Chimaeriplana japonica, Oya & Hagiya, 2023

Oya, Yuki & Hagiya, Morio, 2023, Description of a New Genus of Candimboididae (Polycladida: Acotylea) from the Coast of Sagami Bay, Species Diversity 28 (2), pp. 255-262 : 256-262

publication ID	https://doi.org/ 10.12782/specdiv.28.255
persistent identifier	https://treatment.plazi.org/id/038EC008-055D-FFF0-32DE-5ADFFE41FC8A
treatment provided by	Felipe
scientific name	Chimaeriplana japonica
status	sp. nov.

Treatment

Chimaeriplana japonica sp. nov.

[New Japanese name: Nue-hiramushi] ( Figs 1–7 View Fig View Fig View Fig View Fig View Fig View Fig View Fig )

Etymology. The specific name is a Latin adjective (japonicus, -a, -um) derived from the occurrence of the new species in Japan. The Japanese name for the new genus and species is derived from “Nue” (a Japanese legendary monster with the face of a monkey, the body of a raccoon dog, the limbs of a tiger, and the front half of a snake for a tail) and “hiramushi” (polyclad flatworm) in the Japanese language.

Material examined. Two specimens were collected by MoH: holotype, ICHUM 7958 View Materials , two slides (thickness unknown, sagittal sections of posterior half of body, stained with HE), intertidal, Moroiso (35°09′18″N, 139°36′27″E), Misaki , Kanagawa, Japan, 17 May 1992; paratype, ICHUM 7981 View Materials , two slides (thickness and sectioning plane unknown, almost horizontal sections of posterior half of body, stained with HE), intertidal, Mitsuishi (35°08′16″N, 139°09′46″E), Manazuru, Kanagawa, Japan, 11 May 2009 GoogleMaps .

Description. Living specimens 30 mm long, 3–4 mm in maximum width (4 mm in holotype). Body elongated, slen- der, narrow toward posterior end ( Figs 1 View Fig , 2A, B View Fig ). General appearance of body pale brownish to yellowish ( Fig. 1 View Fig ). Tentacles lacking. Pair of cerebro-tentacular eye clusters, linear in shape, arranged near median line ( Fig. 2A, C View Fig ). Pharynx ruffled in shape, located slightly anterior to center of body. Penis stylet visible brownish through dorsal surface of body ( Fig. 1 View Fig ; Supplementary Fig. 1 View Fig ). Gonopores well separated.

Male copulatory apparatus immediately located posterior to pharynx, consisting of seminal vesicle, interpolated prostatic vesicle, penis stylet, and numerous prostaoid organs; penis papilla lacking ( Fig. 3 View Fig ). Common sperm duct lacking; pair of sperm duct separately entering proximal end of seminal vesicle. Seminal vesicle pear-shaped, 292–321 µm long (292 µm in holotype), 165–219 µm wide (219 µm in holotype), with thick (9–20 µm) muscular wall. Distal part of seminal vesicle connecting to proximal end of prostatic vesicle. Prostatic vesicle elongated, pear-shaped, 390–404 µm long (390 µm in holotype), 169–217 µm wide (169 µm in holotype), with thick (13–43 µm) muscular wall and long (241–278 µm, 241 µm in holotype) intra-prostatic ejaculatory duct, without tubular chambers ( Fig. 4A View Fig ). Penis stylet 680 µm long (unclear in paratype), tubular, slightly curved, projecting penis sheath and male atrium ( Figs 3 View Fig , 4A, B View Fig ). Surface of stylet smooth in proximal half part; that in distal half consisting of multiple ridges along with long axis ( Fig. 5A–C View Fig ). Each ridge independently constituting tip of stylet in distal end. Stylet with>20 tips, each tip forming curved hook and possessing barb ( Fig. 5D View Fig ). Prostatoid organs, unarmed, ovoid in shape, distributed in the inner surface of male atrium, with two types ( Figs 3 View Fig , 4 View Fig , 6 View Fig ): large (212–293 µm long, 147–217µm wide; Fig. 6B View Fig ) and small (70–92 µm long, 53–64 µm wide; Fig. 6C View Fig ). Five large prostatoid organs present apart from each other in male atrium; numerous small prostatoid organs filling gap among large ones ( Fig. 6A View Fig ). Each prostatoid organ with glandular part opening to male atrium and muscular wall surrounding glandular part ( Fig. 6 View Fig ). Muscular wall especially developed in large prostatoid organs (up to 83 µm) ( Fig. 6B, C View Fig ).

Female copulatory apparatus with bursa copulatrix and without Lang’s vesicle ( Figs 3 View Fig , 7 View Fig ). Vagina 1113 µm long (unclear in paratype) with ciliated epithelium, running anteriorly then turning posteriorly to exit female gonopore; about one-fifth near proximal end of vagina surrounded by cement glands ( Fig. 7A View Fig ). Bursa copulatrix oval, 200 µm long and 113 µm wide (unclear in paratype), with thick (36– 46 µm) muscular wall, lined with epithelium differentiated from that of vagina, directing postero-dorsally ( Fig. 7B, C View Fig ).

Type locality. Moroiso (35°09′18″N, 139°36′27″E), Misaki , Kanagawa, Japan GoogleMaps .

Distribution. Sagami Bay, Japan.

Habitat. Judged from MoH’s lab notebooks and the environment of the sampling sites, the habitat of C. japonica sp. nov. is likely to be a rocky shore in intertidal zones.

Remarks. The new species should be assigned to a new genus in Candimboididae . The presence of numerous prostatoid organs is a diagnostic character of Discocelidae (Discoceloidea) and some genera in Polyposthiidae (Stylochoidea) ( Faubel 1983; Prudhoe 1985). However, discocelid and polyposthiid species have an oval to elongate oval body with marginal eyespots ( Faubel 1983; Prudhoe 1985), whereas the present species has a slender body without marginal eyespots ( Figs 1 View Fig , 2 View Fig ). In addition, discocelids and polyposthiids do not have a prostatic vesicle and a seminal vesicle as a set, while the new species has an interpolated prostatic vesicle with a true seminal vesicle ( Figs 3–7 View Fig View Fig View Fig View Fig View Fig ; Table 1). Except for (i) the presence of the prostatoid organs, (ii) wellseparated gonopores, and (iii) the absence of Lang’s vesicle, the new species closely resembles polyclads of Candimboides ( Table 1; Du Bois-Reymond Marcus and Marcus 1968: figs 34, 35; Prudhoe 1982: fig. 6). Here, we establish Chimaeriplana gen. nov. based on C. japonica sp. nov.

We revise the definition of Candimboididae provided by Faubel (1983: 91), which is almost identical to the concept of Candimboides by Prudhoe (1982: 371), to include Chimaeriplana gen. nov. in the family. The previous diagnosis of Candimboididae by Faubel (1983: 91) mentioned the proximity between the male and female gonopores and the presence of the Lang’s vesicle. For the closeness of male and female gonopores, we do not believe that this character needs to be emphasized as a diagnosis at the family level because it is variable at the species level in some acotyleans (cf. Oya et al. 2022). For Lang’s vesicle, the presence or absence of the organ is often employed for distinguishing between genera in a family (e.g., Planoceridae ). We eliminated these two diagnostic features from Faubel’s (1983) original concept.

The prostatoid organs of C. japonica sp. nov. are more similar to those in Discocelidae than to those in Polyposthiidae . The organs of discocelids and the present polyclad are distributed only in the wall of the male atrium and are independent of the ductal system in the male copulatory apparatus such as the sperm duct, the seminal vesicle, or the prostatic vesicle. On the other hand, prostatoid organs in Polyposthiidae are observed not only in the male atrium but also in other areas on the ventral surface of the body as well as those in the male atrium have connection(s) with the sperm ducts ( Bock 1913; Palombi 1924; Beauchamp 1951). As far as we have observed the histological sections of C. japonica sp. nov., the glandular part and the muscular wall of the prostatoid organs also resemble those of the organs in discocelid flatworms (cf. Bulnes 2010: fig. 11D; Maghsoudlou and Rahimian 2013: figs 4D, 9D). Observation with other staining methods, such as Azan trichrome stain or periodic acid- Schiff stain, may reveal distinct histological or cytological differences in the prostatoid organs between C. japonica sp. nov. and discocelid polyclads.

The penis stylet in C. japonica sp. nov. is remarkable in the polyclads. The penis stylet in most polyclads is a simple, tubular structure with a smooth surface and a single tip. The penis stylet in the new species has distinct ridges on its surface and multiple tips with a barb ( Fig. 5D View Fig ). For now, C. japonica sp. nov. is probably the only polyclad that possesses such a penis stylet; however, the detailed morphology is unclear because it is broken by sectioning. In future studies, collection of new specimens and observation using a scanning electron microscope are desirable to describe the fine 3D morphology of the structure.