Dicyema gozaense Furuya, 2022

Furuya, Hidetaka & Moritaki, Takeya, 2022, Fourteen New Species of Dicyemids (Phylum: Dicyemida) from Seven Species of Decapodiformes (Mollusca: Cephalopoda) in the Kumano Sea, Japan, Species Diversity 27 (1), pp. 181-226 : 189-192

Dicyema gozaense Furuya , sp. nov.

[New Japanese name: Goza-nihaichū] ( Figs 6 , 7 ; Tables 1–3)

Diagnosis. Medium-sized dicyemid; body length reaching 3200 µm. Calotte conical in shape. Vermiform stages with 26–31 peripheral cells: 4 propolar cells+4 metapolar cells+2 parapolar cells+16–21 trunk cells. Infusoriform embryos with 39 cells; refringent bodies solid; and two nuclei present in each urn cell.

Description. Nematogens ( Figs 6a , 7c, d ). Body length 600–3020 µm, width 40–85 µm; widest in region of parapolars; trunk width mostly uniform. Peripheral cell number 26–31 ( Table 2): 4 propolar cells+4 metapolar cells+ 2 parapolar cells+14–19 diapolar cells+2 uropolar cells. Calotte conical in shape, rounded anteriorly; cilia on calotte about 4 µm long, oriented anteriorly. Propolar cells and their nuclei equal to or smaller than metapolar cells and their nuclei. Propolar cells occupy anterior 40–50% of calotte length when viewed laterally ( Figs 6a , 7c, d ). Axial cell cylindrical, rounded anteriorly; cell extending from middle of metapolar cells to base of propolar cells ( Fig. 7c, d ). About 16 vermiform embryos present per axial cell of large individuals. Accessory nuclei seen in trunk peripheral cells.

Vermiform embryos ( Figs 6b , 7e, f ). Full-grown vermiform embryos length 53–108 µm, width 13–18 µm. Peripheral cell number 26–31 ( Table 2); trunk cells arranged in opposed pairs. Anterior end of calotte pointed acutely. Axial cell tapered anteriorly, extending to the base of propolar cells ( Fig 7f ). Axial cell of full-grown embryos with one agamete.

Rhombogens ( Figs 6c, d 7g ). Body length 500–1500 µm in length, similar to that of nematogens, width 50–65 µm. Peripheral cell number typically 28–30 ( Table 2). Calotte shape, axial cell shape, and anterior extent similar to those of nematogens. A maximum of 2 infusorigens present in the axial cell of each parent individual. About 25 infusoriform embryos present per axial cell of large individuals.

Infusorigens ( Figs 6e , 7h; n =10). Mature infusorigens medium-sized, composed of 4–9 (mode 5) external cells (oogonia and primary oocytes)+3–6 (mode 3) internal cells (spermatogonia, primary spermatocytes, and secondary spermatocytes)+4–10 (mode 7) spermatozoa. Mean diameter of fertilized eggs 13.0 µm; that of spermatozoa 2.1 µm. Axial cell ovoid or round, diameter 12–17µm.

Infusoriform embryos ( Figs 6f, g , 7i–k; n =20). Full-grown embryos large, length 28.6±1.7 µm (mean±SD, excluding cilia); length–width–height ratio 1.0: 0.83: 0.81; ovoid, bluntly rounded to pointed posteriorly; cilia at posterior end 7 µm long. Refringent bodies present, solid, occupying anterior 30–40% of embryo length when viewed laterally ( Fig. 6g ). Cilia projected from ventral internal cells into urn cavity ( Fig. 7k ). Capsule cells contain small granules ( Figs 6g , 7k ). Mature embryos with 39 cells: 35 somatic+4 germinal cells. Somatic cells of several types present: external cells covering large part of anterior and lateral surfaces of embryos (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 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 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 contains two nuclei and a single germinal cell ( Fig. 7k ). All somatic nuclei pycnotic in mature infusoriform embryos.

Remarks. Dicyema gozaense sp. nov. is characterized by an acutely pointed calotte of vermiform embryos, a large and a variable number of peripheral cells that ranges from 26 to 31 ( Table 2). Dicyema conocephalum sp. nov. and D. oxycephalum are very similar to D. gozaense sp. nov. in the shape of the calotte in vermiform stages and the number of peripheral cells ( Furuya 2009). However, D. gozaense sp. nov. differs from D. conocephalum sp. nov. in the cell number of infusoriform embryos (39 vs. 37). The number of peripheral cells of D. oxycephalum ranges from 28 to 34 ( Furuya 2009), which is a few more than that of D. gozaense sp. nov. In addition, D. oxycephalum has two agametes in full-grown vermiform embryos ( Furuya 2009). Therefore, D. gozaense sp. nov. can be distinguished from D. oxycephalum .

Etymology. The species name “ gozaense ” refers to the westernmost tip of the Shima Peninsula, Mie Prefecture. The Goza-misaki lighthouse there watches over the safety of ships across the Kumano Sea.

Taxonomic summary. Type material: a syntype slide (NSMT-Me-59) collected on 10 April 2016; additional syntypes on slide series No. SK3514 (5 slides) in the author’s collection.

Type locality: off Minami-Ise (34°08′N, 136°40′E), Mie Prefecture, Honshu, the Kumano Sea, Japan, depth 150 m .

Other materials examined: slide series No. SK3515, 3516 (each 5 slide) collected off Minami-Ise (34°08′N, 136°40′E), Mie Prefecture, Honshu , the Kumano Sea, Japan, depth 150 m, in the author’s collection .

Host: symbiotype, Sepia kobiensis Hoyle, 1855 (Mollusca: Cephalopoda: Sepiida ), female (immature), 62 mm ML (NSMT-Mo-85902).

Collector of host: T. Moritaki.

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

Figures

Fig. 6. Dicyema gozaense sp. nov., photographs of syntype specimens on slide NSMT-Me-59: a, Nematogen, anterior region; b, vermiform embryo within axial cell; c, d, rhombogen, anterior region; e, infusorigen; f, g, infusoriform embryos, horizontal section (f), sagittal section (g). Scale bars: 10µm.

Fig. 7. Dicyema gozaense sp. nov., drawn from syntype specimens on slide NSMT-Me-59: a, Nematogen, entire; b, rhombogen, entire; c, d, nematogen, anterior region; e, f, vermiform embryo within axial cell, cilia omitted (e), optical section (f); g, rhombogen, anterior region; h, infusorigen; i–k, infusoriform embryos, dorsal view (i: cilia omitted), ventral view (j: cilia omitted), sagittal section (k). Scale bars: a, b, 50µm; c–k, 10µm.