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Home || non-Arthropoda || Oligochaeta (Aquatic Earthworms)

Oligochaeta (Aquatic Earthworms)Introduction

Members of the phylum Annelida are sometimes called true or segmented worms. Of course,the word worm has no taxonomic significance. In fact anything that is round, wriggles, and istoo small to be hit with a club is sometimes called a worm. Annelid worms differ fromflatworms, roundworms, and horsehair worms in many features; a major phylogenetical one isthat annelids have a true coelom. There are two major classes. Members of the classPolychaeta are almost entirely marine. The class Clitellata is composed of two subclasses:Oligochaeta (terrestrial and freshwater earthworms) and Hirudinea (the leeches).

Five of the seven families of freshwater oligochaetes are found in Alberta. These areAeolosomatidae (now considered a separate class by many workers), Naididae (Plate 12.1),Tubificidae, Lumbriculidae (Plate 12.1), and Enchytraeidae. The family Haplotaxidae, whichincludes rare, very long, slender worms (to 40 cm in length), has not been reported fromAlberta. Some freshwater Lumbricidae (the family that contains the terrestrial earthworms)undoubtedly occur in Alberta as well.

General Features, ReproductionOligochaetes have a small preoral region called the prostomium (see OLIGOCHAETA pictorialkeys ). The gut is one-way and terminates at the posterior end of the body. Most freshwateroligochaetes feed by passing mud and debris of the substratum through the gut andextracting organic matter from this material. A feature of oligochaetes is the small bristles andhair-like projections from the body wall. These are setae and there are various types; they arean important diagnostic feature (see OLIGOCHAETA pictorial keys and also GLOSSARY).

Asexual reproduction by fission is the common method of reproduction in Aeolosomatidaeand Naididae. The Tubificidae, Enchytraeidae, Lumbriculidae (and Haplotaxidae) reproducealmost entirely by sexual means. Oligochaetes are hermaphroditic. An important reproductivestructure is the clitellum, which in terrestrial earthworms is a conspicuous swollen area aboutone-third of the way from the anterior end of the worm. However, in most freshwateroligochaetes, the clitellum is not very conspicuous, being obvious only at the time of sexualreproduction. Although hermaphroditic, cross-fertilization is the rule. Eventually a cocoonsecreted by the clitellum and containing a few fertilized eggs will slip off the anterior end of theworm. The fertilized eggs will hatch into "miniature adults;" there is no larval stage.

Collecting, Identifying, PreservingNumerous oligochaetes can usually be collected with a fine-meshed pond-net worked throughthe mud and debris of the substratum. Aeolosomatids, being almost microscopic, are rarelycollected (or at least recognized as such) by standard collecting methods, and very little isknown about this group. They are found mainly on the substratum of standing waters.Tubificidae and Naididae are common in both running and standings waters. Some tubificidsare numerous on the substratum of organically polluted lakes and streams. Most members ofthe Enchytraeidae are terrestrial, but some are apparently truly aquatic or at least semi-aquatic. Members of the Lumbriculidae are quite large and usually are easily spotted in netsamples. They are found in and on the substratum of both standing and running waters.

Small specimens, such as aeolosomatids and some Naididae, are best identified from livingmaterial. In routine collections, oligochaetes should first be fixed in the field in about 5%formalin-for at least a day-and then stored in 70% alcohol and examined in various mountingmedia. For a temporary mounting medium, Brinkhurst (1986) recommends Amman'slactophenol (400 g carbonic acid, 400 ml lactic acid, 800 ml glycerol, and 400 ml water-storein a dark bottle). [NOTE: THIS MEDIUM IS TOXIC IF INHALED OR IF SOLUTION TOUCHESSKIN.] Place a drop of Amman's on a slide and then immerse the worm or worms and add acoverslip. Some worms can be identified immediately, but it is best to clear the worms inAmman's for about a day. Permanent mounts can be made with a variety of mounting media(see Pennak 1978, Klemm 1985c, and Brinkhurst 1986).

Alberta's Fauna and Pictorial KeysThe pictorial keys are based mainly on diagnostic features given in Hiltunen and Klemm (1985a), Simpson et al. (1985) and Brinkhurst (1986). The keys should be satisfactory at thefamily level regardless of state of material, but should be used with caution at the genus level,especially for tubificids, because separating members of the "tubifex complex" (namelyTubifex and Ilyodrilus - both very common in Alberta) is difficult for nonspecialists. Also, for allgroups, intact mature worms are usually needed for identification, because detailedexamination of the genital segments is usually required. In old worms, the setae (one of themost important diagnostic features) can wear down and therefore be of little use in identifyingoligochaetes. Mature worms can appear slightly swollen from the genital segments rearward,

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because of sperm and eggs in the coelom; also live specimens might appear white in certainbody areas because of sperm in the coelom. For tubificids, the shapes of the genital setae(spermathecal setae of segment X and penial setae of segment XI) and penial sheaths (seeTUBIFICIDAE pictorial keys ) are often needed for identification. Size and shape of genitalsetae are quite different from the setae in the dorsal and ventral bundles of the othersegments - the oil immersion lens is often needed to see the dorsal setae clearly. Note thatsetae begin in segment II. For keys to all North American oligochaetes, see Klemm (1985a)and Brinkhurst (1986).

Species ListMost of the distributional records of oligochaetes of Alberta are taken from Brinkhurst (1978).Many common species have not yet been found in Alberta.

Family LumbriculidaeLumbriculus variegatus (Muller)Rhynchelmis elrodi Smith and DickeyStylodrilus heringinanus Claparede

Family TubificidaeAulodrilus americanus Brinkhurst and CookAulodrilus limnobius BretscherAulodrilus pigueti KowalewskiAulodrilus pluriseta (Piquet)Bothrioneurum vejdovskyanum StolcBranchiura sowerbyi BeddardIlyodrilus templetoni (Southern)Isochaetides curvisetosus (Brinkhurst and Cook)Isochaetides freyi (Brinkhurst)Limnodrilus claparedianus RatzelLimnodrilus hoffmeisteri ClaparedeLimnodrilus profundicola (Verrill)Limnodrilus udekemianus ClaparedePotamothrix bavaricus (Oschmann)Psammoryctides californianus BrinkhurstPsammoryctides minutus BrinkhurstQuistadrilus multisetosus (Smith)Rhyacodrilus coccineus (Vejdovsky)Rhyacodrilus montana (Brinkhurst)Rhyacodrilus sodalis (Eisen)Spirosperma nikolskyi (Lastockin and Sokolskaya)Tubifex kessleri americanus Brinkhurst and CookTubifex tubifex (Muller)Varichaetadrilus pacificus (Brinkhurst)

Family AeolosomatidaeAeolosoma spp.

Family NaididaeArcteonais lomondi (Martin)Chaetogaster diaphanus (Gruithuisen)Chaetogaster diastrophus (Gruithuisen)Chaetogaster limnaei von BaerDero digitata (Muller)Nais behningi (Michaelsen)Nais elinguis MullerNais pardalis PiguetNais pseudobtusa PiguetNais simplex PiguetNais variabilis PiguetPristina breviseta BournePristina foreli (Piguet)Pristina longiseta EhrenbergSlavina appendiculata (d 'Udekem)Specaria josinae (Vejdovsky)Stylaria lacustris (Linnaeus)Uncinatis uncinais (Qrsted)Vejdovskyella comata (Vejdovsky)

Survey of ReferencesThe following references have information on Alberta's oligochaete fauna: Anholt (1983, 1986),Brinkhurst (1978, 1987), Fillion (1967), Kussat (1969), Lock et al. (1981), Osborne and Davies(1987), Rasmussen (1979, 1982), Reynoldson (1978, 1987), and Tynen (1970). See alsobottom fauna references listed at the end of Chapter 3 (Porifera).

Pictorial KeysPictorial Key for Oligochaeta

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Pictorial Key for Naidide

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Pictoral Key for Tubificidae

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Pictorial Key for Tubificidae (A)

Pictorial Key for Tubificidae (B)

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Pictorial Key for Tubificidae (B)

PlatesPlate 12.1 Upper, left to right: Plumatellafungosa (Bryozoa) [10 mm];Fredericella sultana (a dead colonyshowing statoblasts) [each statoblastis about 0.4 mm in diameter]; Middle, left to right: Lumbriculidae(Olgicochaeta) [50 mm]; Specariajosinae (Oligochaeta: Naididae) [10mm];Lower: Macrobiotus (Tardigrada) [8mm]

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