Somatic Infraciliature in the Haptorid Ciliate Homalozoon vermiculare (Kinetophragminophora, Gymnostomata) Ditransversalia N. Subcl. and Phylogenetic Implications

The ultrastructure of the cortex of Homalozoon vermiculare is described. The ventral side bears 13–15 iongitudinal kineties composed of monokinetids. On the dorsal surface, there are 3 kineties, 2 of which are composed of dikinetids in the anteriormost part of the cell. Consequently there exist 3 different kinds of kinetids within the somatic cortex: 1) The monokinetids on the ventral side are associated with a kinctodesmal fibril, 2 transverse microtubular ribbons and 7 postciliary microtubules in a double-row configuration; 2) The monokinetids on the dorsal side are very similar but they are associated with just 3 very 'short postciliary microtubules; 3) The posterior kinetosome of the dorsal dikinetids bears the same fibrillar associates as the dorsal monokinetid, but it lacks the second transverse ribbon. The anterior kinetosome of each pair is associated with a single postciliary' microtubule. The kinetid organization of Homalozoon is compared to that of other members of the Haptorida. Their phylogeny is discussed. A monophyleiic taxon within the litostomate ciliates is characterized by data on the somatic kinetids, and the new subclass Ditransversalia n. subcl. is constituted. The new subclass comprises the genera Balantidium, Bryophyllum, Enchelydium, Homalozoon, Isotricha, Lacrymaria, Lepidolrachelophyllum, Spathidium and Vestibulongum .     

THE ORGANIZATION AND EVOLUTION OF MICROTUBULAR ORGANELLES IN CILIATED PROTOZOA

(1) Ciliated protozoa are viewed as unicellular organisms structured in a hierarchy of organizational levels that include the macromolecular, suborganellar, unit organellar, organellar complex, and organellar system. (2) The ciliate cortex is divided into two major functional regions, the somatic region and the oral region. The fundamental component of the cortex is an organellar complex, the kinetid, whose organizing centre is the kinetosome with which are associated three fibrillar associates diagnostic of ciliates. These three fibrillar associates are the periodically striated kinetodesmal fibril and two microtubular ribbons, the transverse and postciliary ribbons. (3) Somatic and oral kinetids are found to be of three major types: monokinetids are composed of one kinetosome and its fibrillar associates; dikinetids are composed of two kinetosomes and their fibrillar associates; polykinetids are composed of more than two kinetosomes and their fibrillar associptes. (4) The mechanisms underlying kinetid function and development remain largely unexplored. Research into the molecular biology and ultrastructure, especially of mutant forms, should provide basic insights in the near future. (5) The conservation of kinetid structure across major phyla of organisms suggests that this subcellular structure should be useful in phylogenetic analysis despite the concepts of ‘chemical identity’ and ‘organic design’. (6) The evolutionary rate of change of oral features is greater than that of somatic features, probably due to developmental and ecological factors. Nevertheless both cortical regions are constrained by the phenomenon of structural conservatism; that is, the conservation of structure through time is inversely related to the level of biological organization. (7) Eight major groupings of ciliate species are recognized, based on ultrastruc-tural features of the cortex. Several examples of differences between these eight groups and the groups presently recognized are discussed.     

The Kinetid Structures of the Choreotrichous Ciliate Strobilidium velox and an Assessment of Its Evolutionary Lineage1

The ciliary (kinetid) structures of the ciliate Strobilidium velox have been examined with scanning and transmission electron microscopes. Somatic kineties consist of a linear row of kinetosomes (monokinetids) and short cilia lying partially beneath a thin fold of cytoplasm. The only fibrillar kinetid structure extending from the kinetosomes is a transverse ribbon of microtubules. The paroral membrane is a single-file polykinetid possessing a possible transverse ribbon of microtubules and a nematodesma. The oral polykinetids or membranelles are complex, with microtubules extending from both anterior and posterior rows of cilia. While the kinetid structures do not satisfy the criteria for the order Choreotrichida, they are similar to the tintinnids in several other relevant ways. Strobilidium velox is proposed to be an unusual ciliate that is an exception to the concept that somatic kinetids are conservative and reliable phylogenetic indicator structures.     

Ultrastructure of Prorodon (Ciliophora, Prostomatida) I. Somatic Cortex and Some Implications Concerning Kinetid Evolution In Prostomatid and Colpodid Ciliates

ABSTRACT. This study describes the ultrastructure of the somatic cortex of Prorodon aklitolophon and Prorodon teres. the meridionally arranged somatic kineties of both species can be separated into two parts: a short anterior part, which consists of a few somatic dikinetids (in which both kinetosomes are ciliated), and a longer posterior consisting of monokinetids. the somatic monokinetids are associated with a convergent postciliary microtubular ribbon, a transverse microtubular ribbon flatly inserted in front of the kinetosome, a short and steeply extending kinetodesmal fibre attached to kinetosomal triplet 5 and 7, and a desmose anterior to triplet 3. From this desmose, two to five prekinetosomal microtubules originate and extend anteriorly. the posterior kinetosome of the somatic dikinetids is associated with the same microfibrillar and microtubular structures as the somatic monokinetid, except that no prekinetosomal microtubules originate from the desmose. the anterior kinetosome has a single postciliary microtubule and a tangentially oriented transverse microtubular ribbon. the permanent collecting canals of the unique contractile vacuole system extend parallel and adjacent to the somatic kinetics of Prorodon . the collecting canals are supported by the prekinetosomal microtubules. A similarly organized contractile vacuole system is not yet known from any other ciliate group. One of the most surprising results of this investigation was finding a significant similarity between the somatic dikinetid pattern of Prorodon and the colpodid dikinetid pattern. A hypothesis is presented to illustrate the evolution of the somatic kinetid patterns in colpodid and prostomatid ciliates.     

Somatic kinetics or paroral membrane: which came first in ciliate evolution?

The ciliate species which lack a distinctive oral ciliature are considered to represent an ancestral state in ciliate evolution. Consequently, the somatic kineties composed of kinetids (kinetosomes plus cilia and associated fibrillar systems) are thought to be the ancestral ciliature. Results on stomatogenesis in 'gymnostomial ciliates' have shown that these ciliates probably have evolved from ancestors already equipped with an oral ciliature. Thus instead of the somatic, the oral ciliature may be regarded an ancestral. Based on these ideas a hypothesis on the evolution of the ciliate kinetome (assembly of all kinetids covering the body of a given ciliate) is presented. The first step in the evolution of the kinetome was the formation of a paroral membrane, a compound ciliary organelle lying along the right side of the oral area which historically but falsely is termed membrane. It was composed of kinetosomal dyads (dikinetids), derived from the kinetid of a dinoflagellate-like ancestor. From the beginning the paroral membrane was responsible for locomotion, ingestion and for the formation of a cytopharyngeal tube which the first ciliate probably had inherited from its flagellate ancestor. In the second step a first somatic kinety was formed from the right row of kinetosomes of the paroral membrane as a result of a longitudinal splitting of the paroral membrane and a subsequent migration of the forming kinety to the right into the somatic cortex. To increase the number of somatic kineties this process was repeated until the kinety produced first reached the left border of the oral area. By this step the locomotive and the nutritional functions were differentiated between somatic and oral structures. In a third step the adoral organelles were formed from somatic kinetids left of the oral area. The primitive type of stomatogenesis was a buccokinetal one derived from the mode the flagellate ancestor used to distribute its replicated kinetosomes to the offspring cells (buccokinetal means that at least parts of the oral anlage for the posterior offspring cell has its origin in the parental oral apparatus). This hypothesis, based on comparative studies on ciliate morphogenesis, is corroborated by molecular data from other laboratories.     

Morphology and Ecology of Siroloxophyllum utriculariae (Penard, 1922) N. G., N. Comb. (Ciliophora, Pleurostomatida) and an Improved Classification of Pleurostomatid Ciliates

ABSTRACT. The morphology and infraciliature of Siroloxophyllum utriculariae (Penard, 1922) n. g., n. comb. were studied in live cells, with the scanning and transmission electron microscope, as well as in specimens impregnated with protargol and silver carbonate. The new genus, Siroloxophyllum , belongs to the Loxophyllidae and has a specific combination of characters, viz. an oral bulge surrounding almost the entire cell, three perioral kineties, a single brush kinety, and a single right dorsolateral kinety. The ecology and faunistics of S. utriculariae are reviewed. It is a rare and infrequent predator preferring clean freshwaters. The somatic monokinetid of S. utriculariae has typical haptorid ultrastructure, including two transverse microtubular ribbons. The oral bulge is patterned string-like with riffles containing the transverse microtubular ribbons originating from the oral kinetids. Perioral kineties 1 and 2 consist of dikinetids having one basal body each ciliated; the nonciliated basal body is associated with a nematodesmal and a transverse microtubular ribbon. Perioral kinety 3 consists of ciliated monokinetids having a fine structure similar to the somatic kinetids; they form triads with the dikinetids from perioral kinety 2. The classification of pleurostomatid ciliates is reviewed. Two suborders (Amphileptina, Litonotina) and three families (Amphileptidae, Litonotidae, Loxophyllidae n. fam.) are recognized and defined.     

Kinetid structure in Choanocytes of Sponges (Heteroscleromorpha): Toward the ancestral Kinetid of Demospongiae

Every large clade of Eukarya has its own pattern of kinetid (flagellar apparatus) structure, which is stable and specific within the group, thereby being a good phylogenetic marker. The kinetid structure of sponge choanocytes might be a candidate for such marker for the phylogeny of Porifera. Kinetids of two heteroscleromorphs, Halichondria sp. (Suberitida) and Crellomima imparidens (Poecilosclerida), have been investigated here for the first time, and a reconstruction of the kinetid for each species is provided. The kinetids of both species comprise a flagellar kinetosome with a nuclear fibrillar root, a basal foot and satellite producing microtubules; a centriole is absent. Good resolution images reveal a new thin structure, the axial granule, in the flagellar transition zone which might be present in other sponges. The comparison of kinetids in investigated sponges revealed three types of kinetid in Demospongiae, and their distribution in the taxon has been shown on a molecular phylogenetic tree. Kinetid characters of the common ancestor of Demospongiae are discussed. J. Morphol. 277:925–934, 2016. © 2016 Wiley Periodicals, Inc.     

The fine structure of the paralabial organelle in the rumen ciliate Ophryoscolex purkinjei Stein, 1858

The paralabial organelle of the rumen ciliate Ophryoscolex purkinjei, located on the ventral side of the ciliophor, is a highly specialized part of the somatic cortex. It consists of alternating rows of short modified cilia and thin pellicular folds which form a ridge-like structure. The central "top kinety" is composed of monokinetids which bear cilia with 9 + 2 axonemes and 2 microns in length. The top kinety is accompanied by a comb-shaped fold on its distal side and by a broad wedge-shaped fold on its proximal side. To both sides there follow two or three lateral kineties made of dikinetids. The anterior kinetosome of each pair bears a clavate cilium, only 0.5-0.7 micron in length and with a 9 + 0 axoneme while the cilium of the posterior kinetosome is even shorter. Lateral folds with numerous microtubules cover these lateral kineties and rows of barren basal bodies. The fine structure of this supposed sensory organelle show a basic pattern in four other ophryoscolecids, and its increasing complexity parallels the suggested phylogenetic line of evolution of these ciliates.     

The Fine Structure of the Paralabial Organelle in the Rumen Ciliate Ophryoscolex purkinjei Stein, 1858

The paralabial organelle of the rumen ciliate Ophryoscolex purkinjei , located on the ventral side of the ciliophor, is a highly specialized part of the somatic cortex. It consists of alternating rows of short modified cilia and thin pellicular folds which form a ridge-like structure. The central "top kinety" is composed of monokinetids which bear cilia with 9 + 2 axonemes and 2 μm in length. The top kinety is accompanied by a comb-shaped fold on its distal side and by a broad wedge-shaped fold on its proximal side. To both sides there follow two or three lateral kineties made of dikinetids. The anterior kinetosome of each pair bears a clavate cilium, only 0.5–0.7 μm in length and with a 9 + 0 axoneme while the cilium of the posterior kinetosome is even shorter. Lateral folds with numerous microtubules cover these lateral kineties and rows of barren basal bodies. The fine structure of this supposed sensory organelle show a basic pattern in four other ophryoscolecids, and its increasing complexity parallels the suggested phylogenetic line of evolution of these ciliates.     

Ultrastructural aspects of the somatic and buccal infraciliature ofColeps amphacanthus Ehrenberg 1833

Summary Somatic and buccal infraciliature ofColeps amphacanthus Ehrenberg 1833 were studied by light and electron microscopy. The somatic kineties are composed of monokinetids and 2 dikinetids at the anterior end of each kinety. The monokinetids are associated with postciliary microtubules at triplet 9, a kinetodesmal fiber at triplet 5 and 7 and nearly radially arranged transverse microtubules at triplet 4. The associated fibrillar systems of the posterior kinetosome of the dikinetids are like those of the monokinetids. The anterior kinetosome is associated with transverse microtubules at triplet 4 and one or few postciliary microtubules at triplet 9. The anterior kinetosome bears only a short cilium.The oral ciliature is composed of a kinety of nearly circumorally arranged paroral dikinetids and 3 adoral organelles at the ventral left side of the oral opening. Nematodesmata arising from the oral ciliature form the major component of the cytopharyngeal apparatus which is lined by microtubular ribbons of postciliary origin. The buccal cavity is surrounded by oral papillae which often contain toxicysts.     

Redescription of Parasonderia vestita () comb. nov. (Ciliophora,Plagiopylida), with notes on its phylogeny based on SSU rRNA gene

During faunistic studies on psammophilic ciliates along the coast of Qingdao, China, a population of the poorly known species Parasonderia vestita (Kahl, 1928) comb. nov. (basionym: Plagiopyla vestita Kahl, 1928) was found and investigated using silver staining methods. These revealed that its oral ciliature is rather unique and composed of polykinetids comprising four parts: prebuccal polykineties, postbuccal polykineties, parabuccal polykineties, and intrabuccal polykineties. Both the pre- and the postbuccal polykineties are, as extensions of the somatic kineties, spiraling and extending from cell surface into buccal cavity. The somatic kineties are composed mainly of dikinetids with some monokinetids and trikinetids inserted. They are separated into two types: four circle kineties and 24–28 bipolar kineties. The circle kineties start from the side of oral region and connect with the opposite section at the end of the body. Phylogenetic analysis based on SSU rRNA gene sequence data indicates that P. vestita falls into the core part of the order Plagiopylida and groups with an environmental sequence with high support and forms a sister clade with Lechriopyla mystax, Plagiopyla frontata and P. nasuta.     

Morphogenesis of infraciliature in the entodiniomorphid ciliate Eudiplodinium maggii

The morphogenesis of ciliary zones has been studied in the ciliate Eudiplodinium maggi which has a vestigial somatic infraciliature consisting of subcortical barren kinetosomes. These replicate and migrate into the subequatorial ciliary anlagen of the dividing cells. The kinetid pattern of the barren kinetosomes changes sequentially to that of the ciliary zones. Postciliary and transverse microtubules are derived from basal and cortically directed microtubules while a dense spur coincides with the origin of the kinetodesma. All kinetics produce potential cytopharyngeal components. Nematodesmata originate in granular subkinetosomal dense plates, while two of the three types of cytopharyngeal ribbon are formed from tansverse microtubules. A spatial selectivity ensures that these components extend only from specific kinetids. It is concluded that 91) morphogenesis of the intricate cytoskeletal network of infraciliature involves a “pattern generator” in the vestigial somatic kinetids; and 92) entodiniomorph stomatogenesis in not truly apokinetal but is more like the telokinetal process of related ciliates.     

Balanion masanensis n. sp. (ciliophora: prostomatea) from the coastal waters of Korea: morphology and small subunit ribosomal RNA gene sequence

The planktonic ciliate Balanion masanensis n. sp. is described from living cells, from cells prepared by quantitative protargol staining (QPS), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM) preparations, and the sequence of its nuclear small subunit rDNA (SSU rDNA) is reported. This species is almost ovoid with a flattened anterior oral region when the cells are alive and stained. The flattened anterior region of a living cell often forms a dome with the perimeter receded in a groove, and this region is easily inflated or depressed. In SEM photos, a brosse of six to nine monokinetids (or possibly three to five dikinetids) was observed inside the circumoral dikinetids. In TEM photos, circumoral microtubular ribbons were observed below the oral cilia, which along with the oral flaps were 8-16 microm in length. The cytostome is a slight funnel-like central depression on the flattened anterior end. The morphological characteristics of this ciliate are identical to those of the genus Balanion (Order Prorodontida). The ranges (and mean+/-standard deviation) of cell length, cell width, and oral diameter of living cells (n=23-26) were 27-43 microm (35.2+/-4.6), 25-32 microm (28.6+/-2.3), and 25-30 microm (27.6+/-1.3), respectively, while those of the QPS-stained specimens (n=70) were 23-37 microm (30.6+/-3.5), 26-35 microm (30.7+/-2.2), and 26-33 microm (29.5+/-1.5), respectively. Forty-six to 55 somatic kineties (SKs) were equally spaced around the cell body and extended from the oral to near the posterior regions with 24-50 monokinetids per kinety. Each kinetid bore a cilium 2.8-7.2 microm long. A caudal cilium (ca 14 microm long) arose on the posterior end. The single ellipsoid macronucleus is 6.8-13.4 x 6.8-10.5 microm, accompanied by a single micronucleus (2.0-2.8 x 1.5-2.5 microm) visible only in QPS specimens. Because, the cell size, the number of SKs, and the number of kinetosomes per SK of this ciliate were much greater than those of Balanion comatum and Balanion planctonicum, the only two Balanion species so far reported, we have established B. masanensis n. sp. When properly aligned, the sequence of the SSU rDNA of B. masanensis n. sp. (GenBank Accession No. AM412525) was approximately 9% different from that of Coleps hirtus (Colepidae, Prorodontida) and 12% different from that of Prorodon teres (Prorodontidae, Prorodontida).     

Somatic and Oral Cortical Ultrastructure of the Plagiopylid Ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 19331

The somatic and oral cortical ultrastructure of the plagiopylid ciliates Lechriopyla mystax Lynch, 1930 and Plagiopyla minuta Powers, 1933 are described. The somatic kinetids are monokinetids with an anteriorly directed kinetodesmal fibril originating near triplets 5, 6, 7, a divergent postciliary ribbon originating at triplet 9, and an unusual transverse ribbon originating in dense material adjacent to triplets 1, 2, 3. The transverse ribbon extends beneath the right surface of the cortical ridge adjacent to the kinety from which it originated. The oral kinetids are also monokinetids from whose base rootlet fibrils extend inwards beneath the oral kineties and converge on the furcula. The striated band on these ciliates is composed of a series of short ridges orthogonal to the longitudinal axis of the band. The sides of the striated band groove are apparently supported by macrotubules. The cortical ultrastructure of the plagiopylids is discussed with reference both to the optical microscopy of the organisms and to the ultrastructure of other ciliate taxa. The plagiopylids are not clearly related to any other higher taxon and are placed incertae sedis in the Subphylum Cyrtophora Small, 1976.     

Redescription of Licnophora chattoni Villeneuve-Brachon, 1939 (Ciliophora, Spirotrichea), associated with Zyzzyzus warreni Calder, 1988 (Cnidaria, Hydrozoa)

Licnophora chattoni, found in association with Zyzzyzus warreni, a tubulariid hydroid epizoic in sponges from São Sebastião (SP, Brazil), is redescribed and illustrated using light and electron microscopy. The ciliate has a flexible, transparent body formed by an oval anterior region linked to the posterior basal disc via a flexible neck region. Numerous cortical granules are observed scattered throughout the body and densely packed along the neck. The adoral zone is formed by about 81 external and 24 infundibular paramembranelles. The paroral membrane, formed by a row of long cilia arranged in monokinetids, extends through a groove in the body to the adhesive disc. Two dorsal kinetids are present along the right body margin and around the neck. The adhesive disc (18 μm in diameter) lacks cilia in the area above the velum. The velum covers a row of dikinetids bearing long cilia and four dikineties, two or three of which are interrupted on the ventral surface. Nine to twelve macronuclear nodules connected by isthmuses are distributed in the cytoplasm, plus two nodules located in the adhesive disc and between those there is an ovate micronucleus.     

A Comparison of Three Populations of the Ciliate Genus, Paracichlidotherus Grim 1992. New Fish Hosts, and Biogeography; Revised Genus Description

ABSTRACT Two populations of Paracichlidotherus (Ciliophora. Nyctotheridae) were collected from the intestines of the Surgeon-fishes, Zebrasoma flavescens. and Acanthurus nigricans , from waters around the island of Guam. They were examined after Protargol staining and compared with the type population for 14 morphological characters. Right and left posterior short kinetal rows of very close kinetosomes and apparently fused cilia are described based on light microscopy and scanning electron microscopy. They often appear to be part of a second posterior suture system on each side. From transmission electron microscopic studies, kinetid structures of somatic dikinetids are described and compared for normal and fused cilia. They are similar, but in the latter, a fibril connects adjacent dikinetids. The buccal overture is V shaped at its posterior aspect. The genus is described more fully based on these characteristics.     

Cortical ultrastructure of Coleps bicuspis Noland, 1925 and the phylogeny of the class Prostomatea (Ciliophora)

The ultrastructure of Coleps bicuspis Noland, 1925 is described. The ciliate is a typical prostomate: the somatic kinetid is a monokinetid with a postciliary ribbon at triple 9, a kinetodesmal fibril originating near triplets 5, 6, 7 and an apparently radial transverse ribbon at triplet 4. The oral area is circular and has three brosse kineties associated with it. The brosse kineties are composed of dikinetids whose anterior kinetosome bears a tangential transverse ribbon and whose posterior kinetosome bears the fibrillar associates typical of a somatic monokinetid. The oral dikinetids are oriented parallel to the circumference of the oral cavity, which is surrounded by oral papillae and oral ridges. Pairs of nematodesmata, originating from oral dikinetid kinetosomes, are typically triangular in transection. A phylogeny of rhabdophoran ciliates is presented using the mixed parsimony algorithm and is discussed with reference to the systematic revisions of the phylum Ciliophora.     

Strombidinopsis jeokjo n. sp. (ciliophora: choreotrichida) from the coastal waters off western Korea: morphology and small subunit ribosomal DNA gene sequence

The planktonic ciliate Strombidinopsis jeokjo n. sp. is described from Quantitative Protargol-Stained (QPS) preparations, and the sequence of the small subunit rDNA (SSU rDNA) from cultured cells is reported. This species is ovoid and bluntly tapered towards the posterior. The ranges (and mean +/- standard deviation, n = 31) of cell length, cell width, and oral diameter of the QPS-stained specimens were 100-190 microm (149 +/- 25), 60-105 microm (79 +/- 13), and 55-80 microm (64 +/- 5), respectively. Fifteen to seventeen external oral polykinetids had oral membranelle cilia 20-35 microm long. Twenty-six to twenty-eight somatic kineties were equally spaced around the cell body and extended from the oral to the posterior regions with 23-44 dikinetids per kinety. Both kinetosomes of each kinetid bore cilia 3-7 microm long. Strombidinopsis jeokjo had two ovoid macronuclei of 25-38 microm x 12-15 microm. When properly aligned, the sequence of the SSU rDNA of S. jeokjo (GenBank Accession No. AJ628250) was approximately 2% different from that of an unidentified Strombidinopsis species (GenBank Accession No. AF399132-AF399135), the closest species in the SSU rDNA sequence.     

Description of Leptopharynx bromelicola n. sp. and characterization of the genus Leptopharynx Mermod, 1914 (Protista, Ciliophora)

Using morphological, morphometrical, and molecular methods, we describe Leptopharynx bromelicola n. sp. from tank bromeliads of Jamaica. We add significant data to Leptopharynx costatus and briefly characterize and review the genus Leptopharynx Mermod, 1914, including four new combinations. Nine species can be distinguished when applying the following main features and assuming that most or all have the ability to produce macrostomes (MAs): distinct ridges along the right side ciliary rows; special features like spines or wings on the body and of the oral basket; dikinetids present vs. absent from somatic kinety 3; number of kinetids in kinety 6 as two for the costatus pattern and ≥ five for the bromelicola pattern; beginning and structure of kinety 9 as either underneath or far underneath the adoral membranelles and with or without dikinetids; postoral complex present vs. absent; and preoral kinety 4 continuous vs. discontinuous. The 18S rDNA sequences of L. bromelicola and L. costatus differ by 1.7% and show that Leptopharynx forms a distinct clade within the Nassophorea Small & Lynn, 1981. Leptopharynx bromelicola is possibly closely related to Leptopharynx euglenivora Kahl, 1926, which, however, lacks the basket nose so typical of the former. Leptopharynx forms thin-walled, non-kinetosome-resorbing resting cysts maintaining most of the trophic organelles.