Text Box: Glacier Ice Worms Taxonomy (Mesenchytraeus solifugus) The traditional (morphology-based) classification for glacier worms is as follows: Kingdom: Animalia Phylum: Annelida Class: Clitellata Subclass: Oligochaeta Order: Haplotaxida Suborder: Tubificina Family: Enchytraeidae Genus: Mesenchytraeus Species: solifugus Oligochaete classification focuses on reproductive organs and setae. Brinkhurst and Nemec, in a comparative study of Oligochates based on morphological data, report that Tubificida is separated from other oligochaetes by the presence of gonads in segments II and II, and multiple chaetae with hair chaetae (1987:70). They concluded that Enchytraidae formed the very first branch along the Tubificida tree, developing their characteristic penial bulb, multiple chaetae, and spermetheca in segment V after divergence from the tubificid ancestor (72). Eisen provided a description and systematic review of Enchytraeidae in 1904. Coates performed multiple analyses of more than 100 Enchytraeidae morphological characters, including over a hundred species in her study (1989). Enchytraids are distinguished by their prominent penial bulb, and differences between its genera focus on the penial bulb structures as well as number and shape of setae. Enchytraeidae are found across polar and temperate regions (Michaelsen 1900 and Welch 1914, cited in Goodman 1971:22), and include terrestrial, freshwater, and marine species. Brinkhurst observed that enchytraeids include the only non-aquatic members of Tubificina (1982:1046). Shain et al. take this as evidence of an aquatic origin for the family (2000:195-196), but as Brinkhurst also notes that there are other terrestrial Oligochates (1982:1043), this may be premature. Brinkhurst’s note (1946) that Haplotaxidae are often found in glacial refugia may bear evidence on this question. Members of Enchytraeidae represented in Jamieson et al. (2002), McHugh (2000), Siddall et al. (2001) and Erseus et al. (2002), fell within Oligochaeta, albeit with only one to several enchytraeid species represented in each of these studies. Erseus et al. (2002), analyzing 18S rDNA in their clarification of the phylogeny of the Tubificidae, included three enchytraeid species (Buchholzia fallax, Enchytraeus sp. and Fridericia tuberosa), but found Enchytraeus sp. with Lumbricus spp., as paraphyletic to Tubificidae, making it appear as if the enchytraeids and lumbricids may not be monophyletic groups after all, although since the study had such a distant focus, this pattern may have been due to differences in resolution. The genus Mesenchytraeus was first described by Eisen in 1878, with an excellent summary later provided by Goodman (1971:2-8). Mesenchytraeus as a genus is distinguished by its prominent penial bulb, the position of its head pore, and the structure of the nephridia (Goodman 1971:5). The only other enchytraeid with a head pore at the tip of the prostomium is Achaeta, about which Goodman states "there need be no confusion, for the genus Achaeta is unique in that setae are wholly absent, and it is one of only two genera [Fridericia being the other] in which a considerable portion of the neprhridium is anteseptal" (5). Many of the members of this genus are found in cold regions. Besides M. solifugus, M. altus is reported to live near and under snow, and M. hydrius in meltwater streams (Welch 1917, 1919)[1]. Initial work by Hartzell based on 28S ribosomal DNA supports the monophyletic status of Mesenchytraeus solifugus within Oligochaeta. These findings deserve substantiation by better representation of species within that genus, when sequences become available. Welch argues for a subspecies of glacier ice worms (rainierensis) as endemic to Mount Rainier on the basis of a number of minor (although perhaps significant) morphological differences (1916a:103-118). No further work has been done to confirm or deny morphological differences in ice worm populations, although non-systematic observation of specimens from Byron Glacier in Alaska with those collected from the North Cascades in Washington State suggests that size, at lest, may be significantly different between these groups. (Glacier ice worm specimens from Byron Glacier, AK, are incorrectly referred to as rainierensis in **.) Current multi-loci molecular study by Hartzell of glacier ice worm populations from across their range should quantify the amount of genetic diversity within and between populations, as well as gene flow between glacier ice worm populations. Her results should help to establish if glacier ice worms are indeed one species, if populations experience gene flow between glaciers, and if there is molecular evidence for subspecial ranking. [1] Welch (1916) also reports a ‘snowpack’ worm, Mesenchytraeus gelidus, reported as very close to M. solifugus, but has since not been identified in either scientific or adventure literature (while ice worms have been noted regularly). After interviewing dozens of highly experienced mountaineers and naturalists, and not a single one having ever heard of a ‘snow worm’ (and all had seen ice worms), and because Welch tends to be an extreme ‘splitter’, I believe this species does not in reality exist. It is very possible that the specimens were ground or stream-inhabiting Mesenchytraeus (or even glacier ice worms) that were fortuitously collected from snowpack; or perhaps the ranger who collected them just noted the locational context incorrectly. Text Box: Contact us at phartzell@clarku.edu Last updated 2 January 2004 Text Box: World Glacier Biology Program