Dondersiidae diversity in the abyss and adaptations to the deep sea Formal descriptions of Pholidoskepia species have only been made for specimens from the South Atlantic Basins sampled during DIVA expeditions, six species in the present work and one species recently described by Cobo & Kocot (2020). The presence of Pholidoskepia and Dondersiidae at abyssal depths has also been recorded from the North West Pacific (Bergmeier et al. 2017, 2019; Ostermair et al. 2018). Previously, it was thought that abyssal species were endemic to a single oceanic basin (e.g. Gil-Mansilla et al. 2009, 2011; Cobo et al. 2013). However, of the ten species of the Angola Basin (Gil-Mansilla et al. 2009, 2011, 2012; Cobo & Kocot 2019), one may have been found by Bergmeier et al. (2017, 2019) in the Kuril-Kamchatka Trench (NW Pacific) and the abyssal species Micromenia amphiatlantica has an amphi-Atlantic distribution (Cobo & Kocot 2020). In addition, habitus and sclerites of some of the species treted in the present work have a great resemblance to specimens from the Northwest Pacific (Bergmeier et al. 2019 and personal communication). Molecular data from Atlantic species would be desirable for comparison. It does not appear that the new abyssal Dondersiidae species have organs or characters representing exclusively special adaptations to these abyssal environments whereas species from hydrothermal vents do have special adaptions (Handl & Todt, 2005; Salvini-Plawen, 2008) as do interstitial species (Morse & Scheltema 1988; García-Álvarez et al. 2000; Kocot & Todt 2014; Bergmeier et al. 2016). However, a posterior gland of unknown function has been described in Inopinatamenia calamitosa sp. n. and Dondersia todtae (Klink et al. 2015). This sort of cell grouping is considered characteristic of interstitial species (García-Álvarez et al. 2000). Such glands have been hypothesized to have an adhesive function (Morse & Scheltema 1988; Salvini-Plawen 1985b) or to be responsible for secretion of mucus during egg-laying (Bergmeier et al. 2016).

Published as part of Cobo, M. Carmen & Kocot, Kevin M., 2021, On the diversity of abyssal Dondersiidae (Mollusca: Aplacophora) with the description of a new genus, six new species, and a review of the family, pp. 63-97 in Zootaxa 4933 (1) on page 93, DOI: 10.11646/zootaxa.4933.1.3, http://zenodo.org/record/4547986