Megascolecidae Rosa, 1891

Misirlioğlu, Mete, Reynolds, John Warren, Stojanović, Mirjana, Trakić, Tanja, Sekulić, Jovana, James, Samuel W., Csuzdi, Csaba, Decaëns, Thibaud, Lapied, Emmanuel, Phillips, Helen R. P., Cameron, Erin K. & Brown, George G., 2023, Earthworms (Clitellata, Megadrili) of the world: an updated checklist of valid species and families, with notes on their distribution, Zootaxa 5255 (1), pp. 417-438 : 426

Megascolecidae Rosa, 1891

The Megascolecidae is the most speciose family of earthworms (2,208 spp. and 127 subspecies) and includes 85 genera. The most speciose genera are Amynthas (713 spp./ssp.), Metaphire (242 spp./sspp.), Pheretima (171 spp./ sspp.), and Megascolex (104 sp. /sspp.). The available molecular studies all support its monophyly and show just slight differentiation inside the family. Therefore, given the contradictory taxonomic divisions (e.g., Jamieson et al. 2002; Blakemore 2013) here we do not distinguish subordinate family rank taxa.

The Megascolecidae show a predominantly Australasian distribution being most speciose in Australia (ca. 45 genera and 400 species), New Zealand (8 genera and 50 spp.), Eastern and Southeastern Asia (over 1,500 spp.) ( Sims 1980; Jamieson 2000). But interestingly, the North American megascolecids seem to be basal to several modern megascolecid groups such as the Asian Amynthas and Australian Perionychella , Megascolides , and Diporochaeta ( Buckley et al. 2011) . These include Arctiostrotus (7 species), Argilophilus (9 species), Chetcodrilus (3 species), Kincaidodrilus (1 species), Macnabodrilus (2 species), Nephrallaxis (2 species) and Toutellus (4 species), present mostly in the Pacific Northwestern States of the United States and Southern Canada (near Vancouver), but also in California ( Reynolds, 2020, 2022).

At least 27 species in the genera Amynthas and Metaphire , as well as Perionyx excavatus Perrier , Pithemera bicincta (Perrier) , Polypheretima elongata (Perrier) , Polypheretima taprobanae (Beddard) and Pontodrilus litoralis (Grube) are probably some of the most widely distributed earthworms in the world ( Blakemore, 2009). In fact, many of these species were described from specimens collected outside their native ranges in Asia: for instance, Metaphire californica (Kinberg) from San Francisco, Amynthas gracilis (Kinberg) from Rio de Janeiro, Amynthas corticis (Kinberg) from Hawaii, and P. elongata from Peru. Therefore, they had been already extensively transported by humans from Asia to other continents even before they were recorded from their home ranges. The presence of parthenogenetic morphs, and wide plasticity in terms of soil and habitat preferences in several of these species means that they are excellent invaders, particularly in subtropical, tropical and even temperate regions ( Brown et al. 2006; Chang et al. 2017). Some species, such as Pi. bicincta may have been extensively transported with Polynesians that sailed throughout the Pacific Ocean, as well as in flotsam or sailing ship ballast ( Blakemore 2007; James 2011). Several Amynthas and Metaphire species have invaded cold-temperate regions, including the continental USA, causing extreme alterations in the native ecosystems ( Chang et al. 2021).