Dicyemennea moritakii, Furuya, 2018

Furuya, Hidetaka, 2018, Eleven New Species of Dicyemids (Phylum Dicyemida) from Octopus longispadiceus and O. tenuicirrus (Mollusca: Cephalopoda: Octopoda) in Japanese Waters, Species Diversity 23, pp. 143-179 : 162-164

Dicyemennea moritakii sp. nov.

( Figs 16 , 17 ; Tables 2, 3)

Diagnosis. Large dicyemid; body length to 4,600 µm. Calotte shape conical. Vermiform stages with 23 peripheral cells; 4 propolars+5 metapolars+2 parapolars+12 trunk cells. Infusoriform embryos with 37 cells; refringent bodies solid; and nucleus present in each urn cell.

Description. Nematogens ( Figs 16a, b , 17a, c ). Body length 500–2,890 µm and width 50–82 µm; widest in region of metapolars; trunk width mostly uniform. Peripheral cell number 23 ( Table 3); 4 propolars+5 metapolars+2 parapolars+10 diapolars+2 uropolars. Calotte conical in shape, round anteriorly; cilia on calotte about 4 µm long, oriented anteriorly. Propolar cells and their nuclei smaller than metapolar cells and their nuclei. Ratios of lengths of propolar to metapolar cells, 1.0: 1.3 to 3.0. Propolar cells occupying anterior 25–38% of calotte length when viewed laterally ( Fig. 16a, b ). Cytoplasm of propolar and metapolar cells more darkly stained by hematoxylin than cytoplasm of other peripheral cells. Verruciform cells absent. Axial cell cylindrical, rounded anteriorly; cell extending forward to propolar cells ( Figs 16a, b , 17a, c ). About 50 vermiform embryos per axial cell of large individuals.

Vermiform embryos ( Figs 16c , 17e, f ). Full-grown vermiform embryos length 90–145 µm and width 11–17 µm. Peripheral cell number 23 ( Table 3); trunk cells arranged in opposed pairs. Anterior end of calotte bluntly pointed. Axial cell rounded anteriorly and extending to propolar cells; nucleus usually located in middle of axial cell. Anterior abortive axial cell absent. Axial cell of full-grown embryos with up to 8 agametes.

Rhombogens ( Figs 16d, e , 17b, d ). Body similar in length but slightly stockier than nematogens, length 500–4,610 µm and width 50–110 µm. Peripheral cell number typically 23 ( Table 3). Calotte conical, round anteriorly. Verruciform cells absent. Axial cell shape and anterior extent similar to nematogens. Usually 2 to 3 (rarely 5) infusorigens per axial cell of each parent individual. About 70 infusoriform embryos present per axial cell of large individuals. Accessory nuclei occasionally present in trunk cells.

Infusorigens ( Figs 16f , 17g; n =20). Mature infusorigens middle-sized, composed of 11–47 (mode 23) external cells (oogonia and primary oocytes) +5–47 (mode 17) internal cells (spermatogonia, primary spermatocytes, and secondary spermatocytes)+8–28 (mode 16) spermatozoa. Mean diameter of fertilized eggs 12.0 µm and that of spermatozoa 2.7 µm. Axial cell round, diameter 15–35 µm.

Infusoriform embryos ( Figs 16g, h , 17h–j; n =25). Fullgrown embryos large, ovoid, bluntly rounded to pointed posteriorly, length 30.6±1.7 µm in (mean±SD, excluding cilia); length-width-height ratio 1.0: 0.75: 0.74; cilia at posterior end 8 µm long. Refringent bodies present, solid; occupying anterior 40% of embryo length when viewed laterally ( Figs 16h , 17j ). Cilia projected from ventral internal cells into urn cavity ( Figs 16h , 17j ). Capsule cells containing small granules. Mature embryos with 37 cells: 33 somatic+4 germinal cells. Somatic cells of several types present: external cells that cover large part of anterior and lateral surfaces of embryo (2 enveloping cells); external cells with cilia on external surfaces (2 paired dorsal cells+1 median dorsal cell+2 dorsal caudal cells+2 lateral caudal cells+1 ventral caudal cell+2 lateral cells+2 posteroventral lateral cells); external cells bearing refringent bodies (2 apical cells) without cilia (1 couvercle cell+2 first ventral cells+2 second ventral cells+2 third ventral cells); internal cells with cilia (2 ventral internal cells); internal cells without cilia (2 dorsal internal cells+2 capsule cells+4 urn cells). Each urn cell contains single germinal cell and single nucleus ( Fig. 17j ). All somatic nuclei pycnotic in mature infusoriform embryos.

Remarks. Dicyemennea moritakii sp. nov. is the first species obtained from Octopus tenuicirrus . This species is similar to D. canadensis , D. kaikouriensis , D. littlei , D. minabense , D. ophioides , and D. ryukyuense in the number of peripheral cells of vermiform stages, the shape of the calotte, and the lack of an anterior abortive axial cell ( Short and Hochberg 1969; Hochberg and Short 1970; Furuya 1999, 2006c; Furuya et al. 2002).

The presence of a pair of anterior lateral cells and refringent bodies in the infusoriform embryos separate D. moritakii sp. nov. from D. canadensis (Furuya et al. 2002. The new species differs from D. kaikouriensis , D. minabense , D. ophioides , and D. ryukyuense in the number of nucleus of the urn cell in the infusoriform embryos (1 vs. 2; Short and Hochberg 1969; Furuya 1999).

Dicyemennea littlei was described from the enteroctopodid octopus, Muusoctopus eureka Robson, 1929 [= Benthoctopus magellanicus Robson, 1930 ] in the Falkland Islands, South Atlantic Ocean ( Hochberg and Short 1970). It has distinct arrowhead-shaped calottes and ratios of lengths of propolar to metapolar cells, 1.0: 3.3 to 1.0: 10.0. In contrast, D. moritakii sp. nov. has conical calottes and ratios of lengths of propolar to metapolar cells of 1.0: 1.6 to 3.0. In addition, differences of the locality and host genus separate D. moritakii sp. nov. from D. littlei .

Etymology. The species name moritakii is given in honor of Mr. T. Moritaki (Toba Aquarium) who firstly found this dicyemid.

Taxonomic summary. Type material: a syntype slide (NSMT-Me-54) collected at 13 January 2016. Additional syntypes on slide series No. OT3347 (5 slides) in the author’s collection.

Type locality: off Minami-Ise (34°05′N, 136°50′E), Mie Prefecture, Honshu , Kumano-nada Sea, North Pacific Ocean, Japan, depth 360 m .

Other materials examined: slide series Nos. OT1449–1452 (each 5 slides) collected off Owase (33°54′N, 136°18′E), Mie Prefecture, Honshu , Kumano-nada Sea, North Pacific Ocean, Japan, depth 360 m, 9 June 2004; Nos . OT3308– 3311 (each 5 slides) collected off Kii-Nagashima (33°58′N, 136°28′E), Mie Prefecture, Honshu , Kumano-nada Sea, North Pacific Ocean, Japan, depth 300 m, 18 November 2015 in the author’s collection .

Host: symbiotype, Octopus tenuicirrus ( Sasaki, 1929) (Mollusca: Cephalopoda: Octopoda ), male (mature), 67 mm ML (NSMT-Mo-85870).

Site : anterior ends (calottes) inserted into crypts of the renal appendages within the renal sacs.

Prevalence: all 48 of 48 examined specimens of hosts (100%).

Figures

Fig. 16. Dicyemennea moritakii sp. nov., photographs of syntype specimens on slide NSMT-Me-54: a, b, nematogen, anterior region; c, vermiform embryos within axial cell; d, e, rhombogen, anterior region; f, infusorigen; g, h, infusoriform embryos, horizontal section (g), sagittal section (h). Scale bars: 20µm in a–e, 10µm in f–h.

Fig. 17. Dicyemennea moritakii sp. nov., drawn from syntype specimens on slide NSMT-Me-54: a, nematogen, entire; b, rhombogen, entire; c, nematogen, anterior region; d, rhombogen, anterior region; e, f, vermiform embryo within axial cell, cilia omitted (e), optical section (f); g, infusorigen; h–j, infusoriform embryos, dorsal view (h; cilia omitted), ventral view (i; cilia omitted), sagittal section (j). Scale bars: 100µm in a, b, 20µm in c, 50µm in d, 10µm in e–j.