World Polychaeta Database (WPolyDb). Review of the family
[Introduction] The family Arenicolidae Johnston, 1835 includes some of the best known polychaete species in the world, the ‘lugworms’, due to their commercial exploitation and visible presence on many beaches (Fig. 1A–C). It comprises four genera: Arenicola Lamarck, 1801, Abarenicola Wells, 1959, Arenicolides Mesnil, 1898 and Branchiomaldane Langerhans, 1881, between them containing nearly 30 species and sub-species. Together, Arenicola and Abarenicola comprise the majority of the species (including several subspecies but see Darbyshire (2017) for a review of Abarenicola subspecies) and are the genera to which the term ‘lugworm’ refers (Wells 1980). Species in these genera are large in form (Fig. 1D), create burrows in sandy areas from high to low tide (Fig. 1A, C) and are exposed to predation when they move their tail towards the surface for defecation. The specialized tail has no vital organs and is renewed via backward growth from where it joins the trunk, meaning that losses through predation can be accommodated more readily without severely affecting the worm (Wells 1980). The remaining genera, Arenicolides and Branchiomaldane, currently contain two and four species respectively, are much smaller in form, less commonly encountered and lack the specialized tails of the aforementioned lugworms. The family was regarded as ‘tentatively’ monophyletic by Fauchald & Rouse (1997) but more recent morphological and molecular analyses (Bartolomaeus & Meyer 1997, Bleidorn et al. 2003, 2005, Darbyshire 2017) have presented further evidence to support monophyly while a sister-group relationship with the Maldanidae has long been supported (Bartolomaeus & Meyer 1997, Rouse & Fauchald 1997, Rouse & Pleijel 2001, Bleidorn et al. 2003, 2005, Bartolomaeus et al. 2005, De Assis & Christoffersen 2011, Weigert et al. 2014, Zrzavý et al. 2009). Branchiomaldane is also strongly supported as belonging within the family (Bleidorn et al. 2005, Darbyshire 2017), despite past debate about its position (Rouse & Pleijel 2001).