Americobdella, Caballero y Caballero, 1956

SIDDALL, MARK E. & BORDA, ELIZABETH, 2004, Leech Collections from Chile Including Two New Species of Helobdella (Annelida: Hirudinida), American Museum Novitates 3457 (1), pp. 1-20 : 14-15

Americobdella

In the original description ( Phillippi, 1872), the monotypic Americobdella valdiviana was classified as an erpobdellid ( Phillippi, 1872) because it was a predator and had rudimentary jaws, typical of erpobdellid leeches ( Weber, 1915; Blanchard, 1917; Harant, 1929). Philippi (1867) remarked on its resemblance ‘‘to the European Trocheta in both appearance and habit’’. Moore (1924: 43) argued that this comment caused ‘‘all subsequent writers to be misled’’, and he recommended reclassifying Americobdella in the distichodont series of Hirudinidae , because several external characteristics pointed directly to an affinity with the Hirudinidae . Caballero (1956) placed A. valdiviana in its own family, but still classified it with the Hirudiniformes , where it remained ( Ringuelet, 1985 a, 1985b; Sawyer, 1986). The unstable classification of A. valdiviana can be attributed to its being reminiscent of an ancestral arhynchobdellid leech, retaining morphological traits and habitat preferences seemingly transitory between rhynchobdellid and arhynchobdellid leeches. Most significant is the presence of the intergonadal conducting tubules, connecting the male atrium and the female ovarian ducts, typically found in rhynchobdellid piscicolid leeches. As a result, Moore (1924; see also Ringuelet, 1954; Soós, 1966) proposed that A. valdiviana belonged to an ancestral lineage that originated before other arhynchobdellid groups. Likewise, Siddall and Burreson’s (1995, 1996) phylogenetic analyses based on morphology and life­history data found that A. valdiviana was in a transitional position between the two major groups of leeches (i.e., Rhynchobdellida and Arhynchobdellida ). Recent phylogenetic work by Borda and Siddall (2004), using combined morphological and molecular data, indicates that A. valdiviana is more closely related to the erpobdelliforms (i.e., Barbronia spp. , Erpobdella spp. ), and not the hirudiniforms as previously suggested ( Moore, 1924; Ringuelet, 1944 a, 1976, 1985 a, 1985b; Caballero, 1956; Sawyer, 1986). As the most basal lineage of the erpobdellid leeches, it should be formally removed from the Hirudiniformes and placed under the Erpobdelliformes , together with the families Erpobdellidae and Salifidae .

Phillippi (1872) provided conflicting information regarding the habitat preference of A. valdiviana . In his description he noted that A. valdiviana was a species living in damp earth and feeding on earthworms. However, the specimens he examined were collected in ‘‘ditches of mill races’’ and from a brook. Corroborating this were descriptions of the species suggesting external color variation to be associated with habitat preference ( Weber, 1915; Moore, 1924; Ringuelet, 1985 a, 1985b). Weber (1915) described terrestrial specimens collected from Corral as being dorsally dark gray, with a uniform yellowishgray venter. Moore (1924) received specimens ‘‘collected in damp earth in Valdivia’’ (p. 30) and a letter from a Professor Montealegre Randolph describing an aquatic Americobdella (= Phillippia) that was ‘‘blueslate [in color] and bears only one red stripe on the back’’ (p. 29, footnote). On our expedition, a terrestrial dark gray to maroon specimen (found in the midst of consuming an oligochaete) and an aquatic slate­gray specimen with a yellow mid dorsal line were collected. These collections are at variance with color types associated with a specific habitat. Regardless, the fact that 18S rDNA sequences were found to be identical for both specimens suggests that A. valdiviana is neither exclusively terrestrial nor aquatic, but rather amphibious in habit. The variation in color pattern and habitat preference could be age specific or developmental; darker specimens appear to be smaller in size than their lighter counterparts.

The presence or absence of eyes in A. valdiviana has been a matter of speculation ( Weber, 1915; Blanchard, 1917; Pinto, 1923; Moore, 1924; Ringuelet, 1985 a, 1985b; Sawyer, 1986). Americobdella valdiviana was described by Phillippi (1872) as lacking eyes, a diagnostic character for the species in subsequent reports ( Weber, 1915; Blanchard, 1917; Pinto, 1923). The lack of eyes was recognized as being associated to a partial subterranean habitat preference similarly found in other burrowing, blind oligochaete predators in the genera Trocheta and Cylicobdella ( Phillippi, 1872; Weber, 1915). To the contrary, Moore (1924: 33) suggested that ‘‘this leech has always been considered to be eyeless, and my first examination led to the same conclusion. However, under intense lighting... there is no difficulty in making out... several whitish areas within small deeply pigmented fields which are evidently eyes.’’ Consequently, other authors followed this revision and even illustrated the presence of six pairs of eyes or ‘‘eyelike organs’’ ( Ringuelet, 1944 a, 1985 a, 1985b; Sawyer, 1986). However, examination of the live specimen suggests once again that A. valdiviana in fact does not have eyes.