Functional morphology of the mouthparts and associated structures of Pagurus rubricatus (Crustacea: Decapoda: Anomura) with special reference to feeding and grooming

Summary Pagurus rubricatus is predatory, detrivorous, macrophagous, and to a small degree, a suspension feeder. The crab searches for small invertebrates by digging shallow pits in the sediment. During this process it feeds on detritus obtained either directly from the sediment or scoured off gravel granules. Particles trapped by the dense setation of the 2nd and 3rd maxillipeds are brushed off and ingested.The distribution of the various types of setae on the mouthparts is mapped and structure of the mouthparts and their setae is correlated with function. Sediment collected by the pereiopods is brushed off by the endopodites of the 3rd maxillipeds and transferred to the inner mouthparts by the endopodites of the 2nd maxillipeds. The basipodites of the 1st maxillae form a filter screen through which particles of suitable size are pushed by the 2nd maxillae. Rejected particles are discarded by the exhalant stream via the currents generated by the exopodites of the maxillipeds. Specialized setae on the 2nd maxillae scour detritus from the surface of gravel granules applied to these appendages by the 2nd and 3rd maxillipeds. Interlocking setae from different appendages form a number of screens the main function of which is to retain material in the buccal region. The exopodite and endopodite of the 1st maxilliped and the endopodites of the 1st and 2nd maxillipeds form a channel which funnels the exhalant respiratory current away from the crab. The main grooming appendages are the endopodites of the 3rd maxillipeds, however, most of the other mouthparts have a self-cleaning function.     

Setal morphology of grooming appendages in the spider crab,Libinia dubia

In crustaceans, grooming behaviors decrease fouling by removing debris from the exoskeleton and body structures; these grooming behaviors improve respiration, sensory reception, movement, and reproduction. Setal morphologies of the following grooming appendages in the decapod crustacean spider crab Libinia dubia are examined including the first pereiopod (cheliped), first, second, and third maxillipeds (mouthparts), and first, second, and third epipods (internal extensions of the maxillipeds). The objective of this study was to describe setal morphologies of these grooming appendages and to elucidate possible functions and efficiencies of setal structures. Spider crabs are hypothesized to have elaborate setal morphologies, mainly for cleaning specialized decorating setae as well as for cleaning inside the gill chamber, which has a higher likelihood of becoming fouled compared to other decapods such as shrimps. Fourteen setal types are documented and included several varieties of serrate and pappose setae as well as simple setae, cuspidate setae, papposerrate setae, and canoe setae. Maxillipodal epipods in the gill chamber are free of fouling, suggesting the setation on the third maxilliped protopod has an efficient functional morphology in removing debris before water enters the gill chamber. Serrate setae may function for detangling and separating structures whereas pappose setae may function for fine detailed grooming. The cheliped is the only grooming appendage that can reach decorating setae and it contains only pappose setae; thus decorating setae is not likely groomed in a manner that would greatly decrease fouling. J. Morphol. 277:1045–1061, 2016. © 2016 Wiley Periodicals, Inc.     

Setal morphology and cirral setation of thoracican barnacle cirri: adaptations and implications for thoracican evolution

Thoracic cirripedes are sessile crustaceans that use six pairs of thoracic appendages (the cirri) to catch and handle food. We used scanning electron microscopy to examine the cirri, which include one to three pairs of maxillipeds in six species of thoracican barnacles, in search of correlations between cirral setation and feeding mode. The species studied comprise both pedunculate and sessile forms and represent a wide range of marine habitats as well as morphologies, viz., Ibla cumingi , Octolasmis warwickii , Capitulum mitella , Pollicipes polymerus , Tetraclita japonica japonica and Megabalanus volcano . Of the pedunculates, I. cumingi has the least complex setation pattern consisting of only serrulate types. This is consistent with its very simplified feeding mode and an apparent inability to discriminate between food items. Octolasmis warwickii is slightly more modified, while both P. polymerus and C. mitella have a more diversified setation. The balanomorphan species exhibit by far the most complex cirral setation. This is consistent with the several types of suspension feeding seen in these species, their ability to identify and sort captured food items and even to perform microfiltration in the mantle cavity using the setae on their three pairs of maxillipeds. Our results indicate that in thoracican barnacles, adaptations in feeding behaviour are associated with changes in the setation pattern of the cirri. In addition, the setal types and their distribution on the cirri are potential new characters in future morphology-based analyses of the phylogeny of the Cirripedia Thoracica.     

Mechanical functions of setae from the mouth apparatus of seven species of decapod crustaceans

The mouthpart setae of seven species of decapods were examined with macro-video recordings and scanning electron microscopy. The general mechanical (nonsensory) functions of the different mouthparts are described and an account of their setation is given. This offers the possibility to determine the mechanical functions of the different types of setae. Pappose setae do not participate in food handling but in general make setal barriers. Plumose setae likewise do not contact food objects but assist in current generation. Papposerrate setae are rare but they were seen to assist in pushing food particles into the mouth. Serrulate setae are very common and mainly participate in gentle food handling and grooming. Serrate setae are used for more rough food manipulation and grooming. The roughest shredding, tearing, and manipulation of prey items are handled by the cuspidate setae. Simple setae seem to be divided into two populations with very different functions. On the maxillipeds of Panulirus argus they are used for shredding, tearing, and holding the food objects, but on the basis of maxilla 2 of three other species they appear to have very little mechanical influence and only when handling small prey items. The functional scheme seems to be consistent within the Decapoda.     

Comparative functional morphology of feeding in three species of caprellids (Crustacea,Amphipoda) from the northwestern Florida Gulf Coast

The functional morphology of feeding has been investigated in three species of caprellid amphipods. Feeding preferences are correlated with the increased setation and stoutness of the head appendages, the denser the setae the greater the trend toward filter-feeding. It was found that Caprella penantis Leach fed primarily by filter-feeding and scraping; Paracaprella tenuis Mayer relied on filter-feeding, scraping, scavenging, and predation; and Luconacia incerta Mayer depended almost entirely on predatory habits. The observed feeding patterns were verified by stomach content analysis.     

Scanning Electron Microscopy of Mouth Appendages in Six Species of Barnacles (Crustacea Cirripedia Thoracica)

The morphology and setation of mouth appendages (trophi) are investigated with scanning electron microscopy in the balanomorph barnacles Semibalanus balanoides, Balanus balanusand B. nubilusand in the pedunculate barnacles Pollicipes polymerus, P. cornucopiaand Lepas anatifera.It is difficult to uphold a clearcut distinction between denticles and setae and several types of setae also intergrade with each other. The trophi of Pollicipes polymerusand P. cornucopiahave the most ‘generalized’ morphology. The palps of Pollicipesand L. anatiferaare simpler than those in balanomorphs and carry a single type of seta. In L. anatiferathe mandibles and maxillules are adapted to a semi-predatory feeding habit by carrying large, pointed teeth, but this species lacks the foliate-serrate setae which populate the palps in the other species studied. Compared with Pollicipesand Lepas, the three balanomorphs have palps with a complex setation. The trophi in S. balanoidesdiffer from the two species of Balanusin numerous features of setation and denticulation, notably in having the palps populated by plumodenticulate setae homologous to purely denticulated types in Balanus.It is suggested that SEM studies of barnacle trophi will provide characters of use in estimating phylogeny.     

Acanthodiaptomus denticornis another omnivorous calanoid copepod: description of its mouth appendages and feeding experiments on animal prey

The mouthpart morphology of the freshwater calanoid copepod Acanthodiaptomus denticornis was examined with optical microscopy. The mouthparts have sharp teeth and stout appendages with clawlike setae, typical of omnivorous calanoid mouthpart morphology. Observation of the buccal aperture with Scanning Electron Microscopy shows a large opening permitting feeding on prey as large as Keratella cochlearis. These observations agree with our feeding experiments which show that A. denticornis feed on K. cochlearis.     

Chemosensory neurons in the mouthparts of the spiny lobsters Panulirus argus and Panulirus interruptus (Crustacea: Decapoda)

We studied electrophysiological properties of single chemosensory neurons in the mouthparts of the spiny lobsters Panulirus argus and Panulirus interruptus to complement our growing understanding of the behavioral roles of mouthparts of decapod crustaceans. Food mixtures and 13 single compounds were used to characterize the response specificity, sensitivity, and time course of individual neurons in the endopods of maxilliped 2 and 3. Additional chemoreceptors were found in the mandibular palp and basis of maxilliped 1 but they were not characterized. Neurons were broadly tuned, with the five most potent single compounds being ammonium, adenosine-5′-monophosphate, taurine, glutamate, and aspartate. Cluster analysis indicated that the neurons constitute a heterogeneous population that could be placed into seven groups linked according to their most excitatory compound. These neurons in the mouthparts had concentration-dependent responses, with thresholds between 10⁻⁷ and 10⁻⁴ M and without saturation even at 10⁻³ or 10⁻² M. They also quickly adapted when exposed to their best compounds at 10⁻⁴ and 10⁻³ M. A comparison of the response properties of these neurons in the mouthparts with those of chemosensory neurons in other crustacean appendages shows that neurons in the mouthparts have relatively broad tuning biased toward detecting and resolving high concentrations. Based on these comparisons, we suggest a functional distinction among the chemosensors on the different appendages: long distance detection by the antennae, precise location and collection by the pereiopods, and detailed assessment of quality by the mouthparts.     

Some harpacticoid copepods (Crustacea) of the family Tachidiidae from sublittoral soft sediments in Norway, the Celtic Sea and Gulf of Mexico

From an examination of the original material of G. O. Sars and new material from Björnehodebukta, Oslofjord, Psammis longisetosa Sars is redescribed, noting in particular the presence of 2 inner setae on P2 endopod 2 and 1 inner seta on P4 exopod 1. A new species is described from the Celtic Sea, Paradanielssenia biclavata , characterized by the presence of club-shaped appendages on the mouthparts and differing from P. kunzi Soyer in mouthpart structure and limb setation. Specimens from the Gulf of Mexico have been assigned to a new subspecies, Thompsonula hyaenae elongata , after careful comparison with specimens of the nominate T. hyaenae (I. C. Thompson) from Europe and South Carolina.     

On the diurnal rhythm and feeding electivity in kilka (<Emphasis Type="Italic">Clupeonella cultriventris</Emphasis>) in Rybinsk Reservoir

Diurnal rhythms, feeding electivity, and feeding resources were studied for the new for Rybinsk Reservoir fish species, kilka (Clupeonella cultriventris). It is revealed that, in Rybinsk Reservoir, kilka actively feeds during day time. Selective feeding is a characteristic of this fish. Yearlings prefer small Cyclopoida and their young specimens dominating in zooplankton. Two-year-old fish actively select innumerous but large crustaceans of genera Heterocope, Bythotrephes, Leptodora, and Cyclops. Possible factors determining selection of food items by kilka are discussed. These factors are as follows: zooplankters’ biomasses, the extent of plankters’ aggregations, body size, and visibility of some prey species for kilka (as determined by movement pattern, transparency and cuticle color, presence of eggs, or large eye).     

Fishborne Trematode Metacercariae Detected in Freshwater Fish from Vientiane Municipality and Savannakhet Province, Lao PDR

Freshwater fish from Vientiane Municipality and Savannakhet Province, Lao PDR were examined by the muscle compression and artificial digestion methods to know the infection status with trematode metacercariae. In the fish from Savannakhet, 2 species of metacercariae, Opisthorchis viverrini and Haplorchis taichui, were detected. O. viverrini metacercariae were found in 6 species of fish, Puntius brevis, Hampala dispar, Esomus metallicus, Mystacoleucus marginatus, Puntioplites falcifer, and Cyclocheilichthys armatus. H. taichui metacercariae were detected in 3 species of fish, P. brevis, P. falcifer, and M. marginatus. In the fish from Vientiane, 4 species of metacercariae, O. viverrini, H. taichui, Haplorchis yokogawai, and Centrocestus formosanus, were detected. Among them, O. viverrini metacercariae were found in 7 species of fish, Onychostoma elongatum, C. armatus, H. dispar, P. brevis, Cyclocheilichthys repasson, Osteochilus hasseltii, and Hypsibarbus lagleri. The metacercariae of H. taichui were detected in 6 species of fish, C. repasson, O. elongatum, C. armatus, H. dispar, Labiobarbus leptocheila, and Cirrhinus molitorella. The metacercariae of H. yokogawai were found in 9 species of fish, C. repasson, O. elongatum, C. armatus, H. dispar, Labiobarbus leptocheila, O. hasseltii. C. molitorella, Hypsibarbus wetmorei, and H. lagleri. The metacercariae of C. formosanus were detected in 4 species of fish, C. repasson, P. brevis, O. hasseltii, and C. molitorella. From these results, it is confirmed that fishborne trematode metacercariae, i.e. O. viverrini, H. taichui, H. yokogawai and C. formosanus, are prevalent in various species of freshwater fish from Savannakhet Province and Vientiane Municipality, Lao PDR.     

Appendage patterning in the primitively wingless hexapods Thermobia domestica (Zygentoma: Lepismatidae) and Folsomia candida (Collembola: Isotomidae)

Arthropod appendages are among the most diverse animal organs and have been adapted to a variety of functions. Due to this diversity, it can be difficult to recognize homologous parts in different appendage types and different species. Gene expression patterns of appendage development genes have been used to overcome this problem and to identify homologous limb portions across different species and their appendages. However, regarding the largest arthropod group, the hexapods, most of these studies focused on members of the winged insects (Pterygota), but primitively wingless groups like the springtails (Collembola) or silverfish and allies (Zygentoma) are underrepresented. We have studied the expression of a set of appendage patterning genes in the firebrat Thermobia domestica and the white springtail Folsomia candida. The expressions of Distal-less (Dll) and dachshund (dac) are generally similar to the patterns reported for pterygote insects. Modifications of gene regulation, for example, the lack of Dll expression in the palp of F. candida mouthparts, however, point to changes in gene function that can make the use of single genes and specific expression domains problematic for homology inference. Such hypotheses should therefore not rely on a small number of genes and should ideally also include information about gene function. The expression patterns of homothorax (hth) and extradenticle (exd) in both species are similar to the patterns of crustaceans and pterygote insects, but differ from those in chelicerates and myriapods. The proximal specificity of hth thus appears to trace from a common hexapod ancestor and also provides a link to the regulation of this gene in crustaceans.     

Setal morphology of the grooming appendages of Macrobrachium rosenbergii (Crustacea: Decapoda: Caridea: Palaemonidae) and review of decapod setal classification

Setae are vital in grooming activities and aiding in the removal of epibionts and sedimentary fouling from the body surfaces of decapod crustaceans. Thus, the setal structures and their arrangement on the grooming appendages and sensory structures of the commercially important shrimp, Macrobrachium rosenbergii, were examined using scanning electron microscopy. Macrobrachium rosenbergii is extensively grown in aquaculture and exhibits unique male morphological forms, termed morphotypes. The three male morphotypes are termed blue‐clawed males, orange‐clawed males, and small‐clawed or undifferentiated males and all three differ in their dominance, behavior, body morphology, and reproductive success. Seven setal types, two of which have never been described in the literature, are identified on the grooming appendages (third maxillipeds, first, second, and fifth pereopods) and antennae: simple, serrate, serrulate, spiniform, pappose, crinoid, and spinulate. The latter two setae are newly identified. Certain setal types, such as serrate and serrulate setae were located and associated with specific grooming appendages such as the first pereopods. The types of setae on the grooming appendages varied among females and male morphotypes and the novel setal types (crinoid and spinulate) were found only on two of the male morphotypes. A literature review of terminology related to the structure of setae and setal types in decapod crustaceans is offered as the usage of various terms is ambiguous and conflicting in the literature. The intention of this review is to provide future authors with a comprehensive collection of terms and images that can be used to describe various aspects of setal morphology in decapods. J. Morphol. 275:634–649, 2014. © 2014 Wiley Periodicals, Inc.     

Trophic strategies and functional morphology of feeding appendages, with emphasis on setae, of Upogebia omissa and Pomatogebia operculata (Decapoda: Thalassinidea: Upogebiidae)

Although species of Upogebiidae historically have been considered filter feeders, recent studies show that many species of this group also deposit feed. In this study, the degrees of trophic specialization of two species of this family, Upogebia omissa and Pomatogebia operculata , were analysed. Feeding mechanisms, stomach contents and morphology of the feeding appendages, with emphasis on setae, were examined. U. omissa , found in sandy substrate, is a generalistic feeder while P. operculata inhabits burrows inside corals, being more specialized in filter feeding. Only 21% of the 57 setal types described were common to both species. Setal types were clustered in three main categories: plumed, serrate and plumodenticulate. No simple setae were found. P. operculata has lower setal diversity, with higher ratio of plumodenticulate to serrate setal types than U. omissa. The 1st and 2nd pereiopods have an important role in collecting food. The mouthparts have two main functions: to brush and retain particles so that food can be transported from the pereiopods to the mouth. Generally in these appendages, the dactyli and basal endites are responsible for brushing particles and the meri and coxal endites for particle retention. The diversity of setal types and complexity of their distribution on the appendages may be related to the necessity to select and triturate particles prior to ingestion, reflecting the differences in trophic strategies utilized by U. omissa and P. operculata. Setal characters appear to be indicators of the relative importance of a specific feeding mode for species of this group.     

Morphology of three species of Crotonioidea Thorel, 1876 (Acari: Oribatida), and relations between some genera

The morphology of juveniles of Archegozetes longisetosus Aoki, 1965 (Trhypochthoniidae), and two members of Malaconothridae, Trimalaconothrus angulatus Willmann, 1931, and Malaconothrus monodactylus (Michael, 1888) is described and illustrated, and the tritonymph of A. longisetosus and all juvenile stages of T. angulatus are described and illustrated for the first time. The juveniles of these species differ mainly by the presence of setae f₂ and h₃ in the larva, seta exs and pattern of cuticle in the nymphs, and some setal formulae. Based on the morphology of juvenile stages and adults, the relationship between Malaconothridae and Trhypochthoniidae is discussed, and keys to the larvae and nymphs of some European species of these families are presented.     

The nauplius stages of the cirripede Tetraclita squamosa rufotincta Pilsbry

The nauplius stages of the cirripede Tetraclita squamosa rufotincta Pilsbry from Elat have been cultured and described. There are the usual six larval stages followed by the cypris but the increase in size during development is small compared with many other species. This small increase compares favourably with other species having very large embryos containing an excess of yolk and which do not take external food during larval development. The setation of the larval appendages is less than in other species and on the antenna and mandible does not increase after stage III. It is suggested that the lack of setation, coupled with a reduced development of the labrum, may be a consequence of the lack of a necessity for this species to feed externally during its planktonic life.     

Larval development of the pedunculate barnacles Octolasmis angulata Aurivillius 1894 and Octolasmis cor Aurivillius 1892 (Cirripedia: Thoracica: Poecilasmatidae) from the gills of the mud crab,Scylla tranquebarica Fabricius, 1798

Detailed studies of larval development of Octolasmis angulata and Octolasmis cor are pivotal in understanding the larval morphological evolution as well as enhancing the functional ecology. Six planktotrophic naupliar stages and one non-feeding cyprid stage are documented in details for the first time for the two species of Octolasmis. Morphologically, the larvae of O. angulata and O. cor are similar in body size, setation patterns on the naupliar appendages, labrum, dorsal setae-pores, frontal horns, cyprid carapace, fronto-lateral gland pores, and lattice organs. Numbers of peculiarities were observed on the gnathobases of the antennae and mandible throughout the naupliar life-cycle. The setation pattern on the naupliar appendages are classified based on the segmentation on the naupliar appendages. The nauplius VI of both species undergoes a conspicuous change before metamorphosis into cyprid stage. The cyprid structures begin to form and modify beneath the naupliar body towards the end of stage VI. This study emphasises the importance of the pedunculate barnacle larval developmental studies not only to comprehend the larval morphological evolution but also to fill in the gaps in understanding the modification of the naupliar structures to adapt into the cyprid life-style.     

Prey Detection and Prey Capture in Copepod Nauplii

Copepod nauplii are either ambush feeders that feed on motile prey or they produce a feeding current that entrains prey cells. It is unclear how ambush and feeding-current feeding nauplii perceive and capture prey. Attack jumps in ambush feeding nauplii should not be feasible at low Reynolds numbers due to the thick viscous boundary layer surrounding the attacking nauplius. We use high-speed video to describe the detection and capture of phytoplankton prey by the nauplii of two ambush feeding species (Acartia tonsa and Oithona davisae) and by the nauplii of one feeding-current feeding species (Temora longicornis). We demonstrate that the ambush feeders both detect motile prey remotely. Prey detection elicits an attack jump, but the jump is not directly towards the prey, such as has been described for adult copepods. Rather, the nauplius jumps past the prey and sets up an intermittent feeding current that pulls in the prey from behind towards the mouth. The feeding-current feeding nauplius detects prey arriving in the feeding current but only when the prey is intercepted by the setae on the feeding appendages. This elicits an altered motion pattern of the feeding appendages that draws in the prey.     

Revising the definition of the crustacean seta and setal classification systems based on examinations of the mouthpart setae of seven species of decapods

The crustacean cuticle has numerous projections and some of these projections, the setae, have important mechanical as well as sensory functions. The setae display a wide diversity in their external morphology, which has led to great problems separating setae from other projections in the cuticle and problems in making a consistent classification system. Here, the cuticular projections on the mouthparts of seven species of decapods are examined by scanning and transmission electron microscopy. A new definition is given: a seta is an elongate projection with a more or less circular base and a continuous lumen; the lumen has a semicircular arrangement of sheath cells basally. From the details of the external morphology the mouthpart setae are divided into seven types: pappose, plumose, serrulate, serrate, papposerrate, simple and cuspidate setae, which are suggested to reflect mechanical functions and not evolutionary history. This classification system is compared with earlier systems.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 142 , 233–252.