Prosthiostomum amri, Rodríguez & Hutchings & Williamson, 2021

Rodríguez, Jorge, Hutchings, Pat A. & Williamson, Jane E., 2021, Biodiversity of intertidal marine flatworms (Polycladida, Platyhelminthes) in southeastern Australia, Zootaxa 5024 (1), pp. 1-63 : 54

Prosthiostomum amri sp. nov.

( Fig. 22 )

Material examined: Three specimens, two sagittally sectioned. Holotype: AM W.50286 (8 slides). Paratype: W.50287 (10 slides) . Additional material: AM W.53224 (wet material) .

Type locality: Australia, New South Wales, north east side of Pulbah Island, Lake Macquarie , 33° 5’30.19”S, 151°35’27.65”E. Coll. Jorge Rodriguez, May 18 th, 2018

Additional material locality: Australia, New South Wales, Lake Macquarie, Lake Petit , found on a settlement wood block plate, ~ 0.3m depth amongst Zostera seagrass. Coll. Claire Rowe and Stephen Keable, October 7 th, 2020 .

Etymology: The specific name is dedicated to the Australian Museum Research Institute (AMRI), Sydney, Australia.

Description: Body elongated with rounder anterior region and pointed posterior end. Length 0.7 cm. Dorsal surface translucent white with scattered light brown pigments arranged in circles; median line with two longitudinal dark brown stripes intermittently interrupted reaching the hind end of the body; anterior region above cerebral eyes with marking of same colouration as longitudinal stripes in a fan-like pattern and a transverse V-shaped white line behind cerebral eyes ( Fig. 22A, B ). Tentacles absent. Cerebral eyes located in two clusters above brain area; few marginal eyes present in anterior body margin ( Fig. 22D ). Tubular pharynx located anterior to middle part of the body, oral pore opening anteriorly. Sucker located behind female pore ( Fig. 22G ).

Male and female gonopores located separate below pharynx. Male copulatory apparatus consists of a seminal vesicle, a pair of free prostatic vesicles and an armed penis papilla with a stylet, directed backwards ( Fig. 22E–G ). Vasa deferentia run ventrally and joins distally seminal vesicle. Seminal vesicle oval-shaped and provided with a strong muscular layer. Pair of oval prostatic vesicles provided with a strong muscular layer and lined with smooth glandular epithelium. Ejaculatory duct and both prostatic ducts join distally at base of penis. Penis papilla short and armed with a tubular and pointed stylet. Male copulatory organ housed in an elongated male atrium ( Fig. 22F ).

Female system located posterior to male apparatus. Short vagina runs vertically before joining the uterus. Cement glands concentrated around vagina and emptying their contents in cement pouch ( Fig. 22G ). Lang’s vesicle absent.

Remarks: The new species belongs to the genus Prosthiostomum due to the presence of a pair of prostatic vesicles separate from each other, a median frontal branch in the main intestine and the presence of a pointed tubular stylet.

Among the 50 currently described species, Prosthiostomum amri sp. nov. most closely resembles three species with similar dorsal colouration patterns: P. trilineatum Yeri & Kaburaki, 1920 , P. komaii Kato, 1944 and P. torquatum Tsuyuki, Oya & Kajihara, 2019 . Prosthiostomum trilineatum presents a milky white dorsal surface with two welldefined longitudinal black bands running along either side of a median yellow stripe and a black transverse marking with a yellow border in its head region. Prosthiostomum komaii has a milky white ground colour with a slender orange yellow striation running from the cerebral region to the end of the body, with a transverse band of the same colour in front of the brain area. Lastly, P. torquatum presents a translucent dorsal surface covered with numerous orange maculae and blue dots, a single transverse narrow dark brown line running in front of the cerebral eyes, a transverse white line closely behind the dark brown line, and dark brown pigments forming a mesh-like longitudinal band mid-dorsally. Prosthiostomum amri sp. nov. can be distinguished from the previously mentioned species by the absence of spots and longitudinal bands of conspicuous colours (yellow, orange, blue).

Molecular remarks: Prosthiostomum amri sp. nov. appeared in the Prosthiostomidae clade with Lurymare katoi and L. clavocapitata with high support (100/1.00). Prosthiostomum amri sp. nov. appeared as most closely related to L. katoi also with high support (100/0.98). In the original description of L. katoi there is no mention of a common muscle bulb in the male copulatory system but rather a muscular involvement of the seminal vesicle with the prostatic vesicles, defining trait that differentiates Lurymare from Prosthiostomum . Tsuyuki et al. (2019) remark there is a possibility that the presence of a common muscular bulb in the genus Lurymare might be a later ontogenetic state of development of Prosthiostomum , and thus the two genera would be synonymous. A taxonomic revision employing molecular data of the nominal species of both genera should be carried out in the future to clarify this issue.

Distribution: Known only from type locality.

Figures

FIGURE 22. Prosthiostomum amri sp. nov. A–B. Dorsal view of live specimen. C. Dorsal view of a fixed specimen. D. Arrangement of the eyes. E. Sagittal reconstruction of the reproductive system. F–G. Histological sections of the reproductive system.