Annelids: Segmented Worms Phylum Annelida

1. _____________________ from the Latin word ________________ meaning “little ring”

2. All are ________________________ worms 3. Approximately __________________ species including earthworms, freshwater worms, leeches,

and marine worms

4. Annelid Characteristics • _________________________: 3 cell (body) layers

• Highest level of organization: _____________________ • Bilateral symmetry • Cephalization

• Eucoelomate o Have a true body cavity that is completely surround by ____________. o Draw the coelom below:

• The Coelom o The coelom is a closed, fluid filed cavity that surrounds the gut. o The fluid within acts as a ______________________________ (blood)

o Tissue membranes (____________________) suspend the organs in the coelom • Metamerism

o The body is made up of serially repeating coordinated segments called _____________________ that are separated from one another by

_________________. o Each metamere contains sets of repeating organs. Ex. Gut, blood vessels, nerve cord,

excretory organs.

• Two part head consisting of:

o _____________________________: fleshy lobe that overhangs the mouth

o _____________________________: first body segment

• ___________________: circular rings • _________________________: the last segment

where the anus is • _________________________: reproductive

structure

• Nervous System o 2 cerebral ganglia o A ventral nerve cord with two ganglia per metamere o In some species, sensory organs such as _____________, ____________, and

__________________ have arisen. (________________ are appendages that may or may not be covered in cilia that help the worm find and pull in food)

• Locomotion o Both _____________________ and ________________ muscles o Most have _____________ (chitonous bristles secreted by the epidermis) that aid in

locomotion and burrowing o Setae may be modified into appendages called ___________________

• Skeletal System o Fluid in the coelom acts as a _______________________________

PARAPODIA

• Gas Exchange o Mainly by ____________________ through skin o Class Polychaeta often has specialized structures for gas exchange (ex. Parapodia, gills)

• Digestive System o ____________________________ o Regional ________________________ (digestive organs)

• Circulatory System o ________________ circulatory system composed of blood vessels (some of which are

contractile and act as “hearts”) o Some circulation is also accomplished by the _________________ fluid

• Excretion o Excretion is accomplished by organs called _______________________ (singular

nephridium) • Reproduction

o Sexual

5. Three Classes of segmented worms • _________________________________ • _________________________________ • _________________________________

Class Polychaeta Characteristics

• All _________________ • This class contains 2/3 of all known Annelids • Common species are _________________ , ___________________ , and

_____________________ • Have a well developed head with specialized sense organs

• Commonly called _____________________________ because…. o Have many ________________ (chitonous bristles secreted by the

epidermis)

o (Poly = many, chaeta= setae) o These setae are arranged in bundles on paddle-like appendages called

____________________ o The parapodia function in ______________________, locomotion, and

__________. • _____________________ (tagmosis): the fusion and specialization of formerly

metameric segments

• Many are ____________________ feeders with specialized structures • Many are __________________________ with specialized structures

• Many construct their own homes out of __________ (calcium carbonate), __________________, and _______________________.

• Reproduction

o Usually ___________________ o No permanent sex organs; gametes are shed into coelom where they

stay until time for fertilization o Fertilization is usually ___________________ in water o ________________ development à __________________ larvae

swims around until it grows into adult for by adding segments • Ecology

o Polychaetes often have effective defense strategies: Ø some have tubes to hide in Ø some have vicious jaws

Ø some have modified “stinging” setae o Some Polychaetes have a mutualistic relationship with their host

Ø For example, many scaleworms are found near, or in the mouth, of brittlestars, starfish, and sea urchins.

Ø The scaleworm eats its host’s leftovers and with its vicious jaws, it

will attack any predator trying to eat it’s host.

Class Oligochaeta Characteristics

• Earthworms are the most common • Habitats: __________________________, freshwater, and __________________ • Have few setae (“Oligo” = ________________, “chaeta” = setae • Usually feed on ___________________________ (decaying organic matter) • Depends on habitat, but they can feed on…

o Dead leaves and plant roots o Living things such as other worms, bacteria and fungi o Decomposing remains of other animals

• Do earthworms eat dirt? o Yes and n. o Earthworms ________________________ dirt as they burrow, so yes they swallow it. o HOWEVER, they do not get ______________________ from dirt. Their nutrients come

from decaying plant and animal remains that are in the dirt. • Earthworms have a specialized digestive system to obtain the maximum amount of nutrients out of

the detritus. o Example: pharynx, crop, gizzard, etc.

• Locomotion

o Circular muscles contraction o Longitudinal muscle contraction

• Reproduction o Usually ________________________ o Still have to have a partner o Cross-fertilize by exchanging _______________.

• Ecology o Earthworms are essential soil ___________________, meaning they allow

air to enter the soil. o Mix the soil with their tunnels. o Worm feces are great plant food = ____________________!

Class Hirudenia

• Includes ____________________. • Usually freshwater but there are some ____________________ and

terrestrial species. • No __________________ between metameres • No ___________________ or parapodia • Have two suckers • Have an extendable ____________________ for feeding • Usually have a fixed number of segments (34). Each metamere consists

of several annuli • Lack septa between metameres, so they are incapable of moving like

Oligochaetes. • Instead, they use their anterior and posterior suckers to move. • Reproduction

o usually _________________________ o cross-fertilize by exchanging sperm

• Ecology o Although some leeches are parasitic blood suckers (can be temporary or permanent), many

are predators. o Leeches have been used medicinally since the 19th century. o Currently they are used to increase blood flow following reconstructive surgery o _______________________ is a powerful anticoagulant that is found in the salivary

glands of leeches