Eucestoplana cf. cuneata (Sopott-Ehlers & Schmidt, 1975)

Tsuyuki, Aoi, Oya, Yuki & Kajihara, Hiroshi, 2023, A new species of slender flatworm in the genus Eucestoplana and a record of E. cf. cuneata (Platyhelminthes, Polycladida) from the Okinawa Islands, Japan, with an inference of their phylogenetic positions within Cestoplanidae, Zoosystematics and Evolution 99 (2), pp. 363-373 : 363

Eucestoplana cf. cuneata (Sopott-Ehlers & Schmidt, 1975)

Figs 2 , 3

Cestoplana cuneata ? Cestoplana cuneata Sopott-Ehlers & Schmidt, 1975: 210-212, figs 9, 10; Tajika et al. 1991: 335.

Eucestoplana cuneata ? Eucestoplana cuneata (Sopott-Ehlers & Schmidt, 1975): Faubel 1983: 95.

Material examined.

Japan •1; Okinawa Prefecture, the Okinawa Islands, Kouri Island, Tokei Beach ; 26°42.86'N, 128°1.108'E; intertidal gravelly sediments; 7 Aug. 2021; A. Tsuyuki and Y. Oya leg.; sagittal sections (3 slides); GenBank: LC740488 (COI) and LC740489 (16S); ICHUM 8440 . Japan •1; same data as above, except for the date (11 Aug. 2021); sagittal sections (4 slides); GenBank: LC740486 (COI), LC740491 (18S), LC740493 (28S); ICHUM 8441 . Japan •1; Okinawa Prefecture, the Okinawa Islands, Okinawa Island, Nagahama Beach ; 26°37.45'N, 128°11.06'E; under rocks; 9 Aug. 2021; A. Tsuyuki leg.; sagittal sections (4 slides); GenBank: LC740487 (COI), LC745667 (16S), LC740494 (28S); ICHUM 8442 .

For comparison, we also examined eight serial sections of Eucestoplana cuneata (as Cestoplana cuneata ) (ZMUG 25472 (holotype, three slides) and ZMUG 25473 (paratype, five slides)) and four serial sagittal sections of Eucestoplana cuneata (as Cestoplana cuneata ) collected from the Fiji Island.

Description.

Body slender and elongated, 24-30 mm long and 0.71-0.82 mm wide in living state (Fig. 2A ). Pair of eyespot-clusters, each composed of 11-19 eyespots, distributed along midline in front of brain (Fig. 2B ). Male copulatory apparatus composed of true seminal vesicle, interpolated prostatic vesicle, and penis papilla with stylet (Fig. 2C-E ). Testicular follicles arranged in two lateral, longitudinal rows, about half length of body, running anteriorly from area in front of pharynx (Fig. 2A ). Seminal vesicle antero-posteriorly elongated, posteriorly turning 180° right in front of female copulatory apparatus before running forward for short distance and then descending ventrally; thick muscular wall coating seminal vesicle, being thinner toward distal portion with forming ejaculatory duct seamlessly (Fig. 2C ). Ejaculatory duct 942 µm long, extending from proximal end of prostatic vesicle to proximal end of seminal vesicle. Prostatic vesicle oval, with 19-µm thick muscular wall, lined with thick glandular epithelium (Fig. 2C-E ). Penis papilla with wedged, strongly sclerotized stylet (about 60 µm long) (Fig. 2C, E ). Penis sheath cone-shaped (Fig. 2C, E ). Male atrium lined with cilia (Fig. 2E ), opening to exterior via male gonopore with depth of about 67 µm (Fig. 2C, E ). Pair of oviducts running posteriorly, then connecting to the proximal end of vagina independently. After receiving pair of oviducts, vagina curving dorsally and leading to female gonopore without evident cement pouch (Fig. 2F ). Adhesive organ present at posterior end of body.

Redescription of holotype of E. cuneata .

Male copulatory apparatus composed of true seminal vesicle, interpolated prostatic vesicle, and penis papilla with stylet (Fig. 3A ). Seminal vesicle elongated, posteriorly turning 180° right, and then leading to ejaculatory duct; thick muscular wall coating seminal vesicle, being thinner toward distal portion (Fig. 3A-D ). Ejaculatory duct 455 µm long, extending from proximal end of prostatic vesicle to proximal end of seminal vesicle. Prostatic vesicle oval, with 13-µm thick muscular wall, lined with thick glandular epithelium (Fig. 3A, C ). Penis papilla with sclerotized stylet (Fig. 3A, D ). Penis sheath cone-shaped (Fig. 3A, D ). Male atrium lined with cilia, opening to exterior via male gonopore with depth of about 95 µm (Fig. 3D ). Pair of oviducts running posteriorly, then connecting to proximal end of vagina independently. Vagina curving dorsally after receiving oviducts. Adhesive organ present at posterior end of body (Fig. 3E ).

Supplementary description of the specimen of E. cuneata from the Fiji Islands.

Male copulatory apparatus composed of true seminal vesicle, interpolated prostatic vesicle, and penis papilla. Stylet not well observed possibly due to fixation state. Seminal vesicle elongated, posteriorly turning 180° right, and then leading to ejaculatory duct. Ejaculatory duct running to anterior, curving posteriorly behind male atrium, then connecting to proximal end of prostatic vesicle; part of ejaculatory duct from proximal end of seminal vesicle to proximal end of prostatic vesicle ca. 1 mm long. Prostatic vesicle oval; internal glandular epithelium not well observed possibly due to fixation state. Penis sheath cone-shaped. Male atrium lined with cilia, opening to exterior via male gonopore. Female reproductive organs and adhesive organ not available to be observed possibly due to fixation state.

Remarks.

Eucestoplana cuneata was originally described from the Galapagos Islands. Our re-examination of the holotype revealed that the ejaculatory duct from proximal end of prostatic vesicle to proximal end of seminal vesicle was over twice as long as that in the original description ( Sopott-Ehlers and Schmidt 1975, fig. 9).

We tentatively identified the present specimens from Kouri Island as Eucestoplana cf. cuneata . The specimens were consistent with the type specimens of E. cuneata in having: i) the eyespots distributed only anterior to the brain, ii) the wedged sclerotized stylet, iii) an adhesive organ at posterior end of body, iv) the conical penis sheath, and v) the fully ciliated inner wall of male atrium ( Sopott-Ehlers and Schmidt 1975). The following morphological differences between the specimens from Japan and the Galapagos Islands should be tested by genetic analyses if these are interspecific or intraspecific: i) body length (24-30 mm in our specimens; 10 mm in the original description), ii) eyespot number (about 30 in our specimens; 35-40 in the original description), and iii) length of ejaculatory duct from the proximal end of prostatic vesicle to proximal end of seminal vesicle (over 900 µm in our specimens; 455 µm in the holotype).

The wide range of distribution of E. cuneata needs to be verified in future studies. So far, this species has been collected from the Galapagos Islands ( Sopott-Ehlers and Schmidt 1975) and the Fiji Islands ( Tajika et al. 1991). Our re-examination of a specimen collected from the Fiji Islands suggested that it corresponded to the holotype of E. cuneata in having the i) conical shape of penis sheath and ii) the fully ciliated inner wall of male atrium. However, the Fiji specimen might be identical to E. cf. cuneata from the Okinawa Islands because it was more similar to Japanese specimens by having a long ejaculatory duct (about 1 mm). Future studies will resolve the doubt of the actual distribution of E. cuneata by comparing their morphology such as the body length, the eyespot number, and the male reproductive organs in more detail between different populations from the Galapagos Islands and the Fiji Islands.

Figures

Figure 2. Eucestoplana cf. cuneata (Sopott-Ehlers & Schmidt, 1975). A. ICHUM 8442, whole animal in living state, dorsal view; B. ICHUM 8442, magnification of anterior body in living state, dorsal view, showing eyespot distribution; C. ICHUM 8440, schematic diagram of male copulatory apparatus in sagittal view, anterior to the right; D, E. ICHUM 8440, photomicrographs of sagittal sections, anterior to the right, showing male copulatory apparatus; F. ICHUM 8441, photomicrograph of sagittal section, showing female copulatory apparatus, anterior to the right. Abbreviations: br - brain; cg - cement glands; ed - ejaculatory duct; fg - female gonopore; ma - male atrium; mg - male gonopore; ph - pharynx; pv - prostatic vesicle; st - stylet; sv - seminal vesicle; te - testicular follicle; va - vagina; ♀ - female copulatory apparatus; ♂ - male copulatory apparatus. Scale bars: 1 mm (A, B); 100 µm (C - F).

Figure 3. Eucestoplana cuneata (Sopott-Ehlers & Schmidt, 1975), holotype (ZMUG 25472), schematic diagram (A) and photomicrographs of sagittal sections (B - E) (anterior to the right). A. Male and female copulatory apparatuses; B - D. Male copulatory apparatus; E. Adhesive organ. Abbreviations: ad - adhesive organ; ed - ejaculatory duct; fa - female atrium; fg - female gonopore; ma - male atrium; mg - male gonopore; ps - penis sheath; pv - prostatic vesicle; spv - spermiducal vesicle; st - stylet; sv - seminal vesicle; va - vagina. Scale bars: 100 µm (A - E).