The phylogenetic position of the East Asian freshwater crayfish Cambaroides within the Northern Hemisphere Astacoidea (Crustacea, Decapoda, Astacida) based on molecular data

The phylogenetic position of the four East Asian freshwater crayfish species of the genus Cambaroides is not settled. Morphological phylogenetic analyses suggest close affinities of Cambaroides with North American Cambaridae. This view is based mainly on characters of the male and female reproductive organs. In contrast, the only molecular phylogenetic analysis so far available leaves the phylogenetic position of Cambaroides unresolved. The question of whether Cambaroides is monophyletic or paraphyletic has so far been neither addressed morphologically nor with molecular data sets. Here we present the first comprehensive phylogenetic analysis of all four currently described species of Cambaroides in the framework of Northern Hemisphere freshwater crayfish (Astacoidea) relationships based on partial sequences of two mitochondrial genes ( CO1 and 12S rRNA). Despite some evidence in favour of a monophyletic Cambaroides more data is needed to resolve this question. Our analyses suggest a close relationship of the North American Cambaridae and the European Astacidae, leaving the Asian Cambaroides basal to them. If these results hold true the similar reproductive organs of Cambaroides and American Cambaridae must be either homoplastic or ancestral for Northern Hemisphere Astacoidea.     

Early embryonic development of the freshwater shrimp Caridina multidentata (Crustacea,Decapoda, Atyidae)

Decapod crustaceans show a great diversity of developmental modes at all levels. In particular, early cleavage varies from total via mixed to superficial modes and from determinate cleavage with a stereotyped pattern to indeterminate cleavage. However, the ground pattern of early decapod development is not clear. To address this problem, we studied the early embryonic development of the caridean shrimp Caridina multidentata with a combination of confocal laser scanning microscopy, scanning electron microscopy, 4D microscopy and 3-D reconstruction software. Despite a yolk-rich egg, the cleavage is holoblastic and shows a distinct pattern of blastomere arrangement, characterized by two interlocking cell bands. This resembles the conditions in dendrobranchiate shrimps, which most likely are the sister group to Pleocyemata to which C. multidentata belongs. Hence, our results offer the possibility to assume total cleavage with blastomeres arranged in two interlocking cell bands as ancestral cleavage mode for Decapoda.     

Brood care in freshwater crayfish and relationship with the offspring's sensory deficiencies

Prolonged brood care is one of the evolutionary clues for the successful colonization of freshwater habitats by freshwater crayfish (Astacida). By means of macrophotography, light microscopy, and scanning electron microscopy we investigated all phases of brood care in freshwater crayfish, with particular emphasis on the morphological structures involved. We selected the recently discovered parthenogenetic marbled crayfish (species identity not yet known) as a model organism due to its fast reproduction and high resistance to handling stress. In order to examine if there is a causal relationship between brood care and the developmental status of the offspring's sensory apparatus, we additionally investigated major sense organs of juvenile Stages 1-5 in comparison with those of the adults. Brood care in the marbled crayfish is characterized by initial and final "active" phases dominated by specific maternal or juvenile behavior and a medial "passive" phase based more on the action of temporarily developed structures rather than on behavior. The most remarkable feature of this period, which includes permanent carrying of the eggs and the first two juvenile stages under the mother's abdomen, is safeguarding of hatching by a telson thread that keeps the helpless newborn hatchlings linked to the egg cases on the maternal pleopods and thus prevents them from being lost. Further important transient structures are the recurved hooks on the first pereiopods of Stage 1 and 2 juveniles that are used to firmly attach these nonfeeding stages to the mother's abdomen. In hatchlings all sense organs necessary for an independent life, such as eyes, olfactory aesthetascs, gustatory fringed setae, hydrodynamic receptor hairs, and statocysts are not developed or are underdeveloped, making brood care indispensable. Most of these sense organs appear in Stage 2 juveniles, but only from Stage 3, the first freelancing and feeding stage, are all sense organs well developed and operating, thus reducing brood care in this final period to temporary provisioning of shelter. Brooding of the eggs and postembryonic brood care are to some extent also found in other freshwater Decapoda like freshwater crabs and aeglid anomurans, but safeguarding of hatching is confined to the Astacida only. This sophisticated mode of passive brood care is unique in the animal kingdom and is apparently related to the sensory deficiencies of the first juvenile stage.     

Development of the female reproductive system in the freshwater crayfish Cherax quadricarinatus (Decapoda, Parastacidae)

Abstract. The differentiation of the female reproductive system from a macroscopic and microscopic point of view was studied in Cherax quadricarinatus. For this characterization, 184 females were dissected and processed for the histological analysis. From the differentiation of the ovary up to its maturity, three ovarian morphotypes could be distinguished macroscopically: parallel strands without any contact between them, an H-shaped ovary, and a Y-shaped ovary. These morphotypes were compared within the Astacida. Four ovarian developmental stages were recognized based on ovary color, and the histological structure and relative proportion of cellular types. The post-spawning ovary was also characterized. The components of the female reproductive system sheath were described and its modifications in the ovary and oviducts were determined and compared. Theoretical aspects of the study of sexual differentiation in C. quadricarinatus were discussed within a phylogenetic framework.     

The growth, development and reproduction of a deep sea cumacean (Crustacea: Peracarida)

A single sample of over 1000 individuals of Leuconjonesi Bishop, 1982, taken at a depth of about 1500 m on the continental slope off Surinam, was studied. The carapace length of individuals in the first postmarsupial instar was already about half that of brooding females. Growth increments at early moults were of 20–25. Males reached the final morphological form in the sixth postmarsupial instar. A prepuberty moult was recognized between the third and fourth male instars. Females reached the preparatory stage in the fourth postmarsupial instar. Brooding condition occurred for the first time after the next moult. The brooding form could then alternate at successive moults with an inter-brood form, resembling the preparatory female, with small, non-overlapping oostegites. Preparatory and inter-brood females were morphologically separable; vitellogenesis was restricted to these instars. Broods were of 6–12 young. The individuals in each brood probably completed marsupial development, and were released, one by one. The copepod parasite Sphaeronella infested 10", of brooding-form females.     

On the marine sister groups of the freshwater crabs (Crustacea: Decapoda: Brachyura)

Freshwater crab sister group relationships with marine eubrachyuran families were investigated. A morphology-based cladistic analysis was conducted on representatives of the freshwater crab families Deckeniidae, Gecarcinucidae, Parathelphusidae, Potamidae, Potamonautidae, Pseudothelphusidae, and Trichodactylidae using a disparate assemblage of marine heterotreme and thoracotreme brachyurans as possible sister groups. The monophyly of the freshwater crabs sensu lato is falsified. The family Trichodactylidae and the marine portunid subfamily Carcininae form basal groups within the superfamily Portunoidea. The monophyly of the Pseudothelphusidae and the Paleotropical freshwater crab families is supported, and this clade is the sister group of the Thoracotremata (Gecarcinidae, Grapsidae s.l., and Ocypodoidea). The origin, groundplan, and diversification of freshwater crabs are discussed in the context of previously published scenarios of their evolution.     

The embryonic development of the Mediterranean freshwater crab, Potamon edulis (=P.fluviatile) (Crustacea, Decapoda, Potamonidae)

The mating of the crabs is described. The incubation period of the macrolecithal egg of the freshwater crab, Potamon edulis (Latr.) is 46 ± 1 days long. One of the main features of the development of the egg is its extreme abbreviation. In addition to the nauplius, metanauplius, and zoea, the megalopa stage is also imprisoned in the egg. The extent to which direct development is carried in Potamon is unique among the Brachyura. This is considered to have been a pre-adaptation to the colonization of a freshwater habitat by the Potamonidae.     

Complete mitochondrial DNA sequence of the Japanese spiny lobster,Panulirus japonicus (Crustacea: Decapoda)

We determined the complete nucleotide sequence of the mitochondrial genome for a Japanese spiny lobster, Panulirus japonicus (Crustacea: Decapoda). The entire genome was amplified using long polymerase chain reaction, and the products were subsequently used as templates for direct sequencing using a primer-walking strategy. The genome (15,717 base pairs) contained the same 37 genes (two ribosomal RNA, 22 transfer RNA, and 13 protein-coding genes) plus the putative control region as found in other arthropods, with the gene order identical to that of typical arthropods. Preliminary phylogenetic analyses of selected arthropods using concatenated amino acid sequences of the 13 protein-coding genes strongly supported monophyly of Decapoda species and confidently rejected "Macroura", a conventional taxon that shares an elongated abdominal body.     

Mitochondrial phylogenomics reveals insights into taxonomy and evolution of Penaeoidea (Crustacea: Decapoda)

The taxonomy and phylogeny of Penaeoidea have long been fraught with controversy. Here, we carried out the first mitochondrial phylogenomic analysis on all the penaeoid families and tribes, including nine newly sequenced and 14 published mitogenomes, towards elucidating the phylogeny and evolutionary history of Penaeoidea. All these nine mitogenomes exhibit the pancrustacean ground pattern, except that Benthonectes filipes contains two additional clusters of tRNA^Ala, tRNA^Arg and tRNA^Asn and an uncommon noncoding region. The resulted phylogenetic tree is generally well resolved with Benthesicymidae sister to Aristeidae, forming a clade with Solenoceridae. Contrary to traditional classification, this clade has a sister relationship with the tribe Penaeini of the family Penaeidae. The family Sicyoniidae is deeply nested within the penaeid tribe Trachypenaeini which forms a sister clade with the remaining penaeid tribe, Parapenaeini. As the family Penaeidae is recovered to be polyphyletic, the three tribes in Penaeidae are all elevated to familial status. On the other hand, the family Sicyoniidae is retained to accommodate Trachypenaeini because they are now synonyms and the former name is more senior. This work is the first molecular analysis concurring with the latest findings in fossil assessments showing that Parapeaneini is the most primitive in Penaeoidae. Our results also illustrate a shallow‐water origin and an onshore–offshore evolutionary shift in penaeoid shrimps.     

Larval and post-larval development of the branchiopod clam shrimp Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Conchostraca, Spinicaudata)

The larval and post-larval development of Cyclestheria hislopi is examined by SEM. There are at least nine stages (excluding the adult) – six larval and three post-larval stages. The first four stages are passed within the egg-membrane. The larval and the post-larval phase are separated by a profound change in morphology that takes place between stages VI and VII. The larva shifts from a dorso-ventrally flattened 'larval' appearance up to stage VI to a laterally flattened, more 'adult' appearance from stage VII. New morphological data have been revealed by this study, including (1) a large and globular larval dorsal organ; (2) the carapace starts its development from the segments of the first and second maxillae; (3) the anterior ramus of the second antenna in adult Cyclestheria hislopi is the endopod, and the posterior ramus the exopod. Direct development of the brood in Cyclestheria hislopi – unique among conchostracans – is compared with that of the Cladocera. If Cyclestheria is the sister group to the Cladocera, as favoured in this work, the classical neoteny theory of the Cladocera must be reconsidered, as there is no particular similarity between any adults of the Cladocera and any of the larval stages of Cyclestheria . It is suggested that Cyclestheria displays the type of development present in a cladoceran ancestor. A comparison between Cyclestheria and the Upper Cambrian 'Orsten' fossil Rehbachiella kinnekullensis reveals a remarkable similarity in the endite morphology of the trunk limbs.     

Embryonic development of the Caridean prawn Macrobrachium mammillodactylus (Crustacea: Decapoda: Palaemonidae)

The freshwater knob-tooth prawn Macrobrachium mammillodactylus is a commercially exploited species in the Philippines. To study the biology of this species, broodstock from the wild was collected, transported to the laboratory and kept in pairs in indoor polyethylene tanks for breeding. Eggs from berried females were sampled to follow the stages of embryonic development until hatching to zoea larva. It took 18.0?±?2.1?days for the eggs to hatch at ambient water temperature between 25 and 28?°C. The morphological landmarks of development at the different stages (pre-cleavage, cleavage, blastula, pre-nauplius, post-nauplius and pre-hatching) of the live embryos are described. Incremental percentage staging was adopted from 0% at fertilization to 100% at hatching and were matched with corresponding morphological development. Egg volume increased significantly toward the mid-to-later stages of development. The eye index also showed a significant increase as the egg developed. The colour of the egg mass changed from light olive green to grey as the eggs progressed in development. The general pattern of development was comparable to other members of the genus Macrobrachium.     

Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life‐history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean‐type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico‐chemical factors and phytoplankton availability in freshwater habitats. These life‐history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r‐ to K‐strategy in freshwater decapods are traded‐off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio‐temporal alteration of their socio‐ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.     

Constant morphological patterns in the hemolymph vascular system of crayfish (Crustacea,Decapoda)

We present a study of the hemolymph vascular system of the marbled crayfish, Procambarus fallax f. virginalis, the only crayfish species known to be parthenogenetic. To identify potential evolutionary patterns, we compared data from a total of 48 specimens of P. fallax with 22 specimens of Orconectes limosus. Visualizations (2D and 3D) were carried out using a combination of classical and modern morphological techniques. Our data were compared to the existing literature.Like all Decapoda, both P. fallax and O. limosus have a hemolymph vascular system, consisting of a globular heart with seven off-branching arteries. We were able to visualize in detail the heart of crayfish for the first time, i.e., the myocard with its clusters of muscles running through the lumen of the heart, the valves and flaps of ostia and arteries. Furthermore, the branching patterns of the seven artery systems were analyzed. Anatomical structures identified to be consistent in all specimens of both species were combined as ground pattern of hemolymph vascular system features for Astacida.     

Mating behavior,spawning, parental care,and embryonic development of some marine pseudocerotid flatworms (Platyhelminthes: Rhabditophora: Polycladida) in Singapore

The reproductive biology of tropical marine cotylean polyclads is presently poorly known. Reproductive aspects of 16 polyclad species from the family Pseudocerotidae in the genera Acanthozoon, Nymphozoon, Phrikoceros, Pseudobiceros, Pseudoceros, Thysanozoon, and Tytthosoceros from Singapore were documented for the first time. Penis fencing was observed to be just a mating ritual and not necessary for insemination, not always aggressive, and could also result in eventual reciprocal insemination. Results showed that all species underwent similar embryonic developmental stages and hatched as Müller's larvae. Only Pseudoceros concinnus and Pseudoceros laingensis, with mean developmental times of >20 days and mean brood sizes of <1,000 eggs, displayed long‐term parental care. Polyclads producing larger brood sizes had shorter developmental times and only covered their egg masses for about one day. Phrikoceros baibaiye and Pseudobiceros spp. produced egg capsules with pointed opercula, whereas all other species possessed smooth, rounded opercula. All genera hatched with brownish‐orange larvae, except for Pseudoceros spp., which hatched with reddish‐purple larvae regardless of the initial embryo color (either grayish‐yellow or reddish‐purple). These could potentially complement current taxonomic characters in distinguishing polyclad genera and species.     

The first report on the occurrence of twins in a freshwater crayfish,Pacifastacus leniusculus (Decapoda,Astacoidea)

Twin stage 1 juveniles from the signal crayfish, Pacifastacus leniusculus, were observed in this study. No such observations have been found in the literature. The twins consist of two stage 1 juveniles that are fused at the head. Each juvenile has a separate abdomen and thorax and has the appropriate number of appendages and a telson, all characteristic of a normal stage 1 juvenile.     

Ontogenetic development of electric-organ discharges in a mormyrid fish, the bulldog Marcusenius macrolepidotus (South African form)

The emergence and development of the electric-organ discharge (EOD) in larvae and juvenile bulldog Marcusenius macrolepidotus was investigated. Larvae hatched 4–5 days after spawning, and the first EODs were recorded on days 9 and 10 at a standard length ( L _S) of c. 6·5 mm. The larval EOD waveform was virtually monopolar, with a strong head-positive phase followed by a weak head-negative phase of long duration. A small separate potential preceded the EOD by c. 1·6 ms (believed to represent postsynaptic potential from electrocyte stalks). In contrast to previous reports on Pollimyrus adspersus with its distinct larval and adult EODs, in M. macrolepidotus there was a gradual transformation of the larval into the adult EOD waveform. The transformation started at an L _S of c. 17 mm (at an age of c. 40 days), first indications being a decrease in duration of the head-negative phase, and an increase of its peak amplitude relative to that of the head-positive phase. Still later, the weak postpotential of the adult EOD emerged on the rising edge of the head-negative phase. The transformation was nearly completed at an L _S of c. 30 mm (at an age of c. 60 days). Evolutionary and behavioural consequences of this alternative path of EOD ontogeny are discussed.     

Tyrosine hydroxylase activity in the central nervous system of the crayfish,Pacifastacus leniusculus (Crustacea,Decapoda)

Summary Tyrosine hydroxylase, responsible for the formation ofl-dopa froml-tyrosine, has been identified in the central nervous system of the crayfish,Pacifastacus leniusculus (Crustacea, Decapoda). It requires pterine as cofactor and is inhibited by a number of known tyrosine hydroxylase inhibitors; iron-chelators, tyrosine analogues and also by the catecholamines, dopamine and noradrenaline. Iron enhances the activity of the enzyme. It differs from the vertebrate tyrosine hydroxylase in having a more alkaline pH optimum and a higher affinity for the pterine cofactor. Kinetic studies were performed andK _m andV _max values are presented. Dopa formed was identified and quantitatively measured by high pressure liquid chromatography (HPLC) and electrochemical detection.     

The metabolism of astaxanthin during the embryonic development of the crayfish Astacus leptodactylus Eschscholtz (Crustacea, Astacidea)

The developing eggs of the crayfish Astacus leptodactylus are found to contain important carotenoid amounts. Free astaxanthin, mainly associated with protein and lutein represent the main pigments occurring in the yolk at the end of the embryonic period. Esterification processes affecting astaxanthin appear concomitantly with the resorption of vitellin reserves, the activation of the digestive gland and the rapid decrease of lutein amounts. Esterified astaxanthin contents increase significantly within the interval between the juvenile stages I and II. Nevertheless, free astaxanthin levels appear insufficient to balance the amounts of the esterified form, scored at the end of the endotrophic period.     

Osteological development of the lumpfish,inimicus japonicus (pisces: Synanceiidae)

The osteological development of the synanceiidInimicus japonicus, was described on the basis of five larvae and four juveniles (4.2–10.1 mm BL) reared in the laboratory, and two wild adult specimens. All bones, except for the basisphenoid, were formed in all larvae and juveniles, but fusions between the uppermost actinost and scapula, upper caudal plate and urostyle, and third preural centrum and hemal spine were not completed by 10.1 mm BL. Following comparison with the adult condition, a rod-like ossified bone without a tooth plate on the upper branchial arch of larvae and juveniles was considered homologous with the second pharyngobranchial. The number of epurals and length of the neural spine on the second preural centrum varied (unrelated to growth) and it is inferred thatJ. japonicus shows intraspecific variations in these bones.