Patterns of comb row development in young and adult stages of the ctenophores Mnemiopsis leidyi and Pleurobrachia pileus

The development of comb rows in larval and adult Mnemiopsis leidyi and adult Pleurobrachia pileus is compared to regeneration of comb plates in these ctenophores. Late gastrula embryos and recently hatched cydippid larvae of Mnemiopsis have five comb plates in subsagittal rows and six comb plates in subtentacular rows. Subsagittal rows develop a new (sixth) comb plate and both types of rows add plates at similar rates until larvae reach the transition to the lobate form at ～5 mm size. New plate formation then accelerates in subsagittal rows that later extend on the growing oral lobes to become twice the length of subtentacular rows. Interplate ciliated grooves (ICGs) develop in an aboral‐oral direction along comb rows, but ICG formation itself proceeds from oral to aboral between plates. New comb plates in Mnemiopsis larvae are added at both aboral and oral ends of rows. At aboral ends, new plates arise as during regeneration: local widening of a ciliated groove followed by formation of a short split plate that grows longer and wider and joins into a common plate. At oral ends, new plates arise as a single tuft of cilia before an ICG appears. Adult Mnemiopsis continue to make new plates at both ends of rows. The frequency of new aboral plate formation varies in the eight rows of an animal and seems unrelated to body size. In Pleurobrachia that lack ICGs, new comb plates at aboral ends arise between the first and second plates as a single small nonsplit plate, located either on the row midline or off‐axis toward the subtentacular plane. As the new (now second) plate grows larger, its distance from the first and third plates increases. Size of the new second plate varies within the eight rows of the same animal, indicating asynchronous formation of plates as in Mnemiopsis. New oral plates arise as in Mnemiopsis. The different modes of comb plate formation in Mnemiopsis versus Pleurobrachia are accounted for by differences in mesogleal firmness and mechanisms of ciliary coordination. In both cases, the body of a growing ctenophore is supplied with additional comb plates centripetally from opposite ends of the comb rows. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.     

Cilia and the life of ctenophores

Ctenophores, or comb jellies, are a distinct phylum of marine zooplankton with eight meridional rows of giant locomotory comb plates. Comb plates are the largest ciliary structures known, and provide unique experimental advantages for investigating the biology of cilia. Here, I review published and unpublished work on how ctenophores exploit both motile and sensory functions of cilia for much of their behavior. The long‐standing problem of ciliary coordination has been elucidated by experiments on a variety of ctenophores. The statocyst of ctenophores is an example of how mechanosensory properties of motile cilia orient animals to the direction of gravity. Excitation or inhibition of comb row beating provides adaptive locomotory responses, and global reversal of beat direction causes escape swimming. The diverse types of prey and feeding mechanisms of ctenophores are related to radiation in body form and morphology. The cydippid Pleurobrachia catches copepods on tentacles and undergoes unilateral ciliary reversal to sweep prey into its mouth. Mnemiopsis uses broad muscular lobes and ciliated auricles to capture and ingest prey. Beroë has giant smooth muscles and toothed macrocilia to rapidly engulf or bite through ctenophore prey, and uses reversible tissue adhesion to keep its mouth closed while swimming. Ciliary motor responses are calcium‐dependent, triggered by voltage‐activated calcium channels located along the length (reversed beating) or at the base (activation of beating) of ciliary membranes. Ciliary and muscular responses to stimuli are regulated by epithelial and mesogleal nerve nets with ultrastructurally identifiable synapses onto effector cells. Post‐embryonic patterns of comb row development in larval and adult stages are described and compared with regeneration of comb plates after surgical removal. Truly, cilia and ctenophores, like love and marriage, go together like a horse and carriage.     

Primary inhibition: a mechanism for sudden stoppage of metachrony in ctenophores

The ctenophores Beroë cucumis and Pleurobrachia pileus exhibit rapid stoppage of comb plate beating, without accompanying muscular contraction, in response to an orally applied mechanical stimulus. This phenomenon, termed ‘primary inhibition’ by Göthlin, was re-examined by high-speed video microscopy and intracellular recording. The most remarkable features of this event were that (1) inhibition was associated with only one or two comb plates in the row, (2) inhibition occurred nearly anywhere in the ciliary beat cycle, (3) the inhibited plate acted as a mechanical blockade to the propagation of additional metachronal waves, and (4) a single depolarizing post-synaptic potential occurred nearly simultaneously with comb plate inhibition. B. cucumis and P. pileus have evolved a neurally controlled behavior to rapidly stop comb plate metachrony.

     

Visualization of calcium transients controlling orientation of ciliary beat

To image changes in intraciliary Ca controlling ciliary motility, we microinjected Ca Green dextran, a visible wavelength fluorescent Ca indicator, into eggs or two cell stages of the ctenophore Mnemiopsis leidyi. The embryos developed normally into free-swimming, approximately 0.5 mm cydippid larvae with cells and ciliary comb plates (approximately 100 microns long) loaded with the dye. Comb plates of larvae, like those of adult ctenophores, undergo spontaneous or electrically stimulated reversal of beat direction, triggered by Ca influx through voltage-sensitive Ca channels. Comb plates of larvae loaded with Ca Green dextran emit spontaneous or electrically stimulated fluorescent flashes along the entire length of their cilia, correlated with ciliary reversal. Fluorescence intensity peaks rapidly (34-50 ms), then slowly falls to resting level in approximately 1 s. Electrically stimulated Ca Green emissions often increase in steps to a maximum value near the end of the stimulus pulse train, and slowly decline in 1-2 s. In both spontaneous and electrically stimulated flashes, measurements at multiple sites along a single comb plate show that Ca Green fluorescence rises within 17 ms (1 video field) and to a similar relative extent above resting level from base to tip of the cilia. The decline of fluorescence intensity also begins simultaneously and proceeds at similar rates along the ciliary length. Ca-free sea water reversibly abolishes spontaneous and electrically stimulated Ca Green ciliary emissions as well as reversed beating. Calculations of Ca diffusion from the ciliary base show that Ca must enter the comb plate along the entire length of the ciliary membranes. The voltage-dependent Ca channels mediating changes in beat direction are therefore distributed over the length of the comb plate cilia. The observed rapid and virtually instantaneous Ca signal throughout the intraciliary space may be necessary for reprogramming the pattern of dynein activity responsible for reorientation of the ciliary beat cycle.     

Calcium control of ciliary reversal in ionophore-treated and ATP- reactivated comb plates of ctenophores

Previous work showed that ctenophore larvae swim backwards in high-KCl seawater, due to a 180 degrees reversal in the direction of effective stroke of their ciliary comb plates (Tamm, S. L., and S. Tamm, 1981, J. Cell Biol., 89: 495-509). Ion substitution and blocking experiments indicated that this response is Ca2+ dependent, but comb plate cells are innervated and presumably under nervous control. To determine whether Ca2+ is directly involved in activating the ciliary reversal mechanism and/or is required for synaptic triggering of the response, we (a) determined the effects of ionophore {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 and Ca2+ on the beat direction of isolated nerve-free comb plates dissociated from larvae by hypotonic, divalent cation-free medium, and (b) used permeabilized ATP- reactivated models of comb plates to test motile responses to known concentrations of free Ca2+. We found that 5 microM {"type":"entrez-nucleotide","attrs":{"text":"A23187","term_id":"833253","term_text":"A23187"}}A23187 and 10 mM Ca2+ induced dissociated comb plate cells to beat in the reverse direction and to swim counterclockwise in circular paths instead of in the normal clockwise direction. Detergent/glycerol-extracted comb plates beat actively in the presence of ATP, and reactivation was reversibly inhibited by micromolar concentrations of vanadate. Free Ca2+ concentrations greater than 10(-6)M caused reversal in direction of the effective stroke but no significant increase in beat frequency. These results show that ciliary reversal in ctenophores, like that in protozoa, is activated by an increase in intracellular free Ca2+ ions. This allows the unique experimental advantages of ctenophore comb plate cilia to be used for future studies on the site and mechanism of action of Ca2+ in the regulation of ciliary motion.     

The ctenophore Mnemiopsis in native and exotic habitats: U.S. estuaries versus the Black Sea basin

The native habitats of the ctenophore, Mnemiopsis, are temperate to subtropical estuaries along the Atlantic coast of North and South America, where it is found in an extremely wide range of environmental conditions (winter low and summer high temperatures of 2 and 32 °C, respectively, and salinities of <2–38). In the early 1980s, it was accidentally introduced to the Black Sea, where it flourished and expanded into the Azov, Marmara, Mediterranean and Caspian Seas. We compile data showing that Mnemiopsis has high potentials of growth, reproduction and feeding that enable this species to be a predominant zooplanktivore in a wide variety of habitats; review the population distributions and dynamics of Mnemiopsis in U.S. waters and in the Black Sea region; and examine the effects of temperature and salinity, zooplankton availability and predator abundance on Mnemiopsis population size in both regions, and the effects of Mnemiopsis on zooplankton, ichthyoplankton and fish populations, focusing on Chesapeake Bay and the Black Sea. In both regions, Mnemiopsis populations are restricted by low winter temperatures (<2 °C). In native habitats, predators of Mnemiopsis often limit their populations, and zooplanktivorous fish are abundant and may compete with the ctenophores for food. By contrast, in the Black Sea region, no obvious predators of Mnemiopsis were present during the decade following introduction when the ctenophore populations flourished. Additionally, zooplanktivorous fish populations had been severely reduced by over fishing prior to the ctenophore outbreak. Thus, small populations of potential predators and competitors for food enabled Mnemiopsis populations to swell in the new habitats. In Chesapeake Bay, Mnemiopsis consumes substantial proportions of zooplankton daily, but may only noticeably reduce zooplankton populations when predators of Mnemiopsis are uncommon. Mnemiopsis also is an important predator of fish eggs in both locations. In the Black Sea, reductions in zooplankton, ichthyoplankton and zooplanktivorous fish populations have been attributed to Mnemiopsis. We conclude that the enormous impact of Mnemiopsis on the Black Sea ecosystem occurred because of the shortage of predators and competitors in the late 1980s and early 1990s. The appearance of the ctenophore, Beroe ovata, may promote the recovery of the Black Sea ecosystem from the effects of the Mnemiopsis invasion.     

Ciliary reversal without rotation of axonemal structures in ctenophore comb plates

We have used a newly discovered reversal response of ctenophore comb plates to investigate the structural mechanisms controlling the direction of ciliary bending. High K+ concentrations cause cydippid larvae of the ctenophore Pleurobrachia to swim backward. High-speed cine films of backward-swimming animals show a 180 degree reversal in beat direction of the comb plates. Ion substitution and blocking experiments with artificial seawaters demonstrate that ciliary reversal is a Ca++-dependent response. Comb plate cilia possess unique morphological markers for numbering specific outer-doublet microtubules and identifying the sidedness of the central pair. Comb plates of forward- and backward-swimming ctenophores were frozen in different stages of the beat cycle by an "instantaneous fixation" method. Analysis of transverse and longitudinal sections of instantaneously fixed cilia showed that the assembly of outer doublets does not twist during ciliary reversal. This directly confirms the existence of radial switching mechanism regulating the sequence of active sliding on opposite sides of the axoneme. We also found that the axis of the central pair always remains perpendicular to the plane of bending; more importantly, the ultrastructural marker showed that the central pair does not rotate during a 180 degree reversal in beat direction. Thus, the orientation of the central pair does not control the direction of ciliary bending (i.e., the pattern of active sliding around the axoneme). We discuss the validity of this finding for three-dimensional as well as two-dimensional ciliary beat cycles and conclude that models of central-pair function based on correlative data alone must now be re-examined in light of these new findings on causal relations.     

Eoandromeda and the origin of Ctenophora

The Ediacaran fossil Eoandromeda octobrachiata had a high conical body with eight arms in helicospiral arrangement along the flanks. The arms carried transverse bands proposed to be homologous to ctenophore ctenes (comb plates). Eoandromeda is interpreted as an early stem‐group ctenophore, characterized by the synapomorphies ctenes, comb rows, and octoradial symmetry but lacking crown‐group synapomorphies such as tentacles, statoliths, polar fields, and biradial symmetry. It probably had a pelagic mode of life. The early appearance in the fossil record of octoradial ctenophores is most consistent with the Planulozoa hypothesis (Ctenophora is the sister group of Cnidaria + Bilateria) of metazoan phylogeny.     

Novel bridge of axon-like processes of epithelial cells in the aboral sense organ of ctenophores

We describe by light and electron microscopy a novel structure in the aboral sense organ (apical organ) of cydippid (Pleurobrachia) and lobate (Mnemiopsis) ctenophores. An elevated bundle of long, thin, microtubule-filled processes arises from the apical ends of two groups of epithelial cells located on opposite sides of the apical organ along the tentacular plane of the body. This bundle of axon-like processes arches over the epithelial floor like a bridge, with branches at both ends running toward opposing pairs of ciliary balancers that are motile pacemakers for the rows of locomotory ciliary comb plates. The bridge in Pleurobrachia is approximately 40 microm long and 3-4 microm wide and consists of approximately 60 closely packed processes, 0.2-0.8 microm thick, containing vesicles and numerous microtubules running parallel to their long axes. There are approximately 30 epithelial cells in each of the two groups giving rise to the bridge and each cell forms a single process, so roughly half of the processes in the bridge must originate from cells on one side and diverge into branches to a pair of balancers on the opposite side of the apical organ. The 150-200 cilia in each balancer arise from morphologically complex cellular projections with asymmetric lateral extensions directed towards a fork of the bridge. Presynaptic triad structures and vesicles are found in this region but clear examples of synaptic contacts between bridge processes and balancer cells have not yet been traced. Cydippid larvae of Mnemiopsis have a conspicuous bridge along the tentacular plane of the apical organ. Beroid ctenophores that lack tentacles at all stages do not have a bridge. We discuss the possibility that the bridge is an electrical conduction pathway to balancers that coordinates tentacle-evoked swimming responses of ctenophores, such as global ciliary excitation.     

Trichodina ctenophorii N. Sp., a Novel Symbiont of Ctenophores of the Northern Coast of the Gulf of Mexico

ABSTRACT. Peritrich ciliates of the genus Trichodina are internal or external symbionts of invertebrate and vertebrate hosts. We describe here Trichodina ctenophorii n. sp., a symbiont of Mnemiopsis mccraydii and Beroë ovata (Phylum Ctenophora). The morphology of fixed and living specimens is revealed by silver impregnation, scanning electron microscopy, and differential interference microscopy. Distinguishing features of Trichodina ctenophorii include a denticular morphology composed of falcate, blunt-tipped blades, and long, straight thorns, with five pins per denticle. Trichodina ctenophorii is found only on the comb plates of these ctenophores. To the best of our knowledge, this is the first report of a trichodinid from the Gulf of Mexico and the first associated with ctenophores.     

Gap junctions suggest epithelial conduction within the comb plates of the ctenophore Pleurobrachia bachei

Intercellular gap junctions occur between the ciliated cells that make up the comb plates of the ctenophore Pleurobrachia. Similar junctions are found within the ciliated grooves which run from the apical organ to the first plate of each comb row, as well as throughout the endoderm of the meridional canals. Gap junctions were not found in the ectodermal tissue between the comb rows. The distribution of junctions suggests that excitation conduction within the ciliated grooves, comb plates and meridional canal endoderm may be epithelial.     

Protistan epibionts of the ctenophore Mnemiopsis mccradyi Mayer

Mnemiopsis mccradyi, a common coastal ctenophore, was observed to bear two distinct, exclusive assemblages of protistan epibionts. The mobiline peritrich, Trichodina ctenophorii (Estes et al., 1997), and small Flabellula-like gymnamoebae inhabited only the surface of the comb plates. By contrast, small Vexillifera-like gymnamoebae and large Protoodinium-like dinoflagellates were found on the ectoderm. The relationship of the epimicrobial protists with their host varied from possible mutualism (vexilliferids) to commensalism (trichodinids) to parasitism (flabellulids and protoodinids). Trichodinids may benefit from comb plate attachment by enhanced food capture. Although they did not obviously impair comb plate beating, they did distort the surface and appear to produce fissures in the comb plate surface, which could provide inroads for more severe comb plate damage by amoebae. By contrast, when flabellulid amoebae occurred in very high surface densities (up to 5000 mm^–2), they clearly damaged comb plates by eroding the surface. Where flabellulid pseudopodia invaded the comb plate, we observed local degradation of comb plate cilia, as evidenced by central pair disorientation and plasma membrane perturbation and overt phagocytosis of comb plate cilia. Ectodermal vexilliferids, which occurred at much lower densities, did not appear to have any degradative impact on the ctenophore. By contrast, clusters of ectodermal protoodinids were found in localized depressions most likely caused by invasive phagocytosis. The impact of the protistan assemblages on ctenophore populations is unclear, but under conditions of severe infestation they might depress ctenophore population density.     

THE RECLASSIFICATION OF PFIESTERIA SHUMWAYAE (DINOPHYCEAE): PSEUDOPFIESTERIA,GEN. NOV.1

Pfiesteria shumwayae Glasgow et Burkholder is assigned to a new genus Pseudopfiesteria gen. nov. Plate tabulation differences between Pfiesteria and Pseudopfiesteria gen. nov. as well as a maximum likelihood phylogenetic analysis based on rDNA sequence data warrant creation of this new genus. The Kofoidian thecal plate formula for the new genus is Po, cp, X, 4′, 1a, 6′′, 6c, PC, 5+s, 5′′′, 0p, 2′′′′. In addition to having six precingular plates, P. shumwayae comb. nov. also has a distinctive diamond or rectangular‐shaped anterior intercalary plate. Both Pfiesteria and Pseudopfiesteria gen. nov. are reassigned to the order Peridiniales based on an apical pore complex (APC) with a canal (X) plate that contacts a symmetrical 1′, four to five sulcal plates, and the conservative hypothecal tabulation of 5′′′, 0p, and 2′′′′. These morphological characters and the life histories of Pfiesteria and Pseudopfiesteria are consistent with placement of both genera in the Peridiniales. Based on the plate tabulations for P. shumwayae, P. piscicida, and the closely related “cryptoperidiniopsoid” and “lucy” groups, the family Pfiesteriaceae is amended to include species with the following tabulation: 4‐5′, 0‐2a, 5‐6′′, 6c, PC, 5+s, 5′′′, 0p, and 2′′′′ as well as an APC containing a pore plate (Po), a closing plate (cp), and an X plate; the tabulation is expanded to increase the number of sulcal plates and to include a new plate, the peduncle cover (PC) plate. Members of the family have typical dinoflagellate life cycles characterized by a biflagellated free‐living motile stage, a varying number of cyst stages, and the absence of multiple amoeboid stages.     

The genus Glochidinium gen. nov., with two species: G. penardiforme comb. nov. and G. platygaster sp. nov. (Peridiniaceae)

Glochidiniumgen. nov., a ncw genus of Peridiniaceae based on Peridinium penardiforme Lindemann, is herewith erected. Its plate formula is: Po+X+4′+6′′+3C+4S+5′′′+2′′′′ Main diagnostic characters of this new genus are the presence of only 3 cingular plates (it lacks the transitionalone), the third cingular contacting the anterior sulcal plate, and an unusual sulcus holding a small triangular posterior sulcal plate. The thecal morphology and structure of two freshwater planktic species of the genus are described on the basis of LM and SEM observations. G. penardiforme comb. nov. is an infrequent species, albeit widely distributed world-wide. It has been recorded under the names of Peridinium, Glenodinium and Peridiniopsis. Peculiar features in the tabulation of the furrows and of the surface sculpture show that the species does not fit any of the known genera, for which reason the new genus Glochidinium is established. G. platygaster sp. nov., the second species included in the genus, differs from the former by its elongated body, the regular pentagonal shape of its large first apical plate, an equally large sulcal anterior plate, and well developed sculpture, chiefly on the antapical plates. Glochidinium penardiforme and G. platygaster were found in some reservoirs from central and northern Argentina. G. penardiforme was also found in several Argentine rivers and ponds.     

Development and dehiscence of the cephalothecoid peridium in Aporothielavia leptoderma shows it belongs in Chaetomidium

The development of the cephalothecoid peridium of Aporothielavia leptoderma was examined using light and electron microscopy. Early stages in ascoma initiation were consistent with previous reports for other species in the Chaetomiaceae. However, as young cleistothecia increased in size, clusters of peridial cells in the outer textura angularis elongated in a radial pattern around a central cell or cell cluster to form rosettes of relatively thick-walled segments that marked the central areas of incipient cephalothecoid plates. The external flank along median portions of the radial cells became thin walled and swelled outwards so that each plate became concave and was separated from adjacent plates by a more or less circular to polygonal ridge of knuckle-shaped swellings. When dry, mature peridia split apart along some of the ridges demarcating individual plates but an internal mechanism for liberating ascospores from the confines of the ascoma was not observed. Physical disturbance of mature cleistothecia by beetles, when enclosed together in a Petri dish, shattered the peridia, liberating the ascospores. Smaller insects were unable to cause disarticulation of the cephalothecoid plates. Because of the presence of an apical germ pore in the ascospores and morphological similarity to Chaetomidium arxii, the new combination Chaetomidium leptoderma (syn. Thielavia leptoderma) comb. nov. is proposed.     

Cloning,Sequencing, Expression and Structural Investigation of Mnemiopsin from <Emphasis Type="Italic">Mnemiopsis leidyi</Emphasis>: An Attempt Toward Understanding Ca<Superscript>2+</Superscript>-Regulated Photoproteins

A comparison of the two most famous groups of calcium-regulated photoproteins, cnidarians and ctenophores, showed unexpectedly high degree of structural similarity regardless of their low sequence identity. It was suggested these photoproteins can play an important role in understanding the structural basis of bioluminescence activity. Based on this postulate, in this study the cDNA of mnemiopsin from luminous ctenophore Mnemiopsis leidyi was cloned, expressed, purified and sequenced. The purified cDNA, with 621 base pairs, coded a 206 residues protein. Sequence of mnemiopsin showed 93.5 and 51% similarity to other ctenophore proteins and cnidarians, respectively. The cDNA encoding apo-mnemiopsin of M. leidyi was expressed in Escherichia coli. The purified apo-protein showed a single band on SDS-PAGE (molecular weight ~27 kDa). A semi-synthetic mnemiopsin was prepared using coelenterazine and EDTA and its luminescence activity was measured in the presence of CaCl₂. The results showed an optimum pH of 9.0 and lower calcium sensitivity compared to aequorin. Comparison of amino acid residues in substrate binding site indicated that binding pocket of ctenophores contains less aromatic residues than cnidarians. This can lead to a decline in the number of stacking interactions between substrate and protein which can affect the stability of coelenterazine in binding cavity. Structural comparison of photoproteins with low sequence identity and high 3D structural similarity, can present a new insight into the mechanism of light emission in photoproteins.     

Electrophysiological control of ciliary motor responses in the ctenophorePleurobrachia

Prey capture by a tentacle of the ctenophore Pleurobrachia elicits a reversal of beat direction and increase in beat frequency of comb plates in rows adjacent to the catching tentacle (Tamm and Moss 1985). These ciliary motor responses were elicited in intact animals by repetitive electrical stimulation of a tentacle or the midsubtentacular body surface with a suction electrode. An isolated split-comb row preparation allowed stable intracellular recording from comb plate cells during electrically stimulated motor responses of the comb plates, which were imaged by high-speed video microscopy. During normal beating in the absence of electrical stimulation, comb plate cells showed no changes in the resting membrane potential, which was typically about -60 mV. Trains of electrical impulses (5/s, 5 ms duration, at 5-15 V) delivered by an extracellular suction electrode elicited summing facilitating synaptic potentials which gave rise to graded regenerative responses. High K+ artificial seawater caused progressive depolarization of the polster cells which led to volleys of action potentials. Current injection (depolarizing or release from hyperpolarizing current) also elicited regenerative responses; the rate of rise and the peak amplitude were graded with intensity of stimulus current beyond a threshold value of about -40 mV. Increasing levels of subthreshold depolarization were correlated with increasing rates of beating in the normal direction. Action potentials were accompanied by laydown (upward curvature of nonbeating plates), reversed beating at high frequency, and intermediate beat patterns. TEA increased the summed depolarization elicited by pulse train stimulation, as well as the size and duration of the action potentials. TEA-enhanced single action potentials evoked a sudden arrest, laydown and brief bout of reversed beating. Dual electrode impalements showed that cells in the same comb plate ridge experienced similar but not identical electrical activity, even though all of their cilia beat synchronously. The large number of cells making up a comb plate, their highly asymmetric shape, and their complex innervation and electrical characteristics present interesting features of bioelectric control not found in other cilia.     

ALEXANDRIUM SATOANUM SP. NOV. (DINOPHYCEAE) FROM MATOYA BAY,CENTRAL JAPAN1

The gonyaulacoid dinofiagellate Alexandrium satoanum Yuki et Fukuyo sp. nov. is described from Matoya Bay, Pacific coast of central Japan. The species is distinctive in its conical epitheca with almost straight sides and dorsal concavity of the hypotheca. The plate formula is Po, pc, 4′, 6″, 6c, 10s, 5″″, and 2″″, including two accessory plates inside the sulcus. The apical pore plate is triangular and possesses an anterior attachment pore at the right margin. The first apical plate does not make contact with the apical pore plate and lacks a ventral pore. A posterior attachment pore lies at the center of the posterior sulcal plate. In Matoya Bay, vegetative cells occur as solitary cells or sometimes in pairs during late spring and early summer in low concentrations. In connection with this study, the following new combination is proposed: Alexandrium pseudogonyaulax (Biecheler) Horiguchi ex Yuki et Fukuyo comb. nov.     

Regeneration of the growth plate

The occurrence of growth plate regeneration has been doubted. However, in 5 different series of experiments reported between 1950 and 1986 regeneration of injured parts of growth plates in long bones of rabbits and pigs could be demonstrated. The 1st series implied partial X-ray injury of growth plates in rabbits aged 3-6 weeks. The 2nd series implied autotransplantation of the head of the fibula in rabbits aged 10-21 days. The 3rd, 4th and 5th series implied transplantation of autologous fat grafts into provoked defects of growth plates in rabbits and pigs. The findings show that regeneration of a growth plate occurs when a part of it is injured in such a manner that a bone bridge is not formed between the epiphysis and the metaphysis. Regeneration of a plate is much faster in relation to the growth in length of the bone in the rabbit than in the pig. The 1st and 2nd series suggest that regeneration takes place by interstitial proliferation of cells from the germinal layer of the uninjured parts of the plate. Signs of partial regeneration of growth plates have been seen in radiographs after operation for partial closure of growth plates in children.     

Physical constrints on the evolution of ctenophore size and shape

Summary Cilia bundled into combs or ctenes are an evolutionary innovation that allow comb jellies (animals in the phylum Ctenophora) to swim faster and grow to sizes at least two orders of magnitude larger than animals that propel themselves by beating single cilia. Ctenophore size, shape and swimming behaviors, however, may be constrained by the mechanisms that coordinate comb plate oscillations.Oscillations of comb plates onPleurobrachia bachei (a cydippid comb jelly), are coupled by fluid interactions between combs. Ctenes beat metachronously (in sequence) and the flows generated byP. bachei are retarded by the amount of time it takes a wave to pass down a group of ctenes. Our model predicts thatP. bachei size is constrained by the maximum thrust that can be produced by ctenes that beat in sequence and our flow visualization studies suggest that swimming via metachronous comb oscillations may constrainP. bachei to spherical shapes.In contrast, comb plate oscillations onMnemiopsis leidyi, a lobate comb jelly, are neurally coordinated and groups of ctenes beat in synchrony. As a result, fluid flows generated byM. leidyi are not retarded by the passage of metachronal waves down each comb row.M. leidyi reach sizes 15 times larger, but swim relatively slower (body lengths per second) thanP. bachei.We propose that propulsion via metachronous or synchronous comb plate oscillations has played an important role in the evolution of ctenophore shape and size and may have divided comb jellies into two evolutionary lineages.