Phaenoplana kopepe, Oya & Kajihara, 2019

Phaenoplana kopepe sp. nov.

( Figs 2 View Fig , 3 View Fig )

Etymology. The new specific name is an indeclinable noun, taken from the type locality, Kopepe Beach. According to a local anecdote, Kopepe was the name of a man who came from the Gilbert Islands all the way across the Pacific to Chichijima island and lived near the beach.

Material examined. Two specimens: holotype, ICHUM 5343 View Materials , 10 View Materials slides (1 slide for whole mount of the anterior body and 9 slides for serial sagittal sections), intertidal, Kopepe Beach (27°03′52″N, 142°11′32″E), Chichijima island, the Ogasawara Islands, Japan, 3 September 2016, Y GoogleMaps . Oya leg GoogleMaps .; paratype, ICHUM 5344 View Materials , 5 View Materials slides (1 slide for whole mount of the anterior body and 4 slides for serial sagittal sections), collected along with the holotype .

Description. Live specimens 17–21 mm (21 mm in holotype) in length, 5.5–7 mm (7 mm in holotype) in width. Body thin, elongate oval, narrow toward posterior end. Ground body color translucent to whitish opaque. General appearance of body light brown ( Fig. 2A, B View Fig ). Dorsal body tinged with light brown due to minute granules scattered over entire surface except around margin. Dorsal surface of body around pharynx brown. Body margin translucent. Pair of tentacles present at between one-fifth to one-sixth body length (3.4–3.5 mm, 3.5 mm in holotype) from anterior end ( Fig. 2A View Fig ); each tentacle containing at least 30 eyespots ( Fig. 2C View Fig ). Cerebral eye clusters arranged along median line and congregated anterior to tentacles, consisting of 29–44 eyespots (29 in right cluster, 30 in left cluster in holotype, Fig. 2D View Fig ). Pharynx whitish, ruffled in shape, occupying twoninths to one-third of body length (3.7–7 mm, 7 mm in holotype), located slightly anteriorly to center of body ( Fig. 2B View Fig ). Mouth opening ventrally at near posterior end of pharyngeal cavity ( Fig. 3A View Fig ). Intestine highly branched and not anastomosing, spreading throughout body except margin and brain region. Pair of whitish sperm ducts and oviducts visible through ventral body wall ( Fig. 2B View Fig ). Male and female gonopores separate; male gonopore opening at about one-third of body length (5.6–7 mm, 7 mm in holotype) from posterior end; female gonopore situated 0.5–0.7 mm (0.7 mm in holotype) posterior to male gonopore ( Fig. 2B View Fig ).

Male copulatory apparatus located posteriorly to pharynx ( Fig. 3A View Fig ), consisting of true seminal vesicle, interpolated prostatic vesicle, and penis rod ( Fig. 3B, C View Fig ). Pair of sperm ducts running anteriorly, then turning medially at point of about one-fifth length (1.4mm in holotype, not clearly visible in paratype) of pharynx from posterior end, subsequently running posteriorly along both sides of pharynx and extending further posteriorly for short distance beyond level of posterior end of pharynx, before turning medially ( Fig. 2B View Fig ) to enter separately proximal end of elongated ovate seminal vesicle. Seminal vesicle directing anteriorly and having strong muscular wall ( Fig. 3B View Fig ). Distal end of seminal vesicle slender, running dorsally before connecting to prostatic vesicle. Prostatic vesicle oval-shaped, located dorsally above seminal vesicle, having thick muscular wall lined with smooth, thick epithelium ( Fig. 3B View Fig ). Canals of extra-vesicular gland penetrating prostatic vesicle wall. Distal end of prostatic vesicle forming elongated penis rod. Penis rod muscular, without stylet, projecting into cylindrical male atrium; ejaculatory duct passing through penis rod ( Fig. 3C, F View Fig ). Lining epithelium of male atrium smooth. Prostatic vesicle and male atrium enclosed by muscle bulb ( Fig. 3 View Fig B–D, F).

Pair of oviducts commencing from level of anterior end of pharynx, running posteriorly, extending further posteriorly for short distance beyond level of posterior end of pharynx before curving medially and fusing with each other at midline to form common oviduct, which runs upward to enter vagina ( Fig. 3D, E View Fig ). From this point, Lang’s duct, lined with ciliated epithelium, running posteriorly, then curving ventrally, and leading posteriorly to Lang’s vesicle. Lang’s vesicle horseshoe-shaped ( Fig. 3E View Fig ) and lined with columnar cells ( Fig. 3D View Fig ). Vagina lined with ciliated and smooth epithelium, curving antero-ventrally for short distance, then recurving postero-dorsally, then twisting again, eventually turning ventrally to exit at female gonopore ( Fig. 3D, F View Fig ). Lang’s duct and vagina surrounded by circular muscle fibers; vagina surrounded by cement glands.

Habitat. Found intertidally on the undersurface of stones and dead corals along sheltered beach.

Sequence data. The partial COI sequences (610 bp) from the two specimens ( LC369778 and LC369779 ) almost coincide with each other except one synonymous substitution at the 3rd codon position (transition) . At present, there is no stylochoplanid sequence entry in DDBJ/EMBL/GenBank databases that are comparable to ours. A 627-bp COI sequence from Comoplana agilis (Lang, 1884) has been registered ( MF371145 View Materials ), but this region in the COI does not overlap with what we sequenced . Our sequences represent the first Phaenoplana entry in the public databases.

Remarks. Among the six species of Phaenoplana , P. kopepe resembles P. challengeri ( Graff, 1892) and P. conoceraea ( Schmarda, 1859) . They are from the Indo-Pacific, and share the following characters: i) a pair of tentacles are present, ii) the mouth opens near posterior end of the pharyngeal cavity, and iii) the Lang’s vesicle is horseshoe shaped ( Table 1 View Table 1 ). Phaenoplana kopepe differs from P. challengeri in the shape of vagina (anteriorly curved in P. kopepe ; almost vertical in P. challengeri ) and the distance between male and female gonopores (well separated in P. kopepe ; close in P. challengeri ), and from P. conoceraea in the length of the Lang’s duct (shorter than the length of vagina in P. kopepe ; longer than the length of vagina in P. conoceraea ) in addition to the two characters mentioned above.

Japanese polyclad fauna in warm-water areas, such as the Ogasawara Islands, requires further investigation. Stimpson (1855, 1857) described 18 polyclad species (seven acotyleans, nine cotyleans, and two with uncertain suborder affiliation) from the Amami and Okinawa Islands; however, 12 (including four acotylean species) of the 18 species are regarded to be of uncertain position (cf. Tyler et al. 2006 –2016) because details about the copulatory-organ anatomy are not known for these species. Since Stimpson (1855, 1857), the fauna of Polycladida in these regions were surveyed sporadically, with several species having been described and reported so far (e.g., Cannon and Grygier 1991; Okuno and Aizawa 2010; Okuno and Naruse 2013). In the Ogasawara Islands, nine named species and 3–6 undetermined ones have been reported ( Bock 1923; Kato 1944; Ooishi 1970; Akasaka 2016), of which five— Boninia mirabilis Bock, 1923 , Callioplana marginata Stimpson, 1857 , Pericelis beyerleyana Collingwood, 1876 , Pseudoceros ferrugineus Hyman, 1959 , Pseudobiceros gratus (Kato, 1937) , and Pseudocerotidae gen. sp. ( Bock 1923; Akasaka 2016)—have a conspicuous body color and/or shape, thus cannot be confused with other species. However, the rest of 5–8 species— Notocomplana humilis ( Stimpson, 1857) , Planocera reticulata ( Stimpson, 1855) , Pleioplana delicata (Yeri and Kaburaki, 1918) , Paraplanocera oligoglena ( Schmarda, 1859) , and 1–4 unidentified Paraplanocera spp. ( Kato 1944; Ooishi 1970; Akasaka 2016)—are inconspicuous in external appearance. Of these inconspicuous species, N. humilis and Ple. delicata , as well as Ph. kopepe , belong to Leptoplanoidea, and they all have a uniformly pale brown body. Therefore, Ph. kopepe might have been overlooked or confused with such inconspicuous species in the previous studies, given that Kato (1944) and Ooishi (1970) did not provide detailed internal morphology in terms of the material from Ogasawara.