Ceratoplana falconerae Rodríguez & Hutchings & Williamson 2021, sp. nov.

Ceratoplana falconerae sp. nov.

(Fig. 14)

Material examined: Three specimens, two sagittally sectioned. Holotype: NMV F248135.1 – F248135.4 (4 slides). Additional material: AM W.51327 (2 slides). AM W.53223 (wet material).

Type locality: Australia, Victoria, Cape Paterson, Boat Ramp area, found intertidally on the blades of the seagrass Amphibolis antarctica, 38°40’28.6”S, 145°37’16.5”E. Coll. Audrey Falconer and Jorge Rodriguez, March 25 th, 2019.

Additional material locality: Australia, Victoria, Cats Bay, Phillip Island 38°30’24.6”S, 145°07’33.8”E. Coll. Jorge Rodriguez, Patrick Burke and Louise Tosetto, July 12 th, 2018.

Etymology: The specific name is dedicated to Ms. Audrey Falconer of the Field Naturalists’ Club of Victoria for her invaluable help in conducting fieldwork in the state of Victoria.

Description: Body oval with expanded anterior region and pointed posterior end. Length 0.9 cm. Dorsal surface greyish-brown with scattered dark brown and cream spots and semi-transparent body margin interrupted by light brown spots; region above pharynx with cream colour and small brown pigments (Fig. 14A). Nuchal tentacles present. Tentacular eyes inside tentacles, cerebral eyes located in two elongated parallel clusters above brain area (Fig. 14B, D). Ruffled pharynx located anterior to middle part of the body, oral pore opening in its centre (Fig. 14B, C).

Male and female gonopores located separate behind pharynx. Male copulatory apparatus consists of a seminal vesicle, an interpolated prostatic vesicle and a penis papilla, directed backwards (Fig. 14E–G). Vasa deferentia run ventrally and join distally seminal vesicle (Fig. 14F). Seminal vesicle S-shaped and provided with a strong muscular layer (Fig. 14F). Ejaculatory duct narrows into a thin tube and joins distally prostatic vesicle. Prostatic vesicle and penis papilla included in a muscular penis sheath. Oval prostatic vesicle provided with a muscular layer and lined with smooth glandular epithelium (Fig. 14G). Penis papilla conical-shaped and directly connected to prostatic vesicle, provided with a strengthening at the distal tip formed by the base membrane (also referred to as penis sheath) and housed in a ciliated male atrium (Fig. 14G).

Female system located posterior to male apparatus (Fig. 14E, H, I). Vagina externa runs vertically reaching dorsal side of the animal (Fig. 14H), connects with vagina interna and loops ventrally and anteriorly towards male system before turning back posteriorly and receiving oviducts (Fig. 14I). End of vagina interna connects back to its middle region through a ductus vaginalis, forming a loop (Fig. 14H), Lang’s vesicle absent. Female gonopore and ductus vaginalis share a common female atrium.

Remarks: The presence of a well-defined seminal vesicle, an interpolated prostatic vesicle with smooth glandular epithelium, and an unarmed penis papilla positions the new species in the Stylochoplanidae family. Among all Stylochoplanidae genera, the new species aligns best with the genus Ceratoplana Bock, 1925a due to its long pharyngeal cavity with the mouth opening in its anterior region, separate gonopores, presence of a well-defined seminal vesicle, an interpolated prostatic vesicle with smooth glandular epithelium, an unarmed penis papilla, a female system provided with a ductus vaginalis that loops back into the vagina interna, and Lang’s vesicle lacking.

Ceratoplana falconerae sp. nov. can be distinguished from Ceratoplana colobocentroti Bock, 1925a, the type and only other species of the genus, by the presence of a short penis papilla provided with a penis sheath (also referred to as a strengthening at the distal tip by a styliform developing of the base membrane by Faubel (1983)). The presence of a penis sheath is currently considered to be diagnostic character of specific level in another Stylochoplanidae genus, Emprosthopharynx Bock, 1913. In comparison, C. colobocentroti presents a very long and narrow penis papilla housed in a tall male atrium.

Molecular remarks: Ceratoplana falconerae sp. nov. appeared nested within the Leptoplanoidea superfamily with strong support (95/0.96) and as part of a common clade with Parabolia megae gen. et sp. nov., Gnesioceros sargassicola (Mertens, 1833), and Phaenoplana kopepe Oya & Kajihara, 2019 with high support (90/1.00). This clade appeared as most closely related to another clade formed by Styloplanocera fasciata (Schmarda, 1859), Comoplana agilis (Lang, 1884), Stylochoplana clara Kato, 1937 and Echinoplana celerrima Haswell, 1907 with strong BS support (73) in the ML analysis while the Bayesian analysis had lower support (0.57) and included Neostylochus ancorus sp. nov.

Distribution: Australia, Victoria: Cape Paterson, Boat Ramp area; Cats Bay, Phillip Island.