Annelida Flashcards
Name the 9 traits of Phylum Annelida
- Bilateral protosotmes - mesoblast, 4d. Gives rise to mesoderm
- Segmentation - teloblastic growth; new segment forms at the posterior end
- Complete, regionally specialized gut
- Metanephridia - coelomate
- Closed circulatory system
- 2-parted heart - pre-semental
- Post-segmental - pygidium
- Parapodia - chaeta
- Nervous system centralized and ventral - ladder nervous system merged into one
What are the 3 synapomorphies of Annelida?
- 2-parted head
- Post-segmental - pygidium
- Parapodia - “side feet”. Chaeta
Major subgroups of Annelida - Errantia
Polychaeta. Move around for food
Predators and scavengers
Major subgroups of Annelida - Sedentary
Polychaeta. Tube worms
Major subgroups of Annelida - Clitellata
Crassiclitellata - terrestrial. Earthworms. No parapodia and has direct deposit feeding
Hirudinoidea - terrestrial. Leeches. They secrete something to prevent coagulation and can slurp the animal whole. No parapodia and no chaetae. Has strong heteronomy
What does metamerism mean? And what are the 2 types of metamerism?
Metamerism means the animal is segmented
- Homonomous - the segments of the animal are similar
- Heteronomous - the segments of the animal are differentiated with different functions
Peristomial cirri
Sensory organ located on the persitomium
Antennae
Sensory appendage located on the prostomium
Palp
Located on the prostomium. Functions in feeding and sensing
Parapodia
Side foot that are paired. Used for locomotion and bears chaetae
It is a biramous appendage - has 2 branches
In marine annelids, they are also used for gas exchange
Chaetae
Chitinous bristle that allows for sinusoidal movement - locomotion
Pygidium
The hind segment of the Annelid. Bears the anus
Nuchal region
Highly ciliated chemoreceptors for taste and smell. Located on the prostomium
Notopodium
Dorsal subsection of parapodium
Neuropodium
Ventral side of the parapodium, because the nervous system is on the ventral side
Are there any intrinsic muscles in Annelida?
NO. They only have extrinsic muscles, which are used to control the parapodia
Aciculum
Skeletal elements for muscles to attach
Trunk
Consists of the many segments of the Annelid. The segments are between the prostomium and pygidium
Clitellum in Clitellata (Crassiclitellata and Hirudinoidea)
Thick and non-segmented. Found in the epidermis. Used in sexual reproduction - it forms a cocoon for its eggs
Qualities of Hirudinoidea
It’s a predator leech and not parasitic
No parapodia
No chaetae
Strong heteronomy
Contains hirudin
What does hirudin do?
It is a compound that’s an anti-cogulent, preventing blood from coagulating so the animal can slurp its prey
Anatomy of Hirudinoidea
Oral sucker (segments 1 - 4)
Clitellum - sexual reproduction (segments 9 - 11)
Posterior sucker (segments 28 - 34)
Anus is on the dorsal side of its body near the posterior sucker
Digestive system general parts
Mouth, then pharynx, then esophagus, then crop (stores food), then gizzard (functions in mechanical digestion - grinds food), then intestine (nutrient absorption), then proctodeum, then anus
Calciferous glands
Removes excess calcium ions from the blood and will secrete them into the gut so it can be expelled through the anus
Chloragogen tissue
Has a liver-like function. Regulates sugar content in blood and breaks down fat. Expels urea
Typhlosole
Used for surface enlargement for more efficient absorption of digested nutrients
General circulation and gas exchange
Has tail-to-head blood flow
Blood vessels are mesodermal origin
Dorsal blood vessel to ventral blood vessel to segmental blood vessel
How many hearts does an earthworm have? Do they have an open or closed circulatory system?
5 hearts. Closed circulatory system
Mesentary (also septum)
Allows for circulatory vessels and nerves to connect the main body wall to the gut
Are earthworms coelomic?
Yes, they are coelomic, and it is enveloped by mesoderm, called a peritoneum
Its coelom allows them to be tough and robust
Metanephridium
A type of nephridium that functions as an excretory organ to excrete urine. This is also where gametes exit
Cuticle
Covers the outer body wall that helps the keep the worm moist. Secreted by the epidermis
Longitudinal muscles
When it contracts, the worm becomes shorter and fatter
Circular muscles
When it contracts, the worm becomes skinnier and longer
General nervous system
Has a brain and a double ventral nerve cord
Nephrostome
Entrance of the metanephridium orientated towards the coelom covered in cilia to push metabolic wastes inside the metanephridium
Nephridiopore
External opening of the nephridium where wastes are expelled
What do their nervous system consist of?
A ladder-like single, or double ventral nerve cord
Circumenteric nerve ring
Sensory receptors
Name the 7 sensory receptors
- Tactile - touch
- Chemoreceptors - taste and smell (in nuchal organ)
- Photoreceptors - eyes
- Georeceptors - balance receptors
- Phonoreceptors - sound
- Proprioceptors - stretch receptors. Are aware of the different parts of the body and know where they are without seeing them
- Thermoreceptors - temperature receptors
3 types of asexual reproduction
- Regeneration
- Bud-like outgrowths. Identical clones of the animal will grow and pop off when they are mature
- Isolated fragments - new individuals will form and will pop off when mature. The oldest individual is most posterior, and the youngest is nearest the parent posterior
4 types of sexual reproduction
- Errantia and Sedentaria: mostly dioecious. Gametes come from peritoneoum
- Clitellata: hermaphrodites. Complex and permanent reproductive systems
- Gamete formation
- Epitoke - portion will pop off depending on environment
Brooding
Mixed indirect reproductive process where the mother will take care of the eggs until they’re mature and pop off
Stereoblastula
When it undergoes gastrulation, a stereogastrulation results
Epiboly
Process of the ectodermal layer migrating to cover the ball of cells
Prostomium and peristomium
Prosotmium - the head portion of the annelid. Where the brain is located
Peristomium - the second segment behind the head portion (prostomium). Mouth is located here
Apical sense organ
Will become the brain and will develop into the prostomium
Prototroch
Develops into the peristomium
Telotroch of the trochophore larva
Very posterior end
Polytroch larva
Stage where teloblastic growth occurs and the hollowing out of the mesoderm
