Abstract
Sponges are amongst the most difficult benthic taxa to properly identify, which has led to a prevalence of cryptic species in several sponge genera, especially in those with simple skeletons. This is particularly true for sponges living in remote or hardly accessible environments, such as the deep-sea, as the inaccessibility of their habitat and the lack of accurate descriptions usually leads to misclassifications. However, species can also remain hidden even when they belong to genera that have particularly characteristic features. In these cases, researchers inevitably pay attention to these peculiar features, sometimes disregarding small differences in the other “typical” spicules. The genus Melonanchora Carter, 1874, is among those well suited for a revision, as their representatives possess a unique type of spicule (spherancorae). After a thorough review of the material available for this genus from several institutions, four new species of Melonanchora, M. tumultuosa sp. nov., M. insulsa sp. nov., M. intermedia sp. nov. and M. maeli sp. nov. are formally described from different localities across the Atlanto-Mediterranean region. Additionally, all Melonanchora from the Okhotsk Sea and nearby areas are reassigned to other genera; Melonanchora kobjakovae is transferred to Myxilla (Burtonanchora) while two new genera, Hanstoreia gen. nov. and Arhythmata gen. nov. are created to accommodate Melonanchora globogilva and Melonanchora tetradedritifera, respectively. Hanstoreia gen. nov. is closest to Melonanchora, whereas Arhythmata gen. nov., is closer to Stelodoryx, which is most likely polyphyletic and in need of revision.
Highlights
Accurate species-level taxonomy is a fundamental keystone for conservation assessment, planning, and management (Myers et al, 2000; Groves et al, 2017)
Remarks: The genus Melonanchora was erected by Carter (1874) for Melonanchora elliptica on the account of this species singular anchorate-derived chelae, placing it tentatively with the “Halichondria” family concept built around H. (= Myxilla) incrustans (Johnston, 1842)
Contrary to biogeographic distributions of other sponge genera, which suggest they may have a Tethyan or Gondawanan origin (e.g., Acarnus, van Soest, Hooper & Hiemstra, 1991; Rhabderemia, van Soest & Hooper, 1993; Hajdu & Desqueyroux-Faúndez, 2008; Hamigera, Santín et al, 2020), the current distribution of Melonanchora might be better explained by trans-Arctic exchanges
Summary
Accurate species-level taxonomy is a fundamental keystone for conservation assessment, planning, and management (Myers et al, 2000; Groves et al, 2017). The dispersal capabilities vary greatly among benthic species even within the same phyla (Uriz et al, 1998) and they can be differentially reduced by natural barriers (Allcock et al, 1997; Waters & Roy, 2004). In this sense, some invertebrate Phyla, such as sponges and corals, produce short-lived, free larvae that are seemingly incapable of countering apparently weak marine barriers such as littoral currents or substrate discontinuity, often resulting in extremely low dispersal capabilities (Hellberg, 2009). For instance, genetically structured populations, even at short spatial scales, have been repeatedly reported (Duran et al, 2004; Duran, Pascual & Turon, 2004; Calderon et al, 2007; Blanquer, Uriz & Caujapé-Castells, 2009; Blanquer & Uriz, 2010; Guardiola, Frotscher & Uriz, 2016), which favours speciation and makes the existence of widely distributed or cosmopolitan species unlikely
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