Cheliplana izuensis, Jimi & Hookabe & Imura & Diez, 2024

Jimi, Naoto, Hookabe, Natsumi, Imura, Satoshi & Diez, Yander L., 2024, Two new species of Schizorhynchia (Kalyptorhynchia, Rhabdocoela, Platyhelminthes) from Japan, Zoosystematics and Evolution 100 (4), pp. 1585-1598 : 1585-1598

Cheliplana izuensis sp. nov.

Figs 5 , 6 , 7 (New Japanese name: Izu-kuchibashi-mushi )

Video material.

Video of male copulatory organ of Cheliplana izuensis (https://doi.org/10.6084/m9.figshare.25568256.v1).

Type material.

Holotype • ( NSMT -Pl 6479 ): intertidal sands, Imaihama Beach , 30 Oct. 2019 collected by NJ . Two reference specimens were collected together with the holotype, one used for SEM observation ( NSMT -Pl 6480 ) and the other for DNA extraction.

Description.

Body 2 mm long and 0.38 mm at its widest point. Live animals brownish and translucent (Fig. 5 A ), without eyes. Proboscis 100 μm long and 50 μm at its widest point (Fig. 5 A, B : pr), with one pair of hooks and one pair of sidepieces (Figs 6 A , 7 A : h & sp, respectively). Proboscis hooks 15 μm long, 3 μm wide at the base, smooth and curved. Sidepieces straight, cylindrical in shape, not bifurcated. Pharynx 350 μm long and 150 μm wide (Figs 5 A, B , 6 A ). Prepharyngeal cavity with spines (Fig. 6 A : cp). One adhesive ring with duo-adhesive glands, without papillae located in the subcaudal body end (Fig. 6 A : dashed line indicated by black arrow Fig. 7 B : ar).

One testis located anterolaterally to the pharynx, 690 μm long and 70 μm wide (Figs 5 A , 6 A : t). Atrial organs and ovary located in the caudal body fourth. Seminal ducts form a pair of seminal vesicles at the beginning of the caudal body fourth, each 100 μm long and 20 μm wide (Fig. 6 A, B : sv). Seminal vesicles fuse in a single duct just before entering the male copulatory bulb. Male copulatory bulb comprising a prostate vesicle and a cirrus. Prostate vesicle pear-shaped, 100 μm long and 65 μm wide. Male duct forms in its distal half a cirrus, which separates by a sphincter (Fig. 5 D : sph, Fig. 6 B : ed, sp). Cirrus 65 μm long, 20 μm wide, consisting of three sections (Fig. 6 B ): (i) proximal unarmed region (approximately proximal 20 % of its length), (ii) armed part with fine spines (approximately 15 μm long), and (iii) rhomboid area at distal end of cirrus, armed with fine spines (approximately 20 μm long) and two strong hooks (22 μm long) with bifurcate tips (encircling most distal part of cirrus).

Vitellarium extending from posterior region of pharynx to the caudal body end (Figs 5 A , 6 A : v). Ovary located posterior to the male copulatory bulb. Common gonopore located just caudally to the male copulatory bulb. Vagina present, a ring of circular muscles surrounding its aperture to the outside.

Etymology.

The specific name is derived from a Latin adjective referring to the type locality in the Izu Peninsula.

Distribution and habitat.

The new species is only known from the type locality ( Imaihama , Izu Peninsula, Shizuoka), fine-grained sand in the lower intertidal.

Remarks.

At present, the genus Cheliplana contains 49 species ( Gobert et al. 2021). Cheliplana izuensis sp. nov. is placed in the genus Cheliplana due to having a pair of curved proboscis hooks, soft proboscis sidepieces, a single adhesive girdle, and a cylindrical, barrel-shaped pharynx with a long pre-pharyngeal cavity (de Beauchamp 1927; Schilke 1970; Gobert et al. 2017, 2021). It is distinguished from its congeners by the following combination of characteristics: (i) two strong hooks with bifurcate tips, encircling the distal part of the cirrus; (ii) a cirrus with the proximal 20 % of its length unarmed, posteriorly armed with 15 - μm-long and fine spines; (iii) proboscis sidepieces lacking bristles; (iv) paired seminal vesicles; and (v) the presence of a vagina.

The morphology of the cirrus of C. izuensis sp. nov. allows us to state that the new species is related to C. evdonini Karling, 1983 , and C. setosa Evdonin, 1971 . This morphological similarity was tested using the identification key provided by Gobert et al. (2021), and, indeed, the three species have a convergent morphology of the cirrus. Therefore, we will mainly compare the new species with the other two morphologically similar ones. The cirrus in these three species has differentiated regions (unarmed or armed with spines differing in size) and includes hooks ( C. evdonini and C. izuensis sp. nov.) or well-differentiated spines ( C. setosa ) more or less organized in a ring. In C. izuensis sp. nov., two hooks occur subterminally in the cirrus, whereas six hooks occur about the midlength of the cirrus in C. evdonini ( Karling 1983) , and 5–6 strong spines are present at the beginning of the distal third of the cirrus in C. setosa ( Gobert et al. 2021) . The hooks are distally pointing in C. evdonini and C. setosa but rounded and bifurcate at both ends in C. izuensis sp. nov. Furthermore, the proximal unarmed part of the cirrus distinguishes C. izuensis sp. nov. from the other two related species that have the cirrus armed of spines over its whole length. Another possible related species, C. pusilla Brunet, 1968 , shows a multi-part cirrus; however, it was considered to belong to a different morphological species group due to the lack of hooks in the cirrus as occurs in the previously mentioned species ( Gobert et al. 2021). Moreover, C. izuensis sp. nov. is differentiable from C. pusilla because in the latter species the cirrus shows two distinct spiny regions, a proximal curved area armed with very fine spines and a distal asymmetric one displaying larger spines ( Brunet 1968).

The number and morphology of the seminal vesicles are also important to differentiate species of Cheliplana (see Diez et al. 2019; Gobert et al. 2021). Cheliplana izuensis sp. nov. presents two seminal vesicles, as is the case in C. setosa , whereas there is only one in C. evdonini . However, it was not clearly observed if both seminal vesicles are connected to the testis in C. izuensis sp. nov., while one of the vesicles is blind in C. setosa . Nevertheless, both seminal vesicles contain sperm in C. izuensis sp. nov., and, therefore, we can suppose that, indeed, they are connected to the testis. Among these three species, C. izuensis sp. nov. is also unique by the fact that the proboscis sidepieces do not bear bristles.

Figures

Figure 5. Cheliplana izuensis sp. nov., live specimen, holotype (NSMT - Pl 6479). A. Whole specimen, dorsal view; B. Anterior end; C. Pharynx; D. Overview of internal organs. Scale bars: 1 mm (A); 100 μm (B – D). Abbreviations: c, cirrus; h, hook; pr, proboscis; pc, proboscis cavity; t, testis; p, pharynx; pv, prostate vesicle; sp, side piece; sph, sphincter; sv, seminal vesicle; v, vitellarium.

Figure 6. Cheliplana izuensis sp. nov., drawing based on holotype (NSMT - Pl 6479). A. Whole body; B. Male prostate vesicle and cirrus. Scale bars: 5 mm (A); 100 μm (B). Abbreviations: c, cirrus; cp, cuticular pockets; ed, ejaculatory duct; h, hook; pr, proboscis; pc, proboscis cavity; pv, prostate vesicle; t, testis; p, pharynx; sp, side piece; sm, stomach; sph, sphincter; sv, seminal vesicle; ov, ovary; v, vitellarium. Break line indicates adhesive girdle.

Figure 7. SEM observation of Cheliplana izuensis sp. nov., reference specimen (NSMT - Pl 6480). A. Proboscis; B. Posterior end. Scale bars: 30 μm (A); 50 μm (B). Abbreviations: ar, adhesive ring. Arrows indicate hooks. Arrowheads indicate sidepieces.