Olfactory projection neuron pathways in two species of marine Isopoda (Peracarida,Malacostraca, Crustacea)

The neuroanatomy of the olfactory pathway has been intensely studied in many representatives of Malacostraca. Nevertheless, the knowledge about bilateral olfactory integration pathways is mainly based on Decapoda. Here, we investigated the olfactory projection neuron pathway of two marine isopod species, Saduria entomon and Idotea emarginata, by lipophilic dye injections into the olfactory neuropil. We show that both arms of the olfactory globular tract form a chiasm in the center of the brain, as known from several other crustaceans. Furthermore, the olfactory projection neurons innervate both the medulla terminalis and the hemiellipsoid body of the ipsi- and the contralateral hemisphere. Both protocerebral neuropils are innervated to a comparable extent. This is reminiscent of the situation in the basal decapod taxon Dendrobranchiata. Thus, we propose that an innervation by the olfactory globular tract of both the medulla terminalis and the hemiellipsoid body is characteristic of the decapod ground pattern, but also of the ground pattern of Caridoida.     

Phylogenetic analysis of the Malacostraca (Crustacea)

The Malacostraca comprises about 28 000 species with a broad disparity in morphology, anatomy, embryology, behaviour and ecology. The phylogenetic relationships of the major taxa are still under debate. Is the Leptostraca the sister group of the remaining Malacostraca, or is this taxon more closely related to other Crustacea? Does the Stomatopoda or the Bathynellacea represent the most basal taxon within the remaining taxa? Is the Peracarida monophyletic or are some peracarid taxa more closely related to other ‘caridoid’ taxa? Is the Thermosbaenacea part of the Peracarida or its sister group, and how much support is there for a taxon Amphipoda + Isopoda? To answer these questions a phylogenetic analysis of the Malacostraca combining different phylogenetic approaches was undertaken. In a first step, the monophyly of the Malacostraca including the Leptostraca is shown using the ‘Hennigian approach’. A computer cladistic analysis of the Malacostraca was carried out with NONA and PEE ‐WEE , based on 93 characters from morphology, anatomy and embryology. Nineteen higher malacostracan taxa are included in our analysis. Taxa whose representatives are exclusively fossils were not included. The Leptostraca was used as an operational out‐group. The present analysis supports the basal position of the Stomatopoda. Syncarida and Peracarida (including Thermosbaenacea) are supported as monophyletic, the Eucarida is not. Instead a sister‐group relationship is suggested between Euphausiacea and Peracarida (including Thermosbaenacea), with the Syncarida as the sister group to both taxa. Certain embryonic characters are interpreted as support for the monophyly of the Peracarida (without Thermosbaenacea) because convergences or reversals of these characters seem implausible. Within the Peracarida, the Mysidacea (Lophogastrida + Mysida) represents the sister group to the remaining taxa. A sister‐group relationship between Amphipoda and Isopoda is not supported.     

Benthic isopods (Crustacea,Malacostraca) from the Ross Sea,Antarctica: species checklist and their zoogeography in the Southern Ocean

In this study isopod species of the Ross Sea were investigated. Literature until May 2008 was checked to provide an overview of all known and described species in the Ross Sea. This species checklist was then enlarged through material of the 19th Italica expedition in 2004. During this expedition for the first time a small mesh net (500 μm) was used. Nine thousand four hundred and eighty one isopod specimens were collected during this expedition. Through this material the number of isopod species in the Ross Sea increased from 42 to 117 species, which belong to 20 families and 49 genera. Fifty-six percentage of the isopods species collected during the Italica expedition are new to science. The zoogeography of the 117 species was investigated. A non-transformed binary presence-absence data matrix was constructed using the Bray–Curtis coefficient. The results were displayed in a cluster analysis and by nonmetric multidimensional scaling (MDS). This paper gives a first insight into the occurrence and distribution of the isopod species of the Ross Sea.     

Spermiogenesis in Anaspides tasmaniae (Thomson) (Crustacea,Malacostraca, Syncarida)

Spermiogenesis of the syncarid Anaspides tasmaniae (subclass Eumalacostraca) was investigated by transmission electron microscopy. The spermatozoan of Anaspides is an ovoid cell with an acrosome covering the anterior pole and a lobulated nucleus and mitochondria occupying the rest of the cell. A long subacrosomal filament bypasses the nucleus and forms a spiral that supports a thin extension of the posterior cytoplasm, giving the spermatozoan a bell-shaped appearance. No flagellum is present at any stage. The immobile spermatozoans are embedded in a hard capsule, secreted by the cells of the wall of the vas deferens.     

The terrestrial isopods (Crustacea) of Aldabra

Among a collection of terrestrial isopods from Aldabra were 13 species, six of which are new: Littorophiloscia aldabrana, Philoscina insularis, Trichorhina triocellata, Nagurus kensleyi, Pseudodiploexochus cuspidatus and Venezillo pseudoparvus. Alloniscus pigmentatus Budde-Lund and Tura angusta Budde-Lund are re-described and figured. The taxonomy of six species of Alloniscus Dana from the Indian Ocean is discussed and Alloniscus nacreus Collinge from Madagascar is illustrated. The species Armadillo parvus Budde-Lund and Sphaerillo collaris Budde-Lund are transferred to the genus Venezillo Verhoeff. The distribution of all the species is given together with the composition of the oniscidean fauna of Aldabra.     

Occurrence, diversity and community structures of peracarid crustaceans (Crustacea, Malacostraca) along the southern shelf of Greenland

The species composition of peracarids (Crustacea: Malacostraca) of the Greenland shelf between 60°N and 65°N was investigated by means of 10 qualitative epibenthic samples in relation to environmental factors. In total, 59,234 specimens were collected belonging to 219 species. The relative abundance was much higher on the western shelf (total of 41,594 specimens) than on the eastern shelf (total of 17,640 specimens with same effort). Three species were new to science, while five records were new for the investigated area. The species composition was dominated by amphipods (58%), while the relative abundances of isopods (25%), cumaceans (11%) and tanaidaceans (6%) were much lower. Diversity and evenness were similar in the eastern and the western areas. Multivariate analyses of the species relative abundances divided the peracarids into a southeastern and southwestern Greenland fauna. Based on a correlation analysis between faunal data and five environmental variables, the separation between the two areas was mainly based on sediment type. Species contributing most to the separation between eastern and western fauna included the amphipods Hardametopa nasuta, Photis reinhardi and Phoxocephalus holboelli, the isopods Pleurogonium spinosissimum, Iolella laciniata and Nannoniscus oblongus and the cumaceans Leucon cf. nasicoides and Campylaspis horrida. Species distribution patterns are discussed in the light of habitat and feeding preferences.     

Phyllocarid remains (Malacostraca, Crustacea) from the basal Famennian (Late Devonian) of the Montagne Noire (Southern France)

From the early Famennian of the Montagne Noire 19 different morphotypes of probably phyllocarid (Crustacea) affinities are described. Apart from formerly unknown enamel-like structures that veil the uppermost tips of the denticles on most of the gnathal lobe morphs, the stratigraphic implications concerning extinction behaviour across the Kellwasser mass extinction event and during early Famennian diversification are discussed. In addition, phyllocarids in the Famennian seem to form a useful stratigraphic tool for biostratigraphical correlation. Therefore, three basal Famennian phyllocarid assemblage zones are distinguished.      

Comparative analysis of the circulatory system in Amphipoda (Malacostraca, Crustacea)

We present data on the haemolymph vascular system (HVS) in four representatives of the major amphipod lineages Gammaridea, Hyperiidea and Caprellidea based on corrosion casting and three‐dimensional reconstructions of histological semi‐thin sections. In all these species the HVS comprises a dorsal pulsatile heart, which is continued in the body axis by the anterior and posterior aortae. The heart is equipped with three pairs of incurrent ostia. The number of cardiac arteries that lead off the heart varies among species: in the studied Gammaridea four pairs occur, in Hyperia galba only the three posterior pairs of cardiac arteries occur, while in Caprella mutica cardiac arteries are absent. In all the studied species the posterior aorta leads as a simple tube into the pleon attached to the dorsal diaphragm. The anterior aorta runs from its origin in the anterior part of the second thoracic segment into the cephalothorax. Both pairs of antennae have an arterial supply off the anterior aorta. An overview of previously studied species including our present findings shows the amphipod HVS to be relatively uniform and the gammarid form is discussed as being closest to the ground pattern of Amphipoda.     

Ultrastructure of CaCO3 deposits of terrestrial isopods (Crustacea, Oniscidea)

 The ultrastructure of the sternal CaCO₃ deposits of 3 species of the Diplochaeta and 15 of the Crinochaeta was investigated by means of scanning electron microscopy of fractured surfaces. In the Diplochaeta Li-gia italica and L. oceanica, the deposits consist exclusively of individual spherules with diameters between 0.2 and 1.4 μm. No material was observed within the spaces between the spherules. In Ligidium hypnorum, two structurally distinct regions exist. A proximal layer resembling the deposit of Ligia italica and L. oceanica and a distal layer in which the spherules appear to be fused with each other. In the species of the Crinochaeta, the CaCO₃ deposits comprise a spherular region which resembles the deposits of Ligidium hypnorum, and a homogeneous layer located between the spherular part of the deposit and the hypodermal cell layer. In some species the diameters of the spherules may be up to 3.1 μm. In the homogeneous layer and the distal spherular layer more calcium per volume can be stored than in the proximal spherular layer in which the spaces between the spherules are devoid of CaCO₃. This suggests that the multiple layered deposits are an adaptation to terrestrial life, as a consequence of the need for increased resorption of cuticular calcium. Accepted: 7 January 1997     

Limb ontogeny and trunk segmentation in Nebalia species (Crustacea, Malacostraca, Leptostraca)

The ’egg-larval’ development of two species of Nebalia has been examined with SEM. Various details concerning limb ontogeny and trunk segmentation are described. The most important of these are the following. The tripartite state of the peduncle of antenna 2 in the adult of Nebalia species is derived from the fusion of the third and fourth podomeres, present in late larvae. The proximal portion of the mandible in the adult of Nebalia brucei, carrying the ’coxal process’, is, based on the ontogenetic evidence, interpreted as the combined basis and coxa, and the bipartite palp is interpreted as the endopod. The early development of the thoracopods and the three anteriormost pleopods is identical. They all start as laterally directed, biramous limb buds. This suggests that tagmatisation of the trunk of the Leptostraca (and other Malacostraca) has been developed from an ancestor with an undivided trunk region with serially similar limbs. Certain early stages reveal an extra, ’eighth’, limbless pleon segment, as compared with the normal number of seven pleomeres of adult Leptostraca. The presence of a row of ventral, sternitic, triangular processes between the bases of the thoracopods, as they are found in certain stages of a species of Nebalia, is suggested as a possible ground pattern for the Malacostraca. Accepted: 1 February 2000     

Flabelliferan isopods (Crustacea) parasitic on freshwater fishes of Thailand

Two species of flabelliferan isopods are described based on specimens found in the gill cavities and/or body surfaces of 13 species of Thai inland fishes. They are: Alitropus typus Milne-Edwards, 1840 (Aegidae) from Belodontichthys dinema, Cirrhinus jullieni, Cyclocheilichthys enoplos, Cynoglossus microplepis, Hampala macrolepidota, Kryptopterus bleekeri, Mystus nemurus, Mystus wyckii, Pangasianodon gigas, Pangasius larnaudii, Puntius gonionotus and Wallagonia attu; and Corallana grandiventra n. sp. (Corallanidae) from Pangasianodon gigas and Tilapia nilogica. This report establishes the first true occurrence of Corallana in the inland water.     

Cleavage and gastrulation of the dendrobranchiate shrimp Penaeus monodon (Crustacea,Malacostraca, Decapoda)

The cleavage pattern of the black tiger shrimp Penaeus monodon was analyzed from the first division until gastrulation. Observations were based on microscopy combined with the use of fluorescent dyes, histological techniques, and computer based three-dimensional reconstructions. Early cleavage is holoblastic and follows a stereotypic pattern, which largely corresponds to what is known from other dendrobranchiate decapods. However, for the first time in this group, we report the presence of an intracellular structure throughout early development. This intracellular body (icb) marks the lineage of one of the two enlarged and division-delayed mesendoderm cells that initiate gastrulation. The identity of the icb as a natural marker and putative determinant of the germ line and its implications on the establishment of the body axes are discussed. The icb as a landmark reveals that the same stereotypic cell division pattern can lead to different fates of individual cells. Hence, the results of this study permit an additional approach to study the relation between cell lineage pattern and the identity of cell lineages.     

The organization of the olfactory lobes in Euphausiacea and Mysidacea (Crustacea,Malacostraca)

Summary The structural organization of the olfactory lobes in representatives of euphausiid and mysid crustaceans was investigated and compared, also with these structures described in other crustaceans and in insects. In the investigated euphasiid and mysid species, the olfactory-globular tract and the position of cell clusters associated with the olfactory lobes show a similar arrangement. This arrangement is in agreement with that described in decapod crustaceans. The olfactory lobe neuropil in representatives of both taxa shows glomerular arrangement. These glomeruli are partly enclosed in a glial wrapping, and they represent the only site where synaptic contacts are established within the olfactory lobes. This glomerular arrangement appears similar to that described in the antennal lobe of insects, but differs from the columnar arrangement described in decapod crustaceans. Furthermore, about 15–20 FMRFamide-like immunoreactive globuli cells were labeled and they occupy a similar position in the investigated species. Neurites from these cells terminate only in the olfactory lobe glomeruli, and they are therefore regarded as intrinsic interneurons. The absence of serotonin-like immunoreactivity in the olfactory lobes is a feature only ascribed to the euphausiids and mysids. A specific neuropil area is present in male mysids, and it occupy a position forward of the olfactory lobe. The male-specific neuropil in mysids and the macro-glomerular in insects complex are interpreted as analogous structures.     

Histological studies on the marsupium of two terrestrial isopods (Crustacea,Isopoda, Oniscidea)

The marsupium, a brood pouch in peracarid crustaceans (Crustacea, Malacostraca) has evolved in terrestrial environment for providing nutrition and optimal conditions for embryogenesis. In the present study we give details on the histology and ultrastructure of its constituting elements such as oostegites and cotyledons. Marsupia of two different eco-morphological types of woodlice, namely the non-conglobating species Trachelipus rathkii Brandt, 1833 and the conglobating species Cylisticus convexus De Geer, 1778 were investigated. Light microscopic (LM) studies showed some differences in the main structure of the two species’ brood pouch: in Trachelipus rathkii, a ‘clinger’ type woodlice, the oostegites bend outwards during brood incubation as growing offspring require more space, while in Cylisticus convexus, a ‘roller’ type isopod, the sternites arch into the body cavity to ensure space for developing offspring and still allowing conglobation of the gravid females. The quantitative analysis of the oostegites’ cuticle proved that the outer part is about 2.5 - 3 times thicker compared to the inner part in both species. Electron microscopic (TEM) examinations show only small histological differences in the oostegites and cotyledon structure of the two species. Cellular elements and moderately electron dense fleecy precipitate are found in the hemolymph space between the two cuticles of oostegites. The cells contain PAS positive polysaccharide areas. TEM studies revealed some differences in the cotyledon ultrastructure of the two species. Cotyledons of Trachelipus rathkii consist of cells with cristate mitochondria and granular endoplasmic reticulum with cisterns. Cotyledons of Cylisticus convexus consist of cells with densely cristate mitochondria and ribosomes attached to vesicular membrane structures. In both species cells with electron dense bodies were observed. We conclude that - besides the differences in marsupial shapes - the fine structure of the oostegites and cotyledons is hardly affected by the eco-morphological type, specifically the conglobating or non-conglobating character of the studied species.     

The origin of terrestrial isopods (Crustacea: Isopoda: Oniscidea)

Living isopods of the suborder Oniscidea (commonly called woodlice) are the only group of Crustacea almost entirely composed of terrestrial forms. Furthermore, woodlice are completely independent from the aquatic environment from which they originally arose. From marine ancestors, woodlice are a key taxon to study the conquest of the land among arthropods because of their interesting gradation of morphological, physiological and behavioral adaptations for terrestriality. However, the origin and evolution of this model group are still poorly known. Herein, we provide a synthesis of the oniscidean fossil record to replace this group in a deep-time context. Because members of the Oniscidea are difficult to fossilize, their fossil record alone is undoubtedly fragmentary and not representative of their complete evolutionary history, but it maintains an important relevance by providing reference points. To date, the first attested occurrences of Oniscidea are recorded from the Early Cretaceous. At this time, woodlice were already widely distributed (from Western Europe to Eastern Asia) with several species. By evaluating phylogenetic studies, palaeobiogeographic context of fossil specimens and current biological considerations, we discuss and support a pre-Pangaean origin of the Oniscidea, in the Late Paleozoic—most likely during the Carboniferous.     

Angustidontidae (Crustacea: Malacostraca) from the Upper Devonian of Ukraine and Belarus

Previously unknown specimens of angustidontid crustaceans from the Frasnian and Famennian of Ukraine and from the Famennian of Belarus are described.     

Tanaidacea (Crustacea,Malacostraca) of two polar fjords: Kongsfjorden (Arctic) and Admiralty Bay (Antarctic)

The tanaidacean faunas of two polar fjords, Kongsfjorden (Arctic) and Admiralty Bay (Antarctic), were compared. The results show that Tanaidacea in the southern fjord are more diversified than those in the northern one. This difference is especially evident in species richness (12 species vs 3 species, respectively), but is not too significant in terms of diversity. In both polar fjords, the highest densities of tanaids were noted in sites where mud was swept off by the water current or eroded off steep bottom expoing coarser mineral particles used for tube building. The distribution of tanaids is suggested to be based on the joint action of inter alia factors such as the quality of bottom sediments, sedimentation ratio, accessibility of food, predation pressure, behaviour and heterogeneity of habitats.An erratum to this article can be found at     

Isolation and characterization of microsatellite markers from the marine isopods Serolis paradoxa and Septemserolis septemcarinata (Crustacea: Peracarida)

This study reports the successful isolation of highly informative microsatellite marker sets for two marine serolid isopod species. For Serolis paradoxa (Fabricius, 1775), 13, and for Septemserolis septemcarinata (Miers, 1875), eight polymorphic microsatellite markers were isolated using the reporter genome enrichment protocol. The number of alleles per locus (N(A) ) and the observed heterozygosity (H(O) ) encompass a wide range of variation within S. paradoxa (N(A) 3-31, H(O) 6-89%) and S. septemcarinata (N(A) 2-18, H(O) 9-94%). The suitability of the newly isolated markers for population genetic studies is evaluated.