Annelids

Members of the Phylum Annelida (Annelids or ringed worms) are more complex than they seem. They have an elongated body; the vast majority have external segmentations, a body cavity, and complex excretory and nervous systems.

The Annelids included in this report are members of the class Clitellata (segmented worms) characterised by the presence of a girdle (a clitellum), a set of modified body segments that secretes mucus that helps during copulation then forms a protective pocket around the fertilized eggs. Other members of the Phylum Annelida, mostly marine species, will be included in future reports.

There are five species of earthworms and 17 species of freshwater leeches confirmed present in the NWT. An additional four species of earthworms and three species of freshwater leeches are expected to be present. Most species of earthworms may be alien to the NWT, but more studies are required to determine the origin of our populations in the NWT.

Earthworms

Earthworms (Subclass Oligochaeta) are familiar to almost everyone. In North America, they are one of the most popular forms of live bait for fishing: gardeners hold them in high esteem as nature’s ploughmen, folklore and scientific accounts tell of their medicinal uses, and soil inhabiting vertebrates (moles, voles, etc.) store them as a source of food. The role of some species in organic matter decomposition and mineral cycling may be important, and a great deal has been written concerning earthworm farming. Biology students all over the world study their anatomy (mainly Lumbricus terrestris) in great detail. The great amount of literature that has been devoted to a group of organisms that are not sources of human nutrition is truly amazing, yet their biology and distribution are still relatively unknown.

Many of the world’s thousands of megadriles (terrestrial oligochaetes) species are known only from a limited series of one or a few specimens. In Canada there are currently 36 species found in three Families: Lumbricidae, Megascolecidae, and Sparganophilidae. Of these, 18 are considered rare and eight of these are native to Canada, whereas the others are introduced species from Europe or Asia.

The first species reported from the NWT was Eisenia foetida from Yellowknife in 1996 and the second was Eiseniella tetraedra in 2002. Collections in 2018 yielded Eiseniella tetraedra again and Dendrobaena octaedra for the first time. With such limited collecting, reporting so few species is not surprising, but based on recent records from the Yukon and northern Alberta and British Columbia; it is expected with additional sampling several other species found elsewhere in Canada will be located in the NWT.

The following conditions are required in a habitat in order for earthworms to survive: 1) adequate and suitable food supplies, 2) adequate moisture, 3) adequate dissolved oxygen, 4) protection from sunlight, 5) suitable pH, 6) absence of toxic substances, and 7) suitable temperatures.

Although earthworms may be found in the soil and adjacent habitats, there is considerable diversity in their activities and functions in these habitats. The following list of functions includes the main ones: 1) organic matter decomposition, 2) soil neutralization, 3) soil aggregation, 4) soil aeration, 5) infiltration of water into the soil, 6) percolation of water within the soil, and 7) soil turnover.

The terrestrial earthworms, based on their location in soil layers, are categorized ecologically as epigeic, endogeic. and anecic earthworms. Epigeic are smaller to medium sized worms that mainly feed on plant litter and dwell on the soil surface or in litter layers. Endogeic are medium sized worms, soil feeders, which live in horizontal burrows. Anecic worms are large size and live in vertical burrows, mainly feeding on plant litter and soil. There are two other categories that have been used for years – corticolous and limicolous. The corticolous (corticole) species are those which live under the bark of downed trees in the frass (the sawdust like material under the bark) between the bark and the tree wood. Limicolous (limicoles) species are those that live in very wet habitats, often in saturated soils on stream or river banks, flood plains, or saturated tree wood. Many of these species are also found in the litter. Their habitat usage depends on geographical location and the other earthworm species present.

The method of reproduction by most earthworms is amphimixis (cross fertilization, biparental) preceding cocoon production; this is the classical/original case. Beginning in the 1930s, reports began in the literature illustrating parthenogenesis (uniparental) in earthworms. Since that time, many species and some genera have exhibited this type of reproduction.

Earthworms, along with leeches and other less popular groups, are understudied. Recent DNA techniques have had a profound effect of earthworm taxonomy: creation of new species, synonomy of species, genera, and families, and resurrection of those taxa. Northern Canada is essentially under-surveyed and climate change may allow for new and unreported species not previously located in our areas.

Freshwater leeches

Leeches (subclass Hirudinea) are closely related to earthworms, and are similar in having soft, muscular, segmented bodies that can lengthen and contract. The NWT species range from 1 – 15 cm in length. They differ from earthworms in a number of ways: they have suckers at both ends and are more or less flattened from top to bottom. One of the leeches that is expected to be found in NWT, the fish hooking leech (Acanthobdella peledina), has some characteristics of earthworms including small hairs on the anterior portion of its body. A fish parasite, known from Alaska, it is likely to be found in NWT on the dorsal fins of grayling. Over a long time, leeches are believed to have evolved from worms so the primitive fish hooking leech is often called “a living relict”.

An individual leech is both male or female, but only one or the other during any particular mating event. The eggs are fertilized internally, before they are laid. Some leeches attach their eggs directly onto their belly and use their body to protect the developing embryos and the young. This advanced behaviour is not characteristic of most species which excrete their eggs in a protective cocoon. The cocoon is attached to a hard surface. The cocoons of some marine leeches are found on crabs where they benefit from dispersal and perhaps protection.

Many people are afraid of leeches because some kinds will suck on mammalian blood. They are not dangerous to people. They do not transmit infectious diseases like mosquitos and some other bloodsucking organisms, especially if removed carefully. Simply try to stop screaming… This may seem funny but the truth is that there are many phobias, and many are difficult to control, so nobody afraid of leeches should be made to feel bad. Do not pull them off or use a lighter flame or salt to remove them. This may cause them to regurgitate intestinal bacteria into an open wound. The best thing to do is simply use a fingernail (or a credit card) to break the seal on the suckers with which they hold on. Then they can easily be removed.

Worldwide there may be 700 species of leeches. In Canada, we estimate that there are 75 kinds, of which about 50 occur in freshwater and 25 are marine. In the NWT, many species already have been documented and additional species are expected. The Arctic marine leech (Notostomum leave) is expected to occur in the NWT. It is known from the eastern Canadian Arctic where it is a parasite of several species of bottom-dwelling fish including Greenland halibut.

Although many species are parasitic by sucking blood or consuming soft tissue, others attack and eat whole organisms. Some species feed only on the blood of ducks and live inside the nasal region of the duck’s bill, the trachea, and beneath the nictitating membrane of the eyes. Nasal leeches, including the duck leech (Theromyzon rude), are most frequent on swans and ducks. Within North America, infestations of these leeches on waterfowl are most frequent in the northwest including the prairie region and particularly the NWT.

The so-called “predaceous leeches” are scavengers on dead material as well as predators of living snails and aquatic insects. The northern fish leech (Piscicola geometra) is an external parasite confined to fish and mostly found on northern pike and lake trout. The only leeches so far reported on mammals in the NWT were on muskrats, and their identity was not determined.

In the NWT, leeches can be widespread and generally abundant, such as the spotted predacious leech (Erpobdella punctate), to the very rare, like the sidemarked leech (Haemopis lateromaculata) so far found only at Chan Lake. Not many rare species are so rare that they have only been found once in one place in North America. That is the case with the burbot leech (Cystobranchus mammillatus), an external parasite of Eurasian burbot found at Aklavik, NWT. The host subspecies does not occur in North America east of the Mackenzie Delta. More study is required to understand the status of this species in North America!

So why are leeches interesting? They are part of the food chain as predators, parasites, and prey. Although leeches are of limited direct value to people, there are some interesting uses. Leeches are highly regarded for fishing as bait as they are tough, and will stay alive wriggling on a hook for much longer than earthworms. Leeches are used in medicine to gently treat liquid imbalance in injured limbs by drawing excess blood. Substances, such as the anticoagulant called hirudin, originated from them and are used in modern medicine. Future discoveries may be still more beneficial, leading to treatments of cancer and bacterial infection.

Leeches are one of the most understudied groups of organisms. More remarkable discoveries will be made. Recently, DNA studies have revealed new species for which distinctive morphological characters are still unknown. More species will be discovered in NWT, especially marine species that are associated with fish that are expanding north into the Beaufort Sea.