Annelida Flashcards by Greta De Guzman

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

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What are the 3 synapomorphies of Annelida?

2-parted head
Post-segmental - pygidium
Parapodia - “side feet”. Chaeta

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Major subgroups of Annelida - Errantia

Polychaeta. Move around for food

Predators and scavengers

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Major subgroups of Annelida - Sedentary

Polychaeta. Tube worms

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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

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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

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Peristomial cirri

Sensory organ located on the persitomium

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Antennae

Sensory appendage located on the prostomium

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Palp

Located on the prostomium. Functions in feeding and sensing

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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

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Chaetae

Chitinous bristle that allows for sinusoidal movement - locomotion

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Pygidium

The hind segment of the Annelid. Bears the anus

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Nuchal region

Highly ciliated chemoreceptors for taste and smell. Located on the prostomium

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Notopodium

Dorsal subsection of parapodium

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Neuropodium

Ventral side of the parapodium, because the nervous system is on the ventral side

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Are there any intrinsic muscles in Annelida?

NO. They only have extrinsic muscles, which are used to control the parapodia

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Aciculum

Skeletal elements for muscles to attach

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Trunk

Consists of the many segments of the Annelid. The segments are between the prostomium and pygidium

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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

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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

1. Tactile - touch 2. Chemoreceptors - taste and smell (in nuchal organ) 3. Photoreceptors - eyes 4. Georeceptors - balance receptors 5. Phonoreceptors - sound 6. Proprioceptors - stretch receptors. Are aware of the different parts of the body and know where they are without seeing them 7. Thermoreceptors - temperature receptors

3 types of asexual reproduction

1. Regeneration 2. Bud-like outgrowths. Identical clones of the animal will grow and pop off when they are mature 3. 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

1. Errantia and Sedentaria: mostly dioecious. Gametes come from peritoneoum 2. Clitellata: hermaphrodites. Complex and permanent reproductive systems 3. Gamete formation 4. 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