Chapter 11: Annelids

Phylum Annelida

segmented worms, decomposers (eats dead organisms and recycles nutrients back into soil)

Segmentation

Repeated units that allow for growth in an animal

Metamerism

serial repeated units, found in Annelida, Arthropoda, and Chordata but was evolved independently from each other (convergent evolution)

Setae

tiny chitinous bristles found on many annelids like bristle worms

Class Polychaeta (Bristle Worms)

- Bristle worms - Generally marine - Contain bristles called "chaetae' made of chitin - Dioecious (sperate genders) - Don't have permanent sex organs - Scavengers (decomposer) and/or predators

Class Oligochaeta (Earthworms)

- Hermaphrodites - Earthworms - Terrestrial or freshwater - Range from 0.5 mm to 3 meters Aristotle called earthworms "intestines of the soil" Charles Darwin wrote The Formation of Vegetable Mould Through The Action of Worms

Class Hirudinea (Leeches)

- Leeches - Hermaphrodites (similar reproduction to earth worms) - Most between 2-6 centimeters in length - Most freshwater, few marine, in moist terrestrial enviornments - Has mesodermal tissue - Fixed number of segments (usually 24) - Many are parasitic (feeds on blood) some are predators - Lack distinct coelomic compartments - Secrete anticoagulant

Anticoagulant

Secreted by leeches in their saliva that helps the blood continue to flow as they feed

Prostomium

where the mouth is located right underneath

Peristomium

(first segment posterior to head, "mouth")

Pygidium

anus "end"

Hydrostatic Skeleton

found in invertebrates (worms), lack of a bone structure, contraction of muscles allow the worm to move

Chaetae

Bristles that are made of chitin that can be found mostly on Polychaeta (bristle worms) and a little on Oligochaete (earthworms)

Dioecious

having male and female reproductive organs in separate animals, opposite of monoecious

Fireworm

Hermodice carunculata, polychaete that eat corals, hollow setae contains poison to repel predators

Scale Worm

Hesperonoe adventor, flattened body covered with broad scales, very large

Class Sedentaria

- Contains worms with polychaete and oligochaete body plans - Feed on plankton and detritus - Tube worms - Fan worms

Tubeworms

Amphitrite, builds tubes into mud or sand, have long grooved tentacles

Sabella

feather duster worm, filter feeding worm, uses cilia to direct small food particles to the mouth, sand grains are stored in sacs to use later for tube building

Peristalsis

waves of contraction and expansion that sweep along the body of the worm for movement that also helps with digestion

Typhlosole

Found in earthworms, it is a dorsal flap of the intestine that runs along most of its length, effectively forming a tube within a tube, and increasing the absorption area by that of its inner surface. Its function

Castings

worm excrement (poop) that contains many nutrients for the soil

Nephridia

a pair of invertebrate kidneys that operate similarly to vertebrate kidneys. In earthworms, nephridia are responsible for maintaining osmoregulation.

Clitellum

"collar", houses the reproductive organs, before it contains majority of organs, after it to anus is mainly GI tract

Seminal Vesicles

produce the sperm and then fertilize the eggs

Seminal Receptacles

hold the sperm from the other worm

Cocoon

The "larvae" stage for earth worms

Medicinal Leeches

Hirudo medicinalis, leech that is used when fingers or toes are severed to clear out congestion so the veins can grow back

Ecological relationships of annelids

- Burrow into mud or sand - Feed on organic matter - Decomposers - Leeches can be used for medicine - Common food source for larger animals - Earthworms help turn the soil for drainage and aeration

Ancestral annelid features

- Bicellular eyes composed of two cells - Nuchal organs - Paired epidermal setae - Grooved pals - Biramous parapodia with internal setae - Metameric body

N sandersi

a deep ocean worm from hydrothermal vent communities