Eisenia

Eisenia View in CoL + Bimastos + Rhiphaeodrilus clade

The genus Eisenia was found to be monophyletic (Fig. 1). It was classified into two clades, comprising European and Siberian species, confirming previous research ( Shekhovtsov et al., 2020b). This division likely represents an ancient biogeographic divergence. It is worth noting that there is currently insufficient mtDNA data available for Eisenia species from Europe, and no data at all for species from other regions such as Ural or Far Eastern endemics ( Perel, 1979).

Previously, E. lagodechiensis from Georgia was classified under the genus Helodrilus ( Michaelsen, 1910) . Vsevolodova-Perel (1997) considered it to be closely related to E. gordejeffi and E. submontana . However, recent studies ( Blakemore, 2013) and the Drilobase database now treat it as a subspecies of E. nordenskioldi . However, our results indicate that E. lagodechiensis is a part of the E. fetida / E. andrei complex. These species are morphologically similar and have the same number and position of seminal vesicles and spermathecae ( Vsevolodova-Perel, 1997). E. lagodechiensis has a longer clitellum, which ends two segments further compared to E. fetida and E. andrei , and tuberculae pubertatis end one segment further. In contrast to E. fetida and E. andrei , E. lagodechiensis has calciferous glands in the 12th segment and a musculature of the circular type, while E. fetida has a transitional type of longitudinal musculature. In their natural environment, live specimens of E. lagodechiensis closely resemble E. andrei , but are noticeably larger. They have dark purple pigmentation and similar white spots on the lateral surfaces of segments 9–12. Importantly, our findings are not a result of misidentification, as E. lagodechiensis did not match any of the distinct genetic lineages within this group.

E. nordenskioldi View in CoL exhibits extensive morphological and genetic diversity, as shown by various studies ( Malevich, 1956; Perel, 1997; Vsevolodova-Perel, 1997; Blakemore, 2013; Shekhovtsov et al., 2020b). Consistent with previous research on mitochondrial genomes ( Shekhovtsov et al., 2020a), it was divided into two main clades that grouped together with E. tracta and E. altaica (Fig. 1). These findings reinforce the notion that E. nordenskioldi View in CoL sensu lato is not a single species, but rather a complex consisting of multiple species from the Altai Mountains and the surrounding region. The Altai Mountains are known for harboring numerous endemic Eisenia species ( Vsevolodova-Perel, 1997), making it intriguing to investigate how many of these species would also fall within this clade.

Previous studies demonstrated that Eisenia View in CoL , Bimastos View in CoL , and Eisenoides form a clade ( Csuzdi et al., 2017; Marchán et al., 2022). In our study, we also identified a clade consisting of Eisenia View in CoL , Bimastos View in CoL , and Rhiphaeodrilus diplotetrathecus . Initially described as Allolobophora handlirschi diplotetratheca Perel, 1967 , together with P. kaznkovi and several other species, it was later transferred to the subgenus Svetlovia Perel, 1977 View in CoL . Representatives of this subgenus were believed to differ from the rest of the genus Allolobophora Eisen, 1873 View in CoL by the absence of calciferous glands in the diverticulae of the 10th segment, the position of the spermathecae not extending beyond the 10/11 dissepiment, the presence of three to four pairs of seminal vesicles, by weak development of glandular fields around the male genital openings, and long, elongated tuberculae pubertatis stretching almost along the entire clitellum. However, the name Svetlovia View in CoL turned out to be occupied (genus Svetlovia Chekanovskaya, 1975 View in CoL within Tubificidae ); Easton proposed to elevate the taxon to the genus rank with the name Perelia ( Easton, 1983) View in CoL . Subsequently, the species was transferred to Alpodinaridella (Mrsic, 1987) View in CoL , and finally to the monotypic genus Rhiphaeodrilus ( Csuzdi & Pavlíček, 2005) based on three pairs of reddish-violet vesicles and pinnate musculature. Our molecular data support the isolation of R. diplotetrathecus from Perelia View in CoL , as it was not related to P. kaznakovi on our phylogenetic tree (Fig. 1). Unfortunately, the DNA extracted from our samples of another Ural endemic, P. tuberosa , was highly degraded and could not be sequenced.

The three genera, Eisenia , Bimastos , and Riphaeodrilus , have a morphological synapomorphy: their nephridial bladders form a forward-bent loop. This distinguishes them from their sister group on the tree ( Lumbricus , Aporrectodea , Helodrilus species), whose nephridial bladders are bent backwards or were lost. Therefore, the form of nephridial bladders appears to be an important diagnostic character, as suggested by Gates (1975) and Perel (1976) (but with some exceptions ( Marchán et al., 2021b)).

Representatives of the genus Bimastos (Dendrodrilus) are believed to be of North American origin ( Csuzdi et al., 2017; Gates, 1969). Csuzdi et al. (2017) proposed that their ancestors likely dispersed through the Bering Strait into North America, and more recently, a few species, notably B. parvus and B. rubidus , returned to Eurasia as migratory species. We believe that further data is necessary to fully investigate this hypothesis. However, the affinity between the North American and Ural endemic species is intriguing and may reflect dispersal patterns of ancestral taxa.

Therefore, this clade represents an interesting example of phylogeographic patterns across a large territory, in contrast to the rest of the Lumbricidae genera and clades, which are mostly native to the Europe or Middle East. Riphaeodrilus is an endemic of the Urals, Bimastos is reportedly native to North America ( Csuzdi et al., 2017), and Eisenia has clear phylogeographic patterns with an Altai clade ( Shekhovtsov et al., 2020b).