Laboratory for BIO 1016 and BIO 3001

Laboratory for BIO 1016 and BIO 3001

Domain: Eukarya

Kingdom: Animalia

Phylum: Annelida (Segmented Worms)

  • General Characteristics:

    • Segmented worms known as annelids.

    • Habitat: Live in marine, freshwater, and moist terrestrial environments; some species are parasitic.

    • Body Structure:

    • Bilaterally symmetrical.

    • True coelom: a body cavity surrounds and contains digestive tract and other organs.

    • Segmented body adorned with bristles (setae).

    • Peritoneum: Cellular layer lining both sides of the coelom.

    • Digestive System: Begins at the mouth and ends at the anus.

    • Comprises three basic tissue layers.

    • Nervous system includes a brain.

    • Circulatory system features closed blood vessels.

    • Respiration: Many have gills; earthworms lack specialized respiratory structures.

    • Skeletal support: Hydrostatic (no hard parts).

Class: Oligochaeta

  • Etymology: Refers to few (oligo-) bristles (-chaeta).

  • Example: Earthworm genus Lumbricus

  • Body Characteristics:

    • Dorsal (top) side darker than ventral side.

    • Body adaptations for burrowing:

    • Mouth end is pointed and conical.

    • Tail end is dorsoventrally flat.

    • Anus positioned as a vertical slit in the last segment.

    • Setae (singular: seta): Rasping bristles felt along sides of the living worm.

    • Excretory Structures: Nephridia possess tiny pores on the lateral or ventral surfaces, except for end segments.

    • Reproductive Structures:

    • Both ovaries and testes present.

    • Oviducts openings located on sides of segment 14; sperm duct openings with swollen edges on segment 15.

    • Clitellum: Enlarged ring from segment 31 or 32 to 37; glandular and secretes mucus for copulating individuals.

Dissection of Earthworm

  • Procedure:

    • Place preserved earthworm dorsal side up in a dissecting pan.

    • Anchor anterior end with pin; stretch worm and pin posterior end.

    • Incision: Make longitudinal mid-dorsal cut with a razor blade without cutting deeply.

    • Open incision using forceps and cut internal septa.

    • Pin skin back on both sides for internal organ visibility.

  • Internal Anatomy:

    • Brain located at the anteriormost end.

    • Digestive Tract:

    • Mouth → pharynx → tubular esophagus → bulb-like crop → tough-walled gizzard → intestine → anus.

    • Coelomic Space: Encapsulates the digestive system within each segment.

    • Circulatory Structures:

    • Five pairs of dark-colored blood vessels (aortic hearts) surrounding the esophagus; connects ventral to dorsal blood vessels.

    • The dorsal vessel is contractile; pumps blood anteriorly.

    • Reproductive Organs:

    • Seminal vesicles (whitish) contain testes extending ducts to segment 15.

    • Small, bulb-like seminal receptacles located anteriorly to seminal vesicles, part of the female reproductive system.

Microscopic Anatomy

  • Cross-section Features:

    • Intestine is separated by coelom from body wall.

    • Typhlosole: Swollen ridge descending from dorsal side of intestine; increases surface area for nutrient absorption.

    • Vascular Components:

    • Dorsal and ventral blood vessels; ventral nerve cord below subneural blood vessel.

    • Muscle Layers:

    • Inner Longitudinal Layer: Thick, anteroposteriorly running; contraction shortens and fattens segments.

    • Outer Circular Layer: Encircles body; when contracted, the body narrows and elongates segments.

  • Muscle Action:

    • Produces peristalsis, similar to human intestine's two muscular layers.

    • Coordination of muscle contractions allows worms to anchor and move through soil using setae.

Class: Polychaeta

  • Etymology: Polychaetas (many bristles).

  • Habitat: Marine environments, particularly common in shallow intertidal zones.

  • Feeding: Many are carnivores, feeding on various invertebrates.

  • Example: Nereis

    • Features pinching jaws with a horny covering at mouth and sensory palps behind jaws.

    • Tentacles found on segments just posterior to jaws.

    • Locomotion and Respiration:

    • Parapodia: Lateral appendages extending from sides; facilitate movement and gas exchange, functioning as gills.

  • Microscopic Slide Observation:

    • Examine thick microscope slide cross-section of Nereis; observe bunches of black setae extending from body wall and parapodia.

Class: Hirudinea (Leeches)

  • Etymology: Name derived from leech.

  • Habitat: Found in marine, freshwater, and damp terrestrial environments.

  • Body Characteristics:

    • Segmented bodies, though segmentation not visibly external.

    • Suckers present at both ends; used for locomotion.

    • Swimming achieved through body wall contractions.

  • Setae and Parapodia: Leeches lack both.

  • Feeding Habits:

    • Some are predators; others are parasites, with blood-feeding leeches possessing sharp jaws.

    • Anticoagulant secretion prevents blood clotting during feeding.

    • Medicinal leeches are a variety still in current use.