Four new species of Pilargidae (Annelida: Pilarginae) from the Gulf of Thailand Author Plathong, Jintana 0000-0003-3473-1680 Marine Ecosearch Management Co., Ltd., 4 / 31 Moo 1, Namnoi, Hat Yai, Songkhla 90110, Thailand. & Marine Science Learning Center, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90110 Thailand. sakanan 2004 @ yahoo. com; https: // orcid. org / 0000 - 0003 - 3473 - 1680 sakanan2004@yahoo.com Author Dean, Harlan K. 0000-0001-8269-0671 Museum of Comparative Zoology, Department of Invertebrate Zoology, 26 Oxford St. Cambridge, MA 02138, USA. harlan. dean @ umb. edu; https: // orcid. org / 0000 - 0001 - 8269 - 0671 harlan.dean@umb.edu Author Plathong, Sakanan 0000-0003-3473-1680 Marine Science Learning Center, Faculty of Science, Prince of Songkla University, Hat Yai, Songkhla 90110 Thailand. sakanan 2004 @ yahoo. com; https: // orcid. org / 0000 - 0003 - 3473 - 1680 sakanan2004@yahoo.com text Zootaxa 2021 2021-11-25 5071 4 537 562 journal article 3301 10.11646/zootaxa.5071.4.4 9c86da8c-0a46-403a-baba-d35df7a5dce1 1175-5326 5726460 5C61473A-9E6A-4CFE-BCD6-1AE7CF093AE9 Genus Ancistrosyllis McIntosh, 1878 Diagnosis (after Glasby & Salazar-Vallejo 2021 ). Pilargids with body depressed, integument papillose to verrucose, present on both segmental and nonsegmental regions. Antennae, 0–3. Palps unfused, biarticulated; palpostyle minute. Paired ventrolateral palpal papillae present. Pharynx distally with terminal papillae (or absent); proximally smooth or, rarely, with denticles. Two pairs of tentacular cirri. Dorsal and ventral cirri digitate to lobate. Notochaetae are hooks, present from chaetigers 3 to 13 and continuing throughout body. Neurochaetae smooth, or spinulose capillaries, often with bidentate tips. Free living in sediments from intertidal to deep sea, or commensal with other invertebrates.