Two new and unusual species of the genus Fauveliopsis (Annelida: Fauveliopsidae) and first records in coralline environments from the Alacranes Reef National Park, southern Gulf of Mexico

Fauveliopsidae are a family of small polychaetes, found across bathyal or abyssal bottoms in low abundance, with their occurrence in shallow waters very uncommon. However, examining polychaetes from dead coralline fragments collected at Alacranes Reef National Park in very shallow waters (0.5–1 m depth), we came upon two unusual fauveliopsids, whose morphological characteristics did not match any described species, while also differing significantly from one another. We describe them as two new species. Beyond representing the first records of the genus Fauveliopsis in coralline environments, they also constitute the shallowest occurrence of this family ever recorded (0.5–1 m). Fauveliopsis corallicola sp. n. is characterised by: (1) 72 chaetigers per 8.5 mm (the highest number of chaetigers reported so far in this genus); (2) the first 1–4 notopodia bearing one thicker and one thinner acicular chaetae (1A 1a), subsequent anterior notopodia (5–11) bearing thicker acicular chaetae (1A), and median to posterior notopodia with 1–3 thinner acicular chaetae, alongside capillaries (1–3a 1c); and (3) all anterior neuropodia with two thinner acicular chaetae (2a), median neuropodia with 1–2 thicker aciculars (1–2A) and posterior with 2–3 thinner aciculars (2–3a). Fauveliopsis alacranensis sp. n. can be distinguished from closely related species by: (1) 44 chaetigers per 8.3 mm body length; (2) a prominent mid-dorsal groove; (3) notopodia 1–2 possesing one thinner acicular chaeta (1a), all subsequent notopodia with only one thicker acicular chaeta (1A) each; and (4) all neuropodia with thinner aciculars (a), one in anterior neuropodia and two in median and posterior ones, alongside capillaries. Tables detailing the distinctive morphological characteristics and the distribution of all described species of Fauveliopsis are provided.http://www.zoobank.org/urn:lsid:zoobank.org:pub:AA766091-8D22-4438-A958-BEE89443A918http://zoobank.org/CA240BA3-1A44-4227-B6A7-5DBC9418521F