Dicyema cryptocephalum, 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 : 145-147

Dicyema cryptocephalum sp. nov ( Figs 2 , 3 ; Tables 1, 3)

Diagnosis. Medium sized dicyemid, body length reaching 3,150 µm. Calotte cap-shaped. Vermiform stages with 15–17 peripheral cells: 4 propolar cells+4 metapolar cells+2 parapolar cells+5–7 trunk cells. Infusoriform embryos with 37 cells; refringent bodies solid; and nucleus present in each urn cell.

Description. Nematogens ( Figs 2a–d , 3a, c–e ). Body length 500–3,150 µm, width 40–60 µm; widest in region of parapolars; trunk width mostly uniform. Peripheral cell number 15–17 ( Table 3): 4 propolar cells+4 metapolar cells+2 parapolar cells+3–5 diapolar cells+2 uropolar cells. Calotte cap-shaped, rounded anteriorly; cilia about 4 µm long, oriented anteriorly. Propolar cells equal or larger than metapolar cells, their nuclei equal to or smaller than metapolar cell nuclei. Propolar cells occupying anterior 50–75% of calotte length when viewed laterally ( Figs 2b , 3c–e ). Parapolar cells project anteriorly, bifurcating on calotte ( Figs 2c, d , 3c–e, h ), projections covering the longitudinal furrows at cell-cell adhesion lines. Cytoplasm of propolar cells more darkly stained by hematoxylin than that of other peripheral cells ( Fig. 2b ). Axial cell cylindrical, pointed anteriorly, extending forward to base of propolar cells ( Fig. 3d ). About 36 vermiform embryos present per axial cell of large individuals. Accessory nuclei seen in trunk peripheral cells.

Vermiform embryos ( Figs 2e , 3f, g ). Full-grown vermiform embryos length 80–175 µm, and 16–25 µm in width. Peripheral cell number 15–17 ( Table 3); trunk cells arranged in opposed pairs. Anterior end of calotte rounded. Axial cell rounded anteriorly, extending to base of propolar cells ( Figs 2e , 3g ). Axial cell of full-grown embryos with 1 to 2 agametes.

Rhombogens ( Figs 2f , 3b, h ). Body similar in length to nematogens, 1,200 –2,800 µm in length and 60–92 µm in width. Peripheral cell number typically 15–17 ( Table 3). Calotte, axial cell shape and anterior extent similar to nematogens. Maximum of four infusorigens present in axial cell of each parent individual. About 56 infusoriform embryos present per axial cell of large individuals.

Infusorigens ( Figs 2i , 3i; n =20). Mature infusorigens medium-sized; composed of 12–30 (mode 19) external cells (oogonia and primary oocytes)+3–9 (mode 6) internal cells (spermatogonia, primary spermatocytes, and secondary spermatocytes)+4–10 (mode 4) spermatozoa. Mean diameter of fertilized eggs 12.0 µm; that of spermatozoa 2.2 µm. Axial cell round or ovoid, diameter 14–20 µm.

Infusoriform embryos ( Figs 2g, h , 3j–l; n =50). Full-grown embryos large, length 27.0±1.8 µm (mean±SD, excluding cilia); length-width-height ratio 1.0: 0.83: 0.83; shape ovoid, bluntly rounded and pointed posteriorly; cilia at posterior end 6 µm long. Refringent bodies present, solid, occupying anterior 30–40% of embryo length when viewed laterally ( Fig. 2g ). Cilia projected from ventral internal cells into urn cavity ( Fig. 3l ). Capsule cells contain small granules ( Fig. 3l ). Mature embryos with 37 cells: 33 somatic+4 germinal cells. Somatic cells of several types present: external cells covering large part 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 first ventral cells+2 second ventral cells+2 third ventral 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 2 nuclei and germinal cell ( Fig. 3l ). All somatic nuclei pycnotic in mature infusoriform embryos.

Remarks. Dicyema cryptocephalum sp. nov. is the first species of the genus found in Octopus longispadiceus . In the adult vermiform stages, the new species has the unique parapolar cells projected anteriorly and covering half of the calotte surface. In the phylum Dicyemida, this type of parapolar cells has not been reported.

Etymology. The species name is an adjective composed of 2 Greek roots, crypto meaning “hidden” and - kephalos meaning “-headed”, in reference to the characteristic calotte of the adult typically buried within crypts of the renal appendages.

Taxonomic summary. Type material: a syntype slide (NSMT-Me-47) collected at 28 March 2011; additional syntypes on slide series No. OL2594 (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 Nos . OL870, 871 (each 5 slides) collected off Iwase (36°48′N, 137°15′E), Toyama Bay , Toyama Prefecture, Honshu, Japan, depth 350 m, 6 March 2003; Nos . OL1684, 1685 (each 5 slides) collected off Hamasaka (35°55′N, 134°25′E), Hyogo Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m; Nos . OL2230–2236 (each 5 slides) collected off Karo (35°47′N, 134°14′E), Tottori Prefecture, Honshu , the Sea of Japan, Japan, depth 200 m, 4 March 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 . OL2467–2490 (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), 76 mm ML (NSMT-Mo-85865).

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

Prevalence: in 434 of 510 specimens of hosts examined (78.2%).

Figures

Fig. 2. Dicyema cryptocephalum sp. nov., photographs of syntype specimens on slide NSMT-Me-47: a, nematogen, entire; b, nematogen, anterior region; c, d, nematogen, anterior end; e, vermiform embryos within axial cell; f, rhombogen, anterior region; g, h, infusoriform embryos, sagittal section (g), horizontal section (h); i, infusorigen. Scale bars: 50µm in a, 5µm in b–i.

Fig. 3. Dicyema cryptocephalum sp. nov., drawn from syntype specimens on slide NSMT-Me-47: a, nematogen, entire; b, rhombogen, entire; c–e, nematogen, anterior region; f, g, vermiform embryo within axial cell, cilia omitted (f), optical section (g); h, rhombogen, anterior region; i, infusorigen; j–l, infusoriform embryos, dorsal view (j; cilia omitted), ventral view (k; cilia omitted), sagittal section (l). Scale bars: 100µm in a, b, 10µm in c–k.