Three new dicyemids from Octopus sasakii (Mollusca: Cephalopoda: Octopoda)

Three new species of dicyemid mesozoan are described from Octopus sasakii Taki, 1942, collected from Tosa Bay and Kii Strait in Japan. Dicyema shimantoense n. sp. is a medium-size species that reaches about 3,000 microm in length, and lives in folds of the renal appendages. The vermiform stages are characterized by having 22 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. Dicyema codonocephalum n. sp. is also a medium-size species that reaches about 2,000 microm in length. It too lives in folds of the renal appendages. The vermiform stages are characterized by having 17-22 peripheral cells, an elongated calotte, and an axial cell that extends to the middle of propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. Dicyemennea pileum n. sp. is a medium species that reaches about 2,000 microm in length. It attaches to the surface of the renal appendages. The vermiform stages are characterized by having 23 peripheral cells, a disc-shaped calotte, and an axial cell that extends to the propolar cells. An anterior abortive axial cell is absent in vermiform embryos. Infusoriform embryos consist of 38 cells; 2 nuclei are present in each urn cell, and the refringent bodies are liquid. These are the first dicyemids to be described from Octopus sasakii.     

Redescription of Dicyemennea nouveli (Phylum: Dicyemida) from Enteroctopus dofleini (Mollusca: Cephalopoda: Octopoda)

A species of dicyemid mesozoan is redescribed from the giant Pacific octopus, Enteroctopus dofleini (Wülker, 1910), collected off Iwase in Toyama Bay, Honshu, Japan. Dicyemennea nouveli McConnaughey, 1959, is a large species that reaches about 12,000 microm in length. This species lives in folds of the renal appendages. The vermiform stages are characterized as having 30-41 peripheral cells, a conical calotte, and an axial cell that extends to the middle of the metapolar cells. An anterior abortive axial cell is present in vermiform embryos. Full-grown vermiform embryos have as many as 4 agametes. Infusoriform embryos consist of 39 cells; 2 nuclei are present in each urn cell and the refringent bodies are solid.     

A new dicyemid from Benthoctopus sibiricus (Mollusca: Cephalopoda: Octopoda)

A new species of dicyemid mesozoan is described from Benthoctopus sibiricus Loyning, 1930, collected in the eastern Chukchi Sea. Dicyemennea chukchiense n. sp. is a medium species that reaches about 2,000 μm in length; it lives in folds of the renal appendages. The vermiform stages are characterized in having 23 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. An anterior abortive axial cell is present in vermiform embryos. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell and the refringent bodies are solid. This is the first dicyemid described from the Arctic waters.     

Three new species of dicyemid mesozoans (phylum Dicyemida) from Amphioctopus fangsiao (Mollusca: Cephalopoda), with comments on the occurrence patterns of dicyemids

Three new species of dicyemid mesozoans are described from the renal appendages of Amphioctopus fangsiao, collected off Akashi, in Harima Nada, and from Osaka Bay. Dicyema akashiense n. sp. is a small species that reaches about 900 microm in length. The vermiform stages are characterized as having 15-17 peripheral cells, a conical calotte, and an axial cell that extends to the base of the metapolar cells. Infusoriform embryos consist of 37 cells; two nuclei are present in each urn cell, and the refringent bodies are solid. Dicyema helocephalum n. sp. is a small species that reaches about 800 microm in length. The vermiform stages are characterized as having 22 peripheral cells, a disc-shaped calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. Dicyema awajiense n. sp. is a small species that reaches about 300 microm in length. The vermiform stages are characterized as having 22 peripheral cells, a conical calotte, and an axial cell that extends to the middle of the propolar cells. Infusoriform embryos consist of 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. In A. fangsiao various occurrence patterns of dicyemid species were observed, including instances where different dicyemid species were found in the renal appendage on each side. This suggests that dicyemids infect each renal appendage independently. The prevalence, reproductive traits, calotte shapes, and co-occurrence patterns of dicyemids are briefly discussed.     

Dicyemennea canadensis n. sp. (phylum Dicyemida) from Bathypolypus arcticus (Mollusca: Cephalopoda: Octopoda)

Dicyemennea canadensis n. sp. is described from a bathyal octopus collected off Canada in the Bay of Fundy. The dicyemid is a small species that rarely exceeds 600 microm in length. The vermiform stages are further characterized as having 17-23 peripheral cells, a conical-shaped calotte, an axial cell that extends to the base of the propoplar cells, and no abortive axial cells. Infusoriform embryos consist of 37 cells. There is 1 nucleus in each urn cell, and refringent bodies are absent. This is the first dicyemid to be described from the cephalopod Bathypolypus arcticus (Prosch. 1847), and the first dicyemid reported from Canada. In addition, it is the first species of Dicyemennea from the northwestern Atlantic Ocean to be described.     

New species of Dicyemennea (phylum: Dicyemida) in deep-water Graneledone (Mollusca: Cephalopoda: Octopoda) from the Antarctic

Two new species of dicyemids are described from 2 species of deep benthic cephalopods, Graneledone antarctica and G. macrotyla, collected in the Southern Ocean south of the Antarctic Convergence. Dicyemennea bathybenthum n. sp. was found in G. antarctica. It is a medium-sized dicyemid whose length does not exceed 1,000 microm. The calotte is bluntly rounded or conical in small individuals, but the shape becomes discoidal in large individuals. Nematogens and vermiform embryos have 23 peripheral cells. An anterior abortive axial cell is present in vermiform embryos. Other stages in the life cycle were not observed. Dicyemennea dorycephalum n. sp. was found in G. macrotyla. It is a medium to large dicyemid that rarely exceeds 4,000 microm. The calotte is distinctly pointed, similar in shape to a spearhead. Vermiform stages typically have either 25 or 27 peripheral cells. An anterior abortive axial cell is present in vermiform embryos. Infusoriform embryos have 37 cells, the refringent bodies are solid in composition, and 2 nuclei are present in each urn cell.     

A new dicyemid from Octopus hubbsorum (Mollusca:Cephalopoda:Octopoda)

A new species of dicyemid mesozoan is described from Octopus hubbsorum Berry, 1953, collected in the south of Bahia de La Paz, Baja California Sur, México. Dicyema guaycurense n. sp. is a medium-size species that reaches about 1,600 μm in length. It occurs in folds of the renal appendages. The vermiform stages are characterized as having 22 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 39 cells; 1 nucleus is present in each urn cell and the refringent bodies are solid. This is the first of a dicyemid species from a host collected in the Gulf of California.     

A new species of Dicyemennea Whitman, 1883 (Phylum Dicyemida) from Sepia latimanus (Mollusca: Cephalopoda: Decapodidae) off Okinawa, Japan

A new species of dicyemid mesozoan is described from a cuttlefish Sepia latimanus Quoy and Gaimard collected off Nago, Naha and Onnason, Okinawa Islands, Ryukyu Islands, Japan. Dicyemennea ryukyuense n. sp. is a large species that reaches about 5 mm in length. The vermiform stage is characterised by 23 peripheral cells, a conical calotte and an axial cell that extends to the base of the propolar cells. The infusoriform embryo consists of 37 cells; two nuclei are present in each urn cell and the refringent bodies are solid. In the type of reproductive strategy, rhombogens of D. ryukyuense form a small number of infusorigens and produce a relatively large number of gametes per infusorigen. In the family Dicyemidae, Dicyemennea Whitman, 1883 is the largest group after Dicyema von Kölliker, 1849. Other dicyemid species, including those belonging to Dicyema, were not detected. Dicyemids have never previously been detected in cephalopods living on corals and rocks off the Ryukyu Islands, even though they are benthonic in habitat. This is the first report of a dicyemid mesozoan from S. latimanus and also from off the Ryukyu Islands. S. latimanus inhabits coral reefs, often swimming over the coral but usually lying on the sandy bottom. Dicyemids cannot possibly infect cephalopods which live exclusively over coral and rock.     

Dicyema shorti n. sp. (phylum Dicyemida) from Octopus burryi (Mollusca: Cephalopoda: Octopodidae) in the Gulf of Mexico

Nematogens and vermiform embryos of a new species of Dicyema are described from an octopus collected off Veracruz, Mexico. Dicyema shorti n. sp. is a small dicyemid species that rarely exceeds 500 microm in length. It is further characterized by the presence of 18 peripheral cells in the vermiform stages, a conical-shape calotte, and an axial cell that extends to the base of the propolar cells. Other stages in the life cycle of the parasite are not known. This is the first dicyemid to be described from Octopus burryi Voss. 1950, and also from both the southern Gulf of Mexico and the country of Mexico.     

Cell number and cellular composition in infusoriform larvae of dicyemid mesozoans (Phylum Dicyemida)

Cell numbers and cellular composition were examined in infusoriform larvae of 44 species of dicyemid mesozoans belonging to 6 genera; Conocyema, Dicyema, Dicyemennea, Dicyemodeca, Microcyema, and Pseudicyema. In addition, literature on infusoriform larvae of another 20 species was reviewed. Infusoriform larvae consist of a constant cell number which is species-specific. Small interspecific variations are found in total cell numbers, 35, 37, 39, 41 and 42. The most frequent cell number encountered in infusoriform larvae studied is either 37 or 39. Infusoriform larvae with 35 cells are found in three genera. Infusoriform larvae with 37 cells are found in four genera. Infusoriform larvae with 39 cells are found in four genera. Most differences in total cell numbers are due to the absence or presence of particular ventral cells. In all infusoriform larvae, the lateral, dorsal and caudal areas are cell constant, whereas in the apical and ventral areas a distinct and variable configuration of cells are present. In cellular composition, a total of 29 cells (15 cell types) were recognized in all infusoriform larvae examined. Additional cell types are characteristic of a relatively few species. Even in infusoriform larvae with the same total cell numbers, cellular composition varies by species. Thus, there are 7 variations of cellular composition in infusoriform larvae with 37 cells. Differences in larval cell numbers and types do not warrant traditional generic separation of dicyemids.     

The expression of tubulin and tektin genes in dicyemid mesozoans (Phylum: Dicyemida)

Dicyemid mesozoans (Phylum Dicyemida) are endoparasites (or endosymbionts) that typically are found in the renal sac of benthic cephalopod mollusks such as octopuses and cuttlefishes. Adult dicyemids likely adhere to the renal appendage of hosts via cilia of calotte peripheral cells. These cilia seem to be continuously worn away in the interaction between the dicyemids and the epidermal cells of host renal appendages. We cloned 4 cDNAs and genes, alpha-tubulin, beta-tubulin, tektin B, and tektin C, which are thought to play a key role in ciliogenesis, from Dicyema japonicum, and studied expression patterns of these genes by whole-mount in situ hybridization. We detected coexpression of these genes in the calotte peripheral cells, but not in the trunk peripheral cells. This suggests that regeneration and turnover of cilia continuously occur in the calotte. In vermiform and infusoriform embryos, we also detected coexpression patterns of these genes, which might correlate with ciliogenesis during the embryogenesis. We also predicted the secondary structure and the coiled-coil regions of dicyemid tektins.     

Cloning of chitinase-like protein1 cDNA from dicyemid mesozoans (Phylum: Dicyemida)

Dicyemid mesozoans are endoparasites found in the renal sacs of benthic cephalopods. Adult dicyemids insert the distinct anterior region, termed a "calotte," into renal tubules of the host. We cloned cDNA encoding chitinase-like protein from the dicyemid Dicyema japonicum (Dicyema-clp 1), and also cloned the gene fragment corresponding to the cDNA. Dicyema-clp1 has the hydrophobic amino acid-rich region, but not the chitin-binding domains at the C terminus. Analyses using the SignalP prediction program suggest this hydrophobic amino acid-rich region is the anchor sequence to plasma membranes. The putative catalytic site in glyco18 domain exhibited 1 substitution from aspartic acid to asparagine. The gene fragment had short 9 introns (22-26 bp), and the coding sequence consisted of 10 exons (30-233 bp). Specific and strong expression of Dicyema-clpl was detected in the calotte of vermiform stages by whole mount in situ hybridization. N-acetyl-D-glucosamine was detected on the outer surface of both peripheral cells of dicyemids and epidermal cells of host renal appendages. Dicyema-clp appears to be associated with N-acetyl-D-glucosamine in the interface between dicyemid peripheral cells and epidermal cells of the host renal appendage, and possibly aids in adhering the calotte to host epidermal cells.     

Fine structure of dicyemid mesozoans,with special reference to cell junctions

The fine structure of the dicyemid mesozoan, Dicyema acuticephalum, from Octopus vulgaris, was studied with special attention to intercellular junctional complexes between various kinds of cells. Two types of intercellular junction, namely, adherens junctions and gap junctions, were found in both vermiform stages and in infusoriform embryos. Adherens junctions were classified into two types. Zonulae adherentes-like junctions were observed between adjacent peripheral cells at vermiform stages, between adjacent external cells of infusoriform embryos, and between members of groups of internal cells that covered the urn in infusoriform embryos. Maculae adherentes-like junctions were seen between a peripheral cell and an axial cell at vermiform stages. In infusoriform embryos, these junctions were observed between various types of cells, excluding urn cells. Gap junctions were found between adjacent peripheral cells at vermiform stages, whereas in infusoriform embryos these junctions were located between various types of cells excluding urn cells. Dicyemids might be the most primitive multicellular animals to possess these basic types of cell junctions. Ciliary rootlet systems at vermiform stages and in infusoriform embryos were unique in structure compared with those of other primitive multicellular animals. J Morphol 231:297–305, 1997. © 1997 Wiley-Liss, Inc.     

Serotonin immunoreactivity in a highly enigmatic metazoan phylum, the pre-nervous Dicyemida

Dicyemida are simply organized metazoans with a long axial cell surrounded by a layer of ciliated peripheral cells. Stem cells and propagates develop inside the cytoplasm of the axial cell. Two types of propagates exist, asexually formed vermiform embryos and sexually derived infusoriform larvae, neither of which, however, develop by gastrulation. Thus, Dicyemida lack all traits typical of common metazoa and represent a pre-nervous state of organization. In this study, immunofluorescence and immunoelectron microscopy have been used to investigate the presence of a serotonin-like molecule in adults and larvae of Dicyema typus and Dicyemennea antarcticensis. Generally, in the adults of both species, the main immunoreactive structures are confined either to small vesicles inside the peripheral cells or to prominent vesicles in the axial cell, the latter vesicles apparently playing a role during the differentiation of the stem cells and the development of the propagates. In all stages, faint immunoreactivity can be observed over the surface membrane and the ciliary apparatus and over the heterochromatic blocks in the nuclei. Surprisingly, in the infusoriform larva, striking immunoreactivity occurs in the vesicles of the capsule cells covering the urn cells, which contain germinal cells. These vesicles might represent stores used in a later life phase of the animal. The results suggest that, in the pre-nervous Dicyemida, serotonin in its ancestral form may function as a hormone regulating essential developmental and morphogenetic processes.     

Cell number and cellular composition in vermiform larvae of dicyemid mesozoans

Cell numbers and cellular composition were examined in vermiform larvae of 44 species of dicyemid mesozoans phylum Dicyemida belonging to six genera: Conocyema , Dicyema , Dicyemennea , Dicyemodeca , Microcyema and Pseudicyema . In addition, the literature on vermiform larvae of another 59 species was reviewed. Vermiform larvae typically have a constant number of peripheral cells that are species specific. Interspecific variations in the total number of peripheral cells range from 10 to 39. The most frequent number is either 22 or 23. Differences in the total number of peripheral cells are mostly due to differences in the number of trunk peripheral cells, such as parapolar cells, diapolar cells and uropolar cells. The body length of vermiform larvae is positively correlated with the number of trunk peripheral cells. Interspecific variations in the total number of trunk peripheral cells range from 2 to 31. The most frequent number is 14. In species with 14 trunk peripheral cells, individual variations of cell numbers were minimal. In species with more trunk peripheral cells, some individual variations appeared. Increase and decrease of trunk cell number might cause diversity of dicyemids, which is possibly related to speciation in these simple multicellular animals.     

Developmental patterns and cell lineages of vermiform embryos in dicyemid mesozoans.

Patterns of cell division and cell lineages of the vermiform embryos of dicyemid mesozoans were studied in four species belonging to four genera: Conocyema polymorpha, Dicyema apalachiensis, Microcyema vespa, and Pseudicyema nakaoi. During early development, the following common features were apparent: (1) the first cell division produces prospective cells that generate the anterior peripheral region of the embryo; (2) the second cell division produces prospective cells that generate the posterior peripheral region plus the internal cells of the embryo; (3) in the lineage of prospective internal cells, several divisions ultimately result in cell death of one of the daughter cells. Early developmental processes are almost identical in the vermiform embryos of all four dicyemid genera. The cell lineages appear to be invariant among embryos and are highly conserved among species. Species-specific differences appear during later stages of embryogenesis. The number of terminal divisions determines variations in peripheral cell numbers among genera and species. Thus, the numbers of peripheral cells are fixed and hence species-specific.     

Biology of dicyemid mesozoans

We reviewed recent advances of some aspects on the biology of dicyemid mesozoans. To date 42 species of dicyemids have been found in 19 species of cephalopod molluscs from Japanese waters. The body of dicyemids consists of 10-40 cells and is organized in a very simple fashion. There are three basic types of cell junction, septate junction, adherens junction, and gap junction. The presence of these junctions suggests not only cell-to-cell attachment, but also cell-to-cell communication. In the development of dicyemids, early stages and cell lineages are identical in vermiform embryos of four genera, Conocyema, Dicyema, Microcyema, and Pseudicyema. Species-specific differences appear during later stages of embryogenesis. In the process of postembryonic growth in some species, the shape of the calotte changes from conical to cap-shaped and discoidal. This calotte morphology appears to result from adaptation to the structure of host renal tissues and help to facilitate niche separation of coexisting species. In most dicyemids distinctly small numbers of sperms are produced in a hermaphroditic gonad (infusorigen). The number of eggs and sperms are roughly equal. An inverse proportional relationship exists between the number of infusorigens and that of gametes, suggesting a trade-off between them. Recent phylogenetic studies suggest dicyemids are a member of the Lophotrochozoa.