Redescription of two Dicyemennea (Phylum: Dicyemida) from Rossia pacifica (Mollusca: Cephalopoda: Decapoda)

A Perspective Around Cephalopods and Their Parasites, and Suggestions on How to Increase Knowledge in the Field

Although interest in several areas of cephalopod research has emerged over the last decades (e.g., neurobiology, aquaculture, genetics, and welfare), especially following their 2010 inclusion in the EU Directive on the use of animals for experimental purposes, knowledge regarding the parasites of cephalopods is lacking. Cephalopods can be intermediate, paratenic, or definitive hosts to a range of parasites with a wide variety of life cycle strategies. Here, we briefly review the current knowledge in cephalopod parasitological research, summarizing the main parasite groups that affect these animals. We also emphasize some topics that, in our view, should be addressed in future research, including: (i) better understanding of life cycles and transmission pathways of common cephalopod parasites; (ii) improve knowledge of all phases of the life cycle (i.e., paralarvae, juveniles, adults and senescent animals) and on species from polar deep sea regions; (iii) exploration of the potential of using cephalopod-parasite specificity to assess population boundaries of both, hosts and parasites; (iv) risk evaluation of the potential of standard aquacultural practices to result in parasite outbreaks; (v) evaluation and description of the physiological and behavioral effects of parasites on their cephalopod hosts; (vi) standardization of the methods for accurate parasite sampling and identification; (vii) implementation of the latest molecular methods to facilitate and enable research in above mentioned areas; (viii) sharing of information and samples among researchers and aquaculturists. In our view, addressing these topics would allow us to better understand complex host-parasite interactions, yield insights into cephalopod life history, and help improve the rearing and welfare of these animals in captivity.

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.

A new dicyemid from Opisthoteuthis depressa (Mollusca: Cephalopoda: Octopoda)

A new species of dicyemid mesozoan is described from Opisthoteuthis depressa Iijima and Ikeda, 1895, collected from Suruga Bay in Japan. Dicyemennea umbraculum n. sp. is a medium species that reaches approximately 3500 microm in length. This species attaches to the surface of the renal appendages. The vermiform stages are characterized as having 22 or 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 37 cells; a single nucleus is present in each urn cell, and the refringent bodies are solid. This is the first description of a dicyemid from Opisthoteuthis.

Two new dicyemids from Sepia longipes (Mollusca: Cephalopoda: Decapoda)

Two new species of dicyemid mesozoan are described from Sepia longipes, Sasaki, 1913, collected from Tosa Bay in Japan. Dicyema oxycephalum n. sp. is a medium-sized species that is about 1,800 microm in length. It lives in folds of the renal appendages. The vermiform stages are characterized as having 28-34 peripheral cells, a conical calotte, and an axial cell that extends to the base of the propolar cells. Infusoriform embryos consist of 39 cells; 2 nuclei are present in each urn cell and the refringent bodies are solid. Pseudicyema cappacephalum n. sp. is also a medium-size species; it is about 1,000 microm in length. It too lives in folds of the renal appendages. The vermiform stages are characterized as having 32-34 peripheral cells, a cap-shaped calotte, and an axial cell that extends to the base of propolar cells. Infusoriform embryos consist of 39 cells; 2 nuclei are present in each urn cell and the refringent bodies are solid. This is the first description of dicyemids from S. longipes.

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.

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.