Proschizorhynchella quadricaudata Jimi, Hookabe, Imura & Diez, 2024, sp. nov.
Creators: name: Jimi, Naoto
name: Hookabe, Natsumi
name: Imura, Satoshi
name: Diez, Yander L.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Rhabdocoela
Schizorhynchidae
Proschizorhynchella
Proschizorhynchella quadricaudata

description: Proschizorhynchella quadricaudata sp. nov.
Figs 2, 3, 4 (New Japanese name: Yotsuo-kuchibashi-mushi)
Video material.
Video of male copulatory organ of Proschizorynchella quadricaudata (https://doi.org/10.6084/m9.figshare.25568148.v1).
Type material.
Holotype • (NSMT -Pl 6475): adult, intertidal sands, Imaihama Beach, 30 Nov. 2019, collected by NJ and NH; • one reference specimen (NSMT -Pl 6476): intertidal sands, Ishibu Beach, 30 Oct. 2019, collected by NJ and NH; • one reference specimen (NSMT -Pl 6477): intertidal sands, Manazuru, 29 Oct. 2019, collected by NJ and NH; • one reference specimen (NSMT -Pl 6478): intertidal sands, Yoichi, 15 May 2019, collected by NJ and NH; • additional specimen: intertidal sands, Mihama, 29 Oct. 2019, collected by NJ and NH; • additional specimen: intertidal sands, Imaihama Beach, 30 Nov. 2019, collected by NJ and NH, used for DNA extraction.
Description.
Body 2.2 mm long (1.7–2.3 mm, n = 4), 0.4 mm at its widest point (0.4–0.5 mm, n = 4). Live specimens yellowish and translucent (Fig. 2). Two pairs of short bristles (Figs 3 A, 4 A: br) and two pairs of small globular papillae (Figs 3 A, 4 A: gp) at anterior end. Proboscis consisting of two elongated lips, 360 μm in length, 100 μm at the widest part (Figs 2 A, B, 3 A – C, 4 A: pr); a row of glands with 27–37 apertures in the four studied specimens on inner side of proboscis lips (Fig. 3 A, B, C: indicated by white arrow, Fig. 4 A); gland apertures rectangular; glands measuring 14–16 μm long and 6–8 μm in width in the four studied specimens. Pair of black eyes situated posterior to the proboscis (Figs 2, 4 A). Pharynx located at midbody, 160–240 μm in length and 200–260 μm in width in the four studied specimens (Figs 2 B, 3 G).
One adhesive girdle located at the level of the pharynx, composed of six adhesive papillae arranged at regular intervals (Fig. 3 D: indicated by black arrows). Tail with four finger-like projections presents at the posterior end (Figs 3 H, 4 B: fp), each projection similar in size, 40–50 μm in length and 20–30 μm in width in the four studied specimens, muscles strongly developed at their middle part (Fig. 3 H: mc).
Pair of testes, each 180 μm in diameter (Figs 2, 4 A), located anterior to the pharynx. Seminal ducts widen and form a pair of seminal vesicles posterior to the pharynx (Figs 3 E, 4 A, B: sv), each 160 μm in length (150–170 μm, n = 4) and 40 μm in width (40–60 μm, n = 4). Seminal ducts (Fig. 4 B: sd) fuse in a single duct just before entering the male copulatory bulb. Male copulatory organ comprising a proximal prostate vesicle and a distal stylet. Prostate vesicle globular, 80 μm both in length and width (60–120 μm, n = 4) (Figs 3 E, 4 B), separated in two packages; necks of the extracapsular prostate glands enter the copulatory bulb proximally. Stylet enclosed by the male genital duct, cone-shaped, 100–150 μm in length and 20–30 μm in width in the four studied specimens (Fig. 4 B: st, mgd). Male genital duct opens into the common atrium (Fig. 3 E, F: ca), and the latter leads to the exterior through the common genital pore. Common atrium brownish pigmented due to the secretions of atrial glands.
Female genital system consisting of a vitellarium (Fig. 2 A: v) extending between the proboscis and the posterior end of the body, a single ovary (Figs 3 E, 4 B: ov), and bursa located behind the common genital atrium.
Diagnosis.
Species of Proschizorhynchella with its tail end exhibiting four finger-like projections. Proboscis with a well-developed row of glands on each lip. Cone-shaped stylet ~ 100 μm long.
Etymology.
The specific name is derived from a Latin prefix “ quadri ” + adjective “ caudata ”, referring to the tail with four finger-like projections of the new species.
Distribution and habitat.
Northern Japan: Yoichi, on fine-grained sand, lower intertidal. Central Japan: Manazuru, on coarse sand with rocks, lower intertidal; Imaihama (type locality), on fine-grained sand, lower intertidal; Mihama, on fine-grained sand, lower intertidal; and Ishibu, fine-grained sand, lower intertidal.
Remarks.
The studied specimens show characteristics that, provisionally, allow us to include them within Proschizorhynchella. Species of Proschizorhynchella are schizorhynchids characterized by a simple male copulatory bulb forming a spiny cirrus and / or one or two stylets. The stylets are simple funnel structures, spiralized plates, or bear ridges (Schilke 1970; Takeda and Kajihara 2018). The diagnostic characteristics provided by Schilke (1970) are shared by a group of species that likely belong to different genera (Noldt 1985; Karling 1989). As noted by Noldt (1985), the only character differentiating species of Proschizorhynchella from species of Proschizorhynchus Meixner, 1928, is the lack of the curved stylet in the former. However, the presence of a sclerotized mouthpiece in the bursa of species of Proschizorhynchus easily allows their differentiation from species of Proschizorhynchella (Armonies 2023).
Karling (1989) elaborated more on the idea that Proschizorhynchella includes a paraphyletic group of species and questioned the use of the pharynx position and testes number to differentiate among schizorhynchid genera. However, these authors and posterior ones (Takeda and Kajihara 2018) did not refine the diagnosis of Proschizorhynchella or make other taxonomical changes. Unfortunately, the morphological disparities among species of Proschizorhynchella have not been tested through molecular phylogenetic analyses, and none of the 18 previously known species of the genus has been molecularly tested (see Discussion). Therefore, we refrain from updating the diagnosis of Proschizorhynchella until more molecular and morphological data are available to elaborate a comprehensive reclassification of this taxon.
Among the other 18 known species of Proschizorhynchella, P. quadricaudata sp. nov. can easily be differentiated because of the four finger-like projections of its posterior end, a characteristic not present in its congeners. The row of glands that opens along its proboscis lips is also unique in this species, and this character has only been reported for an undescribed species of Proschizorhynchella (see Smith III et al. 2015: Fig. 3 A).
Other characteristics are very variable among species of Proschizorhynchella (see Takeda and Kajihara 2018). Most species have two eyes, two testes, and one gonopore. However, the number of adhesive belts varies from 0 to 3. Proschizorhynchella quadricaudata sp. nov. exhibits a single adhesive belt at the level of the pharynx. Only three other species of Proschizorhynchella present a single belt: P. bivaginata Schilke, 1970; P. robusta Noldt, 1989; and P. schilkei Karling, 1989. Proschizorhynchella bivaginata is unique among these species because it has a cirrus in the copulatory bulb, whereas the other species have a stylet. Proschizorhynchella schilkei has two pairs of testes, and its stylet is a curved, comma-shaped hook, while P. robusta has a spiralized stylet (Karling 1989; Noldt 1989). In contrast, the stylet of P. quadricaudata sp. nov. is a simple and more or less straight tube.
description: Published as part of Jimi, Naoto, Hookabe, Natsumi, Imura, Satoshi & Diez, Yander L., 2024, Two new species of Schizorhynchia (Kalyptorhynchia, Rhabdocoela, Platyhelminthes) from Japan, pp. 1585-1598 in Zoosystematics and Evolution 100 (4) on pages 1585-1598, DOI: 10.3897/zse.100.125042