A New Species of Acoela Possessing a Middorsal Appendage with a Possible Sensory Function.

Acoels, belonging to Xenacoelomorpha, are small worms with a relatively simple body plan and are considered a critical clade for understanding the evolution of bilaterians. Despite acoels' importance, however, many undiscovered species are predicted to be present worldwide. Here, we describe a new marine acoel species, Amphiscolops oni sp. nov., based on materials collected from the intertidal and subtidal zones of rocky shores at several localities along the Japanese Pacific coast. The new species is approximately 3 mm long and shows typical characteristics of the family Convolutidae, such as the presence of eyespots, symbiosis with algae, position of the gonopores, morphology of the bursal nozzles, lack of central singlet microtubules in the axonemes of spermatozoa, and funnel-like posture of the anterior end. Based on morphology and the results of molecular phylogenetic analyses, we assign this species to the genus Amphiscolops. Interestingly, these worms show unique behaviors such as swimming by flapping the lateral sides and actively capturing prey by swinging the anterior funnel. Furthermore, they possess a dorsal appendage-a characteristic previously unreported in Xenacoelomorpha-representing an evolutionary novelty acquired by this species.

A Flatworm from the Genus Waminoa (Acoela: Convolutidae) Associated with Bleached Corals in Western Australia.

A flatworm isolated from bleached colonies of the coral Coscinaraea marshae at Rottnest Island, Western Australia, is described using a combination of morphological and molecular systematics. This flatworm shares morphological features characteristic of the genus Waminoa (Acoelomorpha: Acoela), including the presence of two algal symbionts, but appears to have genital regions different from those of other described species of Waminoa. The design of new oligonucleotide primers enabled the amplification of partial 18S rDNA of the Rottnest Island acoel specimens, and phylogenetic analysis positioned them within Waminoa, confirming their placement in the genus. Furthermore, Waminoa specimens from Rottnest Island grouped into a sister clade to Waminoa brickneri, indicating that the morphological and genetic differences observed are most likely intraspecific and due to geographic variation. As such, we name these Rottnest Island specimens W. cf. brickneri, but highlight that key differences warrant further exploration before assignment to this species can be confirmed. This is the first acoel flatworm described from Western Australia and contributes to our understanding of the diversity and evolutionary relationship of the Acoela.

New replacement name for Anaperus Graff, 1911 (Acoelomorpha: Acoela: Convolutidae).

The acoel genus Anaperus was established by Graff in 1911 for Amphiscolops gardineri Graff, 1910, making Anaperus gardineri (Graff, 1910) its type species. Since then, six more valid species were described: A. tvaerminnensis (Luther, 1912); A. sulcatus Beklemischev, 1914; A. rubellus Westblad, 1945; A. biaculeatus Boguta, 1970; A. ornatus Beltagi, 2001; A. singularis Hooge Smith, 2004. A seventh species, A. australis Westblad, 1952, is incertae sedis (Dörjes Karling, 1975). The genus was placed to family Convolutidae Graff, 1905, until Dörjes (1968) erected the family Anaperidae on the basis of a distinctive male copulatory apparatus. Jondelius et al. (2011) returned it to Convolutidae on the basis of molecular-sequence data.