Annelid Classes: Hirudinida

Characteristics of Hirudinida

• Lack of setae, which differentiates them from other annelids.
• Primarily found in freshwater environments.
• Display a wide range of colors, contributing to their adaptation.

Hirudinida Nutrition

• Most species are parasitic, predominantly feeding on the blood of hosts.
• Some Hirudinida predate on small invertebrates, showcasing a diverse diet.
• They secrete hirudin, an anticoagulant, to facilitate blood feeding.

Class Hirudinidae Reproduction

• Species are hermaphroditic, allowing for cross-fertilization between individuals.
• Clitellum is only visible during the breeding season, where it secretes a cocoon for sperm and egg storage.

Characteristics of Polychaetes

• Possess paired appendages called parapodia on most body segments, aiding in movement and respiration.
• Prostonium, a head region, can retract, which may function in sensory perception.
• Setae are organized in bundles on parapodia, enhancing locomotion and grip.

Polychaetes Reproduction and Development

• Lack permanent sex organs, leading to more flexibility in reproductive strategies.
• Exhibit separate sexes, differentiating male and female individuals.
• Rely on external fertilization to reproduce, allowing for widespread gene dispersal.
• Develop into trochophore larvae, which are free-swimming and lead to juvenile stages.

Polychaeta Nutrition

• Engage in active predation or scavenging, indicating a dynamic role in their ecosystems.

Oligochaeta Characteristics

• Feature a clitellum used in reproductive processes, distinguishing them from other classes.
• Possess four pairs of setae on each segment, aiding locomotion and anchorage.
• Utilize nephridia to perform excretory functions, maintaining internal homeostasis.
• Are hermaphroditic, facilitating reproduction despite potentially sparse populations.