Parabolia megae, 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 : 32-34

Parabolia megae gen. et sp. nov.

( Fig. 11 )

Material examined: Six specimens, two sagittally sectioned. Holotype: AM W.50281 (23 slides) . Paratypes: AM W.50282 (8 slides); AM W.50278, W.50280, W.50283, W.50284 (wet material) .

Type locality: Australia, New South Wales, Toowoon Bay , rocky headland adjacent to SLSC, found under rocks, 33°21’47.01”S, 151°30’7.31”E. Coll. Jorge Rodriguez, Mandy Reid and Alison Miller, May 16 th, 2018 .

Etymology: The specific name is dedicated to the Marine Ecology Group (MEG) of Macquarie University, Sydney, Australia.

Description: Body oval with rounded ends. Fixed specimen 1.3 cm long. Paratypes 1.2 to 1.3 cm long. Dorsal surface with pale cream colour and reddish-brown web-like pattern, darker around the pharyngeal region and tentacles ( Fig. 11A ). Small tentacles present. Tentacular eyes inside the tentacles, cerebral eyes located in two elongated parallel clusters above brain area ( Fig. 11E, F ). Ruffled pharynx located anterior to middle part of the body, oral pore opening in its centre ( Fig. 11B, C ).

Male and female gonopores located close together immediately behind pharynx. Male copulatory apparatus enclosed in a muscular bulb consisting of a seminal vesicle, interpolated prostatic vesicle and a penis papilla armed with a complex, parabolic dish-like stylet, directed backwards ( Fig. 11C, D, G–K ). Ventral fibres of the muscular bulb mix together with the ventral wall anchoring the whole system to the ventral side of the animal. Vasa deferentia run ventrally towards the pharyngeal region before looping back towards the male system in an M-shape formation, swelling into spermiducal bulbs before joining distally the seminal vesicle ( Fig. 11D ). Seminal vesicle oval-shaped, enclosed inside the muscular bulb and covered with a thick muscular layer ( Fig. 11K ). Ejaculatory duct projects distally into the glandular epithelium of the prostatic vesicle. Prostatic vesicle provided with a strong muscular layer and lined with thick ridged glandular epithelium ( Fig. 11F–I ). Distal end of prostatic vesicle covered with the same cuticular material present in the penis stylet. Ejaculatory duct leaves the prostatic vesicle proximally and coils forming a loop before joining the stylet. The complex penis stylet has two different parts: a semi-spherical, parabolic dish-like structure and a conical pointed end extruding from its centre ( Fig. 11G, I–K ). The parabolic dish-like structure presents a serrated surface on the exterior. Male atrium divided in two sections, one non ciliated housing the penis stylet and provided with circular muscle layers clearly separated from the musculature of the prostatic vesicle and the muscular bulb, and another larger and ciliated provided with a glandulo-muscular fold ( Fig. 11G–K ).

Female system located dorsal to the male apparatus. Vagina externa thickened, running dorsally and looping over the male system before receiving the oviducts ( Fig. 11G–J ). Lang’s vesicle absent.

Remarks: Parabolia megae gen. et sp. nov. shares some of the morphological characteristics of the Gnesiocerotidae Marcus & Marcus, 1966 and Cryptocelidae Laidlaw, 1903 families sensu Faubel 1983. Parabolia megae gen. et sp. nov. presents an interpolated prostatic vesicle lined with ridged glandular epithelium, a trait it shares in common with genera from both families. However, the ejaculatory duct of P. megae gen. et sp. nov. projects inside the glandular epithelium of the prostatic vesicle unlike the case present in genera from the abovementioned families.

Parabolia megae gen. et sp. nov. is provided with a muscular bulb enclosing its male reproductive system similar to those present in Gnesiocerotidae , yet these are much more heavily muscularised in Gnesiocerotidae genera than in P. megae gen. et sp. nov. The muscular bulb of P. megae gen. et sp. nov. appears anchored to the ventral side of the animal unlike those present in Gnesiocerotidae genera. Furthermore, the seminal vesicle of P. megae gen. et sp. nov. appears enclosed inside the muscular bulb, a trait that has not been described for any other family.

Parabolia megae gen. et sp. nov. presents a male reproductive system armed with a complex penis stylet. In Cryptocelidae , only two genera have armed male copulatory systems, Macginitiella Hyman, 1953 and Hylocelis Faubel, 1983 . The former possesses a regular penis stylet while the latter is provided with a central cuticular tooth surrounded by two “spoon-shaped” cuticular areas on each side of the cirrus bulb. Meanwhile, Gnesiocerotidae genera are characterised by the presence of a cirrus armed with spines and hooks ( Echinoplana Haswell, 1907 ; Styloplanocera Bock, 1913 ), a cirrus cuticularly lined without spines, teeth or hooks ( Planctoplanella Hyman, 1940 ) or a male copulatory system with a “complicated cuticularized penis” ( Gnesioceros Diesing, 1862 ). The complicated penis described for Gnesioceros consists of a finger-like organ composed of parallel toothed narrow clasps made of cuticular-like material ( Faubel 1983). None of the structures present among these genera resemble the complex parabolic dish-like structure of the stylet of Parabolia gen. nov.

Parabolia megae gen. et sp. nov. presents a heavily muscularised male atrium divided in two sections, with the most exterior one provided with a glandulo-muscular fold. The presence of glandular fibres inside this muscular bulb implies the existence of extra-vesicular masculine secretions. These fibres are clearly different from other glandular organs such as prostatoids or adenodactils present in other polyclad flatworms.

While the presence or absence of a Lang’s vesicle is a variable trait among polyclad genera, including the Gnesiocerotidae and Cryptocelidae families, the presence of a female system extending dorsally over the male system is a unique characteristic not present in any other genera of these two families. Likewise, the presence of tentacles is a variable characteristic among genera from both Gnesioceridae and Cryptocelidae .

Molecular remarks: Parabolia megae gen. et sp. nov. appeared nested within the Leptoplanoidea superfamily with strong support (95/0.96) and as part of a clade with Gnesioceros sargassicola (Mertens, 1833) , Ceratoplana falconerae sp. nov. 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. The clade in the Bayesian analysis has lower support (0.57) and includes Neostylochus ancorus sp. nov. Oya & Kajihara (2020) considered the possibility of Gnesiocerotidae Marcus & Marcus, 1966 being a junior synonym of Stylochoplanidae Meixner, 1907 and refrained from redefining the family until data of the nominal species of the genus Stylochoplana was made available. The close relationship between Gnesiocerotidae and Stylochoplanidae genera is also clearly evident in our molecular results yet not fully resolved. As such, based on our current data we placed Parabolia gen. nov. within the Gnesiocerotidae family as it appeared in the same clade as the nominal species of its nominal genus Gnesioceros , G. sargassicola (Mertens, 1833) , while a species belonging to the nominal genus Stylochoplana , S. clara Kato, 1937 , appeared in a separate clade.

Genus Echinoplana Haswell, 1907

Echinoplana Haswell, 1907: 475–478 , pl. 36, figs 6, 7; pl. 37, figs 1–3.

Diagnosis (after Faubel 1983): Gnesiocerotidae with eyes in elongate cerebral clusters; tentacles lacking. Separate male and female reproductive apertures. Male copulatory apparatus with seminal vesicle and cirrus that is armed with numerous spines and hooks. Female apparatus with vagina bulbosa and bursa copulatrix; Lang’s vesicle rudimentary.

Type species: Echinoplana celerrima Haswell, 1907 .

Figures

FIGURE 11. Parabolia megae gen. et sp. nov. A. Dorsal view of live specimen.B. Dorsal view of a fixed specimen, treated with a clearing agent. C, D. Details of the pharynx and reproductive systems. E, F. Arrangement ofthe eyes. G. Sagittal reconstruction of the reproductive system. H–K. Histological sections of the reproductive system.