Armatoplana albomaculata, 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 : 437-440

Armatoplana albomaculata sp. nov.

( Figs. 2 and 3 )

Etymology. The new specific name albomaculata (- us, - a, - um) is a compound adjective derived from the Latin words albus and maculatus, which mean “white-spotted.” The species was named after small white spots scattered on the dorsal surface of the worms.

Diagnosis. Armatoplana without nuchal tentacles and with white spots on dorsal surface, common sperm duct, elongated oval prostatic vesicle directing posteriorly but curving dorsally in distal part, largely curved penis stylet, and small, oval Lang’s vesicle without accessory vesicles ( Figs. 2 and 3 ).

Material examined. Two specimens (one holotype and one paratype) ( Table 1 ).

Description. Live specimens 12–16 mm in length (16 mm in holotype), 5.9–6.6 mm in maximum width (6.6 mm in holotype). Body elongate oval, narrow toward posterior end ( Fig. 2A, 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. 2A ). Small white spots scattered on dorsal surface ( Fig. 2A, C ). Nuchal tentacles lacking. Pair of cerebro-tentacular eye clusters, each containing 44–57 eyespots (46 in right cluster, 44 in left cluster in holotype), arranged near median line ( Fig. 2C ). Eyespots located anterior to brain widely spreading but forming clear aggregation; those located posterior to brain forming irregular aggregation with small number of eyespots. Length of anterior part of cluster clearly longer than that of posterior one. Pharynx whitish, ruffled in shape, occupying about one-fourth of body length (3.4–3.9 mm in length, 3.9 mm in holotype), located at center of body ( Fig. 2B ). 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. 2B ). Male and female gonopores separate; male gonopore opening at about two-sevenths of body length (3.3–5.2 mm, 5.2 mm in holotype) from posterior end; female gonopore situated 1.2 mm posterior to male gonopore (not observed in paratype).

Male copulatory apparatus located posterior to pharynx, consisting of seminal vesicle, interpolated prostatic vesicle, and penis stylet ( Fig. 3A, B ). Pair of sperm ducts running anteriorly, turning medially at point about onethird to one-half length of pharynx from posterior end (one-half in holotype), 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. 2B ). Distal part of sperm duct forming spermiducal vesicle and fusing to short common sperm duct. Common sperm duct also forming spermiducal vesicle in holotype, entering proximal end of seminal vesicle. Seminal vesicle elongated bean-shaped, directing antero-dorsally and having strong muscular wall ( Fig. 3C ). Distal end of seminal vesicle connecting to prostatic vesicle. Prostatic vesicle directing posteriorly, elongated oval-shaped, and almost same size as seminal vesicle (slightly smaller than seminal vesicle in holotype), having thin muscular wall lined with smooth, thick epithelium and located dorsally above seminal vesicle ( Fig. 3B, D ). Distal end of prostatic vesicle directing dorsally and forming penis papilla. Penis papilla armed with penis stylet directing anteriorly ( Fig. 3D, E ). Penis stylet turning posteriorly, then curving ventrally in penis pocket ( Fig. 3A, B, D ). About two-thirds of proximal part of penis pocket not ciliated. Distal part of penis pocket lined with ciliated epithelium and opening to male atrium ( Fig. 3B ). Male atrium cone-shaped and lined with ciliated epithelium.

Pair of oviducts forming common oviduct, latter running postero-dorsally to enter vagina. From this point, short Lang’s-vesicle duct (about one-fifth of the length of vagina), lined with folded ciliated epithelium, running posteroventrally to connect to Lang’s vesicle ( Fig. 3F ). Lang’s vesicle small, oval, and lined with columnar cells, lacking accessory vesicles ( Fig. 3F ). Vagina running anteriorly, then turning posteriorly to exit at female gonopore; inner lining of about two-thirds of distal part of vagina folded. Vagina surrounded by circular muscle fibers and lined with ciliated epithelium.

Type locality. Tsujishima Island (32°33′09″N, 130°06′32″E), Amakusa, Kumamoto, Japan .

Habitat. Intertidal to subtidal zones, undersurface of stones (Kumamoto) and among kelp holdfasts (Kanagawa).

Sequences of COI. The uncorrected P -distance of the partial COI sequences (712 bp) between the two specimens ( LC672054 – LC672055 ) was 0.008 .

Remarks. Armatoplana albomaculata sp. nov. resembles A. affinis ( Palombi, 1940) , A. lactoalba ( Verrill, 1900) , A. leptalea ( Marcus, 1947) , A. panamensis ( Plehn, 1896) , and A. snadda ( Du Bois-Reymond Marcus & Marcus, 1968) in that they share the following characteristics: i) nuchal tentacle absent and ii) long penis stylet present ( Table 3 ). The present species is distinguished from A. affinis by the presence or absence of the accessory vesicles in the Lang’s vesicle (absent in A. albomaculata sp. nov.; present in A. affinis ); from A. lactoalba , A. leptalea , and A. panamensis by the shape of the Lang’s vesicle (small, oval in A. albomaculata sp. nov.; large, elongated in A. lactoalba , A. leptalea , and A. panamensis ); and from A. snadda by the position of the pharynx relative to the body (located at the center in A. albomaculata sp. nov.; located anteriorly in A. snadda ) as well as the length of the pharynx relative to the body length (about one-fourth in A. albomaculata sp. nov.; about one-sixth in A. snadda ).

The white spots in A. albomaculata are remarkable. In other congeners, white spots on the dorsal surface were only described in A. taurica ( Jacubowa, 1909) ; however, the spots differ from those in A. albomaculata in that the former were represented by two different types in shape (irregular and oblong) ( Jacubowa 1909: 9). Apart from A. taurica , the presence or absence of white spots has not been explicitly mentioned in previous descriptions of other Armatoplana species; therefore, the possibility cannot be ruled out that the presence of white spots like in A. albomaculata could have simply been overlooked. If not, however, this character is useful because it allows the species to be distinguished from other congeners by external appearance alone.

This is the first report of Armatoplana from the West Pacific. Five species, namely, A. colombiana Bolaños et al., 2006 , A. divae ( Marcus, 1947) , A. lactoalba , A. leptalea , and A. snadda , were recorded from the Atlantic coast of Central and South America ( Verrill 1900; Marcus 1947; Du Bois-Reymond Marcus & Marcus 1968; Quiroga et al. 2004; Bahia et al. 2015). Two species, namely, A. panamensis and A. reishi ( Hyman, 1959) , were recorded from the Pacific coast of North and Central America ( Plehn 1896; Hyman 1953, 1959). Four species were described from Africa: A. affinis and A. vesiculata ( Palombi, 1940) from the Atlantic coast ( Palombi 1940) and A. tenuis ( Palombi, 1936) and A. robusta ( Palombi, 1928) from the coast along the Indian Ocean ( Palombi 1928, 1936). Armatoplana taurica was found in the Black Sea ( Jacubowa 1909).

Figures

FIGURE 2. Armatoplana albomaculata sp. nov., photographs taken in life. A and B, ICHUM 6286 (holotype); C, ICHUM 6287 (paratype). 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 3. Armatoplana albomaculata sp. nov., sagittal view of copulatory apparatuses, anterior to the left, ICHUM 6286 (holotype). A, Schematic diagram of male and female copulatory apparatuses; B, male and female copulatory apparatuses; C, D, male copulatory apparatus; E, penis papilla; F, female copulatory apparatus. Abbreviations: cg, cement gland; cov, common oviduct; fg, female gonopore; ld, Lang’s vesicle duct; lv, Lang’s vesicle; ma, male atrium; mg, male gonopore; pp, penis papilla; ppo, penis pocket; ps, penis stylet; pv, prostatic vesicle; spv, spermiducal vesicle; sv, seminal vesicle; v, vagina. Scale bars: 500 μm (A, B), 300 μm (C, D, F), 100 μm (E).