Notocomplana profunda, Oya & Hookabe & Jimi & Furushima & Fujiwara, 2025

Oya, Yuki, Hookabe, Natsumi, Jimi, Naoto, Furushima, Yasuo & Fujiwara, Yoshihiro, 2025, Description of a new bathyal species of Notocomplana (Platyhelminthes, Polycladida) collected from Bathymodiolus aggregations in a deep-sea hydrocarbon seep, Zootaxa 5722 (2), pp. 265-277 : 268-273

publication ID	https://doi.org/10.11646/zootaxa.5722.2.6
publication LSID	lsid:zoobank.org:pub:075ADF37-97E9-4E52-9C46-BECDAC249E57
persistent identifier	https://treatment.plazi.org/id/450F8926-3061-FFE8-F8EC-8BDAEE993EEF
treatment provided by	Plazi
scientific name	Notocomplana profunda
status	sp. nov.

Treatment

Notocomplana profunda sp. nov.

[New Japanese name: shinkai-usu-hiramushi]

( Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Etymology. The new specific name profunda (- us, - a, - um) is a Latin adjective meaning ‘deep’ and refers to the habitat of the flatworms. The new Japanese name for the new species is derived from shinkai (deep sea) and usuhiramushi ( Notocomplana polyclad) in the Japanese language.

Diagnosis. Notocomplana without tentacles, eyespots, and color pattern on dorsal surface of body. Copulatory apparatus consisting of tripartite-like seminal vesicle, prostatic vesicle smaller than seminal vesicle, and long, tubular Lang’s vesicle ( Figs 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 ).

Material examined. Holotype: NSMT-Pl- 9511, 911 m depth, off Hatsushima , Shizuoka Prefecture, Japan, 24 October 2021, coll. N. Hookabe and N. Jimi, sagittal sections of whole body on 37 slides, MT stain . Paratypes: NSMT-Pl-9512, ibid., sagittal sections of anterior 1/3 of body on 19 slides and posterior 2/3 of body containing pharynx and copulatory apparatus on 33 slides, HE stain; NSMT-Pl-9513, ibid., whole mount of anterior 1/3 of body and cross sections of posterior 2/3 of body containing pharynx and copulatory apparatus on 27 slides, HE stain; NSMT-Pl-9514, whole mount of body; NSMT-Pl-9515, whole body fixed and preserved in 99.5% ethanol.

Sequenced material. Paratype: NSMT-Pl-9515.

Description. Living worms elongated oval ( Fig. 1A, B View FIGURE 1 ). Body whitish translucent, no color pattern ( Fig. 1A View FIGURE 1 ). Intestine not anastomosed, spreading throughout body except into the margins. Pharynx, sperm ducts and seminal vesicle visible whitish through ventral body wall ( Fig. 1B View FIGURE 1 ).

Fixed specimens 13–19 mm in length ( 19 mm in holotype), 6.6–9.7 mm in maximum width ( 9.7 mm in holotype) ( Fig. 2A, B View FIGURE 2 ). Pharynx ruffled, about one-fourth of body length ( 3.1–4.5 mm in length, 4.5 mm in holotype), located at slightly anterior to center of body ( Fig. 2B View FIGURE 2 ). Mouth opening at center of pharyngeal cavity. Male and female gonopores separate; male gonopore opening at about two-fifths to one-half of body length ( 5.4–8.9 mm, 8.9 mm in holotype) from posterior end; female gonopore situated 0.6–1.2 mm ( 1.1 mm in holotype) posterior to male gonopore ( Fig. 2B View FIGURE 2 ). Tentacles and eyespots absent ( Fig. 2A, C View FIGURE 2 ).

Male copulatory apparatus located immediately posterior to pharynx ( Fig. 2D View FIGURE 2 ), consisting of seminal vesicle, interpolated prostatic vesicle, and penis papilla ( Figs 3 View FIGURE 3 , 4A View FIGURE 4 ). Pair of sperm ducts running anteriorly from posterior to female gonopore, turning medially at about one-half length of pharynx, subsequently running posteriorly along both sides of pharynx to short distance beyond posterior end of pharynx, then turning anteriorly ( Fig. 1B View FIGURE 1 ) to open separately to seminal vesicle; common sperm duct lacking ( Fig. 3B–D View FIGURE 3 ). Seminal vesicle nearly tripartite-type, with 35–176 µm (25–176 µm in holotype) thick muscular wall formed by intermingle fibers ( Figs 2D View FIGURE 2 , 3 View FIGURE 3 , 4A View FIGURE 4 ). Distal end of seminal vesicle forming intra-prostatic ejaculatory duct of 187–213 μm in length (213 μm in holotype) that projecting deeply into prostatic vesicle. Prostatic vesicle bulbiform in shape, 311–360 μm on long axis (360 μm in holotype), 295–345 μm on short axis (345 μm in holotype), with 41–113 µm (46–113 µm in holotype) thick muscular wall ( Figs 3A View FIGURE 3 , 4A View FIGURE 4 ). Inner lining of prostatic vesicle glandular, forming six tubular chambers surrounding intra-prostatic ejaculatory duct ( Fig. 4B–E View FIGURE 4 ). Post-prostatic ejaculatory duct lined with glandular epithelium similar to that of prostatic vesicle and surrounded by circular muscles ( Fig. 4A, E View FIGURE 4 ). Penis papilla conical in shape, not sclerotized. Male atrium cone-shaped, lined with ciliated epithelium, lacking penis sheath.

Pair of oviducts forming common oviduct, latter running antero-dorsally to enter vagina ( Figs 3A View FIGURE 3 , 4E View FIGURE 4 ). Lang’s vesicle duct 693–737 µm in length (737 µm in holotype), lined with folded ciliated epithelium ( Fig. 4F View FIGURE 4 ). Lang’s vesicle tubular in shape, 1540–1650 µm in length (1650 µm in holotype), lined with columnar cells ( Fig. 4F View FIGURE 4 ). Lang’s vesicle duct and Lang’s vesicle surrounded by thin muscular wall. Vagina 1450–1697 µm in length (1697 µm in holotype), surrounded by circular muscle fibers and lined with ciliated epithelium, running anteriorly, then turning posteriorly to exit at female gonopore. About two-thirds to one-fourth of vagina surrounded by cement glands ( Fig. 4F View FIGURE 4 ). Vagina bulbosa not developed.

Type locality. 911 m depth, off Hatsushima (35°00.94ʹN, 139°13.38ʹE), Sagami Bay, Shizuoka Prefecture, Japan .

Habitat. Mussel beds of Bathymodiolus species. Other invertebrates such as polychaetes, nemerteans, sea spiders, and acoels were also found in the habitat ( Hookabe et al. 2024).

Molecular phylogeny. Notocomplana profunda sp. nov. is nested in a robust clade ( 97 in bootstrap value (BS)/ 1.00 in posterior probability (PP)) formed by Notoplana atomata (Müller, 1776) and five Notocomplana species: N. hagiyai Oya & Kajihara, 2017 , N. humilis (Stimpson, 1857) , N. japonica (Kato, 1937) , N. koreana (Kato, 1937) , and N. septentrionalis (Kato, 1937) ( Fig. 5 View FIGURE 5 ). Here, we call this clade “ humilis clade” named after the clade containing N. humilis , the type species of Notocomplana . In this clade, the present species is the sister to Notoplana atomata with a 99% BS in the ML tree and 1.00 PP in the BI tree.

Remarks. The present polyclads are characterized by possessing i) a seminal vesicle, ii) an interpolated prostatic vesicle with an intra-prostatic ejaculatory duct, iii) several tubular chambers in the prostatic vesicle, iv) a conical penis papilla lacking a penis stylet, v) a Lang’s vesicle, and vi) separated gonopores. The morphology of the species meets the diagnosis of Notocomplana (cf. Faubel 1983; Litvaitis et al. 2019). Our molecular phylogenetic analyses demonstrated that the present species is the sister to a notoplanid species, Notoplana atomata , with high nodal supports; however, the morphology of the species is clearly distinguished from that of Notoplana atomata as mentioned later. In addition, both Notocomplana and Notoplana are not monophyletic ( Fig. 5 View FIGURE 5 ). Here, we assigned the present species to Notocomplana based on the morphological criteria.

The copulatory apparatus of the newly described species Notocomplana profunda sp. nov. is characterized by the presence of a prostatic vesicle smaller than the seminal vesicle and a tubular elongated Lang’s vesicle as well as the absence of a common sperm duct ( Figs 2D View FIGURE 2 , 3 View FIGURE 3 , 4 View FIGURE 4 ). Among the 33 valid species of Notocomplana ( López-Márquez et al. 2025) , the same combination of characters is only observed in N. sanguinea ( Freeman, 1933) . However, N. profunda sp. nov. is distinguished from N. sanguinea by i) the absence of eyespots (present in N. sanguinea ), ii) the absence of color patterns on the body surface (a red saddle across the central part of the dorsal surface in N. sanguinea ), iii) the length of the pharynx relative to the body length (one-fourth in N. profunda sp. nov.; two-fifths in N. sanguinea ), iv) the shape of the seminal vesicle (nearly tripartite shaped in N. profunda sp. nov.; bean-shaped in N. sanguinea ), and v) the presence/absence of a tooth-like elevation in the vagina (absent in N. profunda sp. nov.; present in N. sanguinea ) ( Freeman 1933, pl. XV, figs 11–13; Hyman 1953, figs 81–83).

Notocomplana profunda sp. nov. differs significantly from Notoplana atomata View in CoL in terms of morphology, despite forming a robust clade with the species in the molecular phylogeny. Notoplana atomata View in CoL has a bean-shaped seminal vesicle and a large sac-shaped or reduced Lang’s vesicle as well as eyespots and a penis stylet ( Bock 1913, text-fig. 39; Hyman 1939, pl. 2, fig. 5; Marquina et al. 2015, fig. 3E). In addition, the inner chambers of the prostatic vesicle in N. atomata View in CoL are tightly packed with each other and fill the interior of the prostatic vesicle ( Marquina et al. 2015, fig. 3F) whereas the chambers in N. profunda sp. nov. are separated from each other and similar to those in other Notocomplana View in CoL in the humilis View in CoL clade ( Fig. 4B–E View FIGURE 4 ; Oya & Kajihara 2017, figs 1E, 3E, 5E, 6E). In this study, we were unable to identify any morphological synapomorphies within the clade.