Chimaeradasys, Kieneke & Todaro, 2021

Kieneke, Alexander & Todaro, M. Antonio, 2021, Discovery of two ‘ chimeric’ Gastrotricha and their systematic placement based on an integrative approach, Zoological Journal of the Linnean Society 192 : -

GENUS CHIMAERADASYS GEN. NOV.

Zoobank registration: urn:lsid:zoobank.org:act:832074E4-FCC0-410F-85FB-2AFFCFEC637E

Genus type species: Chimaeradasys oligotubulatus sp. nov.

Diagnosis: A thaumastodermatin characterized by a smooth cuticle and a forked caudal peduncle. Body slender, slightly arched dorsally and flattened ventrally; adults up to 391 µm in total length (TL) and up to 74 µm in maximum width. Head furnished with ample mouth and oral hood but lacking sensory structures, such as knob-like organs and eye spots. Sensorial (?) papillae present on mouth rim and margins of the oral hood. Trunk widest in the mid-intestinal region, tapering gently to the rear before ending abruptly in a peculiar, narrow caudal peduncle; peduncle branched, indenting medially at U93. Five to eight pairs of large epidermal glands along the pharyngeal and posterior trunk region, other smaller glands may be present along the anterior trunk region.

Numerous sensorial cilia are distributed in lateral and dorsolateral columns along the body, sparingly around the head. Locomotor cilia arranged in transverse bands, coveringtheentireventralsurface, excepttheanalregion and peduncle. Anterior adhesive tubes (TbA), one or two per side, in a row just posterior to the mouth; ventral adhesive tubes (TbV) absent or present as a single pair in the anterior pharyngeal region; lateral adhesive tubes (TbL), noticeable, one per side just anterior to the peduncle; ventrolateral adhesive tubes (TbVL), five to ten per side, one of which is in the anterior pharyngeal region and the others distributed along the half to two-thirds of the trunk; dorsal adhesive tubes (TbD) absent; posterior adhesive tubes (TbP), three per side, two of which are at the end of each peduncular branch and one flanking them medially. Mouth wide, (up to 55 µm in breadth), leading to a shallow, funnel-shaped buccal cavity and surmounted dorsally by a scalloped oral hood. Pharynx up to 92 µm in length; pharyngeal pores near the base, with ventrolateral openings at U28–U33. Pharyngeo-intestinal junction (PhIJ) at U32–U34, intestine straight, slightly wider at midbody; anal opening ventral at U80–U88. Hermaphrodite; single testis on right body side, elongate, beginning posterior to the PhIJ; sperm duct presumably opens on the ventral surface, through the anus or near to it; spermatozoa filiform with a corkscrew-like anterior region and a lash-like tail. Ovary solitary, posterior in the trunk region; eggs growing from posterior to anterior with the ripest cell dorsal to the mid-intestine. Caudal organ, compact, posterior to the ovary, glandomuscular in nature, showing several spermatozoa, probably to be released ventrally throughout an independent pore or via the anus; frontal organ inconspicuous, saclike, at midline, adjacent to the caudal organ, with several motile spermatozoa inside. Anatomical and/or functional relationship between testis and the accessory reproductive organs or between the latter structures, indefinite. Type species: Chimaeradasys oligotubulatus ; other species: C. multitubulatus .

Etymology: The new genus name is derived from the Greek Χίµαιρα (Latinized as Chimaera ), a mythological creature composed of a lion, a goat and a snake, and from the Greek δασύς, shaggy, which refers to the dense facing with cilia of the ventral surface of Gastrotricha and which is often used as the second part of generic names of Macrodasyida .

Both authors independently found specimens of the new genus, although with almost exactly eight years between the discoveries, and both faced the challenge of a proper systematic placement, because the animals appeared as ‘chimeras’, showing characters of several genera of the Macrodasyida , viz. Dendrodasys Wilke, 1954 and Ptychostomella (see ‘Taxonomic affinities’ for more details).