Revision of the genus Baltoplana (Rhabdocoela: Schizorhynchia: Cheliplanidae) with the description of two new species

Abstract

Marine microturbellarians are important components of the meiofauna and contribute significantly to the processes and functioning of marine ecosystems. Microturbellarians of the taxon Cheliplanidae are, among other things, characterized by a proboscis with protractile hooks. Within Cheliplanidae, the genus Baltoplana currently includes four described species: B. bisphaera from Kenya, B. cupressus from South Africa, B. magna from the Mediterranean and the European Atlantic coasts, and B. valkanovi from the Black Sea. However, the phylogeny of Baltoplana within Cheliplanidae and Schizorhynchia remains unresolved. This study revises the genus Baltoplana from an integrative framework, using morphology and, for the first time, DNA sequences (18S, 28S, cox1). A preliminary phylogeny of Baltoplana was constructed based on newly collected material, confirming its position within Cheliplanidae. We also provide new distributional data for B. magna, and two new species of Baltoplana are described based on DNA sequences and the morphology of the male copulatory organ, particularly of the cirrus and accessory cirri. In Baltoplana n. sp. 1, the male copulatory organ has an armed cirrus adjacent to an accessory armed cirrus. The ejaculatory duct connects to the cirrus, which has small, robust spines that gradually increase in length from the proximal to the distal region. The accessory cirrus is also armed with long and robust spines extending to the distal area. Baltoplana n. sp. 2, on the other hand, has an armed cirrus with three accessory cirri. The cirrus has short spines in its proximal region, which increase in length towards the distal end. One of the accessory cirri is long, while the other two are oval. All three of them have equally sized spines. These morphological features set these species apart from previously described species of Baltoplana.