Armatoplana kaburakii, Oya & Tsuyuki & Kajihara, 2022

Oya, Yuki, Tsuyuki, Aoi & Kajihara, Hiroshi, 2022, Descriptions of two new species of Armatoplana (Polycladida: Stylochoplanidae) from the coasts of Japan, with their phylogenetic positions in Leptoplanoidea, Zootaxa 5178 (5), pp. 433-452 : 440-441

Armatoplana kaburakii sp. nov.

( Figs. 4 and 5 )

Etymology. The specific name is a noun in the genitive case honoring Tokio Kaburaki, who studied Japanese polyclads.

Diagnosis. Armatoplana without nuchal tentacles and common sperm duct and with prostatic vesicle located above seminal vesicle, elongated Lang’s vesicle without accessory vesicles, and male and female gonopores opening closely to each other ( Figs. 4 and 5 ).

Material examined. Five specimens (one holotype and four paratypes) ( Table 1 ).

Description. Live specimens 9.0– 14 mm in length (13 mm in holotype), 2.5–4.2 mm in maximum width (3.8 mm in holotype). Body elongate oval, narrow toward posterior end ( Fig. 4A, B ). Dorsal body tinged with light brown. Dorsal surface of body around pharynx pale yellow. Body margin translucent. General appearance of body yellowish translucent ( Fig. 4A ). Nuchal tentacles lacking. Pair of cerebro-tentacular eye clusters, each containing 26–43 eyespots (30 in right cluster, 31 in left cluster in holotype), arranged near median line ( Fig. 4C ). Eyespots located anterior to brain widely spreading but forming clear aggregation; those located posterior to brain forming almost linear aggregation. Length of anterior part of cluster almost same or longer than that of posterior one. Pharynx whitish, ruffled in shape, occupying about one-fourth to one-fifth of body length (2.0– 3.7 mm in length, 3.3 mm in holotype), located at center of body ( Fig. 4B ). Mouth opening at slightly posterior to center of pharyngeal cavity. Intestine not anastomosed, spreading throughout body except margin. Pair of whitish sperm ducts and oviducts visible through ventral body wall ( Fig. 4B ). Male and female gonopores close but separated; male gonopore opening at about one-fourth to one-sevenths of body length (2.3–3.7 mm, 3.6 mm in holotype) from posterior end; female gonopore situated 0.07–0.17 mm (0.07 mm in holotype) posterior to male gonopore.

Male copulatory apparatus located posterior to pharynx, consisting of seminal vesicle, interpolated prostatic vesicle, and penis stylet ( Fig. 5A ). Pair of sperm ducts running anteriorly, turning medially at point about one-fifth length 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, then turning anteriorly ( Fig. 4B ) and entering separately proximal end of elongated ovate seminal vesicle. Seminal vesicle directing anteriorly and having strong muscular wall ( Fig. 5B ). Distal end of seminal vesicle slender, running dorsally before connecting to prostatic vesicle. Prostatic vesicle oval-shaped, larger than seminal vesicle, having thick muscular wall lined with smooth, thick epithelium and located dorsally above seminal vesicle ( Fig. 5A, B ). Distal end of prostatic vesicle forming penis papilla armed with stylet ( Fig. 5C ). Penis stylet straight or curved (straight in ICHUM 6091 [holotype] and ICHUM 6090 [paratype]; curved in ICHUM 6283–6285 [paratypes]; Fig. 5A, D ), projecting into penis pocket. Penis pocket lined with ciliated epithelium opening to male atrium ( Fig. 5A ). Male atrium small, cone-shaped, and lined with ciliated epithelium.

Pair of oviducts forming common oviduct, latter running postero-dorsally to enter vagina. From this point, elongated Lang’s-vesicle duct (almost same length of vagina), lined with folded ciliated epithelium, running posteroventrally to connect to Lang’s vesicle ( Fig. 5E ). Lang’s vesicle elongated, sac-shaped, and lined with columnar cells, lacking accessory vesicles ( Fig. 5E ). Vagina curving antero-ventrally, then running postero-ventrally to exit at female gonopore. Lang’s-vesicle duct and vagina surrounded by circular muscle fibers and lined with ciliated and smooth epithelium.

Type locality. Arai-hama Beach (35°09′34″N, 139°36′42″E), Misaki , Kanagawa, Japan .

Habitat. Intertidal to subtidal, on the surfaces of coralline algae (Kanagawa), undersurface of stones (Shizuoka), and among oyster beds on a mooring rope hung in the sea (Kochi) ( Table 1 ).

Sequences of COI. The uncorrected P -distances of the partial COI sequences (712 bp) of the five specimens ( LC582945 – LC582946 and LC672056 – LC672058 ) were 0.001 –0.013 .

Remarks. Armatoplana kaburakii sp. nov. resembles A. reishi ( Hyman, 1959) and A. tenuis ( Palombi, 1936) in that they share the following two characteristics: i) nuchal tentacles absent and ii) male and female gonopores opening closely to each other ( Table 3 ). Armatoplana kaburakii sp. nov. is distinguished from these two species by the shape of the Lang’s vesicle (elongated sac-shaped in A. kaburakii sp. nov.; laterally broadened in A. reishi ; spherical in A. tenuis ).

This is the first report of Armatoplana from the West Pacific along with A. albomaculata sp. nov. The uncorrected P -distances of COI (712 bp) from A. albomaculata sp. nov. were 0.180 –0.188.

Figures

FIGURE 4. Armatoplana kaburakii sp. nov., photographs taken in life, ICHUM 6091 (holotype). A, Dorsal view; B, ventral view; C, eyespots, dorsal view. Abbreviations: cte, cerebro-tentacular eyespot; fg, female gonopore; mg, male gonopore; ph, pharynx; ov, oviduct; sd, sperm duct. Scale bars: 5 mm (A, B), 1 mm (C).

FIGURE 5. Armatoplana kaburakii sp. nov., sagittal view of copulatory apparatuses, anterior to the left. A–C, ICHUM 6091 (holotype); D, ICHUM 6283 (paratype); E, ICHUM 6090 (paratype). A, Schematic diagram of male and female copulatory apparatuses; B, male copulatory apparatus; C, D, penis stylet; E, female copulatory apparatus. Abbreviations: cov, common oviduct; fg, female gonopore; ld, Lang’s vesicle duct; lv, Lang’s vesicle; ma, male atrium; mg, male gonopore; ppo, penis pocket; ps, penis stylet; pv, prostatic vesicle; sd, sperm duct, sv, seminal vesicle; v, vagina. Scale bars: 500 μm (A, E), 300 μm (B–D).