Malacostraca Research Articles

New malacostracan crustaceans from the Lower Coal Measures (Langsettian, Carboniferous) north Lanarkshire, Scotland

Two malacostracan crustacean genera are described from the Langsettian (upper part of the Bashkirian, Lower Pennsylvanian) of the Scottish coal fields in the Midland Valley of Scotland. One is the youngest occurrence of Tealliocaris Peach, 1908 and was found at Polkemmet Colliery near Whitburn, West Lothian. It is recognized as a new species, Tealliocaris elliotti , based on the presence of eight spines on its scaphocerites and lateral convergent carinae of the telson. The other crustacean is a unique specimen from the Ardenrigg Colliery at Wester Bracco, North Lanarkshire in similar shales of Langsettian age. There are no distinguishing characters preserved that would identify it as a new species, but it can be placed in Palaeocaris Meek and Worthen, 1865 based on the well-preserved features of the tail fan. This is the first record of this genus in Scotland, although specimens of Minicaris brandi Schram, 1979 from the Namurian (Serpukhovian, Upper Mississippian) shales of Bearsden are now here also considered to be a species of Palaeocaris .

Discovery of a new species and host record of Holophryxus Richardson, 1905 (Isopoda: Dajidae) from the central Arctic: a model of enhanced descriptive standards for epicaridean isopods

Abstract Adult isopods of the family Dajidae are exclusively ectoparasitic, typically infecting pelagic malacostracan crustaceans. It is assumed that their life cycle involves free-living and parasitic phases, with planktonic copepods acting as intermediate hosts. Most generic diagnoses proposed in the family have traditionally been incomplete, containing imperfect or misleading information, and characters whose states were wrongly assessed. In an attempt to analyse this state of affairs comprehensively, a taxonomic review and updated diagnosis of the species-rich genus Holophryxus are presented. Both traditional and novel morphological characters are critically assessed, forming the basis for updated differential diagnoses of all currently valid species. The presence of previously ignored sensory structures on the body and pereopods is highlighted and its significance discussed. Holophryxus citriformis sp. nov. is recorded on the common shrimp, Hymenodora glacialis, at 4300 m depth in the central Arctic Ocean. Its description, based on light microscopy and confocal laser scanning microscopy analysis of the female holotype, containing a dwarf male inside its marsupium, is proposed as a model of enhanced descriptive standards required in future morphological research on epicaridean isopods. Definitive host records and geographical distributions of all Holophryxus species are summarized as well as records of larval epicaridean stages associated with copepod hosts.

New Record of Brachyuran Crabs from the Visakhapatnam Coast, Andhra Pradesh, India

Crustaceans are a highly diverse group. In particular, the order Decapoda represents a highly diverse order of malacostracan crustaceans. There are 7620 brachyuran species from 104 genera present globally. In India, 910 marine brachyuran crabs are reported, belonging to 361 genera and 62 families. Andhra Pradesh shows typical habitat heterogeneity for Brachyuran crabs. A total of 121 brachyuran crabs have been reported from Andhra Pradesh. Two species of brachyuran crabs, one is Eucrate indica Castro & P.K.L. Ng, 2010 belonging to the family Euryplacidae Stimpson, 1871 and another is Liagore rubromaculata (De Haan, 1983) belonging to the family Xanthidae MacLeay, 1838 are reported here for the first time from the Visakhapatnam coast, Andhra Pradesh, India. These crabs were collected from the Visakhapatnam fishing harbour in the trawl bycatch during the coral reef and reef-associated faunal survey in Andhra Pradesh. The morphological features, taxonomical systematic, colour and distribution of these crabs are discussed here.

Metabarcoding analysis of marine zooplankton confirms the ecological role of a sheltered bight along an exposed continental shelf.

Zooplankton plays an essential role in marine ecosystems as the link between primary producers (phytoplankton) and higher trophic levels in food webs, and as a dynamic pool of recruits for invertebrates and fish. Zooplankton communities are diverse with a patchy distribution at different spatial scales, influenced by oceanographic processes. The continental shelf of eastern South Africa is narrow and exposed to the western-boundary Agulhas Current, with some shelter against strong directional flow provided by the broader KwaZulu-Natal Bight, a coastal offset adjacent to an estuary. We compared zooplankton species richness, diversity and relative abundance of key taxa among sheltered and exposed shelf areas using metabarcoding and community analysis, to explore the ecological role of the bight in a highly dynamic ocean region. Metabarcoding recovered higher richness and diversity at a finer resolution than could previously be achieved with traditional microscopy. Of 271 operational taxonomic units (OTUs) recovered through metabarcoding, 63% could be matched with >95% sequence similarity to reference barcodes. OTUs were dominated by malacostracan crustaceans (161 spp.), ray-finned fishes (45 spp.) and copepods (28 spp.). Species richness, diversity and the relative abundance of key taxa differed between sheltered and exposed shelf areas. Lower species richness in the bight was partly attributed to structurally homogeneous benthic habitats, and an associated reduction of meroplanktonic species originating from local benthic-pelagic exchange. High relative abundance of a ray-finned fish in the bight, as observed based on fish eggs and read counts, confirmed that the bight is an important fish spawning area. Overall, zooplankton metabarcoding outputs were congruent with findings of previous ecological research using more traditional methods of observation.

Neural organization of the third optic neuropil, the lobula, in the highly visual semiterrestrial crab Neohelice granulata.

The visual neuropils (lamina, medulla, and lobula complex) of malacostracan crustaceans and hexapods have many organizational principles, cell types, and functional properties in common. Information about the cellular elements that compose the crustacean lobula is scarce especially when focusing on small columnar cells. Semiterrestrial crabs possess a highly developed visual system and display conspicuous visually guided behaviors. In particular, Neohelice granulata has been previously used to describe the cellular components of the first two optic neuropils using Golgi impregnation technique. Here, we present a comprehensive description of individual elements composing the third optic neuropil, the lobula, of that same species. We characterized a wide variety of elements (140 types) including input terminals and lobula columnar, centrifugal, and input columnar elements. Results reveal a very dense and complex neuropil. We found a frequently impregnated input element (suggesting a supernumerary cartridge representation) that arborizes in the third layer of the lobula and that presents four variants each with ramifications organized following one of the four cardinal axes suggesting a role in directional processing. We also describe input elements with two neurites branching in the third layer, probably connecting with the medulla and lobula plate. These facts suggest that this layer is involved in the directional motion detection pathway in crabs. We analyze and discuss our findings considering the similarities and differences found between the layered organization and components of this crustacean lobula and the lobula of insects.

Insights into the genetic regulatory network underlying neurogenesis in the parthenogenetic marbled crayfish Procambarus virginalis.

Nervous system development has been intensely studied in insects (especially Drosophila melanogaster), providing detailed insights into the genetic regulatory network governing the formation and maintenance of the neural stem cells (neuroblasts) and the differentiation of their progeny. Despite notable advances over the last two decades, neurogenesis in other arthropod groups remains by comparison less well understood, hampering finer resolution of evolutionary cell type transformations and changes in the genetic regulatory network in some branches of the arthropod tree of life. Although the neurogenic cellular machinery in malacostracan crustaceans is well described morphologically, its genetic molecular characterization is pending. To address this, we established an in situ hybridization protocol for the crayfish Procambarus virginalis and studied embryonic expression patterns of a suite of key genes, encompassing three SoxB group transcription factors, two achaete-scute homologs, a Snail family member, the differentiation determinants Prospero and Brain tumor, and the neuron marker Elav. We document cell type expression patterns with notable similarities to insects and branchiopod crustaceans, lending further support to the homology of hexapod-crustacean neuroblasts and their cell lineages. Remarkably, in the crayfish head region, cell emigration from the neuroectoderm coupled with gene expression data points to a neuroblast-independent initial phase of brain neurogenesis. Further, SoxB group expression patterns suggest an involvement of Dichaete in segmentation, in concordance with insects. Our target gene set is a promising starting point for further embryonic studies, as well as for the molecular genetic characterization of subregions and cell types in the neurogenic systems in the adult crayfish brain.

The significant sex-biased expression pattern of Sp-Wnt4 provides novel insights into the ovarian development of mud crab (Scylla Paramamosain)

The wingless-type MMTV integration site family member-4 (Wnt4), a member of the wingless-related integration site (Wnt) family, is widely accepted as a key regulator of ovarian development in mammals. In this study, a full-length cDNA of Wnt4 (designated as Sp-Wnt4) was cloned, characterized, and functionally studied in mud crab (Scylla paramamosain). The full-length cDNA of Sp-Wnt4 consists of 2659 bp with an open reading frame (ORF) encoding 359 amino acids, a 907 bp 5′-UTR and a 672 bp 3′-UTR. Sp-Wnt4 contains 25 cysteine (Cys) residues and three potential N-glycosylation sites. Sp-Wnt4 protein shared the highest identity (98.9%) to the Wnt4 protein of Portunus trituberculatus. The phylogenetic tree showed that Sp-Wnt4 and Wnt4 protein of Malacostracan crustaceans clustered together, indicating that they had a close genetic distance. Sp-Wnt4 was expressed at a higher level in the ovary compared to other tissues, with the highest expression level at the third stage (O-III) of the ovarian development (P < 0.05). A downward trend was observed in the expression level of Sp-Wnt4 from the embryo stage to crablet stages (P < 0.05). After unilateral eyestalk ablation, the expression level of Sp-Wnt4 significantly increased in testis (14-fold) and downregulated (3.1-fold) in the gill (P < 0.05) of females. In situ hybridization (ISH) assay revealed that Sp-Wnt4 transcripts were mainly localized in the cytoplasm of oocyte cells. These findings showed that Sp-Wnt4 play crucial roles in the ovarian development of S. paramamosain. In conclusion, our study provides novel insights into the evolution and roles of the Wnt4 gene.

Strange eyes, stranger brains: exceptional diversity of optic lobe organization in midwater crustaceans.

Nervous systems across Animalia not only share a common blueprint at the biophysical and molecular level, but even between diverse groups of animals the structure and neuronal organization of several brain regions are strikingly conserved. Despite variation in the morphology and complexity of eyes across malacostracan crustaceans, many studies have shown that the organization of malacostracan optic lobes is highly conserved. Here, we report results of divergent evolution to this 'neural ground pattern' discovered in hyperiid amphipods, a relatively small group of holopelagic malacostracan crustaceans that possess an unusually wide diversity of compound eyes. We show that the structure and organization of hyperiid optic lobes has not only diverged from the malacostracan ground pattern, but is also highly variable between closely related genera. Our findings demonstrate a variety of trade-offs between sensory systems of hyperiids and even within the visual system alone, thus providing evidence that selection has modified individual components of the central nervous system to generate distinct combinations of visual centres in the hyperiid optic lobes. Our results provide new insights into the patterns of brain evolution among animals that live under extreme conditions.

Convergent evolution of optic lobe neuropil in Pancrustacea

A prevailing opinion since 1926 has been that optic lobe organization in malacostracan crustaceans and insects reflects a corresponding organization in their common ancestor. Support for this refers to malacostracans and insects both possessing three, in some instances four, nested retinotopic neuropils beneath their compound eyes. Historically, the rationale for claiming homology of malacostracan and insect optic lobes referred to those commonalities, and to comparable arrangements of neurons. However, recent molecular phylogenetics has firmly established that Malacostraca belong to Multicrustacea, whereas Hexapoda and its related taxa Cephalocarida, Branchiopoda, and Remipedia belong to the phyletically distinct clade Allotriocarida. Insects are more closely related to remipedes than are either to malacostracans. Reconciling neuroanatomy with molecular phylogenies has been complicated by studies showing that the midbrains of remipedes share many attributes with the midbrains of malacostracans. Here we review the organization of the optic lobes in Malacostraca and Insecta to inquire which of their characters correspond genealogically across Pancrustacea and which characters do not. We demonstrate that neuroanatomical characters pertaining to the third optic lobe neuropil, called the lobula complex, may indicate convergent evolution. Distinctions of the malacostracan and insect lobula complexes are sufficient to align neuroanatomical descriptions of the pancrustacean optic lobes within the constraints of molecular-based phylogenies.

Sex, camouflage, marvelous adaptations: A writing assignment that inspires

AbstractWriting assignments offer valuable student learning experiences in both live and online courses. But concerns about the challenges and extra work of marking, and about plagiarism, often deter instructors from using them. I used a writing assignment successfully over 20 years in a one‐term invertebrate biology course, despite enrolments exceeding 100. Structured to maximally engage students yet minimize marking load, the assignment often yielded gems of stories for use in subsequent lectures. The Annotated Bibliography assignment asks students: (a) to précis the justification, main results, and significance of three papers from the primary scientific literature in under 250 words each, and (b) to provide a short (150 word) summary of the broader story connecting the three papers. Students liked this assignment because they could choose any aspect of the biology of any invertebrate genus. This inspired them to explore the literature out of personal interest. It's appealing for instructors, because annotations are compact and therefore easy to read, mark, and inspect for plagiarism. It is appealing to host universities, because it generates extensive use of library resources and motivates students to learn how to use them, and online taxonomic databases, effectively. Here I provide: (a) instructions for this assignment, (b) a straightforward marking rubric, (c) two examples of excellent submissions, and (d) comments on the risk and extent of plagiarism. Appendices provide: detailed instructions, a sample annotation with comments to guide student writing, an online submission web page, an online administrator web page, and PHP scripts for both web pages. Finally, I summarize topics and taxa from nearly 2,000 submissions. The five most popular taxa were cephalopods, insects, malacostracan crustaceans, gastropods, and arachnids. Although aspects of sex or reproduction, and camouflage or mimicry were the most popular topics, one paper on extreme limb movements in stomatopods was cited the most.

&lt;strong&gt;Amphipoda from the Late Neogene of Shanxi, China&lt;/strong&gt;

Amphipods are extremely diverse malacostracan crustaceans that have conquered many environments from oceanic abysses to the terrestrial realm. Despite their impressive modern diversity and abundance, they are particularly rare in the fossil record. Herein, we describe the exceptionally preserved Gammaroidorum yooling sp. nov. from the Late Neogene of Xiaobai Formation near Pandao village, Shanxi, China. Due to the limitation of the preservation, namely the non-preservation of setae, we could not establish a precise generic assignment, so used the collective group Gammaroidorum Jarzembowski, Chény, Fang &amp; Wang, 2020. Although there are still doubts on the precise placement of this new species within amphipods, these fossils are important since they represent the first known fossil occurrence of an amphipod in China. Besides, these fossils have an unusual preservation, being almost transparent in most cases, and being most easily seen by reflecting light on the fossil.

Locomotion in Anaspides (Anaspidacea, Malacostraca) – insights from a morpho-functional study of thoracopods with some observations on swimming and walking

Anaspidacea is probably the most enigmatic higher taxon within the Malacostraca. Representatives of the genus Anaspides are often considered “living fossils” due to their strong resemblance to their Triassic relatives. In comparison to other extant Malacostraca, they possess a high number of plesiomorphic characters. Anaspidacea are often combined with another freshwater taxon, Bathynellacea, into the Syncarida, but actual evidence for monophyletic Syncarida is weak. Other potential sister groups are Eucarida, Euphausiacea, or Euphausiacea + Peracarida. Like Euphausiacea, Mysidacea and “natant” decapods, Anaspidacea show what has been called a “caridoid facies”.In malacostracan crustaceans, a prominent mode of locomotion is swimming, as it almost certainly was for the malacostracans’ common ancestor. However, when considered in detail, swimming is found to take quite different forms in the various taxa. To obtain a better understanding of the evolution of swimming, we analyzed locomotion in several species of Anaspides endemic to Tasmania. The morphology of the protopodal and exopodal musculature as well as the exo- and endoskeletal structures of the thoracopods were examined using 3D reconstruction of CLSM- and μCT data. Various aspects of locomotion were documented and described using recording techniques including in-habitat underwater filming and macro high-speed recording.Our analysis shows the high level of complexity of the muscular arrangement and skeletal construction in the thoracopods of these - in many regards plesiomorphic - malacostracans, and demonstrates the presence of epipodal musculature. Our recordings provide insight into various aspects of locomotion of Anaspides, including the congruence of locomotive kinematics in swimming and walking. Our morphological findings and observations on locomotion in Anaspides are compared to findings in other malacostracan shrimps and discussed in a phylogenetic context, with our analysis providing further support for Xenommacarida (sensuRichter, 1999: Anaspidacea + Euphausiacea + Peracarida). Further, a new hypothesis for the origin of the ventral brood pouch, the marsupium, of Peracarida is discussed. On the basis of a comparison of their morphology and biology, the oostegites which form the marsupium are suggested to be derived thoracopodal endites as present in female Anaspides. Finally, an evolutionary scenario is presented and mapped on a cladogram in which the evolution of malacostracan swimming from a common caridoid ancestor up to the different taxa present today is discussed.

Exploring brain diversity in crustaceans: sensory systems of deep vent shrimps

Abstract The current report focuses on shrimps from deep hydrothermal vents of the Mid-Atlantic Ridge that live in an environment characterized by high hydrostatic pressure, lack of sunlight, and with hot and potentially toxic emissions of black smoker vents. Malacostracan crustaceans display a large diversity of lifestyles and life histories and a rich repertoire of complex behavioral patterns including sophisticated social interactions. These aspects promote this taxon as an interesting group of organisms for those neurobiologists interested in evolutionary transformation of brain structures and evolutionary diversification of neuronal circuits. Here, we explore how analyzing the nervous system of crustacean species from extreme habitats can provide deeper insights into the functional adaptations that drive the diversification of crustacean brain structure.

Behavioral Defenses of Shellfish Prey under Ocean Acidification

Biological interactions between predators and prey constitute a key component of the ecology and evolution of marine systems, and animal behavior can affect the outcome of predator–prey interactions. It has been recently demonstrated that CO2-induced ocean acidification can alter the behavior of marine organisms and potentially alter predator–prey dynamics. This study combines both quantitative (meta-analysis) and qualitative approaches to review the effects of ocean acidification on behavioral prey defenses in marine invertebrates. A systematic literature search identified 34 studies that experimentally assessed behavioral defenses under elevated pCO2 spanning three phyla: crustaceans, echinoderms, and molluscs. A meta-analysis suggested that exposure to elevated seawater pCO2 can negatively affect behavioral defenses in bivalve molluscs and malacostracan crustaceans. By contrast, defenses of cephalopod molluscs seem to be positively impacted by elevated pCO2, whereas gastropods and echinoids appear unaffected. A qualitative assessment of studies on combined effects of ocean acidification and warming revealed that combined effects typically differ from ocean acidification–only effects. Based on a qualitative assessment of three studies to date, neurological interference of GABAA receptors under elevated pCO2 may play a major role in ocean acidification effects on prey defense behaviors; however, more research is needed, and other mechanistic underpinnings are also important to consider. Ultimately, the results of this study suggest that behavioral prey defenses in some shellfish taxa may be vulnerable to ocean acidification, that the effects of ocean acidification are often different under warming scenarios than under present-day temperature scenarios, and that GABAA interference may be an important mechanism underpinning behavioral responses of shellfish prey under ocean acidification. Despite the importance of shellfish behavioral defenses in the ecology and evolution of marine biological communities, however, research to date has only scraped the surface in understanding ocean acidification effects. Increased research efforts on the effects of multiple stressors, acclimation and adaptation, environmental variability, and complex situational and ecological contexts are needed. Studies of fish behavioral defenses under ocean acidification can help streamline hypotheses and experimental approaches, particularly given the similar effects of elevated pCO2 on GABAA function.

Mushroom bodies in Reptantia reflect a major transition in crustacean brain evolution.

Brain centers possessing a suite of neuroanatomical characters that define mushroom bodies of dicondylic insects have been identified in mantis shrimps, which are basal malacostracan crustaceans. Recent studies of the caridean shrimp Lebbeus groenlandicus further demonstrate the existence of mushroom bodies in Malacostraca. Nevertheless, received opinion promulgates the hypothesis that domed centers called hemiellipsoid bodies typifying reptantian crustaceans, such as lobsters and crayfish, represent the malacostracan cerebral ground pattern. Here, we provide evidence from the marine hermit crab Pagurus hirsutiusculus that refutes this view. P. hirsutiusculus, which is a member of the infraorder Anomura, reveals a chimeric morphology that incorporates features of a domed hemiellipsoid body and a columnar mushroom body. These attributes indicate that a mushroom body morphology is the ancestral ground pattern, from which the domed hemiellipsoid body derives and that the "standard" reptantian hemiellipsoid bodies that typify Astacidea and Achelata are extreme examples of divergence from this ground pattern. This interpretation is underpinned by comparing the lateral protocerebrum of Pagurus with that of the crayfish Procambarus clarkii and Orconectes immunis, members of the reptantian infraorder Astacidea.

Analysis of the genetically tractable crustacean Parhyale hawaiensis reveals the organisation of a sensory system for low-resolution vision

BackgroundArthropod eyes have diversified during evolution to serve multiple needs, such as finding mates, hunting prey and navigating in complex surroundings under varying light conditions. This diversity is reflected in the optical apparatus, photoreceptors and neural circuits that underpin vision. Yet our ability to genetically manipulate the visual system to investigate its function is largely limited to a single species, the fruit fly Drosophila melanogaster. Here, we describe the visual system of Parhyale hawaiensis, an amphipod crustacean for which we have established tailored genetic tools.ResultsAdult Parhyale have apposition-type compound eyes made up of ~ 50 ommatidia. Each ommatidium contains four photoreceptor cells with large rhabdomeres (R1–4), expected to be sensitive to the polarisation of light, and one photoreceptor cell with a smaller rhabdomere (R5). The two types of photoreceptors express different opsins, belonging to families with distinct wavelength sensitivities. Using the cis-regulatory regions of opsin genes, we established transgenic reporters expressed in each photoreceptor cell type. Based on these reporters, we show that R1–4 and R5 photoreceptors extend axons to the first optic lobe neuropil, revealing striking differences compared with the photoreceptor projections found in related crustaceans and insects. Investigating visual function, we show that Parhyale have a positive phototactic response and are capable of adapting their eyes to different levels of light intensity.ConclusionsWe propose that the visual system of Parhyale serves low-resolution visual tasks, such as orientation and navigation, based on broad gradients of light intensity and polarisation. Optic lobe structure and photoreceptor projections point to significant divergence from the typical organisation found in other malacostracan crustaceans and insects, which could be associated with a shift to low-resolution vision. Our study provides the foundation for research in the visual system of this genetically tractable species.

The \u201camphi\u201d-brains of amphipods: new insights from the neuroanatomy of Parhyale hawaiensis (Dana, 1853)

BackgroundOver the last years, the amphipod crustacean Parhyale hawaiensis has developed into an attractive marine animal model for evolutionary developmental studies that offers several advantages over existing experimental organisms. It is easy to rear in laboratory conditions with embryos available year-round and amenable to numerous kinds of embryological and functional genetic manipulations. However, beyond these developmental and genetic analyses, research on the architecture of its nervous system is fragmentary. In order to provide a first neuroanatomical atlas of the brain, we investigated P. hawaiensis using immunohistochemical labelings combined with laser-scanning microscopy, X-ray microcomputed tomography, histological sectioning and 3D reconstructions.ResultsAs in most amphipod crustaceans, the brain is dorsally bent out of the body axis with downward oriented lateral hemispheres of the protocerebrum. It comprises almost all prominent neuropils that are part of the suggested ground pattern of malacostracan crustaceans (except the lobula plate and projection neuron tract neuropil). Beyond a general uniformity of these neuropils, the brain of P. hawaiensis is characterized by an elaborated central complex and a modified lamina (first order visual neuropil), which displays a chambered appearance. In the light of a recent analysis on photoreceptor projections in P. hawaiensis, the observed architecture of the lamina corresponds to specialized photoreceptor terminals. Furthermore, in contrast to previous descriptions of amphipod brains, we suggest the presence of a poorly differentiated hemiellipsoid body and an inner chiasm and critically discuss these aspects.ConclusionsDespite a general uniformity of amphipod brains, there is also a certain degree of variability in architecture and size of different neuropils, reflecting various ecologies and life styles of different species. In contrast to other amphipods, the brain of P. hawaiensis does not display any striking modifications or bias towards processing one particular sensory modality. Thus, we conclude that this brain represents a common type of an amphipod brain. Considering various established protocols for analyzing and manipulating P. hawaiensis, this organism is a suitable model to gain deeper understanding of brain anatomy e.g. by using connectome approaches, and this study can serve as first solid basis for following studies.

Functional cytology of the hepatopancreas of decapod crustaceans.

This article reviews the morphogenesis, morphology, histology, ultrastructure, and structural-functional relationships of the hepatopancreas, the main metabolic organ of the Decapoda. The hepatopancreas develops in early larval stages from a pair of lateral lobes of the midgut anlage. In adults, it consists of hundreds of blindly ending tubules that are enveloped by a muscle net consisting of longitudinal and circular fibers. Stem cells at the distal ends of the tubules give rise to three ultrastructurally different epithelial cell types, the R-, F-, and B-cells. Histochemistry, immunohistochemistry, in situ hybridization, and monitoring of ultrastructural changes under different experimental conditions allowed the attribution of functions to these cell types. R-cells serve for the absorption and metabolization of nutrients, storage of energy reserves and minerals, synthesis of lipoproteins for export to other organs, detoxification of heavy metals, and excretion of uric acid. F-cells synthesize digestive enzymes and blood proteins involved in oxygen transport and immune defense. They also detoxify some heavy metals and probably organic xenobiotics. B-cells are assumed to produce and recycle fat emulsifiers. The hepatopancreas tubules lack nerves. The presence of scattered M-cells with putative endocrine function in the epithelium suggests that the hepatopancreas is mainly hormonally controlled. M-cells probably represent a self-perpetuating cell lineage independent from E-cells. The interstitium between the tubules contains connective tissue, arterioles, hemolymph with circulating hemocytes, and fixed phagocytes that eliminate pathogens. The hepatopancreas is histologically and ultrastructurally uniform throughout the Decapoda, despite their broad variety in body size, morphology, life style, and ecology. However, in a few cavernicolous and deep-sea shrimps parts of the hepatopancreas are transformed into large oil storing and bioluminescent compartments. Within the malacostracan crustaceans, the hepatopancreas of the Decapoda is most similar to the digestive gland of the Euphausiacea, supporting close taxonomic relationship of these two taxa.

Structure, function and development of the digestive system in malacostracan crustaceans and adaptation to different lifestyles.

The digestive system of the malacostracan crustaceans, namely the decapods, isopods, amphipods and mysids, is among the most complex organ systems of the animal kingdom serving multiple functions such as food processing, absorption and storage of nutrients, synthesis of digestive enzymes and blood proteins, detoxification of xenobiotics and osmoregulation. It is rather well investigated compared to other invertebrates because the Malacostraca include many ecological keystone species and food items for humans. The Decapoda and Peracarida share food processing with chewing and filtering structures of the stomach but differ with respect to morphology and ultrastructure of the digestive glands. In the Peracarida, the digestive glands are composed of few, relatively large lateral caeca, whereas in the Decapoda, hundreds to thousands of blindly ending tubules form a voluminous hepatopancreas. Morphogenesis and onset of functionality of the digestive system strongly depend on the mode of development. The digestive system is early developed in species with feeding planktonic larvae and appears late in species with direct lecithotrophic development. Some structures of the digestive system like the stomach ossicles are rather constant in higher taxa and are of taxonomic value, whereas others like the chewing structures are to some degree adapted to the feeding strategy. The nutrient absorbing and storing cells of the digestive glands show considerable ultrastructural variation during moult cycle, vitellogenesis and starvation. Some of the various functions of the digestive system are already assigned to specific sections of the digestive tract and cell types, but others still await precise localization.

Macrobenthic functional feeding groups in a microtidal monsoonal estuary (Kodungallur–Azhikode estuary, India)

The functional feeding groups of macrobenthos in the Kodungallur–Azhikode estuary were studied on a monthly basis for a two year period (2009–2011). The main aim of the study was to understand the distribution pattern of macrobenthic functional feeding groups and their relationship to environmental drivers in the estuary. Malacostracan crustaceans dominated the system (60%) by numerical density, while molluscs contributed significantly to macrobenthic biomass (63%). Many species exploit the same class of resources within an assemblage of macrofaunal groups. The suspension feeding corophiid amphipod Americorophium triaeonyx was the most represented macrofaunal species. Other dominant macrofaunal feeding groups were the suspension feeding hydroid colonies of Obelia bidentata, surface deposit feeding polychaetes Prionospio cirrifera, suspension feeding mussels Arcuatula senhousia, carnivorous isopods Cirolana fluviatilis and sub-surface deposit feeding polychaetes Capitella sp. The sampling stations were compared using taxonomic distinctness (AvTD), and variations in taxonomic distinctness (VarTD), the values of AvTD and VarTD for all stations during the entire monthly survey fell within the confidence intervals of probability funnel (95%, p<0.05). However, a significant variation was noticed in the values between stations (AvTD: F (6,161) = 3.105, p=0.007; VarTD: F (6,161) = 2.489, p=0.025). The abundance biomass curves were plotted separately for each site as well as combined for the entire estuary. The relatively high negative trend was observed in the station 5 (W=−0.139) which indicates potential for the relatively high disturbance among all other stations. However, the W-value for the entire estuary was -0.079, which depicted moderate disturbance.