Pseudicyema physocaudatum, Furuya & Moritaki, 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 : 217-219

Pseudicyema physocaudatum sp. nov.

[New Japanese name: Shiribukure-nihaichū] ( Figs 28 , 29 ; Tables 1–3)

Diagnosis. Medium-sized dicyemid, body length reaching 2050 µm. Calotte cap-shaped. Vermiform stages with 31–35 peripheral cells: 4 propolar cells+4 metapolar cells+2 parapolar cells+21–25 trunk cells. Infusoriform embryos with 39 cells; refringent bodies solid; and 2 nuclei present in each urn cell.

Description. Nematogens ( Figs 28a, b , 29a, c ). Body length 1100–2050 µm, width 40–55 µm; widest in region of parapolars; trunk width mostly uniform. Peripheral cell number 31–35 ( Table 2): 4 propolar cells+4 metapolar cells+2 parapolar cells+19–23 diapolar cells+2 uropolar cells. Calotte cap-shaped, rounded anteriorly; cilia about 4 µm long, oriented anteriorly. Propolar cells equal to or larger than metapolar cells, their nuclei equal to or smaller than metapolar cell nuclei. Propolar cells occupy anterior 40% of calotte length when viewed laterally ( Figs 28a, b , 29c ). Cytoplasm of propolar cells more darkly stained by hematoxylin than that of other peripheral cells ( Fig. 28a, b ). Axial cell cylindrical, rounded anteriorly, extending forward to base of propolar cells ( Fig. 29c ). About 10 vermiform embryos present per axial cell of large individuals. Accessory nuclei seen in trunk peripheral cells.

Vermiform embryos ( Figs 28c , 29f, g ). Full-grown vermiform embryos length 71–106 µm, 14–22 µm in width. Peripheral cell number 31–35 ( Table 2); trunk cells arranged in opposed pairs. Anterior end of calotte rounded. Axial cell tapered anteriorly, extending to the base of propolar cells ( Fig. 29g ). Axial cell of full-grown embryos with 3 agametes.

Rhombogens ( Figs 28d, e , 29d, e ). Body length 1140– 1650 µm, similar to that of nematogens, in length and 50–70 µm in width. Peripheral cell number typically 31–35 ( Table 2). Calotte, axial cell shape and anterior extent similar to nematogens. Maximum of 5 infusorigens present in the axial cell of each parent individual. About 50 infusoriform embryos present per axial cell of large individuals.

Infusorigens ( Figs 28f , 29h; n =20). Mature infusorigens medium-sized; composed of 4–11 (mode 5) external cells (oogonia and primary oocytes)+2–6 (mode 3) internal cells (spermatogonia, primary spermatocytes, and secondary spermatocytes)+3–11 (mode 5) spermatozoa. Mean diameter of fertilized eggs 11.9 µm; that of spermatozoa 2.2 µm. Axial cell round or ovoid, diameter 11–16 µm.

Infusoriform embryos ( Figs 28g, h , 29i–k; n =50). Fullgrown embryos large, length 21.2±1.3 µm (mean±SD, excluding cilia); length–width–height ratio 1.0:0.89: 0.84; shape ovoid, pointed posteriorly; cilia at posterior end 7 µm long. Refringent bodies present, solid, occupying anterior 30–40% of embryo length when viewed laterally ( Figs 28h , 29k ). Cilia project from ventral internal cells into urn cavity ( Fig. 29k ). Capsule cells contain small granules ( Fig. 29k ). Mature embryos with 39 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 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 containing 2 nuclei and a germinal cell ( Fig. 29k ). All somatic nuclei pycnotic in mature infusoriform embryos.

Remarks. Pseudicyema physocaudatum sp. nov. is the first species of the genus found in S. lorigera and is very similar to P. anemophilum sp. nov., P. cappacephalum , P. cupulacephalum sp. nov., P. daioense sp. nov., and P. jinshoae in the calotte shape and the number of infusoriform embryos ( Furuya 2009). However, P. physocaudatum sp. nov. is distinguished from P. anemophilum sp. nov., P. cappacephalum , and P. cupulacephalum sp. nov. by the maximum number of infusorigens (5 vs. 2, 3) ( Furuya 2009). It differs from P. daioense sp. nov., and P. jinshoae in the anterior extent of axial cell of adult vermiform stages (propolars vs. metapolars).

Etymology. The species name “ physocaudatum ”is an adjective composed of two Ancient Greek roots, physa and kerkos, meaning “swelling” and “tail” in reference to the characteristic anterior part of vermiform embryos.

Taxonomic summary. Type material: a syntype slide (NSMT-Me-71) collected on 5 December 2019; additional syntypes on slide series No. SM4117 (5 slides) in the author’s collection .

Type locality: off Owase (34°09′N, 136°36′E), Mie Prefecture, Honshu, the Kumano Sea, Japan, depth 180 m .

Other materials examined: slide series No. SM3312 (5 slides) collected off Minami-Ise (34°12′N, 136°40′E), Mie Prefecture, Honshu , the Kumano Sea, Japan, depth 200 m, 30 Nobember 2015, in the author’s collection .

Host: symbiotype, Sepia madokai Adam, 1939 (Mollusca: Cephalopoda: Sepiida ), female (mature), 92 mm ML (NSMT-Mo-85913).

Collector of host: T. Moritaki.

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

Prevalence: in 2 of 21 host specimens examined (9.5%).

Figures

Fig. 28. Pseudicyema physocaudatum sp. nov., photographs of syntype specimens on slide NSMT-Me-71: 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: 10µm.

Fig. 29. Pseudicyema physocaudatum sp. nov., drawn from syntype specimens on slide NSMT-Me-71: a, Nematogen, entire; b, rhombogen, entire; c, nematogen, anterior region; d, e, rhombogen, 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: a, b, 20µm; c–k, 10µm.