Annelids Flashcards
Define annelids
Segmented worms with a metameric body plan
Define metamerism
Segmented arrangement of body, each segment has excretory, nervous and circulatory structures
What are some pros of metamerism
Pros: Creates hydrostatic compartments, Lessens impact of injury, permits tagmatization- which helps with specialization of the parts
How is metamerism developed?
Mesodermal layers split to form body cavity
Peritoneum lines the compartment walls and cover organs
What are setae?
Bristle like structures used for locomotion, sensory and respiratory depending on the organism
What are the 3 clades within Phylum annelid
Errantia
Sedentaria
Clitella
Summarize clade errantia
Motile worms
~5-10cm long but can be shorter or longer
diverse environments
Paired parapodia
Define prostomium, peristomium, and pygidium
The fleshy lobe
First body segment
Terminal segment with anus
What is the function of the aciculum?
A chitinous rod that supports the parapodium and setae which extend from parapodia
How does feeding work for class errantia?
A simple digestive tract runs from mouth to anus, Anterior region has been modified into a proboscis that is an extendable muscle used for feeding
How do class errantia perform gas exchange
Diffusion typically, but some larger organisms may have gills
Closed circulatory system
What are the main pieces of the errantia nervous system?
Supra and Sub pharyngeal ganglions connected by the circumpharyngeal ganglion
the ganglia contain small fibres for movement and giant fibres for escape reactions
What is unique about errantia eyes?
Can be very simple or very developed, similar to a vertebrate
What is the process of epitoky
The sexually immature atoke of a worm grows a sexually mature epitoke, which breaks off in mating seasons and swims to the surface
Name a pro and con of epitoky
Pros: protects the atokes, and is efficient in fertilizing eggs
con: etokes make easy prey
What is the key difference between errantia and sedentaria?
Sedentaria is more sedentary and tends to burrow more, so are adapted to that
otherwise very similar
What are the two groups found in clitellata
Oligochaeta and hirudiniea
What is the distinguishing feature of clade clitellata?
The reproductive structure known as the clitellum which forms a cocoon
What are some unique features of oligochaeta?
Few setae - 4 pairs per segment- ish
No parapodia
a prostomium located before the mouth
How are oligocheata setae moved?
The protractor and retractor muscles
What does digestion look like for oligocheata?
The food enters the pharynx then esophagus, can be stored in the crop, the gizzard grinds it into small pieces then deposits into the intestine
What is important about the oligocheata intestine?
Folded dorsally to form typhlosole, which increases surface area
What is important about the oligocheata circulatory system?
Closed
Heart like structure called a dorsal vessel
Have blood made of hemoglobin and amoeboid cells
Aortic arches help maintain pressure
ventral vessels deliver blood
What is important about the oligocheata nervous system?
Basic “brain” called the paired cerebral ganglia
Solid ventral nerve cord acts as a main nerve pathway
No eyes, but sense organs present over body
Are oligochaeta mono or di oecious? and explain reproduction briefly
Mono, sex organs found anteriorly; The sperm is exchanged and kept just before the oviduct, then the clitellum slides down the worm, acquiring eggs and then sperm and eventually falls off to form cocoon
Do oligocheata have a larval form?
No, they are dirrectly developed
Summarize class hirudiniea
Leeches, they have no parapodia, head or appendages, suckers have evolved on both ends
What is unique about hirudinea?
No metamerism instead a coelomic cavity with spaces called lacunae, and 4 categories of muscle; oblique, circular, longitudal and dorsoventral
What is hirudin?
An anticoagulant secreted by hirudinea members to prevent blood clotting while feeding
