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Digitizing and providing web access to this text was funded in part by the Alberta Conservation Association and the University of Alberta, Department of Biological Sciences

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 is too small to be hit with a club is sometimes called a worm. Annelid worms differ from flatworms, roundworms, and horsehair worms in many features; a major phylogenetical one is that annelids have a true coelom. There are two major classes. Members of the class Polychaeta 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 are Aeolosomatidae (now considered a separate class by many workers), Naididae (Plate 12.1), Tubificidae, Lumbriculidae (Plate 12.1), and Enchytraeidae. The family Haplotaxidae, which includes rare, very long, slender worms (to 40 cm in length), has not been reported from Alberta. Some freshwater Lumbricidae (the family that contains the terrestrial earthworms) undoubtedly occur in Alberta as well.

General Features, Reproduction

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

Asexual reproduction by fission is the common method of reproduction in Aeolosomatidae and Naididae. The Tubificidae, Enchytraeidae, Lumbriculidae (and Haplotaxidae) reproduce almost entirely by sexual means. Oligochaetes are hermaphroditic. An important reproductive structure is the clitellum, which in terrestrial earthworms is a conspicuous swollen area about one-third of the way from the anterior end of the worm. However, in most freshwater oligochaetes, the clitellum is not very conspicuous, being obvious only at the time of sexual reproduction. Although hermaphroditic, cross-fertilization is the rule. Eventually a cocoon secreted by the clitellum and containing a few fertilized eggs will slip off the anterior end of the worm. The fertilized eggs will hatch into "miniature adults;" there is no larval stage.

Collecting, Identifying, Preserving

Numerous oligochaetes can usually be collected with a fine-meshed pond-net worked through the mud and debris of the substratum. Aeolosomatids, being almost microscopic, are rarely collected (or at least recognized as such) by standard collecting methods, and very little is known 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 tubificids are numerous on the substratum of organically polluted lakes and streams. Most members of the 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 net samples. 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 living material. 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 mounting media. For a temporary mounting medium, Brinkhurst (1986) recommends Amman's lactophenol (400 g carbonic acid, 400 ml lactic acid, 800 ml glycerol, and 400 ml water-store in a dark bottle). [NOTE: THIS MEDIUM IS TOXIC IF INHALED OR IF SOLUTION TOUCHES SKIN.] Place a drop of Amman's on a slide and then immerse the worm or worms and add a coverslip. Some worms can be identified immediately, but it is best to clear the worms in Amman'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 Keys

The pictorial keys are based mainly on diagnostic features given in Hiltunen and Klemm (1 985a), Simpson et al. (1985) and Brinkhurst (1986). The keys should be satisfactory at the family 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" (namely Tubifex and Ilyodrilus - both very common in Alberta) is difficult for nonspecialists. Also, for all groups, intact mature worms are usually needed for identification, because detailed examination of the genital segments is usually required. In old worms, the setae (one of the most important diagnostic features) can wear down and therefore be of little use in identifying oligochaetes. Mature worms can appear slightly swollen from the genital segments rearward, because of sperm and eggs in the coelom; also live specimens might appear white in certain body 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 (see TUBIFICIDAE pictorial keys ) are often needed for identification. Size and shape of genital setae are quite different from the setae in the dorsal and ventral bundles of the other segments - the oil immersion lens is often needed to see the dorsal setae clearly. Note that setae begin in segment II. For keys to all North American oligochaetes, see Klemm (1985a) and Brinkhurst (1986).

Species List

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

  • Family Lumbriculidae
    • Lumbriculus variegatus (Muller)
    • Rhynchelmis elrodi Smith and Dickey
    • Stylodrilus heringinanus Claparede
  • Family Tubificidae
    • Aulodrilus americanus Brinkhurst and Cook
    • Aulodrilus limnobius Bretscher
    • Aulodrilus pigueti Kowalewski
    • Aulodrilus pluriseta (Piquet)
    • Bothrioneurum vejdovskyanum Stolc
    • Branchiura sowerbyi Beddard
    • Ilyodrilus templetoni (Southern)
    • Isochaetides curvisetosus (Brinkhurst and Cook)
    • Isochaetides freyi (Brinkhurst)
    • Limnodrilus claparedianus Ratzel
    • Limnodrilus hoffmeisteri Claparede
    • Limnodrilus profundicola (Verrill)
    • Limnodrilus udekemianus Claparede
    • Potamothrix bavaricus (Oschmann)
    • Psammoryctides californianus Brinkhurst
    • Psammoryctides minutus Brinkhurst
    • Quistadrilus multisetosus (Smith)
    • Rhyacodrilus coccineus (Vejdovsky)
    • Rhyacodrilus montana (Brinkhurst)
    • Rhyacodrilus sodalis (Eisen)
    • Spirosperma nikolskyi (Lastockin and Sokolskaya)
    • Tubifex kessleri americanus Brinkhurst and Cook
    • Tubifex tubifex (Muller)
    • Varichaetadrilus pacificus (Brinkhurst)
  • Family Aeolosomatidae
    • Aeolosoma spp.
  • Family Naididae
    • Arcteonais lomondi (Martin)
    • Chaetogaster diaphanus (Gruithuisen)
    • Chaetogaster diastrophus (Gruithuisen)
    • Chaetogaster limnaei von Baer
    • Dero digitata (Muller)
    • Nais behningi (Michaelsen)
    • Nais elinguis Muller
    • Nais pardalis Piguet
    • Nais pseudobtusa Piguet
    • Nais simplex Piguet
    • Nais variabilis Piguet
    • Pristina breviseta Bourne
    • Pristina foreli (Piguet)
    • Pristina longiseta Ehrenberg
    • Slavina appendiculata (d 'Udekem)
    • Specaria josinae (Vejdovsky)
    • Stylaria lacustris (Linnaeus)
    • Uncinatis uncinais (Qrsted)
    • Vejdovskyella comata (Vejdovsky)

Survey of References

The 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 also bottom fauna references listed at the end of Chapter 3 (Porifera).

Pictorial Keys

Plates

  • Plate 12.1
    Upper, left to right: Plumatella fungosa (Bryozoa) [10 mm]; Fredericella sultana (a dead colony showing statoblasts) [each statoblast is about 0.4 mm in diameter];
    Middle, left to right: Lumbriculidae (Olgicochaeta) [50 mm]; Specaria josinae (Oligochaeta: Naididae) [10 mm];
    Lower: Macrobiotus (Tardigrada) [8 mm]