Pericelis tectivorum, Dittmann & Dibiasi & Noreña & Egger, 2019

Dittmann, Isabel L., Dibiasi, Wolfgang, Noreña, Carolina & Egger, Bernhard, 2019, Description of the snail-eating flatworm in marine aquaria, Pericelis tectivorum sp. nov. (Polycladida, Platyhelminthes), Zootaxa 4565 (3), pp. 383-397 : 385-388

publication ID	https://doi.org/ 10.11646/zootaxa.4565.3.5
publication LSID	lsid:zoobank.org:pub:003E948F-6747-450F-80AD-027BD629AFE2
DOI	https://doi.org/10.5281/zenodo.5925662
persistent identifier	https://treatment.plazi.org/id/03ED3E04-FFF7-961B-EEFF-2D07FE08F839
treatment provided by	Plazi
scientific name	Pericelis tectivorum
status	sp. nov.

Treatment

Pericelis tectivorum View in CoL sp. nov.

( Figs. 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Pericelis tectivorum sp. nov. specimens #5; #10, sagittally sectioned.

Type material. Sagittal serial sections of the holotype (NHMW_EvMicro 5771/1-45) and paratype (NHMW EvMicro 5772/1-250), and marginal tissue sample in 100% ethanol of the paratype (NHMW EvWet 21221) submitted to the Natural History Museum Vienna, Austria).

Holotype. One sagittally sectioned specimen (#5) stained with Azan.

Paratype. One sagittally sectioned specimen (#10) stained with Azan.

Type locality. Commercial seawater aquarium 'Alpenriff' in Innsbruck (Tirol; Austria).

Other material observed. Live observations of four live specimens from Landeck (including specimen #2), seven from Innsbruck (including specimens #5, #7 and #10). Partial 28S sequences of one specimen from Landeck (#2) and three specimens from Innsbruck (#5, #7, #10). Histological remarks. One sample, #7, was found to be not fixed well and the tissue appeared broken and disjointed in the sections. Therefore, it was not used for further analyses. The Azan trichrome staining looks markedly different in colour and intensity between holotype (#5) and paratype (#10), although the same recipe was used. The thickness of the sections (25–30 µm in #5 and 10 µm in #10) and the age of the prepared solutions may have influenced the appearance.

Etymology. After the observed prey of the species, Tectus fenestratus ( Gmelin, 1791) , a snail of the family Tegulidae and after the Latin word 'vorare' which means 'devour' in English.

Synonym. In German, this or a related species are referred to as the 'Leopardenstrudelwurm' (the 'leopard turbellarian').

Appearance. Elongated oval body, holotype 7 cm long and 4 cm wide (paratype: 5 cm long and 3 cm wide). The pharynx length is about 50% of the body length. Two thin marginal tentacles at anterior body edge ( Fig 1A, B View FIGURE 1 ). Margin slightly ruffled. Cerebral eyes clusters posterior to a well-marked V-shaped notch between the tentacles, well separated, elongated, oval in form, directly merging to a line of frontal eyes extending in a fan-like shape towards the tentacles. From anterior to posterior, the line of frontal eyes is about the same length as the cerebral eye cluster ( Fig. 2 View FIGURE 2 ). Tentacle eyes are especially dense at the tips ( Figs. 1B View FIGURE 1 , 2 View FIGURE 2 ). Dorsal colouration with white spots on dark brown background, highest density of spots along the margins, darkest in colour along the median line ( Fig. 1A View FIGURE 1 ). Ventral colouration: whitish, nearly bluish grey, dendritic markings in the shade of pearl white ( Fig. 1D View FIGURE 1 ). Genital pores in the posterior third. Male and female genital pores very close (ca. 50 µm apart) to each other, but no common gonopore. Sucker lies just posterior to the female gonopore ( Figs. 1E View FIGURE 1 , 3A View FIGURE 3 , 4B View FIGURE 4 ).

Reproductive system. In both, the holotype and the paratype, the male and female copulatory organs are well developed ( Fig. 3 View FIGURE 3 ). Male copulatory complex shows a spherical seminal vesicle ( Fig. 5 View FIGURE 5 E–K); two paired, heavily muscularised spermiducal bulbs ( Fig. 5 View FIGURE 5 A–B, T–W), laterally orientated. Without prostatic vesicle or prostatic glands; ejaculatory duct narrow and long. Penis papilla cylindrical (0.5–0.6 mm long), U-shaped (holotype, Figs. 5 View FIGURE 5 G–P, 6A) or pointing ventro-posteriorly (paratype, Fig. 4A, C View FIGURE 4 ). Tapered in the last distal section. The whole penis papilla projects into the male atrium.Female genital complex with about six uterine vesicles per side, starting posteriorly at the level of the sucker and proceeding anteriorly ( Figs. 3A View FIGURE 3 , 4B View FIGURE 4 ). Female atrium or vagina externa of P. tectivorum sp. nov. runs upwards from the female gonopore and expands at the level of the cement pouch ( Figs. 3B View FIGURE 3 , 4A View FIGURE 4 ). Vagina interna narrows afterwards, turns downwards and opens into the oviduct.

Lab cultures and feeding. Pericelis tectivorum sp. nov. was observed to prey on Tectus fenestratus mainly at night. During daytime, worms were hidden under stones or other objects in the commercial aquarium (pers. com. Christian Hepperger). In lab cultures, the worms were observed to slide over the snail shell and stay in this position for several minutes. In some cases, the snail started strongly to turn back and forth. However, we were not able to recognise if this was active movement of the snail or if it was moved by P. tectivorum sp. nov. The feeding act could not be observed, but devoured snails were recognised by the presence of empty snail shells and associated opercula. Both the snail shell and the operculum were intact and not damaged by the worm. Dark food particles were clearly noticeable in the gut of Pericelis .

Molecular analyses based on partial 28S rDNA sequences. In our phylogenetic reconstruction of four different species of the genus Pericelis ( Fig. 7 View FIGURE 7 ), the specimens of P. tectivorum sp. nov. are recovered with maximal support as sister group of P. byerleyana , and these two are sister group of P. orbicularis . P. cata is sister group of all other available Pericelis species.

Sequence identity was found to be 100% between all sequences of Pericelis tectivorum sp. nov. (one specimen from Landeck, three from Innsbruck) in the 941-nucleotide partial 28S alignment. Between P. tectivorum sp. nov. and P. byerleyana , 99.35% identity (6 nucleotides difference), and between P. tectivorum sp. nov. and P. orbicularis , 98.18% identity (17 nucleotides difference) was observed.

In a longer alignment with a length of 1362 nucleotides of only P. tectivorum sp. nov. sequences, three sequences from Landeck and Innsbruck were 100% identical (#2, #5, #10), while #7 was in two nucleotide positions (99.85% identity).