diversity Review Fanworms: Yesterday, Today and Tomorrow María Capa 1,* , Elena Kupriyanova 2, João Miguel de Matos Nogueira 3 , Andreas Bick 4 and María Ana Tovar-Hernández 5 1 Departament de Biologia, Universitat de les Illes Balears, 07122 Palma, Spain 2 Australian Museum Research Institute, Australian Museum, Sydney, NSW 2010, Australia; [email protected] 3 Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo 05508-090, Brazil; [email protected] 4 Institut für Biowissenschaften, Allgemeine und Spezielle Zoologie, Universität Rostock, Universitätsplatz 2, D-18055 Rostock, Germany; [email protected] 5 Facultad de Ciencias Biológicas, Universidad Autónoma de Nuevo León, Nuevo León 66455, Mexico; [email protected] * Correspondence: [email protected] Abstract: Sabellida Levinsen, 1883 is a large morphologically uniform group of sedentary annelids commonly known as fanworms. These annelids live in tubes made either of calcareous carbonate or mucus with agglutinated sediment. They share the presence of an anterior crown consisting of radioles and the division of the body into thorax and abdomen marked by a chaetal and fecal groove inversion. This study synthesises the current state of knowledge about the diversity of fanworms in the broad sense (morphological, ecological, species richness), the species occurrences in the different biogeographic regions, highlights latest surveys, provides guidelines for identification of members of each group, and describe novel methodologies for species delimitation. As some members of this group are well-known introduced pests, we address information about these species and their Citation: Capa, M.; Kupriyanova, E.; current invasive status. In addition, an overview of the current evolutionary hypothesis and history Nogueira, J.M.d.M.; Bick, A.; of the classification of members of Sabellida is presented. The main aim of this review is to highlight Tovar-Hernández, M.A. Fanworms: the knowledge gaps to stimulate research in those directions. Yesterday, Today and Tomorrow. Diversity 2021, 13, 130. https:// Keywords: Sabellida; Sabellidae; Serpulidae; Fabriciidae; Annelida; polychaetes; biodiversity assess- doi.org/10.3390/d13030130 ment; systematics; methods; gaps of knowledge Academic Editor: Luc Legal Received: 30 December 2020 1. Introduction Accepted: 10 March 2021 Sabellida Levinsen, 1883 is a morphologically uniform clade of sedentary annelids Published: 17 March 2021 historically given a rank of Order. Sabellida currently includes members of Fabriciidae Rioja, 1923, Sabellidae Latreille, 1825, and Serpulidae Rafinesque, 1815 [1–3]. They are Publisher’s Note: MDPI stays neutral commonly known as fanworms, feather-duster worms, or flowers of the sea, because their with regard to jurisdictional claims in radioles are arranged in a crown, protruding from the tube made of calcium carbonate or published maps and institutional affil- iations. mucus with agglutinated sediment (Figure1). In addition to the presence of protective tube and the prostomial crown made of radioles with secondary ramifications (generally referred as pinnules, but see [4] for Fabriciidae), which are mainly used for feeding and respiration, all members of Sabellida share the presence of chaetal inversion [thoracic chaetigers with simple chaetae on notopodia and uncini (hooks) on neuropodia, and abdominal chaetigers Copyright: © 2021 by the authors. with opposite arrangement]. Sabellida includes about 1200 species distributed world-wide, Licensee MDPI, Basel, Switzerland. from tropical to polar waters and found in all habitats, from freshwater to fully marine This article is an open access article conditions, and intertidal to deepest ocean trenches. distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Diversity 2021, 13, 130. https://doi.org/10.3390/d13030130 https://www.mdpi.com/journal/diversity Diversity 2021, 13, x 2 of 74 Diversity 2021, 13, 130 based on their general morphology and grouped into the section Amphitrites sabelliennes 2 of 73 [5], the family Serpulacei [6], family Serpulacea [7–9], Serpulidae [10], and finally Sabel- lida [11,12]. Figure 1. Comparison of the radiolar crown structure among the three families of Sabellida. (a) Anterior end of Fabricia Figure 1. Comparison of the radiolar crown structure among the three families of Sabellida. (a) Anterior end of Fabricia stellaris, dorsal view; (b) Histological section of crown of F. stellaris at base; (c) Histological section of crown of F. stellaris stellarisat, mid-length; dorsal view; (d) ( bHistological) Histological section section of one of radiole crown and of F. presumed stellaris at pinnules base; ( cof) HistologicalF. stellaris; (e) sectionAnterior of end crown of Laonome of F. stellaris at mid-length;xeprovala, dorsal (d) Histological view; (f) Histological section of section one radioleof crown and of Laonome presumed xeprovala pinnules at base; of (gF.) stellarisHistological;(e) section Anterior of crown end of of LaonomeL. xeprovalaxeprovala, dorsal at mid-length; view; (f) Histological (h) Histological section section of of crown one radiole of Laonome and pinnules xeprovala of L.at xeprovala base; (g; )(i Histological) Anterior end section of Spirobranchus of crown of L. lamarki, ventral view; (j) Histological section of crown of S. lamarcki at base; (k) Histological section of crown of S. lamarcki xeprovala at mid-length; (h) Histological section of one radiole and pinnules of L. xeprovala;(i) Anterior end of Spirobranchus at mid-length; (l) Histological section of one radiole and pinnules of S. lamarcki. Abbreviations: br: base of radioles; bv: lamarkiblood, ventral vessel; view; c: collar; (j) Histological coe: coelom; section cu: cuticle; of crown dl: dorsal of S. lips; lamarcki ep: epithelium;at base; (k fg:) Histological faecal groove; section hc: hyaline of crown cartilage; of S. lamarckimp: at mid-length;mouth (palp;l) Histological op: opercular section peduncle; of one p: radiolepinnules; and pl: parallel pinnules lamellae; of S. lamarcki r: radioles;. Abbreviations: sca: supporting br: cellular base of axis; radioles; vl: ventral bv: blood vessel;lips. c: collar; coe: coelom; cu: cuticle; dl: dorsal lips; ep: epithelium; fg: faecal groove; hc: hyaline cartilage; mp: mouth palp; op: opercular peduncle; p: pinnules; pl: parallel lamellae; r: radioles; sca: supporting cellular axis; vl: ventral lips. With the advent of cladistic analyses, close relationships of sabellids and serpulids withThe Sabellariidae Sabellida conceptJohnston, and 1865, even Siboglinidae the group Caullery, name has1914 changedand Oweniidae over time.Rioja, Since1917 their erectionhave been in the suggested, early 19th and century, consequently sabellids the co (includingmposition of fabriciids), Sabellida expanded building to soft incor- sediment porate these three taxa (e.g., [13]) (Figure 2). However, subsequent molecular analyses tubes, and serpulids, building calcareous tubes, have always been considered related, based on their general morphology and grouped into the section Amphitrites sabelliennes [5], the family Serpulacei [6], family Serpulacea [7–9], Serpulidae [10], and finally Sabellida [11,12]. With the advent of cladistic analyses, close relationships of sabellids and serpulids with Sabellariidae Johnston, 1865, Siboglinidae Caullery, 1914 and Oweniidae Rioja, 1917 have been suggested, and consequently the composition of Sabellida expanded to incorporate these three taxa (e.g., [13]) (Figure2). However, subsequent molecular analyses using increasing number of taxa and DNA markers revealed that the three late incorporated taxa were neither closely related to fanworms, nor to each other [14–16]. DiversityDiversity2021 2021, 13, 13 130, x 3 of3 74 of 73 using increasing number of taxa and DNA markers revealed that the three late incorpo- Morphological lines of evidence related to the ontogeny, internal anatomy, position of rated taxa were neither closely related to fanworms, nor to each other [14–16]. Morpho- the ciliated groove, as well as chaetal morphology and arrangement also supported logical lines of evidence related to the ontogeny, internal anatomy, position of the ciliated this lack of close relationship [17–26]. Consequently, Sabellida now again includes only groove, as well as chaetal morphology and arrangement also supported this lack of close fanworms (Figure2), but the former sabellid subfamily Fabriciinae has been elevated to relationship [17–26]. Consequently, Sabellida now again includes only fanworms (Figure Fabriciidae based on DNA evidence [1–3,24,27]. The sister group of Sabellida, according 2), but the former sabellid subfamily Fabriciinae has been elevated to Fabriciidae based toon the DNA latest evidence phylogenomic [1–3,24,27]. studies, The sister is grou a cladep of Sabellida, including according Spionidae to the Grube, latest 1850phylo- and Sabellariidaegenomic studies, [14, 28is ,a29 clade]. including Spionidae Grube, 1850 and Sabellariidae [14,28,29]. FigureFigure 2. History2. History of of the the evolutionary evolutionary hypotheses hypotheses withinwithin Sabellida.Sabellida. The The coloured coloured taxa taxa indicate indicate the the groups groups that that had had been been considered as members of Sabellida (or Serpulacea) according to the represented phylogenetic hypotheses. In light blue considered as members of Sabellida (or Serpulacea) according