Paravortex karlingi sp. nov. from Cerastoderma edule L., in Britain

Paravortex karlingi sp. nov. collected from the intestine of the bivalve mollusc Cerastorderma edule from the Ythan Estuary, N. E. Scotland, and elsewhere, is distinguished from a closely related species, P. cardii, also occurring in this host, on the basis of differences in habitat occupied by the two species as well as behavioural and morphological differences. P. karlingi is smaller, has fewer embryos in the gravid adult and shows a different behaviour pattern when released from the host intestine. It is also negatively phototactic whereas P. cardii is initially positively phototactic, only later becoming negatively phototactic. The occurrence of both species in Britain is briefly described.Abbreviations bc brood capsules - c core of indigestible particles - ca common atrium - ch chamber - e eye - fa female atrium - fol fibre optic light - gc gut caecum - gp genital pore - j juvenile worm - m mouth - o ovary - oe oesophagus - p pharynx - pe penis - sg shell gland - sv seminal vesicle - t testis - u uterus - vg vitelline gland - w window     

Ultrastructure of multiciliated collar cells in the pilidium larva of Lineus bilineatus (Nemertini)

Summary The ultrastructure of the apical plate of the free-swimming pilidium larva of Lineus bilineatus (Renier 1804) is described with particular reference to the multiciliated collar cells. In the multiciliary collar cells there are several, up to 12, cilia surrounded by a collar of about 20 microvilli extending from the cells' apical surface. The cilia have the typical 9+2 axoneme arrangement and are equipped with striated caudal rootlets extending from the basal bodies. No accessary centriole or rostral rootlet were observed. Microvilli surrounding the cilia are joined in a cylindrical manner by a mucus-like substance to form a collar. In comparison with many sensory receptor cells built on a collar cell plan the multiciliary collar cells of the pilidium larva apical plate are rather simple and unspecialized. In other pilidium larvae monociliated collar cells are found in the apical plate. The possible function and phylogenetic implications of multiciliated collar cells in Nemertini are briefly discussed.List of Abbreviations a axoneme - b basal body - c cilia or flagella - d desmosome - G Golgi apparatus - m mitochondria - mf microfilaments - mu mucus - mv microvilli - n nucleus - nt neurotubules - pm plasma membrane - r rootlet - ri ribosomes - v secretory vesicles     

The ultrastructure of the eyes of<Emphasis Type="Italic"> Paravortex karlingi</Emphasis> (Plathelminthes,Rhabdocoela)

Both eyes of Paravortex karlingi belong to the rhabdomeric type. Each eye consists of a single pigment cup cell and three sensory cells. Modified mitochondria lie in three protrusions of the cup cell, and several of these mitochondria form giant mitochondrial derivates. The centres of the derivates include electron-dense substances. These modified structures may have lenticular functions. Furthermore, it is shown that giant mitochondrial derivates develop by fusion of smaller ones. Embryos have many small mitochondria in the developing eyes whereas the adult possesses less numerous, but giant forms. This circumstance leads to the assumption that all such lenticular structures within the rhabdocoels result from identical processes.     

Ultrastructure of the lycophora larva of Gyrocotyle urna (Cestoda,Gyrocotylidea)

Summary The fine structure of the ciliated epidermis, the body musculature and the neodermis anlage cells of the free-swimming lycophora larva of Gyrocotyle urna Grube and Wagener, 1852, is described. The epidermis is syncytial and covers the whole body including a caudal cavity into which the larval hooks protrude. It contains several types of vesicles, mitochondria and membrane whorls but lacks nuclei, dictyosomes and endoplasmic reticulum. The locomotory cilia exhibit single rostrally directed rootlets. The body musculature consists of about 25 longitudinal and 42 circular muscles. Their nuclei are located proximally to the contractile elements. The neodermis anlage cells show numerous dictyosomes, elaborated cisternae of endoplasmatic reticulum, typical coated vesicles and membranous bodies. Extrusions of these cells do not penetrate the epidermis but contact it by desmosoms.The evolution of epidermal and neodermal structures of Gyrocotyle and other parasitic Platyhelminthes is discussed. The probable consequences of the lack of some types of organelles in the epidermis of Neodermata are considered.Abbreviations bb basal body - bl basal lamina - ci locomotory cilia - Ce epidermis of the caudal cavity - cr ciliary rootlet - di dictyosome - Ep epidermis - er endoplasmic reticulum - Hm hook musculature - ld lipid droplet - Lh larval hook - Lm longitudinal musculature - mi mitochondria - mt microtubule - mv microvilli - mw membrane whorl - Ne neodermis anlage cell - nu nucleus - Re receptor - Rm circular musculature - ve vesicles     

Morphology,ultrastructure, and development of the parasitic larva and its surrounding trophamnion of Polypodium hydriforme Ussov (Coelenterata)

Summary The larval stage of Polypodium hydriforme is planuliform and parasitic inside the growing oocytes of acipenserid fishes. The larva has inverted germ layers and a special envelope, the trophamnion, surrounding it within the host oocyte. The trophamnion is a giant unicellular provisory structure derived from the second polar body and performing both protective and digestive functions, clearly a result of adaptation to parasitism. The trophamnion displays microvilli on its inner surface, and irregular protrusions anchoring it to the yolk on its outer surface. Its cytoplasm contains long nuclear fragments, ribosomes, mitochondria, microtubules, microfilaments, prominent Golgi bodies, primary lysosomes, and secondary lysosomes with partially digested inclusions.The cells of the larva proper are poorly differentiated. No muscular, glandular, neural, interstitial, or nematocyst-forming cells have been found. The entodermal (outer layer) cells bear flagella and contain rough endoplasmic reticulum; the ectodermal (inner layer) cells lack cilia and contain an apical layer of acid mucopolysaccharid granules. The cells of both layers contain mitochondria, microtubules, and Golgi bodies; their nuclei display large nucleoli with nucleolonema-like structure, decondensed chromatin, and some perichromatin granules. At their apical rims, the ectodermal cells form septate junctions; laterally, the cells of both layers form simple contacts and occasional interdigitations. The lateral surfaces of entodermal cells are strengthened by microtubules.     

Two ciliate sense receptors in the larva of Austramphilina elongata Johnston, 1931 (Amphilinidea)

Summary The ultrastructure of a uniciliate and a quadruciliate receptor in the anterior end of the larva of Austramphilina elongata is described on the basis of serial sections. The uniciliate receptor has numerous branched and interconnected microvilli at its surface, several rings forming the electron dense collar, and cross-striated rootlets diverging from the basal body of the cilium. The quadruciliate receptor has four short club-shaped sensory cilia and a single electron-dense collar.Abbreviations used in figures ec electron-dense collar - ep epidermis - m microvilli - nt neurotubules - pe process of electron-dense collar - r rootlet of cilium - sc sensory cilium - sd septate desmosome     

Sensory and secretory cells ofOphryotrocha puerilis (Polychaeta)

Summary As revealed by glyoxylic acid induced fluorescence, the protandric polychaeteOphryotrocha puerilis possesses different types of catecholaminergic primary bipolar sensory cells, the perikarya of which are located beneath the epidermis. About 20 of such receptors are situated in each segment but they are mostly found on antennae, palps, urites and parapodial cirri. The dendrites of these sensory neurones run to the cuticle and dilate to form receptive endings. Three different types of dendritic endings could be distinguished: (1) multiciliary receptors with 4–8 cilia and ciliary rootlets, (2) monociliary receptors with microvilli arranged like a funnel and electron-dense cuffs and (3) monociliary receptors of the collar-type with, constantly, ten microvilli surrounding one single central cilium. The latter type is also characterized by rootlet fragments. Dendrites and dilated receptive endings of all three types contain clear (putative secretory) vesicles, multivesicular bodies and mitochondria. Pharmacological treatment (dopamine, reserpine) does not affect the number of secretory vesicles of the receptor neurones. Extra vesicular storage of catecholamines is discussed. Secretory cells of unknown function containing large numbers of electron-dense vesicles are usually found in close association with sensory cells.Abbreviations CA catecholamines - DA dopamine - RE reserpine     

Occurrence and Ultrastructure of Collar Cells in the Stomach Gastrodermis of Polypodium hydriforme Ussov (Cnidaria)

The existence of collar cells lining the stomach gastrodermis in free-living Polypodium hydriforme and their ultrastructure are described. The collar cells are provided with a collar consisting of 9–10 microvilli which encircles a central flagellum and forms a flagellar pit. At the bottom of the pit around the basal part of the flagellum there is fine crystalline material which extends also in the spaces between the microvilli and keeps them straight. The flagellum has a typical axoneme (9+2), its basal body is located below the apical surface of the collar cell and continues into a striated rootlet. An accessory centriole is situated close to the upper part of the rootlet. The cell nucleus is located in the basal part of the cell. Prominent mitochondria with tubular cristae, Golgi cisternae and fragments of rough endoplasmic reticulum are situated mostly in the basal part of the cytoplasm. Discoidal vesicles are abundant in the apical cytoplasm. The collar cells are connected to each other by septate junctions and interdigitations. The ultrastructure of collar cells described here is discussed in comparison to that of other Cnidarians and in connection with the problem of Polypodium's systematic position.     

Comparative ultrastructure of the zoospores of nine species ofNeochloris (Chlorophyta)

Nine species ofNeochloris can be divided into three groups on the basis of comparative ultrastructure of the flagellar apparatus, the cell wall and the pyrenoid of zoospores. In Group I,N. wimmeri andN. minuta, zoospores are thin-walled, pyrenoids are penetrated by stromal channels, and the basal bodies are in the clockwise absolute orientation and connected by the distal and two proximal fibers. In Group II,N. aquatica, N. vigenis, N. terrestris, N. pyenoidosa, andN. pseudostigmatica, zoospores are naked or covered by fuzzy material, pyrenoids are covered by a continuous starch sheath or invaginated by cytoplasmic channels, basal bodies are directly opposed, the distal fiber is differentiated into a ribbed structure at the central region, a striated microtubule-associated component (SMAC) is continuous between opposite two-membered rootlets and connected to the ribbed structure, proximal ends of basal bodies are covered by partial caps, each two-membered rootlet and a basal body are connected by a striated fiber to the X-membered rootlet associated with the opposite basal body, and the basal bodies, when oriented at wide angles, are joined at their proximal ends by core extensions. In Group III,N. pseudoalveolaris andN. cohaerens, zoospores are naked, pyrenoids are traversed by parallel thylakoids, basal bodies are in the counterclockwise absolute orientation and overlapped, and each X-membered rootlet is connected to the end of the opposite basal body by a terminal cap. It is suggested that the genusChlorococcopsis gen. nov. be erected for the Group I species. Group II, which includes the type species,N. aquatica, should be preserved asNeochloris. The group appears to be closely related to the coenobial generaPediastrum, Hydrodictyon, andSorastrum, and to have affinities with the coenocytic generaSphaeroplea andAtractomorpha as well. It is also suggested that the genusParietochloris gen. nov. be erected in thePleurastrophyceae for the species of Group III.     

Fine structure of the cephalic sensory organ in veliger larvae of Littorina littorea, (L.) (Mesogastropoda,Littorinidae)

The cephalic sensory organ (CSO) in planktonic veliger larvae of Littorina littorea is situated dorsally between the velar lobes at the level of the shell aperture. It consists of ciliated primary sensory cells, adjacent accessory cells and supporting epithelial cells. Cell bodies of the ciliated cells originate in the cerebral commissure and their dendrites pass to the epidermis. The flask-shaped sensory cells are characterized by a deep invaginated lumen with modified cilia arising from the cell surface in the lumen. These cilia are presumed to be non-motile because they lack striated rootlets and show a modified microtubular pattern (6 + 2, 7 + 2 and 8 + 2). The adjacent accessory cells never possess an invaginated lumen; occasionally cilia and branched microvilli arise from the apical surface. These cells may be sensory, but there is no obvious direct connection with the nervous system. The supporting epithelial cells are part of the epidermis and flank the apical necks of the sensory and accessory cells. Morphological evidence suggests that the CSO may function in chemoreception related to substrate selection at settlement, feeding or other behaviour.     

The absolute configuration of the flagellar apparatus in zoospores from two species ofLaminariales (Phaeophyceae

Summary We examined the zoospores produced by the unilocular sporangia ofLaminaria digitata (L.) Lamour. andNereocystis luetkeana Post. & Rupr. by serial sectioning to determine the absolute configuration of their flagellar apparatuses. The basal bodies, which are interconnected by three striated bands, lie parallel to the ventral face of the zoospore, and the posterior basal body always is found to the right of the anterior basal body when the cell is viewed from the ventral face, anterior end up. The four rootlets associated with the basal bodies include a major anterior rootlet of about seven microtubules extending from the anterior basal body along the ventral face towards the apex, a five-membered bypassing rootlet that passes ventral to the basal bodies and is connected to the posterior basal body by a posterior fibrous band, and two short rootlets having a single member each, the minor anterior and posterior rootlets. We consider the configuration observed here to be typical of most phaeophycean motile cells. The flagellar apparatus features suggest a considerable phylogenetic difference between thePhaeophyceae and other classes of chlorophyll c-containing organisms.     

Epidermal ultrastructure of the adult parasitic phase female and encapsulated larva of Kronborgia isopodicola (Platyhelminthes, Fecampiidae): Phylogenetic implications

The parasitic phase female K. isopodicola possesses a ciliated epidermis of polyhedral cells. Adjacent lateral plasma membranes are separated at intervals creating intercellular spaces. Epidermal cilia are anchored by a horizontal rootlet, opposite which a spur projects from the basal body, and a narrow vertical rootlet. The cytoplasm contains coated vesicles, and coated pits lie between microvilli. Large granular and vesicular bodies (rhabdoids) are scattered through the epidermal epithelium; in the epidermis of the encapsulated larva, granular rhabdoids are densely packed and slender, more compact bodies also occur. The compact, granular and vesicular bodies are probably morphological variants of the same epidermal structures, suggested to undergo sequential changes accomplished in later stages by lysosomal activity. Morphologically similar epidermal bodies are found in triclads. They are also characteristic of the parasitic genus Urastoma, which shares other ultrastructural features with K. isopodicola. The Neodermata may have arisen from parasitic turbellarian forms, at a more “primitive” level of organization than ancestors of the contemporary Rhabdocoela.     

Epidermal ciliary ultrastructure of adult and larval sipunculids (Sipunculida)

The ultrastructure of the ciliary apparatus of multiciliated epidermal cells in larval and adult sipunculids is described and the phylogenetic implications discussed. The pelagosphera of Apionsoma misakianum has a dense cover of epidermal cilia on the head region. The cilia have a long, narrow distal part and two long ciliary rootlets, one rostrally and one vertically orientated. The adult Phascolion strombus has cilia on the nuchal organ and on the oral side of the tentacles. These cilia have a narrow distal part as in the A. misakianum larva, but the ciliary rootlets have a different structure. The first rootlet on the anterior face of the basal body is very short and small. The second, vertically orientated rootlet is long and relatively thick. The two ciliary rootlets present in the larval A. misakianum are similar to the basal metazoan type of ciliary apparatus of epidermal multiciliated cells and thus likely represent the plesiomorphic state. The minute first rootlet in the adult P. strombus is viewed as a consequence of a secondary reduction. No possible synapomorphic character with the phylogenetically troublesome Xenoturbella was found.     

Basal bodies in the odontoblasts of the limpet,Patella coerulea L. (Gastropoda)

Summary The odontoblasts in the long radular gland of Patella coerulea L. are arranged in a terminal position; therefore newly formed teeth already have an upright position. The long and slender odontoblasts have only one to three lengthy and ramifying apical microvilli. Between these pinnate microvilli a fine filamentous material appears which probably corresponds to chitin microfibrils. Therefore, the pattern of chitin microfibrils seems to depend on the arrangement of odontoblasts' microvilli. For the first time, basal bodies were found in the apical part of odontoblasts which led to the assumption that the radular gland originally might have been a mucous gland, the secretion of which was transported by cilia.     

Organization of the ciliary basal apparatus in embryonic cells of the sea urchin,Lytechinus pictus

Summary The basal apparatus of embryonic cells of the sea urchin Lytechinus pictus was examined by transmission electron microscopy and compared with the basal apparatus of other metazoan cells. The basal apparatus in these cells is associated with a specialized region of the apical cell surface that is encircled by a ring of microvilli. The basal apparatus includes several features that are common to all ciliated cells, including a basal body, basal foot, basal foot cap, and striated rootlet. However, a component not seen in the basal apparatus of other species has been observed in these cells. This structure is continuous with the striated rootlet, and its ultrastructure indicates that it is composed of the same components as the rootlet. This structure extends from the junction of the basal body and striated rootlet to the cortical region that surrounds the basal body. Based on its morphology and position, this structure is referred to as a striated side-arm. The striated side-arm is always aligned in the plane of the basal foot. Thus, both of these structures extend from the basal body in the plane of the effective stroke. It is suggested that the striated side-arm serves to stabilize the basal apparatus against force exerted by the cilium.     

Comparative morphology of the epidermis of seven species of polyclad flatworms (Platyhelminthes: Rhabditophora)

The ultrastructure of the epidermis of seven species of polyclad flatworms (Phaenocelis medvedica, Phaenocelis peleca, Pleioplana atomata, Boninia divae, Pericelis orbicularis, Enchiridium periommatum, and Cycloporus variegatus) representing six families is described. In all seven species, the epidermis consists of a single layer of columnar cells that rests on a bipartite basement membrane. Epithelial cell surfaces are covered by numerous microvilli and cilia. Cilia contain microtubules arranged in the 9 + 2 pattern, and from their basal bodies two striated rootlets arise, a rostrally directed one running parallel to the apical cell membrane, and a vertical one at a right angle to the first rootlet. Numerous epithelosomes and mitochondria occupy the apical parts of the cells. The basal part of the cells is highly folded, forming a cell web that connects to the basement membrane. The basement membrane consists of a thin basal lamina and a thick, multilayered reticular lamina. The number of layers in the reticular lamina varies among the different species and appears to be correlated with body size. Numerous canals containing either pigment granules or nervous processes perforate the basement membrane. We have identified four different types of glands: rhabdite glands, rhabdoid glands, mucoid glands containing vacuoles filled with flocculent material, and mucoid glands resembling thread cells of hagfish slime glands. The latter have been found only in P. orbicularis. Pigment cells were found in all species examined with the exception of C. variegatus, which takes its coloration from its ascidian prey. Our results further support the unique taxonomic status of Boniniidae.     

Transformation of the flagella and associated flagellar components during cell division in the coccolithophoridPleurochrysis carterae

Summary Immunofluorescence microscopy, conventional and high voltage transmission electron microscopy were used to describe changes in the flagellar apparatus during cell division in the motile, coccolithbearing cells ofPleurochrysis carterae (Braarud and Fagerlund) Christensen. New basal bodies appear alongside the parental basal bodies before mitosis and at prophase the large microtubular (crystalline) roots disassemble as their component microtubules migrate to the future spindle poles. By prometaphase the crystalline roots have disappeared; the flagellar axonemes shorten and the two pairs of basal bodies (each consisting of one parental and one daughter basal body) separate so that each pair is distal to a spindle pole. By late prometaphase the pairs of basal bodies bear diminutive flagellar roots for the future daughter cells. The long flagellum of each daughter cell is derived from the parental basal bodies; thus, the basal body that produces a short flagellum in the parent produces a long flagellum in the daughter cell. We conclude that each basal body in these cells is inherently identical but that a first generation basal body generates a short flagellum and in succeeding generations it produces a long flagellum. At metaphase a fibrous band connecting the basal bodies appears and the roots and basal bodies reorient to their interphase configuration. By telophase the crystalline roots have begun to reform and the rootlet microtubules have assumed their interphase appearance by early cytokinesis.Abbreviations CR1, CR2 crystalline roots 1 and 2 - CT cytoplasmic tongue microtubules - DIC differential interference contrast light microscopy - H haptonema - HVEM high voltage transmission electron microscopy - IMF immunofluorescence microscopy - L left flagellum/basal body - M metaphase plate - MT microtubule - N nucleus - R right flagellum/basal body - R1, R2, R3 roots 1, 2, and 3 - TEM transmission electron microscopy     

Comparative ultrastructural studies of the epidermis, sperm and nerve fibres of Cleistogamia longicirrus and Seritia stichopi (RhabdocoeIa, UmagiIIidae)

The epidermis of Cleistogamia longicirrus consists of columnar, interdigitated cells with apical mitochondria, short microvilli and cilia which have a single horizontal rootlet anchored in the adjacent cytoplasm by transverse bars and a thin side branch. Cells are held together by desmosomes and intermediary junctions. Epidermal cilia have a terminal, electron dense rod between the central microtubules and doublet 1 and a terminal plate; doublets 1 and 6–9 lose one of their microtubules and gradually all doublets lose one microtubule and peripheral doublets disappear. Spermatozoa have a single closed peripheral row of microtubules, numerous electron dense granules and mitochondria and axonemes are of the 9 +"1" type and free for most of their length. Nerve fibres have microtubules and some nerve fibres are surrounded by lamellae and have invaginations of the fibre wall. The epidermis of Seritia stichopi resembles that of Cleistogamia , but cilia have a single horizontal rootlet anchored by transverse bars in the cytoplasm, without a side branch. Spermatozoa also are similar to those of Cleistogamia . Certain ultrastructural similarities between some Umagillidae and Neodermata are apparently due to convergent evolution and do not allow the conclusion that Umagillidae and Neodermata are particularly closely related.     

Quantitative analysis of ultrastructural changes during zygotic and somatic embryogenesis in pearl millet (Pennisetum glaucum [L.] R. Br.)

Ultrastructural changes during zygotic and somatic embryogenesis in pearl millet (Pennisetum glaucum [L.] R. Br.) were quantified using morphometric techniques. The total area per cell profile and the cell volume percentage of the whole cell, endoplasmic reticulum (ER), Golgi bodies, mitochondria, nuclei, lipids, plastids, starch grains and vacuoles were measured and comparisons made between three zygotic and three somatic embryo developmental stages. All measurements were taken from scutellar or scutellar-derived cells. Zygotic embryogenesis was characterized by increases in cell size, lipids, plastids, starch, Golgi bodies, mitochondria and ER. Somatic embryogenesis was characterized by two phases of cell development: (1) the dedifferentiation of scutellar cells involving a reduction in cell and vacuole size and an increase in cell activity during somatic proembryoid formation and (2) the development of somatic embryos in which most cell organelle quantities returned to values found in late coleoptile or mature predesiccation zygotic stages. In summary, although their developmental pathways differed, the scutella of somatic embryos displayed cellular variations which were within the ranges observed for later stages of zygotic embryogenesis.     

Sensory cells in the head skin of pond snails

Summary Several types of receptor endings were identified with scanning electron microscopy and silver-impregnation techniques in the skin of the tentacles, lips, dorsal surface of the head and mouth region of the pond snails Lymnaea stagnalis and Vivipara viviparus. Sensory endings at the tips of dendrites of primary receptor neurones, scattered below the epithelium, differ in structure, i.e., the endings exposed to the surface of the skin possess different proportions of cilia and microvilli, which vary in number, length, and packing. Type-I endings have microvilli and a few (1–5) cilia, 5–12 m in length. Type-2 endings have abundant (20–40), interwoven long (9–12 m) cilia and random microvilli. Type-3 endings show typical packing of 10–25 cilia in the form of bundles or brushes. They may be composed either of long (9–18 m) or short (2–7 m) cilia, or of both long and short ones. Microvilli here are absent. Type-4 endings have only microvilli. Two other types of skin receptors do not extend their sensory endings to the surface and can be indentified only in silver-stained preparations. Type-5 endings are branching dendrites of skin receptors cells that terminate among epithelial cells. In type-6, the sensory endings also terminate among epithelial cells but their cell bodies are located outside of the skin. In both species all skin regions examined possess the receptors of all six types differing only in their relative proportion. Possible functional roles of different receptors are discussed.