Prey Capture Mechanism Research Articles

Oldest true orb-weaving spider (Araneae: Araneidae)

The aerial orb web woven by spiders of the family Araneidae typifies these organisms to laypersons and scientists alike. Here we describe the oldest fossil species of this family, which is preserved in amber from Alava, Spain and represents the first record of Araneidae from the Lower Cretaceous. The fossils provide direct evidence that all three major orb web weaving families: Araneidae, Tetragnathidae and Uloboridae had evolved by this time, confirming the antiquity of the use of this remarkable structure as a prey capture strategy by spiders. Given the complex and stereotyped movements that all orb weavers use to construct their webs, there is little question regarding their common origin, which must have occurred in the Jurassic or earlier. Thus, various forms of this formidable prey capture mechanism were already in place by the time of the explosive Cretaceous co-radiation of angiosperms and their flying insect pollinators. This permitted a similar co-radiation of spider predators with their flying insect prey, presumably without the need for a 'catch-up lag phase' for the spiders.

Modulation and variability of prey capture kinematics in clariid catfishes

Species with narrow or limited diets (trophic specialists) are expected to be less flexible in their feeding repertoire compared to species feeding on a wide range of different prey (trophic generalists). The ability to modulate prey capture kinematics in response to different prey types and prey position, as well as the overall variability in prey capture kinematics, is evaluated in four clariid species ranging from trophic generalist (Clarias gariepinus) to species with morphological specializations and a narrow diet (Channallabes apus and Gymnallabes typus). High-speed video recordings were made of prey captures on two prey that differ in shape, attachment strength and hardness. While the observed amount of strike-to-strike variability in prey capture kinematics is similar for all species and not influenced by prey type, only the two less specialized species showed the ability to modulate their prey capture kinematics in function of the presented prey types. All species did, however, show positional modulation during the strike by adjusting the magnitude of neurocranial elevation. These results indicate that the narrow dietary breadth of trophic specialists is indeed indicative of functional stereotypy in this group of fishes. Although most studies focussing on prey processing found a similar result, the present study is one of the few that was able to demonstrate this relationship when focussing on prey capture mechanics. Possibly, this relationship is less frequently observed for prey capture compared to prey processing because, regardless of prey type, the initial capture of prey requires a higher amount of variability.

Omnivory by the small cosmopolitan hydromedusa Aglaura hemistoma

We investigated the feeding of the small hydromedusa, Aglaura hemistoma (bell diameter < 4 mm), to determine if it occupies a trophic position similar to that of large medusae. Feeding was examined using gut-content analysis of preserved and unpreserved medusae and by analyzing prey-capture events using microvideographic techniques. Analysis of gut contents and prey-capture events revealed that A. hemistoma fed heavily on protistan prey and that it possessed a prey-capture mechanism, specifically a feeding current, that is effective at entraining and capturing protists with low motility. We suggest that many species of small hydromedusae possess prey-capture mechanisms adapted to capture small protistan prey and that many of these small hydromedusae feed omnivorously on microplanktonic prey. The trophic roles of small hydromedusae in different systems are not understood and more studies are needed. However, based on their often high abundances and the cosmopolitan nature, if small hydromedusae are primarily omnivores, they need to be considered when estimating the impact of zooplankton on primary production and, more generally, protistan community dynamics.

The ontogeny of feeding kinematics in a giant salamander Cryptobranchus alleganiensis: Does current function or phylogenetic relatedness predict the scaling patterns of movement?

Studies of the scaling of feeding movements in vertebrates have included three species that display both near-geometric growth and isometry of kinematic variables. These scaling characteristics allow one to examine the “pure” relationship of growth and movement. Despite similar growth patterns, the feeding movements of toads ( Bufo) slow down more with increasing body size than those of bass ( Micropterus), and sharks ( Ginglymostoma). This variation might be due to major differences in the mechanism of prey capture; the bass and sharks use suction to capture prey in water, while the toad uses tongue prehension to capture prey on land. To investigate whether or not these different scaling patterns are correlated with differences in feeding mechanics, we examined the ontogenetic scaling of prey capture movements in the hellbender salamander ( Cryptobranchus alleganiensis), which also has near-geometric growth. The hellbender suction feeds in the same general manner as the teleosts and shark, but is much more closely related to the toad. The feeding movements of the hellbender scale more similarly to the feeding movements of toads than to those of fishes or sharks, indicating that phylogenetic relatedness rather than biomechanical similarity predicts ontogenetic scaling patterns of movement.

Predator–prey interactions on the wing: aerobatics and body size among dance flies and midges

Male dance flies (Diptera: Empididae) are major predators of mating swarms of male nonbiting midges (Diptera: Chironomidae). Studies have indicated that chironomid midges are excellent fliers with extraordinarily high wing muscle power, acceleration and tortuosity for their size. We compared the relative flight performance and morphometrics of male empidsEmpis tesselatta Meigen and their prey, Chironomus plumosus L., in a series of laboratory and field studies. High-speed digital video camera footage revealed that there were no significant differences between predator and prey in terms of straight-line acceleration or maximum flight velocity, although the mean speed of empids was higher. In curved flight, measured as tortuosity, the smaller chironomids held a considerable advantage over their larger predators. Flight muscle ratio (e.g. flight muscle mass/body mass) of chironomids was also greater in chironomids than in empids. In field studies, small male chironomids suffered much lower levels of predation than large males. This result is consistent with the prediction of small midges being less likely to be captured because of superior aerobatics, although we are unable to exclude empirically that empids select large male midges. We discuss the possible mechanisms of prey capture by empids given the greater manoeuvrability of their prey, the coevolutionary dynamics of flight performance and the apparent selective advantage of small size in male chironomids. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

The Effects of Satiation on Strike Mode and Prey Capture Kinematics in the Largemouth bass, Micropterus salmoides

The feeding mechanism and kinematics of prey capture have been studied in many fishes. However, the effects of satiation on the strike mode and prey capture kinematics have never been directly measured. We analyze 12 kinematic variables to determine the effects of satiation on prey capture in five largemouth bass, Micropterus salmoides, by using high speed videography. We also present the first experimental test for modulatory capabilities in response to satiation, by using the ram-suction index. Significant changes in the kinematic variables of maximum lower jaw depression, maximum gape distance, maximum hyoid depression, time to maximum hyoid depression, and time from maximum hyoid depression to recovery were seen with the effects of satiation. Change in the kinematic variables imply a decrease in jaw opening velocity and the magnitude of suction velocity created during repetitive strikes by M. salmoides with increasing satiation. The bass primarily uses a ram strike mode, with some suction bites occasionally. Ram-suction index analyses suggests that M. salmoides does not modulate strike mode in response to satiation. However, the bass modulate prey capture kinematics without altering strike mode with the effects of satiation. Prey capture success decreases in each bass, as the probability of a successful prey capture event becomes lower, with increasing satiation. These findings demonstrate that satiation can have major effects on prey capture kinematics and future studies of feeding kinematics should account for satiation in their analyses.

Mechanisms of benthic prey capture in wrasses (Labridae)

Teleost fishes capture prey using ram, suction, and biting behaviors. The relative use of these behaviors in feeding on midwater prey is well studied, but few attempts have been made to determine how benthic prey are captured. This issue was addressed in the wrasses (Labridae), a trophically diverse lineage of marine reef fishes that feed extensively on prey that take refuge in the benthos. Most species possess strong jaws with stout conical teeth that appear well-suited to gripping prey. Mechanisms of prey capture were evaluated in five species encompassing a diversity of feeding ecologies: Choerodon anchorago (Bloch, 1791), Coris gaimard (Quoy and Gaimard, 1824), Hologymnosus doliatus (Lacepede, 1801), Novaculichthys taeniourus (Lacepede, 1801) and Oxycheilinus digrammus (Lacepede, 1801). Prey capture sequences were filmed with high-speed video at the Lizard Island Field Station (14°40′S, 145°28′E) during April and May 1998. Recordings were made of feeding on pieces of prawn suspended in the midwater and similar pieces of prawn held in a clip that was fixed to the substratum. Variation was quantified among species and between prey types for kinematic variables describing the magnitude and timing of jaw, hyoid, and head motion. Species differed in prey capture kinematics with mean values of most variables ranging between two and four-fold among species and angular velocity of the opening jaw differing seven-fold. The kinematics of attached prey feeding could be differentiated from that of midwater captures on the basis of faster angular velocities of the jaws and smaller movements of cranial structures which were of shorter duration. All five species used ram and suction in combination during the capture of midwater prey. Surprisingly, ram and suction also dominated feedings on attached prey, with only one species making greater use of biting than suction to remove attached prey. These data suggest an important role for suction in the capture of benthic prey by wrasses. Trade-offs in skull design associated with suction and biting may be particularly relevant to understanding the evolution of feeding mechanisms in this group.

Prey resource use by coexistent hydromedusae from Friday Harbor, Washington

Prey selection patterns were quantified for a sympatric group of hydromedusae from Friday Harbor, WA. Selection patterns varied between species, but were largely replicable between sample dates and resembled dietary patterns found in similar studies from neighboring regions. Ambush‐foraging medusae (Aglantha digitale, Sarsia tubulosa, and Proboscidactyla flavicirrata) fed primarily on crustacean and ciliated prey but the dietary niches of these hydromedusan species centered on different fractions of the available plankton. Consequently, little dietary overlap occurred between the ambush foraging hydromedusae. In contrast, the dietary niches of cruising predators (Aequorea victoria, Mitrocoma cellularia, and Phialidium gregarium) overlapped substantially because those species all fed on similar soft‐bodied prey such as eggs and appendicularians. These results have two important implications for trophic patterns involving medusae. First, different mechanisms of prey encounter and capture used by hydromedusae (ambush vs. cruising patterns) result in important interspecific dietary differences and, hence, trophic roles of the medusae. Second, whereas cruising medusae may consume similar prey and hence form a feeding guild, ambush‐foraging medusae may experience substantially less prey overlap and, for the community examined here, do not experience potentially strong feeding competition from other medusan species.

Unusual sensory setae of the raptorial Branchinecta gigas (Branchiopoda: Anostraca)

In many vernal pools, visibility is very poor because of the turbidity from suspended clay particles. For predatory species like Branchinecta gigas, these conditions can be detrimental to successful prey capture. In vernal lakes in central California, B. gigashave developed specialized hunting modes to capture anostracan prey in pools of low visibility. The position of their body, the kinematics of their locomotion, and their reduced eye size suggested the possibility of novel sensory structures on their antennae and/or their cercopods designed to enhance their prey capture abilities. Using Scanning Electron Microscopy, we investigated the presence and design of sensory setae on the antennae and cercopods of B. gigas. On both males and females, there are dense patches of sensilla along the length of the antennae. They are oriented ventrally and slightly anteriorly. These antennal setae appear to be chemosensory in structure and position; they resemble antennal setae of other branchiopods. However, the setae of the cercopods are unusual in their morphology and location on the appendage. The cercopods, which are bent over the head in the hunting position, have a linear arrangement of specialized setae on their ventral side. They are jointed setae with an anterior crown of protective spines. The setal joint only permits limited abduction either toward the head in the hunting position or ventrally when swimming. These setae appear to be mechanosensory in function and may be adaptations to a raptorial lifestyle. They correlate well with the behavioral components of hunting in B. gigasand their complex prey capture mechanism.

First data on the experimental evaluation of predation on Heterobranchus longifilis larvae (Siluroidei; Clariidae) by toad tadpoles (Bufo regularis)

An investigation was conducted under laboratory conditions to analyse the mechanisms of prey capture by tadpoles, Bufo regularis Reuss, and to determine the minimum size at which the predation pressure by tadpoles on the larvae of African catfish, Heterobranchus longifilis Val., becomes insignificant. It was observed that the tadpoles fed on the larvae by suction without any specific capture strategies regardless of their sizes. The predation pressure was very high (100% mortality) during yolk-sac absorption and reduced gradually as the larvae increased in size. Based on these results, it was suggested to transfer the fry into nursing ponds only when they have reached a size greater than 10 mm TL (5–7 days) so as to avoid their predation during the primary nursing phase.

Morphology and kinematics of prey capture in the syngnathid fishes Hippocampus erectus and Syngnathus floridae

The mechanism of prey capture in two syngnathid fishes, the lined seahorse Hippocampus erectus (Perry) and the dusky pipefish Syngnathus floridae (Jordan and Gilbert), is described based on anatomical observations and high-speed video recordings (200 and 400 images s−1) of feeding events by four seahorses and three pipefish. The fish were collected near Turkey Point, Florida, U.S.A., in January 1994 to March 1995. The dominant features of the morphology of these and many other syngnathiform fishes include extreme elongation of the suspensorium and neurocranium with a small mouth located at the anterior tip of the head. In the seahorse, a preparatory phase of prey capture consisted of slow ventral head flexion. This was followed by rapid elevation of the head and snout as the prey was drawn into the mouth by suction. Both H. erectus and S. floridae capture prey rapidly, with peak head excursions and mouth opening occurring within 5 to 7 ms of the onset of the strike. There was no upper jaw protrusion. In both species the time to recovery of the cranium and hyoid apparatus to resting positions was highly variable but took at least 500 ms. Manipulations of freshly dead specimens indicated a biomechanical linkage between head elevation and hyoid depression. However, the predictions of a previously proposed four-bar linkage model that couples hyoid depression to head elevation were not fully supported by kinematic data from one seahorse, suggesting that additional linkages act during the expansive phase of prey capture. These species exhibit the generalized kinematic pattern of prey capture in bony fishes, with head elevation, hyoid depression and mouth opening occurring almost simultaneously. The derived morphology results in a unique feeding behav‐ior, in which prey are captured during a sudden up-swing of the head, which brings the mouth to the prey. Suction is used to draw the prey into the buccal cavity.

The kinematics and mechanism of prey capture in the African pig-nosed frog (Hemisus marmoratum): description of a radically divergent anuran tongue.

High-speed videography and muscle denervation experiments were used to quantify the feeding kinematics of Hemisus marmoratum and to test hypotheses of muscle function. The feeding behavior of H. marmoratum, which feeds on ants and termites, differs radically from that of other frogs that have been studied. During feeding in H. marmoratum, the tongue 'telescopes' straight out of the mouth, as opposed to the 'flipping' tongue trajectory observed in most other frogs. At the time of prey contact, two lateral lobes of tissue at the tongue tip envelop the prey. These lateral lobes are capable of applying significant pulling forces to the prey and the tongue is, therefore, described as prehensile. The trajectory of the tongue can be adjusted throughout protraction so that the frog can 'aim' its tongue in all three dimensions; distance, azimuth and elevation. Bilateral denervation of the genioglossus muscles results in a complete lack of tongue protraction, indicating that the genioglossus muscle is the main tongue protractor in H. marmoratum, as in other frogs. Thus, H. marmoratum provides strong evidence of functional conservatism of the genioglossus muscle within anurans. Bilateral denervation of the hyoglossus muscle indicates that although the hyoglossus is involved in several aspects of normal tongue retraction, including the prehensile capability of the tongue tip, it is not necessary for tongue retraction. Unilateral denervation of the genioglossus muscle causes significant deviation of the tongue towards the denervated side, providing evidence for a mechanism of lateral tongue aiming. On the basis of the kinematics of prey capture, the anatomy of the tongue and the results of the denervation experiments, we propose that H. marmoratum uses a hydraulic mechanism to protract its tongue.

Morphology, fluid motion and predation by the scyphomedusa Aurelia aurita

Although medusan predators play demonstrably important roles in a variety of marine ecosystems, the mechanics of prey capture and, hence, prey selection, have remained poorly defined. A review of the literature describing the commonly studied medusa Aurelia aurita (Linnaeus 1758) reveals no distinct patterns of prey selectivity and suggests that A. aurita is a generalist and feeds unselectively upon available zooplankton. We examined the mechanics of prey capture by A. aurita using video methods to record body and fluid motions. Medusae were collected between February and June in 1990 and 1991 from Woods Hole, Massachusetts and Narragansett Bay, Rhode Island, USA. Tentaculate A. aurita create fluid motions during swimming which entrain prey and bring them into contact with tentacles. We suggest that this mechanism dominates prey selection by A. aurita. In this case, we predict that medusae of a specific diameter will positively select prey with escape speeds slower than the flow velocities at their bell margins. Negatively selected prey escape faster than the medusan flow velocity draws them to capture surfaces. Faster prey will be captured by larger medusac because flow field velocity is a function of bell diameter. On the basis of prey escape velocities and flow field velocities of A. aurita with diameters of 0.8 to 7.1 cm, we predict that A. aurita will select zooplankton such as barnacle nauplii and some slow swimming hydromedusae, while faster copepods will be negatively selected.

VISION, BRAIN, AND BEHAVIOUR IN BIRDS

Part 1 The avian eye view: introduction, Sally A. McFadden producing the image, Graham R. Martin exploring the image, Hans-Ortwin Nalbach et al constructing the three-dimensional image, Sally A. McFadden the visual capabilities of birds, William Hodos colour vision of birds, Francisco J. Varela et al. Part 2 Functional anatomy of the avian visual system: introduction, Onur Gunturkun the avian visual system and the evolution of the neocortex, Toru Shimizu and Harvey J. Karten anatomy of the avian thalamofugal pathway, Onur Gunturkun et al the organization of the tectofugal pathway in birds - a comparative review, Jurgen Engelage and Hans-Joachim Bischof binocular processing in frontal-eyed birds, G. Casini et al. Part 3 Development of the avian visual system: introduction, Hans-Joachim Bischof developmental anatomy of the chick retinotectal projection, Jorg Mey and Solon Thanos development, plasticity, and differential organization of parallel processing of visual information in birds, G. Fontanesi et al development of the tectofugal visual system of normal and deprived zebra finches, Kathrin Herrmann and Hans-Joachim Bischof developmental mechanisms of lateralization, Lesley J. Rogers and Patrice Adret. Part 4 Visuomotor mechanisms: introduction, H. Philip Zeigler eye movements, head movements, and gaze stabilization in birds, Josh Wallman and Juan-Carlos Letelier sensorimotor mechanisms and pecking in the pigeon, H. Philip Zeigler et al control of pecking response topography by stimulus-reinforcer and response-reinforcer contingencies, Robert W. Allan visual mechanisms of prey capture in water birds, Gadi Katzir. Part 5 Vision and cognition: introduction, Jacky Emmerton lateralization and strategies of viewing in the domestic chick, R.J. Andrew and M. Dharmaretnam two eyes and one world - studies of interocular and intraocular transfer in birds, Monika Remy and Shigeru Watanabe what can we learn from experiments on pigeon concept discrimination?, Shigeru Watanabe et al beyond sensation - visual cognition in pigeons, Jacky Emmerton and Juan D. Delius vision, cognition, and the avian hippocampus, Verner P. Bingman.

Kinematics of Aquatic Prey Capture in the Snapping Turtle Chelydra Serpentina

ABSTRACT The kinematics of feeding on two prey types is studied quantitatively in the common snapping turtle, Chelydra serpentina, to provide a description of prey capture mechanisms and to determine whether kinematic patterns can be altered in response to prey that vary in escape capability. High-speed video recordings of prey capture (200 fields s-1) provide data for field-by-field analysis of 12 kinematic variables characterizing head and neck movement. Feedings on fish were accomplished in 78 ms, with peak head extension velocities of 152.5 cm s-1. Worm feedings lasted 98 ms with maximum head extension velocities of 54cms-1. Both univariate and multivariate statistical analyses demonstrate significant differences in kinematic patterns between fish and earthworm feedings: Chelydra serpentina possesses the ability to modulate its kinematic pattern depending on the prey. The pattern of bone movement during the fast opening phase of the gape cycle is similar to that found in ray-finned fishes, lungfishes and aquatic salamanders. However, movements of the cranium and lower jaw during the closing phase are markedly different. Our data show Chelydra to be predominantly a ram-feeder, with any intraoral negative pressures generated during the strike having a negligible effect on the prey, which remains largely stationary relative to a fixed background. Hyoid and esophageal expansion during the closing phase may function to allow a unidirectional flow of water and prey into the mouth until the gape closes and to delay reverse flow until the prey has been trapped inside the mouth. The independent evolutionary acquisition of aquatic feeding in fishes and turtles reveals some kinematic similarities that may be the result of hydrodynamic constraints on aquatic prey capture systems, as well as kinematic differences that result from the fundamentally different morphological design of the prey capture apparatus.

Functional Stereotypy and Feeding Performance Correlated in a Trophic Specialist

If a Jack-of-all-trades is a master of none, is a Jack-of-one-trade a master of only one? Surprisingly, there have been few studies testing whether trophic specialists actually possess a limited breadth of function, and no studies relating degree of functional versatility to feeding performance on prey types that are not usually included in the specialist's diet. I tested the hypotheses that Gomphosus varius Lac6pede, a coral reef fish species which feeds almost exclusively on non-elusive prey, does not adjust its prey capture mechanism and is less proficient when capturing a prey type other than its preferred resource. I used nested ANOVAS to compare highspeed videotaped jaw movements of G. varius and two coexisting confamilial trophic generalists as they captured elusive and non-elusive prey. Both of the generalists, which occasionally consume elusive prey, exhibited functional versatility when capturing elusive prey, but G. varius did not. The significantly lower capture success rate of G. varius when feeding on elusive prey, compared to the generalists, supports a causative link between G. varius' stereotypical kinematics and the virtual absence of elusive prey in its diet. Quantitative assessments of functional versatility and feeding performance are useful in analysing patterns of resource use and predicting their stability over

Quantitative analysis of prey-capture kinematics in Anolis equestris (Reptilia: Iguanidae)

High-speed cinematography was employed to study the mechanics of prey capture in Anolis equestris. Capture of live prey (adult locusts) consists of a cyclic movement of the upper and lower jaws combined with tongue protraction. Kinematic profiles are presented for the jaws, tongue, and forelimbs. The tongue is projected during the "slow open" stage and most of the "fast open" stage. The tongue protrudes beyond the mandibular symphysis during the slow open stage, and rotates simultaneously around a transverse anteromedian axis. The prey is thus contacted by the dorsal sticky surface of the tongue, and then pulled backward into the oral cavity by a combination of a forward movement of the jaws and retraction of the tongue. Gape angle, defined as the angle between the upper and lower jaws, continues to increase during the initial stages of tongue retraction. During the capture process, the anterior part of the body lunges forward, followed by a return to its original position; this displacement is mediated by the forelimbs, which usually remain well anchored to the floor. The cyclic food-capture movements of the jaws and tongue–hyoid system in A. equestris (Iguanidae) and Chameleo dilepis (Chamaeleontidae) are compared. I argue that one of the primary selection forces in the evolution of the different mechanisms of prey prehension in these two lizard groups was enhancement of the locomotor system and, consequently, foraging ability.

Versatility and specialization in labrid fishes: ecomorphological implications.

The term "specialized" has been used to describe species that possess unique functional attributes and/or a narrow, stereotyped range of attributes, but there are few comparative functional analyses of specialists and generalists. If species with functional morphological specializations are capable of functioning over a broad range, the link between morphology and ecology may be relaxed under certain environmental conditions. In this study, high-speed films of jaw movements during prey capture were compared statistically for three coexisting coral reef fish species in the family Labridae, one trophic specialist and two trophic generalists. The trophic specialist possessed a unique functional feature related to the movement of the hyoid in the floor of the mouth, while the trophic generalists were not observed to possess any functional specializations. All three species showed functional versatility in that they were able to adjust their prey capture mechanism in response to the evasive potential of the prey. The functional versatility of trophic specialists has implications for ecomorphological studies, since species characterized as possessing unique functional or morphological features may demonstrate marked flexibility in ecological variables such as diet or foraging behavior, decreasing the likelihood of identifying correlations between morphology and ecology.

Zooplankton capture by a coral reef fish: an adaptive response to evasive prey

High-speed cinematography and video using modified Schlieren optics and laser illumination helped elicit details of prey capture mechanisms used by Chromis viridis while feeding on calanoid copepods and Artemia. Chromis viridis is capable of a ram-jaw, low-suction feeding, as well as a typical suction feeding behavior described for other species of planktivores. By adjusting the degree of jaw protrusion and amount of suction used during a feeding strike, this fish can modulate its feeding strikes according to the prey type being encountered. The ram-jaw feeding mode enables C. viridis to capture highly evasive calanoid copepods within 6 to 10 msec. The use of specialized feeding behavior for evasive prey and the ability to vary feeding behavior are adaptations for feeding on evasive prey.

Siphon structure and prey capture as a guide to affinities in the abyssal septibranch Anomalodesmat a (Bivalvia)

Abstract Four families of predatory abyssal anomalodesmatan bivalves are recognized - the Parilimyidae, Verticordiidae, Poromyidae, and Cuspidariidae. Only in Cuspidaria has prey capture been observed. The prey capture mechanisms in representatives of other families have been inferred by interpretation of either living (Poromya) or dead material (Parilimyidae, Verticordiidae). In all those species examined to date, prey capture is by a raptorial inhalant siphon that is dramatically extended as a result of hydraulic pressure changes within the mantle cavity causing a corresponding translocation of blood from a pallial reservoir into it. The siphon, with captured prey, is returned to the body by pallial retractor muscles. Siphon structure and prey capture mechanisms in the Parilimyidae, Poromyidae and Cuspidariidae are reviewed. For the Verticordiidae a different method of prey capture has hitherto been proposed, all species supposedly grasping their prey with sticky siphonal tentacles. A study of Lyonsiella formosa (JEFFREYS), however. cast doubt on this interpretation and concluded that prey capture was by the eversion of a raptorial inhalant siphon much as in Poromya. This study reinvestigates siphon structure and postulates prey-capture mechanisms for four genera and species of verticordiids, i.e. Verticordia, Policordia, Halicardia, and Lyonsiella. All feed in essentially the same way. Large siphonal tentacles are not sticky but sensory. Ciliary sense organs, essentially similar to those described for Poromya and Cuspidaria are receptive to prey movements. Prey capture is by eversion of an, albeit short, inhalant siphon. Prey thus has to approach the bivalve very closely, unlike other septibranchs which can effect capture at a distance. Siphonal eversion is by pumping of blood from a pallial lacunal system; retraction is by pallial retractors modified in species of Lyonsiella into discrete taenioid muscles. On the basis of this study, a better picture of phylogenetic affinities in these related bivalves is possible. The stem group seems to be represented by verticordiids and parilimyids. Most verticordiids are of relatively simple plan and their siphonal prey-capture mechanism comparatively unspecialized. Parilimyids and Lyonsiella, however, have a pair of taenioid muscles, enhancing the efficiency of siphonal retraction. Lyonsiella formosa (at least) feeds like poromyids, suggesting a phylogenetic link; the latter, however, being the more morphologically specialized. Cuspidariids, like parilimyids, feed on swimming prey, the long inhalant siphon being everted upwards. This also suggests a phylogenetic link, the cuspidariids being the more specialized members of this group. The Palaeozoic and Mesozoic extinctions of large numbers of anomalodesmatans have left few living descendants and these show widely divergent character traits, making the construction of lineages difficult. However, modern descendants of these early abyssal colonists indistinctly linked, seem to feed on two groups of organisms; bottom-dwelling crustaceans and annelids (Verticordiidae and Poromyidae) and swimming crustaceans (Parilimyidae and Cuspidariidae).