appear nearly opposite to the primary OAs, close to but not at the eventual circumferential position of janA1 secondary OAs. The array of contractile vacuole pores (CVPs), normally located adjacent to two ciliary rows centered near 22% of the cell circumference to the right of the primary oral meridian, underwent a two-step transformation: first, the number of adjacent ciliary rows bearing CVPs increased to 3, 4, and sometimes 5, then "skipped" rows appeared within this broadened CVP-arc to split the single set of CVPs into two separated subsets. The CVP transformations occurred gradually and progressively. They began prior to the expression of secondary OAs but accelerated as secondary OAs appeared. As the CVP arc became broader, its midpoint shifted somewhat to the right, away from the primary oral meridian, but ended up close to halfway between the primary and secondary oral meridians. The data provide a better fit to an intercalation model than to an alternative double-gradient model, suggesting that the janA1 mutation alters the large-scale organization of positional values by preventing the expression of a subset of these values and thus provoking reverse-intercalation of the remainder.     

Ultrastructural Observations on the Spermatozoa of Two Temnocephalids (Platyhelminthes)

The spermatozoa of two Temnocephalidae collected in Uruguay, Temnocephala iheringi Haswell, 1893 (Host: Pomacea canaliculata) and Temnocephala axenos Monticelli, 1899 (Host: Parastacus varicosus), were studied with a transmission electron microscope. In both species the spermatozoon is made up of a long sperm body which bears at one extremity two free flagella of the 9+‘1’ flatworm pattern. The sperm body contains the nucleus, mitochondria, dense bodies and parallel, cortical, longitudinal singlet microtubules. Along a part of the sperm body the palissade of the microtubules displays a spiral pattern in transverse sections. A part of the perimeter of the cell is thus lined by two overlapping rows of microtubules. This spiral pattern of the singlets is considered as a synapomorphy of the family Temnocephalidae. The singlet microtubules are interconnected by two kinds of links: tangential links between neighbouring singlets in the same row and radial links between singlets belonging to two rows. The presence of these links suggests that this structure could be a motile system of singlets.     

ISOLATION AND REACTIVATION OF THE AXOSTYLE : Evidence for a Dynein-like ATPase in the Axostyle

The contractile axostyle is a ribbon-shaped organelle present in certain species of flagellates found in the hindgut of wood eating insects. This organelle propagates an undulatory wave whose motion, like flagella and cilia, is related to microtubules. Unlike the axoneme of cilia and flagella, however, the axostyle is composed of singlet microtubules linked together in parallel rows. Axostyles were isolated from Cryptocercus gut protozoa with Triton X-100. Normal motility of the isolated axostyle could be restored with adenosine triphosphate (ATP); the specific conditions necessary for this reactivation were essentially identical with those reported for the reactivation of isolated flagella or whole sperm. ATPase activity of the isolated axostyle was comparable to the values reported for ciliary or flagellar axonemes. The axostyle was reasonably specific for ATP. Most of the proteins of the isolated axostyle comigrated with proteins of the ciliary axoneme on sodium dodecyl sulfate (SDS) polyacrylamide gels (i e. equivalent molecular weights). These included the following: the higher molecular weight component of dynein, tubulin, linkage protein (nexin), and various secondary proteins. Evidence for dynein in the axostyle is presented and a model proposed to explain how repeated propagated waves can be generated.     

The filaments supporting ciliary primordia and fission furrow in the hypotrich ciliateParaurostyla weissei, revealed by the monoclonal antibody 12G9: Studies on wild-type and ciliary hypertrophy mutant

Summary The unique monoclonal antibody FXXXIX 12G9 obtained againstTetrahymena cortices was used to label cytoskeletal structures related to basal body proliferation inParaurostyla weissei. The antibody binds to an amorphous material interconnecting basal bodies in compound ciliary structures: dorsal units, cirri and membranelles in interfission cells, and filamentous structures supporting the primordia of ciliary structures and fission line in dividing cells. The antibody visualized meridional filaments preceding proliferation of new basal bodies in the oral primordium and structures accompanying all developing ciliary primordia. It congregated in differentiating new procirri and membranelles, whereas another population of transient meridional structures accompanied the final distribution of new structures. A meridional filament connecting transverse cirri with the oral apparatus, marking the future stomatogenic meridian, persisted in both division products until completion of cell elongation. The fission line was found to originate from an anterior extension of the pre-oral filament toward the parental oral structures. It then encircled the cell's midbody demarcating the boundary between daughter cells; two additional circumferential structures bordering the anterior and posterior ends of differentiating division products participate in formation of the new poles. They disappear after separation of daughter cells and completion of resorption of parental ciliature. In the enhanced multi-left-marginal mutant expressing gross hyperduplication of basal bodies, the location of the 12G9 antigen corresponded to that in wild-type cells. The sequence of formation of meridional filaments in the mutant was found to be altered. The filaments in the left lateral domain preceded the formation of the preoral filament, yet the temporal pattern of basal body assembly was not modified. The fission line, as in wild-type cells, originated in connection with the oral primordium. We conclude that the nucleation of the filamentous structures bearing the 12G9 antigen and the basal body assembly occur by independent mechanisms reading the same cell cycle signals. We suggest that the 12G9-antigen-bearing protein might be similar to septins: involved in signaling the position of the oral primordium and the fission line and functioning in establishing and maintaining the asymmetric cortical domain characteristics.Abbrevations AZM zone of adorai membranelles - bb basal bodies - CC caudal cirri - FC frontal cirri - Fmf frontal meridional filament - FTV the primordia of fronto-ventro-transverse cirri - LD, RD dorsal rows of bristle units - LM, RM left or right marginal cirral row - OA oral apparatus - OP primordium of the adoral membranelles - pLM, pRM primordium of the left or right marginal cirri - pLD, pRD primordia of the left or right dorsal bristle rows - pUM primordium of the undulating membranes - TC transverse cirri - UM undulating membranes - VC ventral cirral rows     

Morphological Description and Molecular Phylogeny of Two Species of Levicoleps (Ciliophora,Prostomatida), L. taehwae nov. spec. and L. biwae jejuensis nov. subspec., collected in Korea

Two colepid ciliates, Levicoleps taehwae nov. spec. and L. biwae jejuensis nov. subspec., were collected from the brackish water of the Taehwa River and a small freshwater pond in Jeju Island, South Korea, respectively. Their living morphology, infraciliature, and small subunit (SSU) rRNA gene sequences were determined using standard methods. Barrel‐shaped L. taehwae nov. spec. is a small ciliate with an average size of 45 × 25 μm in vivo, about 15 ciliary rows each composed of 12 monokinetids and two perioral dikinetids, and two 20 μm‐long caudal cilia. The sequence length and GC content of the SSU rRNA gene are 1,669 bp, 44.5%. This novel species is similar in body size to Coleps hirtus, and has six armor tiers and hirtus‐type tier plates, and the same number of ciliary rows as C. hirtus; however, it can be distinguished from the latter by the absence of armor spines and its sequence similarity of SSU rRNA gene is about 92.8% which indicates that it is a distinct form. Levicoleps biwae jejuensis nov. subspec., is a medium colepid ciliate which has a barrel‐shaped body, about 22 somatic kineties and 16 transverse ciliary rows, three mini adoral organelles, and four 15 μm‐long caudal cilia. The sequence length and GC content of the SSU rRNA gene are 1,666 bp and 44.4%.     

The filter apparatus of Rana temporaria and Bufo bufo larvae (Amphibia,Anura)

Summary In larvae of Rana temporaria and Bufo bufo the location of filter apparatus within the larval organization, the arrangement of the morphological parts as branchial food trap, ventral velum, and filter rows, as well as their surface anatomy, are similar to that of other species of Orton's larval type IV. The means by which mucous with its entrapped food particles is transported from the filter rows to the esophagus is finally resolved. The dorsally positioned ciliary cushion extends far ventrally between the filter plates. From their contact with the filter rows, the cilia transport the mucous to Kratochwill's caudally positioned Flimmerrinne and from there to the esophagus. The original chordate principle of mucous entrapment and ciliary transport is thus retained by these anuran larvae. The only modification specific to the latter is the division into a ventral filter apparatus, whose epithelia serve for mucus entrapment, and a dorsal ciliary area.Six different types of cell may be distinguished ultrastructurally: (1) The ubiquitous squamous epithelium with merocrine extrusions; (2) the large supporting cells of the filter rows and of the ventral velum; (3) the ciliary cells of the ciliary cushion; (4) three different types of mucous producing secretory cells: (a) A type of cell similar to the goblet cell is found in the ciliary cushion (merocrine extrusion); (b) The secretory pits of the ventral velum and the secretory ridges have similar bottle-shaped merocrine secretory cells; (c) The merocrine apical cells of the filter rows are the final kind. It is evident that the ciliary cushion epithelium resembles that of both the manicotto glandulare of anuran larvae and the trachea and bronchus of Mammalia.Supported by the Deutsche Forschungsgemeinschaft-DFG     

Development of a unique eye: photoreceptors of the pelagic predator Atlanta peroni (Gastropoda, Heteropoda)

 The eyes of different larval stages and juveniles of Atlanta peroni are generally composed of a cornea, a lens and a retina. In juveniles a distinct pigmented shield is visible and an enormous humour is located behind the lens. Larvae have only two sensory cells and the photoreceptors are of the ciliary type. In juveniles a striking feature is the shape of the retina. It is ribbon-shaped and new sensory cells are present which are arranged in three rows. The photoreceptors are of the ciliary type as well. Contrary to the arrangement in larvae, the ciliary plasmalemma in juveniles forms numerous lamellar stacks. In accordance with the sensory cells the stacks are organized in three parallel rows. The lamellae of adjacent stacks within a row overlap each other. The latter unique feature has not yet been found in any other representative of the Heteropoda. These findings demonstrate that (a) the eyes are altered during the development from larvae into juveniles, (b) the larval sensory cells are reduced and replaced by new sensory cells in juveniles and (c) the eyes of juvenile and adult A. peroni are well adapted for their life as visual predators. Accepted: 20 February 1999