Lophotrochozoa Flashcards
What is the defining characteristic of annelids and why is it important
Segmentation – repeated body structures (muscles, coelomic compartments, nervous and excretory systems) allow precise control of movement and functional specialisation
What does the term vermiform mean in the context of annelids
“Vermiform” means worm-shaped – soft-bodied, longer than wide, allowing them to burrow and move efficiently in substrates
Describe the annelid coelom and its function
Annelids have a large, fluid-filled coelom lined with mesodermal epithelium; it acts as a hydrostatic skeleton, resisting compression and aiding movement
What role do circular and longitudinal muscles play in annelids
These muscles act antagonistically – circular muscles contract to elongate segments; longitudinal muscles contract to shorten and widen them
How does segmentation aid annelid movement and function
Segmentation allows independent movement and function of segments; repeated units enhance locomotion, redundancy, and specialisation
What are septa and their function in annelids
Septa are internal walls between segments that separate the coelom into compartments, allowing segment-specific control of movement
What is the VNC and its significance
Ventral Nerve Cord – central to annelid nervous coordination; runs along the belly, often paired with segmental ganglia
Why must annelids live in moist or aquatic environments
Their skin is water-permeable and used for gas exchange; dryness impairs oxygen diffusion
What are the three main classes of annelids
- Polychaeta – mostly marine
- Oligochaeta – mainly freshwater and soil
- Hirudinea – leeches, often ectoparasitic
What habitats do polychaetes typically occupy
Mostly marine – can be free-swimming, burrowing, or tube-dwelling
Differentiate between errant and sedentary polychaetes
Errant: Active, free-moving with eyes and appendages.
Sedentary: Tube/burrow-dwellers with adaptations for limited movement
How do errant polychaetes use their segments for locomotion
Through undulations using longitudinal muscles; segments flex individually due to hydrostatic skeleton. Parapodia provide extra propulsion
How do sedentary polychaetes use their segmentation
Via peristaltic waves (circular and longitudinal muscles) to move water in tubes, aiding in feeding and respiration
Describe the reproductive strategy of polychaetes
Typically dioecious (separate sexes), release gametes into water for external fertilisation; include planktonic larval stages
How do oligochaetes use segmentation for movement
Peristalsis via antagonistic muscle pairs; segment shape changes drive forward burrowing motion
Key differences between oligochaetes and polychaetes
Oligochaetes lack parapodia, eyes, and head tentacles; they are freshwater or terrestrial; hermaphroditic with direct development
Describe oligochaete reproduction
Hermaphroditic reciprocal mating; clitellum secretes mucous cocoon that picks up eggs and stored sperm. No larval stage
What structural difference do leeches have compared to other annelids
They lack internal septa – allows greater body expansion for feeding, but reduces locomotion efficiency
What body features do flatworms lack compared to other bilaterians
No coelom, no respiratory or circulatory system, no skeleton or appendages, and no anus (single opening for mouth and waste)
How does the lack of a coelom affect flatworm movement
No hydrostatic skeleton – muscle contractions are not efficiently transmitted through the body, limiting locomotion power
Why are flatworms small and flat
To allow gas and nutrient exchange by diffusion due to absence of circulatory and respiratory systems
What are triclads and polyclads
Triclads: freshwater flatworms
Polyclads: marine species
How do flatworms move
Glide on cilia and use muscular contractions (“ripples”)
What is a reversible pharynx
A feeding organ that protrudes from the body to ingest food, especially in decaying material
