Lophotochozoa I – Annelids Flashcards
Describe the Annelids
- highly ecologically important and taxonomically narrow phylum
- 12,000 species
- segmentation using septa
Define segmentation
- coincident repetition of characters
- muscles, nervous system, excretory system and coelom
- exclusion: prostomium which is unsegmented
Describe the features of Annelids
- vermiform
- large coelom
- compounded by a hydrostatic skeleton of fluid filled spaces
- movement of the circular and longitudinal muscles, and the ventral nerve cord
- water-permeable skin
vermiform
- lengths are much greater than their widths
- soft-bodied
What is the importance of the epithelial cells?
key to animal organisation
Describe water-permeable skin
- ecologically constrains to aquatic semi-terrestrial wet environments
- facilitate gas exchange to a greater degree
Describe the taxonomic classification of Annelida
3 classes
- the Polychaeta
- the Oligochaeta
Polychaeta
- ragworms
- lugworms
- fanworms
Oligochaeta
e.g. earthworms
Hirudinea
e.g. leeches
Clitellata
- Oligochaeta
- Hirudina
- paraphyletic
Polychaetes can be ecologically classified into:
- errant
- sedentary
- generally marine
Describe errant polychaetes
- eyes and sensory appendages
- use their segments in undulations to crawl or swim
- active predators that bite.
Describe Polychaeta locomotion
- contraction and relaxation of the longitudinal muscles
- extension and contraction of the parapodia for added power
Describe sedentary polychaetes
- live in burrows and tubes
- crown
- mouths fanned by radioles, which lead down into the ventral sac and tube
- water flows in antiparallel
Describe the sedentary polychaete ventral sac
- sand storage
- latterly used for tube building
Describe the sedentary polychaete tube
for consumption
Describe sedentary polychaete radioles
- size-discriminating sorting mechanism: large particles are discarded, smaller particles are consumed
- use food grooves with pinnule extensors that are covered in cilia, creating a ciliary tract to direct food movement for consumption
- ciliary feeding
Describe sedentary polychaete use of segments
- peristalsis
- contacting the circular and relaxing the longitudinal muscles to thin segments and vice versa
Segments and parapodia can be used for
- tube irrigation
- to ensure aquatic freshness
Describe polychaete reproduction
- dioecious
- gametes released into the marine environment for external fertilisation, where the larval stages of the life history will also occur
Dioecious
not hermaphroditic
Describe the Oligochaetes
- use their segments for peristalsis and locomotion
- freshwater or semi-terrestrial, soil-based environment
- no parapodia, eyes or head tentacles
- hermaphroditic mating system
- e.g. earthworms
Describe Oligochaete mating
- secretory clitellum structure
- three specialised gametogenetic segments
- any two oligochaetes can mate
What are three specialised gametogenetic segments of oligochaetes?
- the sperm store (spermatheca)
- the female gonad
- male gonad.
Describe Oligochaete mating post-separation
clitellum secretes mucous cocoon that picks up the self-eggs, and the sperm from the spermatheca, to achieve fertilisation.
Describe the Hirudinea
- predators
- blood-sucking ectoparasites
- hermaphroditic
e.g. leeches
Describe Hirudinea morphology
- similar to Oligochaetes
- secondary loss of septa for stretching capacity: increased volume for consumption of a blood meal, but constrained locomotion
Describe Hirudinea locomotion
looping and suckers
Describe Hirudinea in therapy
- help with post-operative venous congestion and swelling of digits and extremities
- due to the surgical inability to sew the small vein network
Describe the Sipuncula
- marine
- burrowing
- lost their segmentation
- aka peanut worms
Describe the Echiura
- flattened, grooved proboscis that projects over its environmental sediment
- body exists in a burrow
- aka spoon worms
Bonellia viridis
- species of Echiura
- extraordinary sex dimorphism: females generally 10-100cm, males, exist endoparasitically to the female and are 1-3mm
