Neostylochus ancorus, 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 : 20-22

Neostylochus ancorus sp. nov.

( Fig. 5 )

Material examined: One specimen sagittally sectioned. Holotype: AM W.50265 (14 slides).

Type locality: Australia, New South Wales, Catherine Hill Bay, Middle Camp Beach , found in Ecklonia radiata holdfasts washed up onto the rock platform at the north end of the beach, 33° 8’45.93”S, 151°38’18.00”E. Coll. Alex Hegedus and Jorge Rodriguez, May 6 th, 2018 .

Etymology: The name of the species refers to the anchor-shaped seminal vesicle present in the male copulatory system.

Description: Body oval broader anteriorly and with rounded ends. Fixed specimen 0.8 cm long. Dorsal surface slightly transparent with pale brown colour ( Fig. 5A, C ). Tentacular and cerebral eyes lie scattered in frontal region. Marginal eyes present in a band along the anterior margin ( Fig. 5D ). Ruffled pharynx located in middle part of the body, with oral pore opening posterior to its centre ( Fig. 5A ).

Male and female gonopores located very close together in the posterior part of the body. Male copulatory apparatus consists of a seminal vesicle, free prostatic vesicle and a penis papilla armed with a long and tubular stylet, directed backwards ( Fig. 5E ). Vasa deferentia run ventrally along both sides of the pharyngeal cavity ( Fig. 5A ), joining distally the seminal vesicle. Seminal vesicle anchor-shaped. Prostatic vesicle oval-shaped, covered with a thick muscular layer and lined with thin smooth glandular epithelium ( Fig. 5F–I ). Ejaculatory duct joins prostatic duct at base of the penis. Male atrium elongated, housing a long penis stylet ( Fig. 5G–I ).

Female system located close behind male apparatus. Vagina runs dorsally, makes a loop towards the male system, receives the oviducts and continues into the Lang’s vesicle ( Fig. 5G–I ). Lang’s vesicle thick and provided with vacuolar internal lining ( Fig. 5B, F–I ).

Remarks: The new species belongs to the genus Neostylochus due to the presence of tentacular and cerebral eyes scattered in the frontal region with marginal eyes in the anterior margin, male copulatory system with seminal vesicle and elongated tubular stylet and presence of a Lang’s vesicle.

There are currently three known species for the genus Neostylochus : N. caraibica (Palombi, 1923) from the Caribbean Sea, N. fulvopunctatus ( Yeri & Kaburaki, 1920) from Misaki ( Japan), and N. pacificus (Bock, 1923) from Juan Archipelago ( Chile). The most conspicuous characteristics of N. ancorus sp. nov. are the anchor-shaped seminal vesicle and vacuolar Lang’s vesicle. Neostylochus fulvopunctatus presents brown spots scattered in its dorsal region that differ from the colouration pattern of N. ancorus sp. nov. Both N. pacificus and N. caraibica were described based on fixed material and therefore no account of their colour is available. Neostylochus pacificus lacks marginal eyes in the anterior region and presents eyes distributed over the top of the pharyngeal region, which are lacking in N. ancorus sp. nov. Neostylochus fulvopunctatus presents larger tentacular eye spots in respect to the cerebral ones while both are the same size in N. ancorus sp. nov. Neostylochus pacificus presents tentacles reduced to small knobs, which are not present in N. ancorus sp. nov., N. fulvopunctatus and N. caraibica . Neostylochus ancorus sp. nov. differs from the other species by the presence of an anchor-shaped seminal vesicle, in contrast with the oval-shaped seminal vesicle present in the other species. Furthermore, the Lang’s vesicle of N. ancorus sp. nov. is larger and filled with vacuolar elements which are not present in any of the currently described species in this genus.

Molecular remarks: Neostylochus ancorus sp. nov. was positioned inside the Stylochoidea superfamily in the ML analysis with BS support <70 (61) while it appeared within the Leptoplanoidea superfamily with high support (1.00) in the Bayesian analysis as sister taxa for Echinoplana celerrima Haswell, 1907 . The genus Neostylochus is currently located within the Callioplanidae family yet Neostylochus ancorus sp. nov. did not appear together with Callioplana marginata , the type of the family and genus. It is clear that the position of Neostylochus within Callioplanidae is incorrect and a revision of the family is needed, yet with the currently available data its position cannot be determined.

Distribution: Known only from type locality.

Figures

FIGURE 5. Neostylochus ancorus sp. nov. A. Dorsal view of the fixed specimen, treated with a clearing agent. B. Details of the copulatory system. C. Dorsal view of live specimen. D. Arrangement of the eyes. E. Sagittal reconstruction of the reproductive system. F–I. Histological sections of the reproductive system.