Morphological and molecular systematics of the ‘Monanchora arbuscula complex’ (Poecilosclerida : Crambeidae), with the description of five new species and a biogeographic discussion of the genus in the Tropical Western Atlantic Eduardo L. Esteves A,E , Thiago S. de Paula B , Clea Lerner C , Gisele Lôbo-Hajdu B and Eduardo Hajdu D A Departamento de Zoologia, Instituto de Biologia Roberto Alcantara Gomes, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier, 524, PHLC, Sala 520, Rio de Janeiro, RJ, 20550-013, Brazil. B Departamento de Genética, Instituto de Biologia Roberto Alcantara Gomes, Universidade do Estado do Rio de Janeiro, Rua São Francisco Xavier, 524, PHLC, Sala 205, Rio de Janeiro, RJ, 20550-013, Brazil. C Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo – USP, Rua do Matão, Travessa 14, 101, São Paulo, SP, 05508-900, Brazil. D Departamento de Invertebrados, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, s/n, Rio de Janeiro, RJ, 20940-040, Brazil. E Corresponding author. Email: edlealesteves@yahoo.com.br Abstract. Monanchora Carter, 1883 is a genus of shallow-water marine sponges comprising 16 species distributed worldwide, two of them in the Tropical Western Atlantic (TWA): M. arbuscula (Duchassaing & Michelotti, 1864) and M. brasiliensis Esteves, Lerner, Lôbo-Hajdu & Hajdu, 2012. The former species stands out as one of the most variable demosponges, and is very similar in spicule complement and in secondary metabolite chemistry to the Mediterranean/ eastern Atlantic Crambe crambe (Schmidt, 1862), type species of Crambe Vosmaer, 1880. The aim of the present study was to revise the genus Monanchora in the TWA. In addition, we critically analyse the monophyly of Crambe and Monanchora. Maximum Likelihood and Bayesian Inference analyses of 28S and 16S rRNA sequences of the latter genera, and a redescription of the ‘M. arbuscula complex’, revealed three species: M. arbuscula s.s., M. coccinea, sp. nov. and a new species of Acarnidae – Iophon parvachela, sp. nov. Three other new species from the TWA previously assigned to Monanchora were revealed by morphological analyses, and are also described: M. bahamensis, sp. nov., M. megasigmifera, sp. nov. and a new species of Chondropsidae – Batzella catarinensis, sp. nov. A key for species identification is provided. Our results suggest that the Eastern Brazil and Southeastern Brazil Ecoregions may represent centres of diversity for Monanchora in the TWA. Additional keywords: Batzella, Crambe, Demospongiae, guanidine alkaloids, integrative taxonomy, Iophon, marine biogeography, Porifera, 16S, 28S. Received 21 December 2016, accepted 9 August 2017, published online 4 April 2018 Introduction Crambeidae Lévi, 1963 comprises shallow-water marine sponges belonging to Poecilosclerida Topsent, 1928 (van Soest 2002a). The family is composed of four genera distributed worldwide (van Soest 2002a; van Soest et al. 2016): Crambe Vosmaer, 1880; Monanchora Carter, 1883; Discorhabdella Dendy, 1924; and Lithochela Burton, 1929; the former two of which are promising groups for pharmacological and biomedical purposes (e.g. Leal et al. 2012; Mehbub et al. 2014; Sfecci et al. 2016). Crambe and Monanchora are rich sources of polycyclic guanidine and pyrimidine alkaloids (i.e. crambescidins, batzelladines, batzellamids, hemybatzelladines, arbusculidine, monalidine; e.g. Tavares et al. 1994, 1995; Patil et al. 1995; van Soest et al. 1996; Braekman et al. 2000; Ferreira et al. 2011; Arevabini et al. 2014; Santos et al. 2015). Most of these compounds have potential for the treatment of severe human diseases, with many biological properties, e.g. antimicrobial (e.g. Muricy et al. 1993; Tavares et al. 1995; Hua et al. 2007; Seleghim et al. 2007), antitumoural (Aron et al. 2004; Hua et al. 2007), cytotoxic (Gallimore et al. 2005; Seleghim et al. 2007), anti-parasitic (particularly against Leishmania, Plasmodium and Trypanossoma; e.g. Santos et al. 2015; Campos et al. 2017) and anti-HIV (Patil et al. 1995; Hua et al. 2007). Indeed, most of the already mentioned secondary metabolites with medical properties are found Journal compilation Ó CSIRO 2018 www.publish.csiro.au/journals/is CSIRO PUBLISHING Invertebrate Systematics, 2018, 32, 457–503 https://doi.org/10.1071/IS16088