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Megascolex (Promegascolex) mekongianus Cognetti, 1922 - its extent, ecology and allocation to Amynthas (Clitellata/Oligochaeta: Megascolecidae)

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Cognetti (1922) miscounted segments of his Megascolex (Promegascolex) mekongianus and, believing the gizzard in 7 was intermediate between Megascolex, with gizzard in 5, and Pheretima, with gizzard after 7/8, he proposed the subgenus Promegascolex. Next, Gates (1934: 260) redescribed the immature, poorly preserved and abnormal type as Pheretima mekongiana. However, Sims & Easton (1972: 223) listed it as species incertae sedis, excluded it from their Pheretima-group of genera and postulated its gizzard was “clearly in segment 5”. The latter authors also mistook the River Mekong, “Annam” type locality as “Vietnam”. Recently collected material from the River Mekong in Laos is herein described that complies with the corrected type description allowing new designation as Amynthas mekongianus comb. nov. Moreover, A. fluvialis (Gates, 1939) from the Mekong in Thailand is found to be a synonym, although Metaphire fluvialoides (Huynh Thi Kim Hoi, 1998) comb. nov. from Central Highlands of Vietnam remains separate. Reallocation of the type species adds Promegascolex as syn. nov. to Amynthas and its generic diagnosis is amended from Sims & Easton (1972: 211) to permit: Clitellum annular, 14-16, rarely beginning on 13, sometimes extending into 17 (e.g. in A. mekongianus). The slender length and annulations of current specimens: measuring up to 2,900 mm with more than 500 segments, are near the maxima recorded for any earthworm; comparisons are given with “giants” in various families from other regions of the World. Brief comments are made on diversity and ecology of the River Mekong locality.
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... Nevertheless, giant earthworms have successfully and independently colonized a variety of habitats worldwide. Examples include the Giant Gippsland Earthworm, Megascolides australis McCoy 1878 of southern Australia (up to ,2 m; Van Praagh, 1992), Megascolex mekongianus Cognetti 1922 from Vietnam (up to 2.9 m; Blakemore et al., 2005), Microchaetus microchaetus Rapp 1849 from South Aftrica (up to 1.8 m; Plisko, 1999), Tonoscolex birmanicus Gates 1926 from Burma (up to ,3 m in some reports; Gates, 1972), Glossoscolex giganteus Leuckart 1835/6 from South America (up to ,2.7 m; Beddard, 1895), Celeriella gigantean Benham 1906 from New Zealand (up to 1.4 m; Lee, 1959), Driloleirus americanus Smith 1897 from Washington State, North America (up to 1 m; in Blakemore et al., 2005), and several Rhinodrilus species from South America, including the subject of this study, Rhinodrilus priollii Righi 1967. More than 20 species of Rhinodrilus (family Glossoscolecidae) have been described, many of which are native to South America (James and Brown, 2006). ...
... Nevertheless, giant earthworms have successfully and independently colonized a variety of habitats worldwide. Examples include the Giant Gippsland Earthworm, Megascolides australis McCoy 1878 of southern Australia (up to ,2 m; Van Praagh, 1992), Megascolex mekongianus Cognetti 1922 from Vietnam (up to 2.9 m; Blakemore et al., 2005), Microchaetus microchaetus Rapp 1849 from South Aftrica (up to 1.8 m; Plisko, 1999), Tonoscolex birmanicus Gates 1926 from Burma (up to ,3 m in some reports; Gates, 1972), Glossoscolex giganteus Leuckart 1835/6 from South America (up to ,2.7 m; Beddard, 1895), Celeriella gigantean Benham 1906 from New Zealand (up to 1.4 m; Lee, 1959), Driloleirus americanus Smith 1897 from Washington State, North America (up to 1 m; in Blakemore et al., 2005), and several Rhinodrilus species from South America, including the subject of this study, Rhinodrilus priollii Righi 1967. More than 20 species of Rhinodrilus (family Glossoscolecidae) have been described, many of which are native to South America (James and Brown, 2006). ...
... Taken together, the current geographic range of R. priollii is likely to extend well beyond the area surveyed here, and additional sampling may reveal an ancestry considerably older than what has been determined here. Giant earthworms have arisen independently and on multiple occasions, based on their higher-ranked taxonomic positions (e.g., Moniligasteridae, Microchaetidae, Glossoscolecidae, Megascolecidae; Blakemore et al., 2005). Further, they inhabit various environments, climatic regimes and geographic regions (e.g., Australia; Vietnam; South Africa, North America, South America, etc.), leaving open the question as to what underlying mechanism(s) or environmental factor(s), if any, lead to gigantism. ...
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... 5C. Blakemore et al. 2007) Pheretima (Pheretima) (part) -Michaelsen 1928: 8;Michaelsen 1934: 15. Amynthas -Sims andEaston 1972: 211;Blakemore 2002Blakemore : 149, 2007Blakemore , 2008 Type species. ...
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The birds of Northern Thai-land Smith-sonian Institution
  • H G Deignan
DEIGNAN, H.G. (1945): The birds of Northern Thai-land. U.S. National Museum Bulletin 186. Smith-sonian Institution, Washington, D.C