55. Phylum Annelida: important evolutionary changes. Lumbricus terrestris. Hirudo medicinalis.
Introduces the segmented worms of the phylum Annelida, covering their general body plan, muscle and cuticle structure, setae, digestive tract and reproduction. It then describes the common earthworm Lumbricus terrestris, including its size, soil habitat, segmented morphology and mating and cocoon-based life cycle, and closes with the medicinal leech Hirudo medicinalis, covering its two suckers, blood-feeding host range, freshwater habitat and egg-laying behaviour.
Inside: 3 sections · 2 min
Topic 55 of 64 in the MU Sofia syllabus for Biology (Dental Medicine, Year 1). The free AceMed note covers it in 3 sections, about 317 words (2 min of reading).
In this note
Annelida: Overview of Ringed or Segmented Worms
Lumbricus Terrestris (Common Earthworm)
Hirudo Medicinalis (Medicinal Leech)
Annelida: Overview of Ringed or Segmented Worms
General Characteristics
Definition: Annelids are known as ringed or segmented worms, notable for their segmented body structure.
Diversity: This phylum includes varieties such as ragworms, earthworms, and leeches.
Distribution: Found throughout the world in various environments.
Body Composition:
Bilaterally symmetrical.
Triploblastic, consisting of three germ layers: ectoderm, mesoderm, and endoderm.
The body is composed of circular and longitudinal muscle fibers covered by an acellular cuticle.
Equipped with hair-like structures called setae, aiding in locomotion.
Digestive System: Features a complete digestive tract.
Reproduction: Most species are capable of both sexual and asexual reproduction
Lumbricus Terrestris (Common Earthworm)
Size
Typically reaches up to 20 cm in length.
Habitat
Earthworms are non-parasitic and thrive in soil environments.
Morphology
Body: Multi-segmented, featuring both male and female gonopores, usually reproducing sexually.
Digestive System: Includes a mouth leading to a long central intestine.
Nervous System: Comprised of cerebral ganglia and segmented nerves.
Locomotion: Each segment contains chaetae (bristles) that assist movement through soil.
Tail: Characteristically flattened, aiding in burrowing and movement.
Life Cycle
Mating: Earthworms surface to mate, forming a mucous ring to collect eggs and sperm for fertilization.
Egg Cocoon: The mucous ring containing the eggs slips off and is buried underground, where it hardens into a cocoon.
Development: Eggs hatch by the end of the fifth month; juveniles burrow into the soil and reach sexual maturity at one year.
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