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

Abstract

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.

Eleven New Species of Dicyemids (Phylum Dicyemida) from <i>Octopus longispadiceus</i> and <i>O. tenuicirrus</i> (Mollusca: Cephalopoda: Octopoda) in Japanese Waters

“…Thereby, the new species can be separated from other congeners by having 23 peripheral cells and a conical calotte. This species is similar to six species (D. canadensis Furuya, Hochberg and Short 2002, D. kaikouriensis Short and Hochberg, 1969, D. littlei Hochberg and Short, 1970, D. minabense Furuya, 1999, D. ophioides Furuya, 1999, and D. ryukyuense Furuya, 2006 in the number of peripheral cells of vermiform stages, the shape of the calotte, and lacking the anterior abortive axial cell (Short and Hochberg 1969;Hochberg and Short 1970;Furuya 1999Furuya , 2006c. Dicyemennea anteronucleatum sp.…”

A New Dicyemid from Benthoctopus sibiricus (Mollusca: Cephalopoda: Octopoda)

“…In contrast, Dicyemennea ryukyuense Furuya, 2006 was described from Sepia latimanus Quoy and Gaimard, 1832 in subtropical waters of the Ryukyu Islands (Furuya, 2006a). The mean water temperature in these waters is nearly 25.0 C. However, although S. latimanus does not survive at low temperatures, D. ryukyuense survived in vitro for a week at 4.0 C (data not shown).…”

“…The terminology for cell names used in the description of infusoriform larvae is based on Nouvel (1948), Short and Damian (1966), Furuya et al (1992Furuya et al ( , 1997, and Furuya (1999).…”

“…In the northern hemisphere, 19 species of dicyemids have been reported from cold-water cephalopods, Bathypolypus arcticus (Prosch, 1847) (Furuya et al, 2002), Enteroctopus dofleini (Wü lker, 1910) (Bogolepova, 1957;McConnaughey, 1957McConnaughey, , 1959Bogolepova-Dobrokhotova, 1963;Furuya, 1999Furuya, , 2008, Octopus hongkongensis Hoyle, 1885 (Furuya, 1999), Octopus ochotensis (Sasaki, 1920) (Bogolepova, 1957), Octopus sp. (BogolepovaDobrokhotova, 1962), Opisthoteuthis depressa Iijima and Ikeda, 1895 (Furuya, 2009), and Rossia pacifica Berry, 1911 (BogolepovaDobrokhotova, 1960(BogolepovaDobrokhotova, , 1962Hoffman, 1965;Hochberg, 1990;Furuya, 2007).…”

“…There is a negative curvilinear relationship between the number of infusorigens per rhombogen and the number of gametes (egg-line and sperm-line cells) per infusorigen (Furuya et al, 2003;Furuya, 2005Furuya, , 2006aFuruya, , 2006bFuruya, , 2006c. Irrespective of genera, there are 4 distinct groups with respect to reproductive strategy: (1) rhombogens form a relatively small number of medium-to large-sized infusorigens (less than 5) and produce a relatively large number of gametes (more than 20) per infusorigen; (2) rhombogens produce a large number of infusorigens (more than 5), each of which has at most 20 gametes;…”