Patterns of ciliary currents in Atlantic reef corals and their functional significance

Patterns of ciliary currents of 35 species of Atlantic reef corals are described and compared with currents of Pacific corals. Observations were made during the day and at night, during feeding and without food. There is a basic pattern of ciliary currents common to both Atlantic and Pacific species. In all but the family Agaricidae currents flow off the oral disk and up or out between the tentacles. In the centre of the disk region currents flow towards the mouth or the peristome. On the polyp stalk or column there was considerable variation between species in both Atlantic and Pacific forms. In some species currents flow downwards toward the coenosarc while in others, current pass up the stalk towards the tentacles.
In the Atlantic Agaricidae there may be an inward flow towards the mouth, an outward flow or a unidirectional flow across the corallum. The patterns of flow depend upon the state of contraction of the polyps or the shape and proximity of adjacent polyps.
No ciliary current reversal was observed in Atlantic species. Ciliary currents are functional as a cleansing mechanism and facilitated the ability of mucus nets and strands to gather particles.     

Feeding mechanisms and feeding strategies of Atlantic reef corals

The feeding behaviour of 35 species of Atlantic reef corals was examined in the laboratory and in the field. Observations were made during the day and at night, using freshly hatched brine shrimp nauplii and finely ground, filtered fresh fish as food sources. Three feeding strategies were observed: Group I–feeding by tentacle capture only; Group II–feeding by entanglement with a mucus net or mucus filaments; Group III–feeding by a combination of tentacle capture and mucus filament entanglement. Group I included corals of the families Poritidae and Pocilloporidae which were normally expanded during both day and night. Group II included corals of the family Agaricidae which were normally expanded at night and contracted during the day. Group III included corals of the other families examined which, with the exception of Dendrogyra cylindrus , were normally expanded only at night.
Feeding responses were elicited by both chemical and tactile stimuli. A preparatory feeding posture was assumed in response to chemical stimuli and consisted of horizontal positioning of the tentacles, elevation of the oral disk to form a cone-like mouth, a wide mouth opening and secretion of mucus by the epidermis of the oral disk. Following the assumption of the preparatory feeding posture, food capture and ingestive movements were elicited by tactile stimuli. However, food capture and ingestive movements were also elicited by chemical stimuli alone in those species which were normally contracted during the day.
While expanded corals captured food with their tentacles or with mucus filaments, contracted corals were able to feed by capturing fine particulate matter with mucus filaments only and thus acted as suspension feeders. By a combination of feeding strategies, reef corals were able to feed both day and night and a wide range of potential food ranging from fine particulate matter to large zooplankton was available to them.     

Ciliary feeding structures and particle capture mechanism in the freshwater bryozoan Plumatella repens (Phylactolaemata)

Abstract. In contrast to marine bryozoans, the lophophore structure and the ciliary filter‐feeding mechanism in freshwater bryozoans have so far been only poorly described. Specimens of the phylactolaemate bryozoan Plumatella repens were studied to clarify the tentacular ciliary structures and the particle capture mechanism. Scanning electron microscopy revealed that the tentacles of the lophophore have a frontal band of densely packed cilia, and on each side a zigzag row of laterofrontal cilia and a band of lateral cilia. Phalloidin‐linked fluorescent dye showed no sign of muscular tissue within the tentacles. Video microscopy was used to describe basic characteristics of particle capture. Suspended particles in the incoming water flow, set up by the lateral ‘pump’ cilia on the tentacles, approach the tentacles with a velocity of 1–2 mm s^‐1. Near the tentacles, the particles are stopped by the stiff sensory laterofrontal cilia acting as a mechanical sieve, as previously seen in marine bryozoans. The particle capture mechanism suggested is based on the assumed ability of the sensory stiff laterofrontal cilia to be triggered by the deflection caused by the drag force of the through‐flowing water on a captured food particle. Thus, when a particle is stopped by the laterofrontal cilia, the otherwise stiff cilia are presumably triggered to make an inward flick which brings the restrained particle back into the downward directed main current, possibly to be captured again further down in the lophophore before being carried to the mouth via the food groove. No tentacle flicks and no transport of captured particles on the frontal side of the tentacles were observed. The velocity of the metachronal wave of the water‐pumping lateral cilia was measured to be ～0.2 mm s^‐1, the wavelength was ～7 μm, and hence the ciliary beat frequency estimated to be ～30 Hz (～20 °C). The filter feeding process in P. repens reported here resembles the ciliary sieving process described for marine bryozoans in recent years, although no tentacle flicks were observed in P. repens. The phylogenetic position of the phylactolaemates is discussed in the light of these findings.     

Large‐scale ciliary reversal mediates capture of individual algal prey by Müller's larva

We documented capture of microalgal prey by several species of wild‐caught Müller's larvae of polyclad flatworms. To our knowledge, this is the first direct observation of feeding mechanism in this classical larval type. High‐speed video recordings showed that virtually all captures were mediated by large‐scale transient ciliary reversal over one or more portions of the main ciliary band corresponding to individual lobes or tentacles. Local ciliary beat reversals altered near‐field flow to suck parcels of food‐containing water mouthward. Many capture episodes entailed sufficient coordinated flow disruption that these compact‐bodied larvae tumbled dramatically. Similar behaviors were recorded in at least four distinct species, one of which corresponds to the ascidian‐eating polyclad Pseudoceros canadensis.     

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.     

Feeding mechanisms in black corals (Antipatharia)

Feeding in the Antipatharia is very similar to that of reef corals. Food capture is accomplished by the tentacles with their nematocysts, by mucus nets and strands, by directional ciliary currents, and by mesenterial filaments.     

Ciliary filter-feeding structures in adult and larval gymnolaemate bryozoans

Abstract. Ciliary filter-feeding structures of gymnolaemate bryozoans—adults of Flustrellidra hispida and Alcyonidium gelatinosum , larvae of Membranipora sp.—were studied with SEM. In F. hispida and A. gelatinosum , the distal part of each tentacle has a straight row of stiff laterofrontal cilia which carry out "ciliary sieving" to capture suspended food particles that are subsequently transported downward towards the mouth by tentacle flicking; both structure and function resemble those of stenolaemate tentacles. The proximal part of the tentacle and of the ciliary ridge of a cyphonautes larva have strikingly similar structures, except that the laterofrontal cells are monociliate in the adults and biciliate in the larvae. The laterofrontal cells of the tentacles are arranged in a zigzag row and their cilia form two parallel rows, a frontal and a lateral row. The latter probably forms the sieve of stiff filter cilia in front of the water-pumping lateral cilia, whereas the frontal row appears to be held close to the frontal ciliary band of the tentacle. The biciliate laterofrontal cells of the cyphonautes larva have the cilia arranged in similar rows. The detailed morphological similarities between the ciliary bands of adult and larval filtering structures suggest that the feeding mechanisms are similar, contrary to what has been previously thought.     

The Tentacle Cilia of Aglantha digitale (Hydrozoa: Trachylina) and their Control

The tentacles of Aglantha have ciliary bands along the sides. Metachronal waves pass along these bands. The strong ciliary currents produced propel water past the tentacles, increasing the probability of prey capture. The ciliated cells are unusual in having many (up to about 500) cilia per cell, where most cnidarian ciliated cells have only one. The cells are also peculiar in containing numerous axonemes without membrane coverings, lying loose in the cytoplasm. Tentacles show independent, rhythmic, slow flexions in the oral direction and groups of tentacles show coordinated, slow flexions as part of a regularly repeated fishing cycle. In both cases, these slow, graded movements are mediated by a slowly conducting system, probably the network of small neurons present in the ectoderm, and are accompanied by ciliary arrests. Much faster, more powerful, coordinated contractions of the tentacles occur in the context of escape behaviour; these are mediated by giant axons which run down the tentacles and are also accompanied by ciliary arrest. Ciliary and muscle effectors evidently share a common motor innervation. Electron microscopy shows that the giant and non-giant nerves both synapse with muscle cells. The latter are joined to the ciliated cells by gap junctions, and it is suggested that whenever the muscles are excited depolarizations spread to the ciliated cells through the gap junctions and cause ciliary arrests. Neuronal control of ciliary activity has not previously been reported in the Hydrozoa.     

池养大口胭脂鱼鱼种的食性

池养大口胭脂鱼鱼种的食性研究表明 ,大口胭脂鱼鱼种为浮游动物尺寸选择性鱼类 ,其选食行为主要受鱼体及水体中浮游动物的个体大小影响 ,与浮游动物的种类、逃跑能力、运动方式等关系不明显。并初步探讨了 3种浮游生物食性鱼类 (大口胭脂鱼、鲢、鳙 )的食物关系。     

Development of the tentacular apparatus in sipunculans (Sipuncula): I. Thysanocardia nigra (Ikeda, 1904) and Themiste pyroides (Chamberlin, 1920)

The development and arrangement of the tentacular apparatus of Thysanocardia nigra (Ikeda, 1904) and Themiste pyroides (Chamberlin, 1920) are described and illustrated using scanning electron microscopy. In T. nigra, the tentacular apparatus is composed of two crowns: the nuchal arc enclosing the nuchal organ and a crown of numerous oral tentacles arranged in U-shaped festoons. In early juveniles, two dorsal horn-like protrusions develop into the first, or primary, pair of tentacles of the nuchal arc. The second pair of tentacles of the nuchal arc develops dorsolaterally on the bases of the primary tentacles. Two ventrolateral lobes of the oral disk grow and become subdivided by the longitudinal ciliary groove into anlages of one set of dorsal and one set of ventral tentacles, thus forming a first oral festoon. Later, a pair of dorsolateral lobes develop between the first festoons and the nuchal arc to form a second pair of oral festoons. The third and following pairs of oral festoons develop in the dorsolateral growth zones lateral to the borders of the nuchal arc, where they meet the oral crown. The growing festoons extend down the oral disk and run alongside the head. A new oral tentacle appears directly at/on the base of the previous tentacle, thus giving rise to a typical sympodium with an alternating arrangement of tentacles. In T. pyroides, a second pair of tentacles develops from two ciliary lobes that are ventrolateral outgrowths of the circumoral ciliary field around the terminal mouth opening. The third pair of tentacles appears from the dorsolateral lobes at the base of primary tentacles, between the first two pairs of tentacles. These six tentacles determine the position of six main stems of the tentacular apparatus designated the first tentacles in the corresponding stems. The second tentacle in every stem appears as a ventrolateral outgrowth at the base of the first tentacle. The third and following tentacles in the stem are developed between the two previous tentacles according to a sympodial pattern. In both species, the distinct sympodial pattern in the arrangement of tentacles in the tentacular apparatus is well evidenced by the outlines of the ciliary oral grooves. The branched stems of T. pyroides may be homologized structurally and functionally to the oral festoons of T. nigra. J. Morphol. (c) 2006 Wiley-Liss, Inc.     

The effect of age at metamorphosis on the transition from larval to adult suspension‐feeding of the slipper limpet Crepidula fornicata

Slipper limpets use different ciliary feeding mechanisms as larvae and adults. Veliger larvae of Crepidula fornicata developed part of the adult feeding apparatus, including ctenidial filaments, neck lobe, and radula, before metamorphosis, but ctenidial feeding did not begin until well after loss of the larval feeding apparatus (velum) at metamorphosis. Earlier initiation of ctenidial feeding by individuals that were older larvae when metamorphosis occurred suggests continued development toward ctenidial feeding during delay of metamorphosis. Early juveniles produced a ciliary current through the mantle cavity and moved the radula in a grasping action before they began to capture algal cells on mucous strands or form a food cord. Either early juveniles could not yet form mucous strands or they delayed their production until development of other necessary structures. The neck canal for transporting food from ctenidium to mouth cannot develop before velar loss. In their first feeding, juveniles fed much like the adults except that the neck canal was less developed and the path of the food cord toward the mouth sometimes varied. As suspension feeders, calyptraeids lack the elaborations of foregut that complicate transition to juvenile feeding for many caenogastropods, but a path for the food cord must develop after velar loss. Why individuals can initiate ctenidial feeding sooner when they are older at metamorphosis is not yet known. The juveniles became sedentary soon after metamorphosis and were not observed to feed by scraping the substratum with the radula, in contrast to the first feeding by juveniles of another calyptraeid species, observed by Montiel et al. ( 2005 ).     

Phenotype-specific feeding behaviour of two arctic charr Salvelinus alpinus morphs

The feeding performance of two morphs of a trophically polymorphic fish, the arctic charr Salvelinus alpinus, feeding on zooplankton, was studied in the laboratory. Limnetic morphs, with a fusiform body, terminal mouth, short pectoral fins, and relatively long and dense gill rakers, fed at significantly higher rates on Daphnia and Cyclops than did benthic morphs. The benthic morphs were characterized by a chunky body form, subterminal mouth, long pectoral fins, and relatively short and spaced-out gill rakers. The limnetic morphs attacked the prey at significantly higher rates and were more successful in capture. Benthic morphs were more reluctant to start feeding on zooplankton and reaction time was longer than in limnetic morphs. In the absence as well as presence of zooplankton food, the position of the two morphs in the aquaria differed markedly. The results agree with dietary differences found in field-collected fish. The limnetic morphs consume zooplankton, whereas benthic morphs specialize on Lymnaea gastropods. The results suggest that benthic morphs are phenotypically inferior at using the pelagic food niche. This implies that the current role of competitive or predatory interactions in segregating the morphs may be minor.     

Feeding behavior in freshwater bryozoans: function,form, and flow

Bryozoans are impressively active suspension feeders, with diverse feeding behaviors. These have been studied extensively in marine bryozoans, but less so in their freshwater counterparts. Here we identified 16 distinct behaviors in three phylactolaemate species and classified them into behaviors involving separate tentacles, groups of tentacles, lophophore arms, the introvert, or multiple zooids. We examined (1) the repertoire of behaviors in each species, and each behavior's (2) absolute frequency, (3) relative frequency and (4) duration in each of the three species, at two flow velocities (0 and 0.2 cm s^?1). Nine feeding behaviors were shared by all three species, but the occurrence of other behaviors in a given species was limited by its morphology. Behaviors involved in particle capture were the most frequent, and were often faster than the reactions involved in particle rejection. By contrast, the absolute frequency of behaviors varied widely among species without clear associations with species form, or function of the behavior. Flow velocity had only minor effects on the feeding behaviors exhibited by a species, or their frequencies or durations. Our results show that phylactolaemates have the same key feeding behaviors of the individual polypides (especially involving separate tentacles) as previously described in gymnolaemate and stenolaemate bryozoans, although their behaviors tend to be carried out more slowly than those of stenolaemates or gymnolaemates. Feeding behaviors involving multiple zooids were nearly absent in the studied phylactolaemates, but are common in gymnolaemates. Freshwater bryozoans appear to be intermediate between stenolaemate and gymnolaemate bryozoans in terms of richness of the repertoire of feeding behaviors.     

Contrasting scaling of ciliary filters in swimming larvae and sessile adults of fan worms (Annelida: Polychaeta)

Abstract. Both larval and adult fan worms capture particles with opposed bands of cilia. While the larvae use one of the opposed bands (the prototroch) for both feeding and swimming, the sessile adults rely partly on ambient currents to bring food particles to the ciliary bands. The scaling of length of prototrochal cilia with larval body size contrasts with scaling of the opposed latero-frontal cilia with adult body size. In the larva of the serpulid Hydroides elegans , the length of prototrochal cilia increased from 28 to 42 μm in early to late-stage larvae. In contrast, latero-frontal cilia did not increase in length (23 μm) during postlarval development of H. elegans. Among adults of 5 fan-worm species, lengths of latero-frontal cilia ranged from 22 to 35 μm and were weakly correlated with body size. The total area of ciliary filter nevertheless increased with increasing body dry weight of worms with an allometric exponent similar to exponents reported for gill and lophophore areas vs. body weight within species of suspension-feeding bivalves, brachiopods, and gastropods. The similar scaling was remarkable given the striking differences in distribution and function of the ciliary filters. In adult fan worms, increases in filter area depended largely on increases in number and length of radioles; differences in branching of radioles had little effect. Radioles were commonly in 2 or more rows in series, implying refiltration in still water by downstream radioles. Since the allometry of worms' filter area with body size depends on filters in series, it depends on ambient currents that overwhelm ciliary currents.     

Effects of Altered Light and Feeding Regimes on the Zooplankton Feeding Capability of Hydra viridis

The effects of light regime, feeding regime and tentacle number on the zooplankton feeding capability of Hydra viridis were tested in the laboratory. Feeding was measured by exposing Hydra to a known volume of Artemia salina nauplii and recording the number captured and ingested. In all cases there was a correlation between the number of Artemia captured and the number ingested. H. viridis with 7 tentacles captured and ingested more Artemia than Hydra with 6 tentacles. However, changes in light and/or feeding regimes did not alter the number of tentacles/Hydra. Varying light and feeding regimes altered the number of Zoochlorellae/cell and Hydra growth rate. There was no effect on the number of Artemia captured or ingested and no effect on the percent ingestion of captured Artemia. These data suggest that, under these conditions, zooplankton feeding by H. viridis is independent of nutritional history.     

Versatile ciliary behaviour in capture of particles by the bryozoan cyphonautes larva

Cyphonautes larvae of a bryozoan, Membranipora membranacea, used several ciliary mechanisms to capture algal cells upstream from the lateral band of cilia that produces a feeding current. (1) Lateral cilia changed beat and a backcurrent occurred at the time and place that particles were retained. (2) Algal cells were sieved and held stationary at the upstream (frontal) side of a row of laterofrontal cilia that were not beating. (3) Localized extension of cilia toward the inhalant chamber, coincident with particle captures, indicated that laterofrontal cilia flick toward the inhalant chamber. These flicks may aid transport of captured particles toward the mouth. Thus my earlier report that larvae only sieve, in contrast to the adults (which have an active ciliary response) was in error. The similar ciliary bands in adult and larval bryozoans and in other lophophorates (brachiopods, and phoronids) suggest that these animals share a core repertoire of ciliary behaviours in the capture and concentration of suspended food particles.     

Persistent ancestral feeding structures in nonfeeding annelid larvae

Evolutionary loss of the requirement for feeding in larvae of marine invertebrates is often followed by loss of structures involved in capturing and digesting food. Studies of echinoderms suggest that larval form evolves rapidly in response to loss of the requirement for feeding, but a lack of data from other taxa makes it difficult to assess the generality of this result. I show that many members of a large clade of annelids, the Sabellidae, retain ancestral systems for particle capture despite loss of the need and ability to feed. In at least one species, Schizobranchia insignis, an opposed-band system of prototrochal, food-groove, and metatrochal ciliary bands can concentrate suspended particles and transport them to the mouth, but captured particles are invariably rejected because larvae lack a functional gut. The persistence of particle capture systems in larvae of sabellids suggests that they have lost larval feeding very recently, that opposed bands are inexpensive to construct and operate, or that opposed bands have some alternative function. These observations also suggest a hypothesis on how the ability to feed is lost in larvae of annelids and other spiralians following increases in egg size.     

Plasticity of the scleractinian body plan: Functional morphology and trophic specialization ofMycedium elephantotus (Pallas, 1766)

Summary Morphological, histological and behavioral features indicate thatMycedium elephantotus, a zooxanthellate scleractinian species without tentacles, is well adapted for utilizing suspended organic matter for nutrition. The colonies are composed of vertically growing fan-like plates and can reach diameters of more than 1 m in depths below 20 m. The external body surface is coated with a mucus layer (cuticle) which enables the acquisition and accumulation of suspended organic material. The mucus-entangled particles pass to the mouth openings by gravitational transport assisted by water movement. In experiments the corals were able to discriminate between suspended food and mineral particles. Both types of particles were rapidly entangled in fine mucus nets or filaments. Mineral particles were never ingested and instead tumbled down the inclined skeletal plates. In contrast, food particles were actively incorporated when the mucus filaments accidentally touched the stomodaea during the downward gliding. The food-enriched mucus filaments were either transported by ciliary activity into the coelenteron or were sucked into the body cavities by decreasing pressure in the coelenteron caused by contraction of longitudinal, mesenterial muscles. The discriminative reactions to mineral or food particles are probably based on the release of different types of mucus. Nematocysts are infrequent in the oral epidermis, indicating that the capture of living prey plays a subordinate role in nutrition. The mesenterial filaments, in contrast, are densely packed with large nematocysts. Storage products were piled up within the tissues of gastral pockets. The adaptations ofMycedium elephantotus for using suspended food particles may explain the particularly high abundance of this species between ca. 20 and 40 m depth on a steeply inclined fore-reef slope in the Gulf of Aqaba (Red Sea). The evidence indicating the importance of heterotrophic fueling toM. elephantotus is supported by carbonate production rates which are, in contrast to that of many other zooxanthellate scleractinian species, almost constant at depths between 5 and 40 m and which are uneffected by varying light regimes over the year, suggesting that the reduced phototrophic contribution by the zooxanthellae is compensated by mucus suspension feeding.     

Functional diversity of crustacean zooplankton communities: towards a trait-based classification

1. While studies of phytoplankton and terrestrial plant communities have increasingly emphasised the use of functional traits in ecological research, few have yet to apply this approach to zooplankton communities.
2. This study reviews laboratory and observational studies on zooplankton feeding and life history and provides a series of functional trait tables for the North American freshwater zooplankton. Qualitative and quantitative trait tables highlight areas where data were more scarce and point to which types of studies could fill in gaps in our knowledge of zooplankton niches.
3. Data were most complete for the Cladocera across most traits, while feeding information for cyclopoids was most sparse. Qualitative data that distinguished congeneric species were lacking for most groups.
4. A regional community dendrogram for common north-eastern North American zooplankton species was generated and shows that taxonomic differences between species do not capture fully functional differences based on the traits of body length, habitat, trophic group and feeding type.
5. The data collected here, combined with readily measurable species attributes, can be used to generate a multivariate measure of the functional niche of each species found in a community. Armed with this information, functional relationships that are useful for ecological studies of lake ecosystems can be more easily conducted.     

A perforated gastrovascular cavity in the symbiotic deep-water coralLeptoseris fragilis: A new strategy to optimize heterotrophic nutrition

The organization of the zooxanthellate scleractinian coralLeptoseris fragilis was studied. The architecture of the corallite and the histology of the polyparium were analysed for adaptations that enable efficient capture and retention of suspended particles which would increase energy supply. The data indicate that the gastrovascular system ofL. fragilis is not a blind but a flowthrough system. Water entering the coelenteron through the mouth leaves the body not only through the mouth but also through microscopic pores (≂ 1–2 μm) which are located near the crests of the sclerosepta in the oral epithelia. Irrigation is achieved by flagellar and probably also by muscular activity. This type of filtration enablesL. fragilis, which lacks tentacles, to utilize suspended organic material including bacteria. The supposed suspension feeding in combination with effective photoadaptations (presented in former communications) seems to be the basis for the survival ofL. fragilis in an extreme habitat (between-95 and-145 m) and for its, successful competion with other scleractinian species provided with larger catching surfaces, and with other invertebrates depending on filter feeding. Dedicated to W. Weber 1923–1987