Morphological changes in external and internal feeding structures during the transition phyllosoma-puerulus-juvenile in the Western Rock Lobster (Panulirus cygnus,Decapoda: Palinuridae)

External and internal feeding structures of the pelagic final phyllosoma, the transitional puerulus, and the benthic juvenile Western Rock Lobster, Panulirus cygnus, were studied by means of scanning electron microscopy. The study revealed that the external feeding structures of phyllosomata are well equipped for capture and mastication of food. The foregut, however, is not clearly divided into pyloric and cardiac regions and a gastric mill is absent, although a comb row and gland filter are present. Juveniles, on the other hand, have a well-developed gastric mill and gastric teeth, and a cardiopyloric valve separates the foregut into cardiac and pyloric regions. External mouthparts of juveniles are suitable for mastication of solid food particles and bear numerous setae. In contrast, external mouthparts of pueruli are largely non-setose. Furthermore, although the foregut is differentiated into pyloric and gastric regions and a gland filter and comb row are present, a functional gastric mill is absent during the puerulus stage. Absence of such structures indicates that the puerulus may be a non-feeding stage. It is postulated that absence of (or reduced) feeding may be a response to an increased risk of predation rather than a result of the considerable morphological changes taking place during the transition from a planktonic to a benthic lifestyle, as has been previously proposed. © 1994 Wiley-Liss, Inc.     

Pharynx and intestine

The alimentary canal of polychaetes consists of a foregut, midgut, and hindgut. The alimentary canal shows different specializations even in homonomously segmented polychaetes. The foregut gives rise to the buccal cavity, pharnyx and oesophagus, the midgut may be divided into a stomach and the intestine proper. Since polychaetes use a wide spectrum of food sources, structures involved in feeding vary as well and show numerous specializations. In the foregut these specializations may be classified as one of the following types: dorsolateral folds, ventral pharynx, axial muscular pharynx, axial non-muscular proboscis and dorsal pharynx. The latter, typical of oligochaetous Clitellata, occurs rarely in polychaetes. The structure, evolution and phylogenetic importance of these different types are described and discussed. Axial muscular and ventral pharynges may be armed with jaws, sclerotized parts of the pharyngeal cuticle. Terminology, structure, occurrence and development of the jaws are briefly reviewed. Special attention has been paid to the jaws of Eunicida including extinct and extant forms. Conflicting theories about the evolution of the jaws in Eunicida are discussed. The epithelia of the intestine may form a pseudostratified epithelium composed of glandular cells, absorptive cells and ciliated cells or only one cell type having similar functions. A conspicuous feature in the intestine of certain polychaetes is the occurrence of unicellular tubular structures, called enteronephridia. So far these enteronephridia are only known in a few meiofauna species.     

Comparative chewing efficiency in mammalian herbivores

Although the relevance of particle size reduction in herbivore digestion is widely appreciated, few studies have investigated digesta particle size across species in relation to body mass or digestive strategy. We investigated faecal particle size, which reflects the size of ingesta particles after both mastication and specialized processes such as rumination. Particle size was measured by wet sieving samples from more than 700 captive individuals representing 193 mammalian species. Using phylogenetic generalized least squares, faecal particle size scaled to body mass with an exponent of 0.22 (95% confidence interval: 0.16–0.28). In comparisons among different digestive strategies, we found that (1) equids had smaller faecal particles than other hindgut fermenters, (2) non-ruminant foregut fermenters and hindgut fermenters had similar-sized faecal particles (not significantly different), and (3) ruminants had finer faecal particles than non-ruminants. These results confirm that the relationship between chewing efficiency and body mass is modified by morphological adaptations in dental design and physiological adaptations to chewing, such as rumination. This allometric relationship should be considered when investigating the effect of body size on digestive physiology, and digestion studies should include a measure of faecal particle size.     

Hensen's node gives rise to the ventral midline of the foregut: implications for organizing head and heart development

Patterning of the ventral head has been attributed to various cell populations, including endoderm, mesoderm, and neural crest. Here, we provide evidence that head and heart development may be influenced by a ventral midline endodermal cell population. We show that the ventral midline endoderm of the foregut is generated directly from the extreme rostral portion of Hensen's node, the avian equivalent of the Spemann organizer. The endodermal cells extend caudally in the ventral midline from the prechordal plate during development of the foregut pocket. Thus, the prechordal plate appears as a mesendodermal pivot between the notochord and the ventral foregut midline. The elongating ventral midline endoderm delimits the right and left sides of the ventral foregut endoderm. Cells derived from the midline endoderm are incorporated into the endocardium and myocardium during closure of the foregut pocket and fusion of the bilateral heart primordia. Bilateral ablation of the endoderm flanking the midline at the level of the anterior intestinal portal leads to randomization of heart looping, suggesting that this endoderm is partitioned into right and left domains by the midline endoderm, thus performing a function similar to that of the notochord in maintaining left-right asymmetry. Because of its derivation from the dorsal organizer, its extent from the forebrain through the midline of the developing face and pharynx, and its participation in formation of a single midline heart tube, we propose that the ventral midline endoderm is ideally situated to function as a ventral organizer of the head and heart.     

Development and evolution of adult feeding structures in Caenogastropods: overcoming larval functional constraints

SUMMARY Comparative study of the developing foregut in three species of caenogastropods, including an herbivorous grazer ( Lacuna vincta ) and two carnivores ( Euspira [ Polinices ] lewisii and Nassarius mendicus ), suggests how the specialized adult foregut of a carnivorous neogastropod evolved within a life cycle having a planktotrophic larva. Postmetamorphic feeding structures (buccal cavity and radular sac) in all three species achieve advanced differentiation in the larval stage, permitting juvenile feeding at 3 days postmetamorphosis. Recent phylogenetic hypotheses for the Gastropoda predict that foregut developmental patterns in E. lewisii and N. mendicus are derived, relative to that of L. vincta. In hatching larvae of these three, the anlage of postmetamorphic feeding structures is a small patch of nonciliated cells embedded in the ventral wall of the larval foregut and the patch soon forms an outpocketing. During subsequent morphogenesis, Euspira lewisii and N. mendicus share a developmental novelty that involves semi-isolation of the developing, postmetamorphic buccal cavity and radular sac from the larval foregut and formation of a new, definitive mouth at metamorphosis. Nassarius mendicus , a neogastropod, embellishes this novelty by adding the entire anterior esophagus and valve of Leiblein ( de novo structures) to the semi-isolated buccal cavity. Therefore, a valve and long stretch of muscular anterior esophagus, which are necessary for feeding with a pleurembolic proboscis, are preformed in the larval stage of this neogastropod without interfering with larval feeding. The inferred evolutionary events leading to postmetamorphic feeding specialization in N. mendicus are invisible in adults; they require reconstruction from comparative developmental analysis.     

Studies on the tardigrades. II. Fine structure of the pharynx of milnesium tardigradum doyère

The fine structure of the pharynx and associated valve of the tardigrade Milnesium tardigradum is presented. The pharynx consists of a triradiate, cuticle lined lumen surrounded by radially arranged muscle cells and special apical cells which cap each of the ventricles of the lumen. The valve is an unusual structure marking the anterior limit of the pharynx. It is a specialization of the cuticular lining of the foregut and the apical cells of the pharynx. The significance and phyletic affinities of these structures are discussed.     

Structural observations on the alimentary canal of Paranthessius anemoniae, a copepod associate of the snakelocks anemone Ammonia sulcata

Light and electron microscopy has shown the alimentary canal of Paranthessius to be composed of clearly defined foregut, midgut and hindgut regions. The spacious foregut is cuticle-lined and separated from the midgut by a valve. The midgut epithelium is composed of columnar cells with an apparent secretary/absorptive rôle, and amoeboid cells thought to engulf material from the lumen. The amoeboid cells have large electron-dense central vacuoles containing carbohydrate-and protein-staining material. These cells appear to be sloughed off into the lumen to form part of a faecal pellet. Apart from their digestive rôle the midgut cells store lipid and it is considered possible that they have an osmoregulatory function. The hindgut epithelium cell type, lacks a cuticular layer and is thought to be mainly concerned with absorption. The alimentary canal is surrounded by strands of longitudinal and circular muscle.     

Development and functional morphology of the foreguts of larvae and postlarvae of three crustacean decapods

The development of the foregut structure and the digestive function of the decapods Litopenaeus vannamei, Sesarma rectum and Callichirus major larvae and post larvae were examined. The protozoeal foregut of L. vannamei is simple, lacking a cardiopyloric valve and bearing a rudimentary filter press. In mysis, the filter press is more developed. In the juvenile stage, grooves and a small lateral tooth arise. In S. rectum, the foregut has a functional cardiopyloric valve and a filter press. The megalopal and juvenile stages of this species have a gastric mill similar to those in adult crabs. In C. major, the foregut of the zoeae is specialized, with the appearance of some rigid structures, but no gastric mill was found. Calcified structures are observed in the megalopae and they become more developed in the juvenile stage. The results support suppositions, previously reported in other studies, that feeding behavior of each larval and postlarval stage is directly related to the morphological characteristics of the foreguts.     

No distinct stratification of ingesta particles and no distinct moisture gradient in the fore-stomach of non-ruminants: The wallaby,peccary, hippopotamus,and sloth

Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-ruminants. This study describes the distribution of feed particles (and inorganic material) and dry matter (DM) in the digestive tract of non-ruminant foregut fermenters. Results from passage trials led us to hypothesize that specific particle-sorting mechanisms, as observed in ruminants, are unlikely in non-ruminants. Therefore, no systematic particle size distribution effects (indicative of a sorting mechanism) should be evident in the fore-stomachs of these animals, but differences in fluid and particle retention suggest that differences in fluid concentration (measured as DM) could occur in the foregut of macropods and hippos. The gut content of eleven Bennett's wallabies (Macropus rufogriseus), six collared peccaries (Pecari tajacu), three pygmy hippos (Hexaprotodon liberiensis), two common hippos (Hippopotamus amphibius) and one two-toed sloth (Choloepus didactylus) were analyzed with an emphasis on the fore-stomach. The ventral and dorsal regions in sacciform compartments, and peripheral and central regions in tubular compartments, were examined. Results were not uniform across the species studied. A potential sedimentation mechanism was observed firstly by the accumulation of sand in the fore-stomach of the peccary and sloth, and secondly by the lower DM content in peripheral versus central and ventral versus dorsal regions of the fore-stomach of the wallabies and common hippos, respectively. However, pair-comparisons for different gut regions of wallabies and peccaries yielded no differences in mean particle size between fore-stomach regions. To conclude, some digesta fractionation does occur in the fore-stomach of the studied groups of non-ruminants, but not in a uniform manner, which in turn is in accordance with morphological dissimilarities of their respective foregut structures. The absence of systematic fractionation effects in non-ruminant foregut fermenters emphasizes the innovative character of the sorting mechanism in ruminants.     

Foregut morphology and ontogeny of the mud crab Dyspanopeus sayi (Smith, 1869) (Decapoda,Brachyura, Panopeidae)

The morphology of the foregut of the Say's mud crab Dyspanopeus sayi was described in adults and larvae. The ossicle system was illustrated based on a staining method with Alizarin-Red. The gastric teeth and cardio-pyloric valve were dissected and examined using optical and scanning electron microscopy. In the adults, the morphology of ossicles and gastric teeth of D. sayi is very similar to the related species Rhithropanopeus harrisii. The foregut of first zoea (ZI) presented a functional cardio-pyloric valve while the filter press was lacking. The filter press was observed in the pyloric chamber from ZII. The most significant changes in morphology take place after metamorphosis from ZIV to megalopa, including the occurrence of the gastric mill. The organization and morphology of many megalopal foregut ossicles are recognizable in the adult phase, although the morphology of the gastric teeth differs from the morphology of adults. A correlation of gastric mill structures with food preferences and their contribution to the phylogeny are briefly discussed.     

Foregut morphology and ontogeny of the spider crab Maja brachydactyla (Brachyura,Majoidea, Majidae)

We describe the morphology of the foregut of the spider crab Maja brachydactyla Balss, 1922, from first larval stage to adult, with detailed stage‐specific documentation using light and scanning electron microscopy. A total of 40 ossicles have been identified in the foregut of adults of M. brachydactyla using Alizarin‐Red staining. The morphological pattern of the ossicles and gastric mill is very similar to other Majoidea species with only a few variations. The foregut of the zoeae stages appeared as a small and simple cavity, with a cardio‐pyloric valve that separates the stomach into cardiac and pyloric regions. The pyloric filter is present from the first zoea, in contrast to the brachyuran species which have an extended larval development. Calcified structures have been identified in the cardio‐pyloric valve and pyloric region of the zoeal stages. The most significant changes in foregut morphology take place after the metamorphosis from ZII to megalopa, including the occurrence of the gastric mill. In the megalopa stage, the foregut ossicles are recognizable by their organization and general morphology, but are different from the adult phase in shape and number. Moreover, the gastric teeth show important differences: the cusps of the lateral teeth are sharp (no molariform); the dorsal tooth have a small, dentate cusp (not a well‐developed quadrangular cusp); and the accessory teeth are composed of one sharp peak (instead of four sharp peaks). The gastric mill ontogeny from megalopa to adult reveals intermediate morphologies during the earlier juvenile stages. The relationship between gastric mill structures with food preferences and their contribution to the brachyuran phylogeny are briefly discussed. J. Morphol. 276:1109–1122, 2015. © 2015 Wiley Periodicals, Inc.     

Differentiation of animals from different age classes by means of pellet size: Assessment of a field method in European rabbits

Estimating population age structures by faecal pellets sizes is a commonly used field method in some mammal species. We examined the validity of this method in European rabbits based on 1113 pellets from 226 animals with known age, by measuring the intra-individual variation in pellet size and studying the explained variance of calibration curves describing the relation between pellet size and individual age. In addition, we applied a simulation model in order to estimate the accuracy of this method. Pellet size showed a high intra-individual variation and was only moderately correlated with the animals’ age. Modelling revealed that the population age structure assessed by this method deviated considerably from the given structure, indicating a systematic estimation error. We conclude that this method can lead to strongly biased results, restricting its validity. We provide estimation errors, which might be considered if estimates of age structure in wild rabbits populations based on faecal diameters are conducted.     

Abundance and germination capability of resting cysts of Alexandrium spp. (Dinophyceae) from faecal pellets of macrobenthic organisms

The Alexandrium spp. resting cysts were found abundantly in faecal pellets collected from the bottom sediments at two stations in Hiroshima Bay. It is considered that these faecal pellets were excreted by the macrobenthos, such as polychaeta and mollusca, based on their size and morphology. Polychaeta was the most dominant macrobenthos, and mollusca was the second most dominant group in Hiroshima Bay. The resting cysts of Alexandrium spp. in the bottom sediments at the two stations were counted in both the faecal pellets of macrobenthos and in the surrounding sediment. As a result, the number of cysts in the faecal pellets accounted for 28.9-35.2% of total cysts. In addition, cysts isolated from faecal pellets had almost the same germination ability as those in the sediment. Thus, Alexandrium cysts are tolerant to the predation and digestive processes of macrobenthic organisms.     

Leader of the pack: faecal pellet deposition order impacts PCR amplification in wombats

DNA sourced from faeces is notoriously less reliable than that from tissue. Hence, understanding whether faecal pellet quality varies within faecal piles may be important for sample selection. We hypothesized that the order in which faecal pellets are deposited may influence microsatellite polymerase chain reaction (PCR) amplification success from sampled faeces, more specifically, that first pellets deposited will have signatures of greater success than later ones. In a first test of the hypothesis, first and later-deposited pellets, as determined from the direction of footprints, were collected from fresh (overnight) faecal piles of northern hairy-nosed wombats (Lasiorhinus krefftii). DNA extracts were typed for seven microsatellite loci. We found that faecal deposition order significantly affected optical density of bands on autoradiographs (a measure of PCR amplification success) when the first faecal pellet was compared with the last one, but not when the first pellet was only distinguishable from later ones. The absence of a difference in amplification rate between first and later pellets is likely a reflection of the overall high amplification success in this study. That first pellets deposited yield more product suggests they contain more intestinal cells. Although further comparisons are needed, these results may inform sample selection in species for which success of microsatellite PCR amplification of faecal DNA is low. Deposition order may have more of an impact on amplification success and genotyping errors as faecal age increases.     

Functional morphology of the stomach of Corophium volutator Pallas

Corophium volutator Pallas is a small amphipod crustacean which burrows in inter-tidal mud on the British coast, and feeds on organic detritus, mainly vegetable, by selecting particles from the mud.
The alimentary canal consists of foregut, midgut and hindgut. The midgut is produced into a pair of anterior dorsal caeca, a pair of ventral caeca and a pair of posterior dorsal caeca.
The cardiac stomach has a large number of chitinous plates or ridges beset with hooks and spines for the trituration of food.
The pyloric stomach has long fine bristles which form an eifective filter apparatus and allow only fine particles of food to pass into the midgut, where they are digested and absorbed.
The hepato-pancreas secrete digestive enzymes and store reserve food material as oil globules.     

The proventriculus of some trichopterous larvae

A well-developed proventriculus is present in larvae of the Polycentropodidae and Hydropsychidae. Its structure varies greatly between species but there is a common bilaterally symmetrical pattern based on a pair of posterior ventral folds. These are continuous with the sides of a ventral gap in the fold of foregut that invaginates into the midgut. Modifications of this basic structure to form either triturating or filtering devices occur, and there are others where the mechanism of food treatment is not immediately apparent and may be complex.     

Virus particle production in lysogenic bacteria exposed to protozoan grazing

Electron microscopy was used to investigate the apparent induction of virus particle production in bacteria undergoing digestion by ciliates. Results showed that numbers of bacteria containing virus particles increased by a factor of 25 when enclosed within ciliate food vacuoles. It was also found that 10% of these particles survived the digestion process to be released back into the aquatic habitat within faecal pellets. The possibility of virus gene transfer occurring between lysogenically infected bacteria that survive the ciliate digestive processes, is also considered.     

Importance of copepod faecal pellets to the fate of the DSP toxins produced by Dinophysis spp.

An ingestion experiment was carried out in Rı́a de Pontevedra (Spain) with the copepod Temora longicornis in order to determine ingestion rates of the DSP toxin-producers, Dinophysis spp. (Dinophyceae), and the excretion rate of Dinophysis spp. cells within the faecal pellets. Ingestion rate was a function of dinoflagellate abundance and did not vary with either the amount, or the composition of the co-occurring phytoplankton species in the food suspension. Faecal pellet production increased at higher food concentrations. Intact Dinophysis spp. cells representing 34.4% of the total Dinophysis cells ingested by the copepods were found within the pellets. T. longicornis was the only dominant copepod species in the area that fed on Dinophysis spp., thus the pellets produced by T. longicornis were the main source of copepod “toxic” pellets in the media during blooms of Dinophysis spp. These “toxic” pellets might contribute to the maintenance of the toxic algal blooms, if the cells inside the pellets remain viable, can spread the potential toxicity of the toxic dinoflagellates throughout the pelagic food web due to coprophagy, and/or be an important toxic vector into the benthic food web. However, during a Dinophysis spp. bloom, the percentage of cells excreted daily within the pellets was lower than 1% of the total dinoflagellate population and, moreover, copepod faecal pellets represent a small fraction of the sinking material in this area. Although it was not possible to measure the amount of toxins in the pellets, we concluded that copepod faecal pellets do not have an important role in the transport of DSP toxins through the food web in this area.     

Food handling efficiency and particle size selectivity by the southern brown shrimp penaeus subtilis fed a dry pelleted feed

This study investigated the feed handling efficiency and size selectivity of four size groups of Penaeus subtilis fed three commercial feed particle sizes. Shrimp feeding behaviour was recorded with a video‐camera, installed below a glass aquarium, where one shrimp at a time was introduced and allowed to feed. A total of 163 specimens of P. subtilis were examined. Results indicated that over 59% of all food particles placed in the mouth by shrimp were completely or partially consumed, regardless of size. Large pellets however were less preferred than small ones. Manipulation capacity and capture success were also greater when shrimp were fed small particles. Shrimp size had no significant effect on manipulation efficiency, indicating that within the feed size range examined, food handling by juvenile shrimp was as efficient as adults. These results suggest that in aquaculture systems, the use of crumbles and broken pellets may be preferable to large pellets.