Acanthodrilidae Claus, 1880

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 : 419-420

Acanthodrilidae Claus, 1880

The Acanthodrilidae is the second most speciose earthworm family – 746 species and 48 subspecies in 68 genera. Csuzdi (1996) divided it into three subfamilies: Acanthodrilinae , Octochaetinae and Benhamiinae, but the molecular work of James and Davidson (2012) provided evidence that suggested raising the Behamiinae to family level ( Benhamiidae ). Hence, we consider Benhamiidae as a separate family here. Diplocardinae Michaelsen 1899 has been proposed, but differently defined. The African, Central and South American, and Austral-Asian octochaetine worms surely belong to Acanthodrilinae ( Buckley et al. 2011; James & Davidson 2012). Various other subfamilies were proposed by Blakemore (2013), but to date there has been limited acceptance of these subfamilies due to unresolved taxonomic issues and disagreement, and pending further molecular work within the Acanthodrilidae (see Fragoso & Rojas 2016, 2019).

The endemic taxa of Acanthodrilinae can be found throughout the southern continents (South America, South Africa, Madagascar, Australia, New Zealand, New Caledonia and the Antarctic Islands), as well as in the USA, Mexico and the Caribbean Islands ( Fragoso & Rojas 2016, 2019; Buckley et al. 2011). However, they are completely missing from Europe and the Northern part of Asia (the Palearctic Region). This widely distributed Gondwanan subfamily includes 41 genera and ca. 580 species (updated from Fragoso & Rojas 2016). From continental Central America and the Caribbean Islands and Mexico, we know 14 genera ( Balanteodrilus , Borgesia , Diplocardia , Diplotrema , Exxus , Kaxdrilus , Larsonidrilus , Lavellodrilus , Mayadrilus , Protozapotecia , Neotrigaster, Trigaster , Zapatadrilus , Zapotecia ) and around 120 species ( Fragoso & Rojas 2016, 2018, 2019; Cervantes et al. 2016). Further endemic genera are found in Eastern African countries and in Madagascar ( Howascolex and Vazimbascolex, with four and one species, respectively; Csuzdi et al. 2016; Hong et al. 2019).

In USA and Mexico there are over 50 species of Diplocardia , and in Mexico, the following additional native genera can be found: Balanteodrilus (3 species), Diplotrema (6 species), Kaxdrilus (3 species), Larsonidrilus (2 species), Lavellodrilus (3 species), Mayadrilus (1 species), Microscolex (3 species), Protozapotecia (4 species), and Zapotecia (2 species) ( Reynolds 2020; Fragoso & Rojas 2016, updated with new species). In Central America and the Caribbean, there are the following native genera: Balanteodrilus (1 sp.), Diplotrema (4 species), Kaxdrilus (4 species), Parachilota (2 species), Protozapotecia (3 species) and Zapotecia (1 sp.), while in South America, we find mostly Chilota (26 species), Diplotrema (9 species), Microscolex (10 species) and Yagansia (21 species) in the Andean and Pampean regions of Chile and Argentina ( Fragoso & Rojas 2016, 2018; Cervantes & Fragoso 2018). Exxus is of unknown provenance, but suspected to be Caribbean or Central American.

In Africa, the Acanthodrilinae are distributed mainly in South Africa comprising 5 genera ( Chilota, Eodriloides , Microscolex , Parachilota and Udeina ) and ca. 110 species ( Plisko & Nxele 2015). In Australia, native acanthodrilinae include six native genera ( Diplotrema, Kayarmacia , Microscolex, Neodiplotrema, Rhododrilu s and Torresiella ) and approximately 120 species (expanded from Fragoso & Rojas 2016). However, the genus Diplotrema is in need of further work (particularly molecular) within the Acanthodrilinae , which will probably end up splitting off the Neotropical species present in Mexico from those in Oceania ( Fragoso & Rojas 2019).

At least two Acanthodrilinae species – Microscolex dubius (Fletcher) , and M. phosphoreus (Dugés) , probably originally from Southern South America ( Argentina) – are cosmopolitan, although they tend to be more common in subtropical and temperate climate regions ( Rota et al. 2018b). These species were described from specimens collected outside their native range, and have been widely reported from North American and European countries (e.g., Portugal, Spain, France, Italy, Hungary, Serbia, Bulgaria, Albania and Greece), Australia, New Zealand and South Africa. The species M. phosphoreus is a well-known widespread bioluminescent worm, but recent work has shown the need for more detailed analysis of its taxonomy (both morphology and genetics) and questioned the identity of samples deposited throughout the world, due to the presence of cryptic morphs that may be different species ( Rota et al. 2018b). However, this high morphological plasticity and deep genetic differentiation can also be due to its well-known parthenogenetic reproduction mode (as in many peregrine species) ( Gates 1972).