Class archiannelida
• It includes about one dozen genera of small, marine worms
of unknown affinities.
• Segmentation chiefly internal.
• Parapodia and setae are absent.
• Sexes usually separate.
• A trochophore larva is usually present during development
stage.• Examples : Polygordius, Dinophilus, etc.
• Some authors have classified Annelida into 5 classes. Fifth
class is Echiurida. The members of this class are without
external and internal segmentation. Setae are rare. E.g., –
Bonellia, Echiurus.eConomiC imPortanCe of annelida
• In terms of influence on human welfare or economic
importance, the earthworms (Oligochaeta) and leeches
(Hirudinea) are more important than the polychaetes.
economic importance of Polychaeta
• The sexual parts or epitokes of palolo worms are used as
food by the native people. Epitokes are highly nutritive
consisting of almost pure yolk-laden eggs.• Lugworm (Arenicola) is a circulator of soil and considered
even more effective than the common earthworm. It is also
one of the commonest baits for certain fish.
• Some sand and lime-concreting tubicolous polychaetes are
important reef-building agents in some parts of the world.• Species of Polydora (harmful polychaetes) are oyster -
pests, causing mud blisters in the nacreous layers of shells
and making the oysters unfit to be sold. Oyster growers call
it “worm disease”.economic importance of oligochaeta
• All over the world earthworms are used as bait for
fishing.• A small white earthworm (Enchytraeus albidus) is often
grown in soil and used to feed aquarium fish and small
laboratory animals.
• Earthworms are used as food by uncivilised people in many
parts of the world. They are eagerly hunted as food by birds,
frogs, moles, lizards, small snakes and other predatory
invertebrates.
• Earthworms are in general beneficial to agriculture.
• Their habit of burrowing and swallowing earth increases
fertility of soil in many ways.
• Their burrows permit penetration of air and moisture
in porous soil, improve drainage, and make easier the
downward growth of roots.
• Earthworms were used variously as medicines in the past.
• Earthworms were used to cure stones in bladder, yellowness
of jaundice, pyorrhoea, piles, rheumatism or gout and
diarrhoea.
• They are easily obtained and are of convenient size to
be used for dissections. They are, therefore, universally
employed for class studies and for investigation in general
and comparative physiology.
• Earthworms are said to serve as intermediate hosts in
the transmission of some parasites, such as tapeworm
(Amoebotaenia sphenoides) and gapeworm (Syngamus) of
chicken and lung nematode (Metastrongylus elongatus) of
pigs.e conomic importance of hirudinea
• Most of the leeches are economically very significant for
medicinal purposes.
• Phlebotomy or ‘blood-letting’, painlessly achieved
by the application of leeches, was a common, though
erroneous method of medical treatment in Europe in the
early nineteenth century.
• When a person got a ‘black eye’ or conspicuous black and
blue spots on the body, the doctor used to apply a lean
hungry leech to the skin for sucking the impure blood.
• Salivary glands of leeches secrete anticoagulating substance,
called hirudin or anticoagulin.- Describe ectonephric nephridia.
- How is strobilisation different from true metamerism?
- How are earthworms beneficial to agriculturists?