Water fleas (Daphnia magna) provide a separate ventilatory mechanism for their brood

The planktonic filter feeder Daphnia magna depends on a steady oxygen supply by convection. In the ventral carapace chamber, this convection is established by the feeding current which is generated by the movement of the thoracic limbs. The present study revealed that this movement can cause an additional flow of medium which passes through the brood chamber of the animal. To visualise this current, ink or fluorescent microspheres were released by a microcapillary near the posterior opening of the brood chamber. The tracks of these probes were monitored by video microscopy. Digital motion analysis was used for the determination of flow velocity and flow rate. Ambient medium entered the brood chamber at the abdomen of the animal and moved then to the anterior end of the brood chamber before entering the ventral carapace chamber. Two horizontal lamellae, which are attached at both sides of the trunk and project laterally to contact the carapace walls, almost completely separate the dorsal brood chamber from the ventral carapace chamber. Water can only pass these barriers through small depressions in these lamellae at the level of the 3rd and 4th appendages. Female daphnids with embryos at late developmental stages showed more rapid water currents in the brood chamber than those with younger embryos. Moreover, animals showed higher flow rates when exposed to hypoxic conditions. As the oxygen uptake rate of older embryos is approximately three times higher than that of younger embryos, the enhanced brood chamber current could improve the oxygen availability for both the mother and its brood under conditions of reduced oxygen availability.     

External Anatomy of the Female Genital (Eighth) Limbs and the Setose Openings in Myodocopid Ostracodes (Cypridinidae)

The external anatomy of various cypridinid female genital (8th) limbs is described. Scanning electron microscopy shows that each female cypridinid genital limb has a medial depression and associated pore (= spermatophore pore); over all of which a male cements a spermatophore. The limb terminates laterally in a superficially smooth rounded knob bearing an additional small opening (= lateral pore). Dorsolateral to this genital limb there are grouped setae, previously called "brush organs", that are really paired, slit–like posterolateral openings, which are probably subdermally united to the female genital limbs. The "brush organs" of all myodocopid females also are likely to be the setose openings. The setose openings are probably homologous to the setose central lobe of male cypridinid copulatory limbs, but not homologous to the limb–like "brush organ" described for some podocopid males. We speculate that the eggs are fertilized via the spermatophore pore associated with the attached spermatophore, and that they are released from the slightly larger and more lateral setose openings into the brood chamber of the posterodorsal area of the bivalved carapace.     

Water fleas (Daphnia magna) provide a separate ventilatory mechanism for their brood

The planktonic filter feeder Daphnia magna depends on a steady oxygen supply by convection. In the ventral carapace chamber, this convection is established by the feeding current which is generated by the movement of the thoracic limbs. The present study revealed that this movement can cause an additional flow of medium which passes through the brood chamber of the animal. To visualise this current, ink or fluorescent microspheres were released by a microcapillary near the posterior opening of the brood chamber. The tracks of these probes were monitored by video microscopy. Digital motion analysis was used for the determination of flow velocity and flow rate. Ambient medium entered the brood chamber at the abdomen of the animal and moved then to the anterior end of the brood chamber before entering the ventral carapace chamber. Two horizontal lamellae, which are attached at both sides of the trunk and project laterally to contact the carapace walls, almost completely separate the dorsal brood chamber from the ventral carapace chamber. Water can only pass these barriers through small depressions in these lamellae at the level of the 3rd and 4th appendages. Female daphnids with embryos at late developmental stages showed more rapid water currents in the brood chamber than those with younger embryos. Moreover, animals showed higher flow rates when exposed to hypoxic conditions. As the oxygen uptake rate of older embryos is approximately three times higher than that of younger embryos, the enhanced brood chamber current could improve the oxygen availability for both the mother and its brood under conditions of reduced oxygen availability.List of symbols:a specific oxygen consumption rate (nmol mm-³ h-¹), K Krogh constant for oxygen diffusion (nmol mm-¹ h-¹ kPa-¹, P_c critical oxygen partial pressure (kPa), P o₂ oxygen partial pressure (kPa), r radius (mm), s distance (mm), t time (ms)     

Stages and other aspects of the embryology of the parthenogenetic Marmorkrebs (Decapoda, Reptantia, Astacida)

The early development of the parthenogenetic Marmorkrebs (marbled crayfish) is described with respect to external morphology, cell lineage, and segment formation. Due to its parthenogenetic reproduction mode, the question arises whether or not the marbled crayfish is a suitable model organism for developmental approaches. To address this question, we describe several aspects of the embryonic development until hatching. We establish ten stages based on characteristic external changes in the living eggs such as blastoderm formation, gastrulation process, formation and differentiation of the naupliar and post-naupliar segments, limb bud differentiation, and eye differentiation. The study of the post-naupliar cell division patterns, segment formation, and engrailed expression reveals distinct similarities to that of other freshwater crayfish. On this basis, we evaluate the possibility of a generalization of ontogenetic processes in the Marmorkrebs for either freshwater crayfish or other crustacean developmental systems.     

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.     

Cuticle morphogenesis in crustacean embryonic and postembryonic stages

The crustacean cuticle is a chitin-based extracellular matrix, produced in general by epidermal cells and ectodermally derived epithelial cells of the digestive tract. Cuticle morphogenesis is an integrative part of embryonic and postembryonic development and it was studied in several groups of crustaceans, but mainly with a focus on one selected aspect of morphogenesis. Early studies were focused mainly on in vivo or histological observations of embryonic or larval molt cycles and more recently, some ultrastructural studies of the cuticle differentiation during development were performed. The aim of this paper is to review data on exoskeletal and gut cuticle formation during embryonic and postembryonic development in crustaceans, obtained in different developmental stages of different species and to bring together and discuss different aspects of cuticle morphogenesis, namely data on the morphology, ultrastructure, composition, connections to muscles and molt cycles in relation to cuticle differentiation. Based on the comparative evaluation of microscopic analyses of cuticle in crustacean embryonic and postembryonic stages, common principles of cuticle morphogenesis during development are discussed. Additional studies are suggested to further clarify this topic and to connect the new knowledge to related fields.     

Germ band differentiation in the stomatopod Gonodactylaceus falcatus and the origin of the stereotyped cell division pattern in Malacostraca (Crustacea)

We analysed aspects of the embryonic development of the stomatopod crustacean Gonodactylaceus falcatus focusing on the cell division in the ectoderm of the germ band. As in many other malacostracan crustaceans, the growth zone in the caudal papilla is formed by 19 ectoteloblasts and 8 mesoteloblasts arranged in rings. These teloblasts give rise to the cellular material of the largest part of the post-naupliar germ band in a stereotyped cell division pattern. The regularly arranged cells of the genealogical units produced by the ectoteloblast divide twice in longitudinal direction. The intersegmental furrows form within the descendants of one genealogical unit in the ectoderm. Hence, embryos of G. falcatus share some features of the stereotyped cell division pattern with that in other malacostracan crustaceans, which is unique among arthropods. In contrast to the other malacostracan taxa studied so far, stomatopods show slightly oblique spindle direction and a tilted position of the cells within the genealogical units. The inclusion of data on Leptostraca suggests that aspects of stereotyped cell divisions in the germ band must be assumed for the ground pattern of Malacostraca. Moreover, Stomatopoda and Leptostraca share the lateral displacement of cells during the mediolateral divisions of the ectodermal genealogical units in the post-naupliar germ band. The Caridoida within the Eumalacostraca apomorphically evolved the strict longitudinal orientation of spindle axes and cell positions, reaching the highest degree of regularity in the Peracarida. The phylogenetic analysis of the distribution of developmental characters is the prerequisite for the analysis of the evolution of developmental patterns and mechanisms.     

Reflections on the Phylogenetic Position of the Cephalocarida

This essay re-evaluates the phylogenetic position of the Cephalocarida in the light of the recently discovered Orsten (Upper Cambrian) crustaceans, the living Remipedia, and new interpretation of the Paleozoic ‘trilobitomorphs’. The Orsten crustaceans reinforce the belief that cephalocarid external morphology is primitive, except to show that the early crustacean trunk limb was almost surely biramous. The epipod appears to be a synapomorphy of the Cephalocarida, Branchiopoda and Malacostraca, thus justifying the existence of the Thoracopoda, which is coequal to the Maxillopoda and Remipedia. External morphology of the Remipedia is too specialized to support the hypothesis that it approximates that of the urcrustacean. Crustaceans and chelicerates are still best regarded as subgroups of the Schizoramia.     

Development of the turtle carapace: Implications for the evolution of a novel bauplan

The chelonian carapace is composed of the endochondral ribs and vertebrae associated with a specialized dermis. The ribs are found in an aberrant position compared to those of all other tetrapods; they are superficial and dorsal to the limb girdles. This morphological arrangement, which constitutes the unique chelonian Bauplan, is examined from a developmental perspective. Embryos of Chelydra serpentina were studied during stages of carapace development. Tissue morphology, autoradiography, and indirect immunofluorescent localization of adhesion molecules indicate that the outgrowth of the embryonic carapace occurs as the result of an epithelial–mesenchymal interaction in the body wall. A carapacial ridge composed of mesenchyme of the dermis and overlying ectoderm is formed dorsal to the ectodermal boundary between somitic and lateral plate mesoderm. It is the anlage of the carapace margin, in which the ribs will eventually terminate. The ectoderm of the carapacial ridge is thickened into a pseudostratified columnar epithelium, which overlies a condensation in the mesenchyme of the dermis. Patterns of cell proliferation and the distribution of N-CAM and fibronectin in the carapacial ridge are consistent with patterns seen in other structures initiated by epithelial–mesenchymal interactions such as feathers and limb buds. Based on an analogy to this developmental mechanism in the development of the limb skeleton, a further analogy with the evolution of the limbs from lateral fin folds is used to form a hypothesis on the evolution of the carapace from elements of the primitive reptilian integument.     

CAMPANIAN CRUSTACEAN BURROW SYSTEM FROM ISRAEL WITH BROOD AND NURSERY CHAMBERS REPRESENTING COMMUNAL ORGANIZATION

Abstract:  Phosphorite-filled crustacean burrows associated with a Campanian-age omission surface in the north-western Negev are described. The phosphatic burrow casts weather out displaying scratches (bioglyphs) and two types of local swellings (chambers), which are flattened normal to the course of the burrow. The more abundant chamber type is a flattened spheroid (diameter 45–50 mm) or a flattened, highly prolate ellipsoid of larger dimensions, with bioglyphs. The other type is a flattened spheroid (diameter 45 mm), gently rounded on the upper side and flat on the base. Rings of elevations on the cast (representing moats) form interconnected circlets, each capped by about eight rounded hemispherical tubercles (4 × 4 mm) (pits on original), the whole forming a discrete network. The first type of chamber may have hosted the young (nursery chamber) and/or stored food. The second type of cast replicates a chamber with a pitted floor, which may have formed a brood chamber for 60–70 spherical eggs, each about 3 mm in diameter. Brood chambers in crustacean burrow systems were previously suspected, but only at burrow terminations. The interpreted K-type breeding strategy, brood care and associated functions require a high degree of social organization, none of which has been observed in extant crustaceans, but all occur within social insects.     

Brood care in a Silurian ostracod

An exceptionally preserved new ostracod crustacean from the Silurian of Herefordshire, England, preserves eggs and possible juveniles within its carapace, providing an unequivocal and unique view of parental brood care in the invertebrate fossil record. The female fossil is assigned to a new family and superfamily of myodocopids based on its soft-part anatomy. It demonstrates a remarkably conserved egg-brooding reproductive strategy within these ostracods over 425 Myr. The soft-tissue anatomy urges extreme caution in classifying 'straight-hinged' Palaeozoic ostracods based on the carapace alone and fundamentally questions the nature of the shell-based Palaeozoic ostracod record.     

Brooding and embryonic development in the crustacean Paragnathia formica (Hesse, 1864) (Peracarida: Isopoda: Gnathiidae)

The crustacean family Gnathiidae Leach, 1814 (Peracarida: Isopoda) comprises 12 genera known mostly from marine environments. Juvenile gnathiid isopods are fish ectoparasites, feeding on blood and tissue fluids in order to complete their life cycles. Gnathiid juvenile development generally includes three moults, the last involving metamorphosis to non-feeding, adult stages. The blood meal ingested by juveniles provides resources for adult survival, reproduction and embryological development. Reproductive biology in the brackish water gnathiid, Paragnathia formica (Hesse, 1864), is unusual amongst crustaceans, since brooding females have paired internal uterine sacs, rather than an external brood pouch. Known embryological development for P. formica includes three post gastrulation stages. In the current study, brooding and embryological development in this gnathiid were reexamined using histological and fluorescence methods, and by scanning electron microscopy. Novel observations were made of the blastodisc and germ cell migration within developing eggs, release of Stage 2 embryos by rupture of embryonic membranes, the in utero moult of Stage 2 to Stage 3 embryos, and the asynchronous development of the brood within the paired uterine sacs. These findings highlight the remarkable nature of brooding in P. formica and expand the paucity of knowledge of embryological development in gnathiids in general.     

Mating Behaviour in Laevicaudatan Clam Shrimp (Crustacea,Branchiopoda) and Functional Morphology of Male Claspers in a Phylogenetic Context: A Video-Based Analysis

Clam shrimps are freshwater branchiopod crustaceans which often present complicated breeding systems including asexual reproduction (parthenogenesis) and mixed mating systems (in androdioecious species both selfing and outcrossing occurs due to the co-presence of hermaphrodites and males). Reproductive patterns of Spinicaudata, which contains most clam shrimp species, have received much attention. Another group of clam shrimps, Laevicaudata, which holds a key position in branchiopod phylogeny, has practically not been studied. As a part of the mating process, males clasp to the carapace margin of the females with a pair (or two pairs) of anterior trunk limbs modified as claspers. Previous studies have shown that clasper morphology is important in a phylogenetic context, and that some parts of the claspers in Spinicaudata and Laevicaudata may have undergone a remarkable parallel evolution. Here we have used video microscopy to study aspects of the mating behaviour, egg extrusion, and fertilization in Lynceus brachyurus (Laevicaudata). It is shown that fertilization is likely to be external and that the peculiar tri-lobed lateral lamellae of female''s hind body assist in guiding the egg mass to the exopodal egg carriers where they are collected by their distal setation. The functional morphology of the male claspers was studied in detail by close-up video recordings. The movable “finger” of the clasper bends around the female''s carapace edge and serves to hold the female during mating. The larger palp grasps around the female carapace margin in a way very similar to the movable “finger”, possibly indirectly providing sensory input on the “finger” position. A brief comparative study of the claspers of a spinicaudatan clam shrimp showed both similarities and differences to the laevicaudatan claspers. The presence of two pairs of claspers in Spinicaudata seems to give males a better hold of the female which may play a role during extended mate guarding.     

Cypris metamorphosis, injection and earliest internal development of theRrizocephalan Loxothylacus panopaei (Gissler). Crustacea: Cirripedia: Rhizocephala: Sacculinidae.

Rhizocephala is a group of crustaceans that exclusively parasitizes other crustaceans. It is taxonomically placed within the class Cirripedia, the barnacles, with which it shares a unique larval type, the cyprid. The main objective of the cyprid is to find and irreversibly attach to a suitable substratum and initiate metamorphosis. In the presumed sister group to Rhizocephala, the true barnacles or Thoracica, metamorphosis leads to a juvenile filter-feeding version of the adult organism. In Rhizocephala the female cyprid settles on the integument of a crustacean and undergoes metamorphosis into a kentrogon that possesses a hollow cuticular-tube structure, the stylet, which penetrates the integument of the host and acts as a guide tube for the prospective internal parasite. The first, hitherto unknown endoparasitic stage of a rhizocephalan, the vermigon, was recently discovered (Glenner and H?eg [1995] Nature 377:147-150) and its migration through the hemolymph of the host, as well as its internal development, was described in Glenner et al. ([2000] Mar Biol 136:249-257). The present article provides detailed information on kentrogon and vermigon formation, the injection process, and the succeeding developmental stages up to the stage of the earliest primordium reported from the literature. The anlage of the ovary is traced back to the free-swimming cypris stage and it is implied that the mesoderm and ectoderm of the endoparasite are already differentiated in the cyprid.     

Carapace epithelia are rich in large filamentous actin bundles in Daphnia magna,Daphnia pulex,and Sida crystallina (Crustacea: Cladocera)

Cladocerans (water fleas) are planktonic crustaceans that typically have a bivalved carapace. Each valve of the carapace consists of two cuticle‐secreting epithelial layers that are separated by a hemolymphatic chamber and joined by pillar structures. Ultrastructural analyses in several species of Cladocera have shown that the carapace epithelia and pillars contain filamentous structures of unknown composition. In the present study we used a fluorescent phalloidin conjugate to show that the carapaces of three cladocerans, Daphnia magna, D. pulex, and Sida crystallina, are rich in large bundles of filamentous actin (F‐actin). In D. magna we employed confocal microscopy and orthogonal views of three‐dimensional reconstructions to show that these bundles extend radially from foci in the pillars towards the integument surfaces, and their structure is consistent with that of contractile stress fibers. Using a fluorescent lipophilic stain, DiOC₆(3), we show that the F‐actin bundles are distributed in membrane‐rich regions within the carapace epithelia, and that, in the superficial epithelium, these may be large membrane‐bound organelles. In D. magna, the F‐actin bundles are present in embryonic, juvenile instar, and adult, developmental stages, and through development the bundles become larger, contain more F‐actin, and become more widely spaced. We present an alignment of the deduced amino acid sequences of six putative D. pulex actin genes, and discuss the implications that their respective sequences have on the likelihood of their inclusion into the F‐actin bundles of the carapace. Our identification of these large F‐actin bundles within the pillars of three cladocerans provides new insight into the role these structures play in influencing carapace dynamics within this order.     

Axogenesis in the stomatopod crustacean Gonodactylaceus falcatus (Malacostraca)

Abstract. The formation of the central nervous system of the stomatopod crustacean Gonodactylaceus falcatus is described by means of antibody stainings against synapsin and α-tubulin. It is shown that the longitudinal fiber tracts of the ventral nervous system are formed by two centers of origin comprising a number of pioneer neurons, one at the posterior part of the forming brain, the other in the area of the telson anlage at the posteriormost region of the embryo. In addition to the lateral anlagen of the connectives, a median longitudinal nerve is formed beginning in the mandibular segment neuromere. In contrast to those of other segments, the mandibular ganglia are connected by a single commissure. The brain forms a circumoral ring. There is evidence that the deutocerebrum possesses praestomodeal and poststomodeal commissural fibers. The anlage of the nauplius eye reveals a specific pattern of pigment and sensory cells with the two pigment cells expressing synapsin. Clear differences between the expression patterns of synapsin and α-tubulin recommend the combination of a variety of antibodies to gain a complete picture of embryonic neuroanatomy. Our results show overall similarities to other malacostracan and non-malacostracan crustaceans. The comparisons with other crustaceans and arthropods indicate homology of crustacean nauplius eyes, a circumoral deutocerebrum, and a more widespread occurrence of posterior pioneer neurons forming the axon scaffold of the ventral central nervous system than previously thought.     

Egg laying, maternal care and development of young in the scolopendromorph centipede, Cormocephalus anceps anceps Porat

The methods used to observe the construction of the brood chamber and rearing of the young by the female Cormocephalus anceps are described. The period of egg laying and the maternal care, essential for the survival of both eggs and brood, were observed and the behaviour of the female during this time is recorded. Two broods were successfully reared to first year adolescent stages in the laboratory. The two embryonic and three adolescent stages are briefly described and their developmental times recorded. Subsequent stages of development are noted by increase in size until sexual maturity is attained in the second year. The length of life and number of broods per female remains to be investigated.