Dicyemennea leptocephalum, 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 : 159-162

Dicyemennea leptocephalum sp. nov.

( Figs 14 , 15 ; Tables 1, 3)

Diagnosis. Large dicyemid; colonial, body length up to 4,200 µm. Calotte disc-shaped. Vermiform stages with 19 peripheral cells: 4 propolars+5 metapolars+2 parapolars+8 trunk cells. Infusoriform embryos with 39 cells; refringent bodies solid; and nucleus present in each urn cell.

Description. Nematogens ( Figs 14a, b, e , 15a, b, e ). Body length 500–4,210 µm and width 70–400 µm; widest in region of metapolars; trunk width mostly uniform. Peripheral cell number 19 ( Table 3): 4 propolars+5 metapolars+2 parapolars+6 diapolars+2 uropolars. Calotte thin and irregular-shaped; cilia about 6 µm long, oriented anteriorly. Boundary between propolar and metapolar cells obscure ( Figs 14c–e , 15e ). Periphery of calotte attached together with other individuals, expanding surface of renal appendage and forming large sheet or layer ( Fig. 14a ). Verruciform cells present. Axial cell cylindrical and rounded anteriorly; cell extending forward to propolar cells, forming 2 to 5-branches ( Figs 14b, e , 15a, e ). About 90 vermiform embryos per axial cell of large individuals.

Vermiform embryos ( Figs 14g , 15f, g ). Full-grown vermiform embryos length 47–79 µm, width 14–22 µm. Peripheral cell number 19 ( Table 3); trunk cells arranged in opposed pairs. Anterior end of calotte rounded. Axial cell rounded anteriorly and extending to propolar cells; nucleus usually located in center of axial cell. Anterior abortive axial cell present. Axial cell of full-grown embryos with up to 2 agametes.

Rhombogens ( Figs 14c, d, f , 15c, d ). Body similar in length but slightly stockier than nematogens, length 500–3,150 µm and width 100–500µm. Peripheral cell number 19 ( Table 3). Calotte irregular-shaped. Axial cell shape and anterior extent similar to nematogens. Verruciform cells present. Usually, 3–8 infusorigens per axial cell of each parent individual. About 100 infusoriform embryos per axial cell of large individuals. Accessory nuclei occasionally present in trunk cells.

Infusorigens ( Figs 14i , 15h; n =20). Mature infusorigens of large size; composed of 50–131 (mode 66) external cells (oogonia and primary oocytes) +27–117 (mode 42) internal cells (spermatogonia, primary spermatocytes, and secondary spermatocytes)+27–72 (mode 54) spermatozoa. Mean diameter of fertilized eggs 16.1 µm and that of spermatozoa 2.7 µm. Axial cell round or ovoid, diameter 20–76 µm.

Infusoriform embryos ( Figs 14j, k , 15i–k; n =100). Fullgrown embryos large, length 32.0±1.8 µm (mean±SD, excluding cilia); length-width-height ratio 1.0: 0.84: 0.87; shape ovoid, bluntly rounded to pointed posteriorly; cilia at posterior end 7 µm long. Refringent bodies present, solid, occupying anterior 30% of embryo length when viewed laterally ( Fig. 14j ). Cilia project from ventral internal cells into urn cavity ( Fig. 15k ). Capsule cells containing small granules. Mature embryos with 39 cells: 35 somatic+4 germinal cells. Somatic cells of several types present: external cells covering much of anterior and lateral surfaces of embryo (2 enveloping cells); external cells with cilia on external surfaces (2 pairs of 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 with refringent bodies (2 apical cells); external cells without cilia (1 couvercle cell+2 anterior lateral cells+2 first ventral cells+2 second ventral cells+2 third venteral cells); internal cells with cilia (2 ventral internal cells); and internal cells without cilia (2 dorsal internal cells+2 capsule cells+4 urn cells). Each urn cell containing single nucleus and single germinal cell ( Fig. 15k ). All somatic nuclei appear pycnotic in mature infusoriform embryos.

Remarks. Dicyemennea leptocephalum sp. nov. is an unique species by having a thin sheet-like calotte and axial cell branching. Additinally, D. leptocephalum sp. nov. differs from the other congeners principally on the basis of its distinctly multinucleated cellular mass.

Etymology. The species name leptocephalum is composed of a Greek root, leptós meaning “thin”, in reference to the characteristic thinly spread calottes in the adult.

Taxonomic summary. Type material: a syntype slide (NSMT-Me-53) collected at 26 February 2014; additional syntypes on slide series No. OL3193 (5 slides) in the author’s collection.

Type locality: off Nou (37°09′N, 137°54′E), Niigata Prefecture, Honshu, the Sea of Japan, Japan, depth 200 m .

Other materials examined: slide series No . OL871 (5 slides) collected off Iwase (36°48′N, 137°15′E), Toyama Bay , Toyama Prefecture, Honshu, Japan, depth 350 m, 6 March 2003; Nos . OL1676–1685 (each 5 slides) collected off Hamasaka (35°55′N, 134°25′E), Hyogo Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m, 25 September 2006; Nos . OL2142–2178 (each 5 slides) collected off Karo (35°47′N, 134°14′E), Tottori Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m, 28 January 2009, Nos . OL2413–2422 (each 5 slides) collected off Kanazawa (36°49′N, 136°17′E), Ishikawa Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m, 15 February 2010; Nos . OL2466–2473 (each 5 slides) collected off Ohda-shi (35°23′N, 132°19′E), Shimane Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m, 2 March 2010 in the author’s collection .

Host: symbiotype, Octopus longispadiceus ( Sasaki, 1917) (Mollusca: Cephalopoda: Octopoda ), male (mature), 79 mm ML (NSMT-Mo-85869).

Site : surface of renal appendages within renal sac.

Prevalence: in 427 of 535 specimens of hosts (79.8%).

Figures

Fig. 14. Dicyemennea leptocephalum sp. nov., photographs of syntype specimens on slide NSMT-Me-53: a, nematogen, entire, note that individuals adhere together with their thinly expanded calotte; b, nematogen, anterior region, note that an axial cell branches; c–f, rhombogen, separated individual from an assembly, entire (c), (d), anterior region (e), (f); g, vermiform embryos within axial cell; h, young vermiform embryo, note that a calotte is transforming; i, infusorigen; j, k, infusoriform embryos, sagittal section (j), horizontal section (k). Scale bars: 50µm in a, c–f, 10µm in b, g–k.

Fig. 15. Dicyemennea leptocephalum sp. nov., drawn from syntype specimens on slide NSMT-Me-53: a, nematogen, entire; b–d, rhombogen, entire; e, nematogen, anterior region; f, g, vermiform embryo within axial cell, cilia omitted (f), optical section (g); h, infusorigen; i–k, infusoriform embryos, dorsal view (i; cilia omitted), ventral view (j; cilia omitted), sagittal section (k). Scale bars: 100µm in a–d, 50µm in e, 10µm in f–k.