Eulatocestus australis, 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 : 23-25

Eulatocestus australis sp. nov.

( Fig. 6 )

Material examined: One specimen sagittally sectioned. Holotype: AM W.50261 (10 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, August 6 th, 2018 .

Etymology: The specific epithet refers to the geographical location of its discovery, Australia, following the naming convention of the other species in the genus.

Description: Body slender and elongated with rounded ends. Fixed specimen 1.0 cm long. Dorsal surface with reddish brown colour. Tentacles absent. Cerebro-frontal eyes scattered in a fan-like pattern from brain to anterior margin; marginal eyes present in a single band alongside anterior margin ( Fig. 6A ). Ruffled pharynx located in the most posterior part of the body, with oral pore opening in its posterior region ( Fig. 6B ).

Male and female gonopores located close together in most posterior part of the body. Male copulatory apparatus consists of a free prostatic vesicle and a small penis papilla, directed backwards ( Fig. 6C ). Vasa deferentia run ventrally along both sides of posterior body region ( Fig. 6B ), swelling into spermiducal vesicles before joining ejaculatory duct at base of penis papilla ( Fig. 6F ). No seminal vesicle. Prostatic vesicle oval-shaped, covered in a well-developed muscle layer and provided with a web-like glandular epithelium ( Fig. 6E ). Male atrium small, housing a short, unarmed penis papilla ( Fig. 6F ).

Female system located directly behind male apparatus. Vagina runs dorsally, makes a small loop towards the male system, receives oviducts and loops back towards the female atrium through a ductus vaginalis. Lang’s vesicle lacking ( Fig. 6D, F ).

Remarks: The new species belongs to the genus Eulatocestus due to the presence of cerebro-frontal eyes scattered in a fan-like pattern, ruffled pharynx located in the most posterior part of the body, male copulatory system without seminal vesicle and with spermiducal bulbs, and prostatic vesicle with thick glandular layers consisting of a web of follicles.

There are currently three known species of Eulatocestus : E. caribbeanus ( Prudhoe, 1944) from the Cayman Islands, E. galapagensis ( Hyman, 1953a) from the Galapagos Islands ( Ecuador), and E. pacificus ( Laidlaw, 1903a) from the Rotuma ( Fiji) and Palau Islands. Descriptions of these species were based on fixed material and therefore their colouration is unknown. The most conspicuous difference of Eulatocestus australis sp. nov. to these other described species is the lack of a Lang’s vesicle with presence of a ductus vaginalis.

The type species of the genus Eulatocestus is E. pacificus , described from two immature specimens collected in Rotuma (Rotuma Islands, Fiji) and therefore lacking details of the reproductive system which are important generic characters. These specimens were first described as a new species, Latocestus pacificus , by Laidlaw in 1903 and at that time only one other species had been described in the genus Latocestus , L. atlanticus Plehn 1896 , which looked different externally from these specimens. Later, Faubel (1983) created the genus Eulatocestus in 1983 for Latocestidae species with a thick web-like glandular epithelium in their prostatic vesicle, and selected Latocestus pacificus Laidlaw, 1903 , as the type species with the new combination Eulatocestus pacificus (Laidlaw, 1903) . However, the internal anatomy of E. pacificus was never described and therefore its position in the genus Eulatocestus is dubious. Furthermore, its classification as the type species of the genus should be considered and may need to be changed in the future.

Molecular remarks: Eulatocestus australis sp. nov. appeared as sister taxa of Latocestus sp. with high support (99/0.91) in the Latocestidae family clade. As stated above, the genus Eulatocestus was created for Latocestidae species with a prostatic vesicle lined with a web-like glandular epithelium, a character present in this new species. Some morphological traits proposed by Faubel (1983) used to separate genera and families in the Order Polycladida , such as the nature of the internal epithelium and location of the prostatic vesicle, may not have such relevant phylogenetic value due to topology of our molecular phylogeny. Nevertheless, we propose to establish this newly described species in the genus Eulatocestus until more molecular data from species of Latocestidae is available.

Distribution: Known only from type locality.

Genus Leptostylochus Bock, 1925b

Leptostylochus Bock, 1925b: 111–120 , text figs 10–12.

Diagnosis (after Faubel 1983): Stylochidae with or without tentacles. Tentacular, cerebral, marginal, and often frontally strewn eye-spots present. Male copulatory apparatus with papilla-like unarmed penis and predominantly with spermiducal bulbs. Female apparatus with well-developed Lang’s vesicle.

Type species: Leptostylochus elongatus Bock, 1925b .

Figures

FIGURE 6. Eulatocestus australis sp. nov. A. Arrangement of the eyes. B. Dorsal view of the posterior half of the fixed specimen, treated with a clearing agent. C. Sagittal reconstruction of the reproductive system. D–G. Histological sections of the reproductive system.