Swimming and cleaning in the free-swimming phase of Argulus larvae (crustacea, branchiura)--appendage adaptation and functional morphology

The free-swimming early larval stages of Argulus foliaceus (Linneaus) (Branchiura) are studied using digital video, light microscopy, and SEM. We analyze and document the mode of swimming in the hatching stage of A. foliaceus and the subsequent juvenile stages with fully developed thoracopods. We present new observations and an analysis of the functional morphology of a cleaning behavior in the first stage. This stage swims very efficiently using the large exopods of the second antennae in concert with the mandibular palp (naupliar limbs), while the subsequent stages use the now developed thoracopods for propulsion. This posterior shift in propulsion is similar to--but independent from--what is seen in other crustaceans. The hatching stage has previously been referred as a "metanauplius" but as the first and second maxillae are developed and active, and buds of all four thoracopods are present, it is too advanced to be included in the naupliar phase. The hooks of the first antennae and the distal hooks of the maxillae are demonstrated to function not only as attachment organs (to the host), but also to play a significant role in the cleaning of the naupliar swimming appendages. A digital video-based analysis of the swimming mode is provided. The larval swimming pattern is generally similar to that of other crustaceans such as Branchiopoda and Cirripedia, but autapomorphies of the Branchiura include the following: 1) While actively swimming, the naupliar appendages are almost straight during the recovery stroke and 2) they have a relatively small deflection during movement ( approximately 25 degrees or approximately 35 degrees for mandible and second antenna respectively), 3) the larval mandible has a uniramous palp which is the retained exopod. The morphological implications of the transition from the possibly nonfeeding pelagic, or free-swimming, first larval stage to the feeding, parasitic second stage are discussed and compared with other crustaceans.     

A bridge between original and novel states: ontogeny and function of "suction discs" in the Branchiura (Crustacea)

The emergence of novel structures in the course of evolution faces an explanatory problem, leaving the gap from the ancestral structures difficult to bridge. This difficulty is caused by the lack of intermediate stages. Branchiurans are ectoparasitic crustaceans which use a pair of "suction discs" to attach to their host. These structures are modified first maxillae. During ontogeny, the first maxillae transform from a normal cephalic appendage to the specialized suction disc. However, supposedly ancestral branchiurans lack the suction discs in the adults and the first maxilla remains a normal appendage throughout. We describe the muscular arrangements in the developing first maxillae in Argulus coregoni. The suction discs originate as a fusion of the first and second podomeres. The sucker muscles of the suction discs are homologous to the muscles that insert in the second podomere at the early larval stages. The developmental process of the suction disc can be seen as a "recapitulation" of the evolutionary process. We thus show how the first maxilla can maintain not just the biological role but also a functional continuity during the evolution of the novel structure. From this example it is obvious that the intermediate stages of the emerging novelty, if present in the ontogeny, can help solve at least some of the enigmatic appearances of novel structures.     

Chonopeltis australis (Crustacea) male reproductive system morphology; Sperm transfer and review of reproduction in Branchiura

The morphology of the male reproductive system as well as sperm transfer in Branchiura has been described for Dolops ranarum and Argulus japonicus. In this study, the reproductive system and accessory structures are described for male Chonopeltis australis using histology, light microscopy, and scanning electron microscopy. For the first time, we describe sperm transfer by means of a spermatophore in this genus. The internal and external morphology and mechanism of sperm transfer is compared with other Branchiura, where it has been described. The morphology of the reproductive system of C. australis is similar to that of D. ranarum while the accessory structures and the spermatophore produced are similar to that of A. japonicus. A revision of the definition of Branchiura with respect to reproduction is provided. J. Morphol. 276:209–218, 2015. © 2014 Wiley Periodicals, Inc.     

The little-known Dipteropeltis hirundo Calman, 1912 (Crustacea, Branchiura): SEM investigations of paratype material in light of recent phylogenetic analyses

The Branchiura are fish ectoparasites which include the well-known and very commonly found genus Argulus. But the Branchiura also contains the monotypic genus Dipteropeltis, about which only very little is known. In this investigation of two female paratype specimens we describe for the first time the external morphology of Dipteropeltis based on Scanning Electron Microscopy. We show that Dipteropeltis has a pre-oral spine, unique suction disc support structures, an Argulus-like mouth cone and second maxillae with a combination of features seen in both Argulus and Chonopeltis. These data are compared with data from the three remaining branchiuran genera Dolops, Chonopeltis and Argulus and discussed in a phylogenetic context based on a recently proposed phylogeny of the group.     

Transmission and scanning electron microscopic studies of crustacean shell disease in fish lice of the genus Argulus (Crustacea: Branchiura)

Juvenile and adult specimens of the branchiuran crustacean parasite, Argulus foliaceus , have been found to exhibit the brown areas of damaged cuticle typical of crustacean shell disease. Transmission and scanning electron microscopy of such lesions at a variety of sites on the body surface have demonstrated that they harbour dense populations of bacteria and occasionally fungi, in zones of superficial cuticular erosion. Complete penetration of the exoskeleton was inferred in instances when circular lesions were associated with bacteraemia of underlying soft tissues.     

On some species of Chonopeltis (Crustacea: Branchiura) from the rivers of the extreme South West Cape region of Africa

Two new species of Chonopeltis (Crustacea: Branchiura), parasitic on cyprinid fishes, are described from rivers in the extreme S.W. Cape region of Africa. These emphasize the remarkable nature of the fauna of these rivers, which includes several endemic fishes. Like their hosts these closely related parasites came from the north and have close affinity with a species from the Orange River system. Their probable evolutionary history is discussed. Keys to both sexes of all described species of Chonopeltis are given.     

Phylogeny of Selected Maxillopodan and Other Crustacean Taxa Based on 18S Ribosomal Nucleotide Sequences: A Preliminary Analysis

Relationships among the following taxa were examined based on 18S ribosomal RNA and DNA nucleotide sequences: Branchiopoda (Branchinecta packardi), Ostracoda (two podocopid species), Branchiura (Argulus nobilis), Pentastomida (Porocephalus crotali), Copepoda (Calanus pacificus, Macrocyclops albidus), Thoracica (Balanus eburneus, Calantica villosca), Acrothoracica (Trypetesa lampas), and Decapoda (Procambarus leonensis, Callinectes sapidus). Phylogenetic relationships were inferred by maximum parsimony and results evaluated by bootstrapping. With Branchinecta packardi as an outgroup, the following tree was inferred: the first branch leads to a node that joins a pentastome, a branchiuran and the two ostracodes; the second branch leads to a node that has the two copepods as a sister taxon to a clade that includes the acrothoracican and thoracicans; the last branch leads to a node joining the two decapods. The analyses suggest: (1) acrothoracicans diverged very early from the cirripede line and are not derived from a lepadomorph-like ancestor; (2) branchiurans are not related to either copepods or thecostracans but are closely allied with pentastomes; and (3) the Maxillopoda, broadly defined, is not a monophyletic taxon. These results differ from previous studies of these groups.     

Structure of the adult ovary and oogenesis in Argulus japonicus thiele (Crustacea: Branchiura)

The adult ovary of the branchiuran Argulus japonicus is a single, median, long sac-like organ located in the thorax above the alimentary canal. A long germarium, including oogonia, very early previtellogenic oocytes, and young somatic cells (interstitial cells), is embedded in the dorsal ovarian wall along the median longitudinal line of the ovary. The ovarian wall, consisting of a layer of the ovarian epithelial cells, is folded repeatedly and distinctively in the lateral and ventral portions of the ovary. Growing oocytes, previtellogenic and vitellogenic, occur on the outer surface of the ovarian wall, not in the ovarian lumen. The smaller oocytes are located nearer to the germarium and the larger ones on the more ventral surface of the ovary. These structural features of the branchiuran ovary are compared with those of other crustaceans and the pentastomids to consider their phylogenetic implications. J. Morphol. 231:29–39, 1997. © 1997 Wiley-Liss, Inc.     

Deuterostome phylogeny and the sister group of the chordates: evidence from molecules and morphology

Complete coding regions of the 18S rRNA gene of an enteropneust hemichordate and an echinoid and ophiuroid echinoderm were obtained and aligned with 18S rRNA gene sequences of all major chordate clades and four outgroups. Gene sequences were analyzed to test morphological character phylogenies and to assess the strength of the signal. Maximum- parsimony analysis of the sequences fails to support a monophyletic Chordata; the urochordates form the sister taxon to the hemichordates, and together this clade plus the echinoderms forms the sister taxon to the cephalochordates plus craniates. Decay, bootstrap, and tree-length distribution analyses suggest that the signal for inference of dueterostome phylogeny is weak in this molecule. Parsimony analysis of morphological plus molecular characters supports both monophyly of echinoderms plus enteropneust hemichordates and a sister group relationship of this clade to chordates. Evolutionary parsimony does not support chordate monophyly. Neighbor-joining, Fitch-Margoliash, and maximum-likelihood analyses support a chordate lineage that is the sister group to an echinoderm-plus-hemichordate lineage. The results illustrate both the limitations of the 18S rRNA molecule alone for high- level phylogeny inference and the importance of considering both molecular and morphological data in phylogeny reconstruction.      

Global diversity of fishlice (Crustacea: Branchiura: Argulidae) in freshwater

The Branchiura of freshwater habitats, consisting of the valid genera Argulus, Chonopeltis, Dipteropeltis, and Dolops, presently contains 113 valid species and 12 undescribed species. The entire group is composed of ectoparasitic species that usually live on fishes. The highest diversity of genera and species occurs in the Afrotropical and Neotropical regions. The diversity of the freshwater species surpasses that of species in marine and brackish waters, but this could be due to inadequate study of the fauna of the latter habitats. One species, Argulus japonicus, has been introduced from east/southeast Asia to all other continents, except Antarctica. Studies of higher level relationships place the Branchiura with either Pentastomida or Ostracoda. Hypotheses about phylogenetic relationships of either the genera or species in this group have not been proposed. Guest editors: E. V. Balian, C. Lévêque, H. Segers & K. Martens Freshwater Animal Diversity Assessment The present paper was intended as a very brief overview of the known diversity of the Branchiura in freshwaters only, and regrettably is deficient in mention of much information and many relevant citations pertaining to the group.     

A study of the hatching process in aquatic invertebrates. XVI. Events of eclosion in Calopsectra neoflavellus Malloch (Diptera,Tendipedidae). XVII. Hatching in Argulus megalops Smith (Crustacea,Branchiura)

Summary Hatching in the tendipedid, Calopsectra neoflavellus involves first a slow uptake of water by the embryo during development, whereby it increases in size and comes to fill entirely the space within the chorion. After completion of embryonic development, the prolarva increases still more in size by swallowing and absorbing water. Internal pressure thus generated results in the bursting of the chorion. The larva then frees itself by active movements.In the branchiuran, Argulus megalops, hatching is similar to that previously described for Copepoda, in that an inner egg membrane swells osmotically and splits the outer chorion. Subsequent bursting of the inner membrane throws the larva nearly out of the egg, but final emergence is by active struggle of the larva.

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Zusammenfassung Das Ausschlüpfen von Calopsectra neoflavellus enthält erstens eine langsame Wasseraufnahme durch den Embryo, wodurch der Embryo wächst und das Wasser den ganzen Raum zwischen Embryo und Chorion füllt. Nach Vollendung der Entwicklung quillt der Embryo noch mehr auf durch den Schluckakt und Aufnahme des Wassers. Dann zerreisst das Chorion durch den intraovularen Druck. Endlich befreit sich die Larve durch Sträuben.In Argulus megalops (Branchiura) gleicht das Ausschlüpfen dem vorher dargestellten für den Copepoden. Eine innere Membran schwillt osmotisch und zerreisst; das Chorion dann zerreist auch die innere Membran selbst and wirft die Larve nahezu aus dem Ei hinaus, aber die schliessiiche Befreiung geschieht durch Sträuben.

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Supported by National Science Foundation grant GB-219, entitled A study of hatching and of the ecology of egg masses of aquatic invertebrates.     

A case of tongueworms (Pentastomida): a specific problem in context of the modern phylogenetics

A short essay on anatomy, ultrastructure and larval development, life cycles, classification, palaeontology and phylogenetic relationships of Pentastomida is given. Currently, the Pentastomida are usually placed within Crustacea, as sister group of Branchiura (Crustacea, Maxillopoda). The grounds are striking similarities in ultrastructures of spermatozoa and congruence in the 18S rRNA nucleotide sequence. Both taxa are however sharply disparate in all other characters concerning morphology, embryology, life cycles and geological history. A direct introduction of Pentastomida in the system of Crustacea implies an unjustified inflation of the taxonomic diagnosis of the latter group; hence it is unacceptable. Two alternative hypotheses are suggested as tentative phylogenetic relationships to be tested. Each hypothesis infers however a very complex and unlikely evolutionary scenario. 1) Pentastomida and Branchiura are true sister groups as justified by coincidence in spermatozoan ultrastructure and sequence of ribosomal RNA. Since their divergence, the evolutions of pentastomids and branchiurans ran in different milieus, in different shapes and with different rates. To present time, the pentastomids lost nearly all characters of maxillopods and crustaceans as well as majority of anthropod features. 2) Pentastomida and Branchiura are not close related. The similarity in ultrastructural details of spermatozoa may be occasional or resulted from convergent evolution with unknown factors. Coincidence in nucleotide sequences or ribosomal RNA should be reexamined and tested with other pentastomid species. The second hypothesis seems to be more likely.     

Occurrence and distribution of Dolops ranarum Stuhlmann, ectoparasite of freshwater fish in the Transvaal, South Africa

During 1982–83 fish parasitological surveys were carried out in 15 dam reservoirs in the Transvaal. The fish ectoparasite Dolops ranarum was found on eight different fish species of which Oreochromis mossambicus. Clarias gariepinus and Barbus marequensis are regarded as main hosts. Distribution records and infestation statistics are presented. It was found that D. ranarum is restricted to the Limpopo Drainage System. An evaluation of site preference on host fish reveals that the mouth cavity, in the case of O. mossambicus , and skin and fins, in the case of C. gariepinus , were the sites most intensively infested by this parasite.     

The flowerpiercers' hook: an experimental test of an evolutionary trade-off

The evolution of features that enhance an organism's performance in one activity can adversely affect its performance in another. We used an experimental approach to document a trade-off associated with the evolution of the long hook at the tip of the bill of birds belonging to the genus Diglossa (flowerpiercers). In Diglossa, the more derived flower-robbing nectarivorous species have maxillae (upper jaws) that terminate in enlarged curved hooks. The ancestral frugivorous species have maxillae with relatively small hooks. We mimicked bill evolution by clipping the terminal bill hook of nectarivorous Cinnamon-bellied Flowerpiercers (Diglossa baritula) to resemble the frugivorous condition. We found that birds with experimentally shortened bills ingested fruit more efficiently, but had a reduced ability to rob flowers. Birds with intact bills, by contrast, were good flower robbers but poor frugivores. The evolution of a hooked bill endowed flowerpiercers with the ability to efficiently pierce flowers and extract nectar, but hindered their efficiency to feed on fruit.     

Phylogeny of the cricket subfamily Eneopterinae (Orthoptera, Grylloidea, Eneopteridae) based on four molecular loci and morphology

The phylogenetic relationships of 39 species of Eneopterinae crickets are reconstructed using four molecular markers (16S rRNA, 12S rRNA, cytochrome b, 18S rRNA) and a large morphological data set. Phylogenetic analysis via direct optimisation of DNA sequence data using parsimony as optimality criterion is done for six combinations of weighting parameter sets in a sensitivity analysis. The results are discussed in a twofold purpose: first, in term of significance of the molecular markers for phylogeny reconstruction in Ensifera, as our study represents the first molecular phylogeny performed for this insect suborder at this level of diversity; second, in term of corroboration of a previous phylogeny of Eneopterinae, built on morphological data alone. The four molecular markers all convey phylogenetic signal, although variously distributed on the tree. The monophyly of the subfamily, that of three over five tribes, and of 10 over 13 genera, are recovered. Finally, previous hypotheses on the evolution of acoustic devices and signals in the Eneopterinae clade are briefly tested, and supported, by our new data set.     

Phylogenetic position of Protoopalina intestinalis based on SSU rRNA gene sequence

A robust recognition of phylogenetic affinities of Opalinidae-the peculiar multinucleated intestine commensals of frogs-is hindered by the absence of reliable molecular data. Up to now all attempts to sequence opalinid genes failed, as the obtained sequences labeled as Protoopalina intestinalis, Cepedea virguloidea, and Opalina ranarum in GenBank apparently originate from a zygomycete contamination. In this paper, we present the first molecular data for the family Opalinidae-SSU rRNA gene of P. intestinalis. Our phylogenetic analyses undoubtedly show opalinids as a sister group to Proteromonas within the Stramenopila clade, confirming the monophyly of Patterson's order Slopalinida. The enigmatic genus Blastocystis is resolved with high statistical support as a sister group to Slopalinida. The information contained in the SSU rRNA gene proved insufficient to uncover broader affinities of this group to other groups of Stramenopila. Nevertheless, our analyses clearly demonstrate that Cavalier-Smith's phylum Bigyra, which comprises Oomycetes and their relatives together with Slopalinida and Blastocystis, is not monophyletic.     

Morphological characterization of testicular cells,spermatogenesis and formation of spermatophores in a fish ectoparasite Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

The present study has been carried out to describe the cell morphology of the developing male gametes in a fish ectoparasite, Argulus bengalensis Ramakrishna, 1951. With respect to cell volume and nucleoplasmic index, spermatogonia are the smallest and primary spermatocytes are the largest in this lineage. The spermatogonia and the differentiating spermatogenic cells are in separate niches and confined to different enclaves within each testicular lobe. Spermiogenesis occurs within the inner enclave of each testicular lobe. During this process the nucleus becomes streamlined; an acrosome is formed, axoneme is originated, and residual cytoplasm is discarded through the flagellum. The sperm cell morphology displays a general pattern comprising head, mid-piece, and a full length flagellum. In the axoneme 9 + 2 arrangement of the microtubule is conserved. In addition to the axoneme, some more singlet microtubules are found surrounding a fiber sheath and around one of the mitochondria adjacent to the axoneme. This arrangement indicates a close phylogenetic relationship with pentastomida. In the present study, structure and formation of spermatophore are described in this branchiuran parasite.     

Congruence between molecular phylogeny and cuticular design in Echiniscoidea (Tardigrada,Heterotardigrada)

Although morphological characters distinguishing echiniscid genera and species are well understood, the phylogenetic relationships of these taxa are not well established. We thus investigated the phylogeny of Echiniscidae, assessed the monophyly of Echiniscus, and explored the value of cuticular ornamentation as a phylogenetic character within Echiniscus. To do this, DNA was extracted from single individuals for multiple Echiniscus species, and 18S and 28S rRNA gene fragments were sequenced. Each specimen was photographed, and published in an open database prior to DNA extraction, to make morphological evidence available for future inquiries. An updated phylogeny of the class Heterotardigrada is provided, and conflict between the obtained molecular trees and the distribution of dorsal plates among echiniscid genera is highlighted. The monophyly of Echiniscus was corroborated by the data, with the recent genus Diploechiniscus inferred as its sister group, and Testechiniscus as the sister group of this assemblage. Three groups that closely correspond to specific types of cuticular design in Echiniscus have been found with a parsimony network constructed with 18S rRNA data. © 2013 The Linnean Society of London