Annelids, Metamerism (8) Flashcards
What is metamerism?
Segmentation of the body into repeated units, both externally and internally
What are annelids commonly known as?
Segmented worms
Which other phyla exhibit metamerism besides Annelida?
Arthropoda and Chordata
What is an evolutionary advantage of metamerism in annelids?
The creation of hydrostatic compartments, lessening the impact of injury, and permitting tagmatization.
What is schizocoelous development?
A process in which mesodermal layers split to form body cavities.
What is the function of peritoneum in annelids?
It lines the body wall of each compartment and forms mesenteries that cover organs.
What are the two main clades within Pleistoannelida?
Errantia and Sedentaria.
What is a distinctive feature of Errantia?
Paired parapodia found in most segments used for locomotion and respiration.
What is the function of parapodia in Errantia?
Locomotion and, in some species, respiration
What is a proboscis in Errantia and what is its function?
An extendable muscular structure used for feeding, often equipped with paired jaws.
How does gas exchange occur in Errantia?
Via diffusion across the body wall and parapodia, sometimes with parapodial gills
What circulatory system do Errantia possess?
A closed circulatory system with contractile dorsal and ventral aortas
What sense organs are present in Errantia?
Eyes (ranging from simple eyespots to image-resolving eyes), nuchal organs (chemoreception), and statocysts (body orientation).
What is epitoky in polychaetes like Eunice viridis?
The transformation of part of the body into a sexually mature form (epitoke) during the breeding season.
What is the adaptive significance of epitoke swarming behavior in Errantia?
It protects non-reproductive individuals (atokes) and ensures synchronous maturation of epitokes, maximizing fertilization.
What distinguishes Sedentaria from Errantia?
Sedentaria are generally burrowers or tube dwellers with reduced parapodia, often used for anchoring or respiration.
What is the defining feature of Clitellata?
The presence of a clitellum, a reproductive structure that produces a cocoon for eggs.
Which groups are included in Clitellata?
Oligochaeta (earthworms) and Hirudinea (leeches).
Do earthworms have parapodia?
No
What are setae in earthworms?
Bristle-like structures set in sacs within the body wall, moved by muscles for locomotion.
What is the function of the gizzard in earthworms?
To grind food into smaller pieces for digestion
How do earthworms exchange gases?
Through their moist skin; they lack specialized respiratory organs
What circulatory system do earthworms have?
A closed circulatory system with a dorsal vessel (heart-like), aortic arches, and ventral vessels
How do earthworms reproduce?
They are monoecious and exchange sperm during copulation, producing a cocoon where fertilization and development occur.
