Download Chapter 27: Mollusks and Annelids

Chapter 27: Mollusks and Annelids
Section 2: Annelids
Annelids

The soft-bodied earthworm is the most common terrestrial, or land-dwelling,
segmented worm

There are approximately ___________________ species of segmented worms
that live in moist soil, in fresh water, and in the sea

Segmented worms, or _______________________________, live just about
everywhere in the world
What Is an Annelid?

Phylum ____________________________

An annelid is a round, wormlike animal that has a long, segmented body

Annelids range in size from tiny aquatic worms less than half a millimeter long to
giant earthworms more than 3 meters long

Annelids also vary greatly in color, patterning, number of bristles, and other
superficial features
Form and Function in Annelids

The many segments of an annelid’s body are separated by internal walls called
____________________

Most of the body segments are virtually identical to one another

However, some segments are modified to perform special functions

For example, the first few segments may carry one or more pairs of ___________,
several pairs of _____________________________, and other _______________
_____________________
Feeding

The digestive tract extends from the ____________________ to the
______________

Food enters through the mouth and travels through the gut, where it is
___________________________

Like mollusks, annelids have evolved structures and behaviors that allow them to
use a wide variety of foods

One feeding organ that has evolved many different forms in different groups of
annelids is the __________________________, or the muscular front end of the
digestive tube

Many annelids can extend the pharynx through the mouth

In carnivorous annelids, this type of pharynx usually has two or more
_________________________________ attached to it

When a suitable animal approaches, the worm lunges forward, rapidly extends the
pharynx, and grabs the prey with its jaws

When the pharynx returns to its normal position, it carries the food back to the
___________________
Respiration

Aquatic annelids often breathe through __________________

Terrestrial annelids take in oxygen and give off carbon dioxide through their
____________________

Because the skin must stay moist to make gas exchange possible, _____________
__________________________________________________________________

To help guard against this, terrestrial annelids, such as earthworms, secrete a thin
protective coating called a _______________________ to hold moisture around
them
Internal Transport

Annelids typically have ______________________________________________
organized around two blood vessels that run the length of their bodies

In each body segment is a pair of smaller vessels called _____________________
____________________________ that connect the two main blood vessels and
supply blood to the internal organs

In annelids such as earthworms, several of the ring vessels near the anterior end of
the worm are larger than the other ring vessels and have muscle tissue in their
walls
o These vessels are often called ______________________ because they
contract rhythmically and help pump blood through the system
Excretion

Annelids produce two kinds of wastes
o __________________________________ pass out through the anus at the
end of the gut
o Wastes resulting from cellular metabolism are eliminated by
_______________________________

A pair of nephridia in each body segment removes waste products
from the body fluids and carries them to the outside
Response

Many annelids are active animals with __________________________________
____________________________

The ______________________ sits on top of the gut at the front end of the body

Two large nerves pass around the gut and connect the brain with a pair of ganglia
below

From these ganglia, a ventral nerve cord runs the entire length of the worm

Nerves from each segment of the worm enter and leave the nerve cord at a pair of
small ganglia

These nerves help carry messages from sense organs and coordinate the
movements of muscles

Sense organs are best developed in the __________________________________
__________________________________ of annelids
o Have sensory tentacles, statocysts, chemical receptors, and two or more
pairs of eyes

Many other annelids have much simpler sensory systems
o Earthworms have no specialized sense organs
o They rely on simple sensory cells in the skin
Movement

Annelids have ______________________________________________________
in their body walls
o ___________________________________ muscles

Runs from the ___________________ of the worm to the
__________________

When contracted, they make the worm ______________________
o _____________________________ muscles

Runs in circles around the body of the worm

When contracted, they make the worm ______________________
Reproduction

Most annelids reproduce _________________________________

In some annelids, the sexes are separate

However, annelids such as earthworms and leeches are hermaphrodites that
undergo ____________________________________________

Although an individual worm produces both sperm and eggs, it rarely fertilizes its
own eggs

Instead, worms pair up, attach themselves to each other, and exchange sperm

Each worm stores the sperm it has received in special sacs

When eggs are ready for fertilization, a band of thickened, specialized segments
called the _______________________________ secretes a mucus ring into which
eggs and sperm are released

The ring then slips off the worm’s body and forms a _______________________
that shelters the eggs
Sandworms, Bloodworms, and Their Relatives

Class ______________________________________
o Common and important marine worms
o Polychaetes are characterized by paired paddle like appendages on their
body segments
o These appendages are tipped with _________________________
o Polychaetes live in cracks and crevices in coral reefs, in sand, mud, and
poles of rocks, and even out in the open water
Earthworms and Their Relatives

Class ___________________________________
o Contains earthworms and related species
o Oligochaetes are annelid worms that live in soil and open water
o Most oligochaetes live in soil or freshwater
o Oligochaetes have fewer bristles than polychaetes
Leeches

Class ___________________________
o Contains the _________________________, most of which live in
tropical countries
o Freshwater organisms that exist as external ________________________,
drinking blood and body fluids from their host
o All leeches have powerful suckers at both ends of their bodies
o These suckers are used to attach a leech to its host

Leeches penetrate the skin of their host in one of two ways
o Use a muscular _____________________________

Tubular organ that they force into the tissue of their host
o Use razor sharp ___________________

Once the wound has been made, the leech uses its muscular
pharynx to suck blood from the area

Both types of leeches release a special secretion from their salivary glands to
prevent _______________________________________________________ as
they drink it

Some leeches also produce a substance that ______________________________
the wound – thus keeping the host from knowing it has been bitten

During feeding, a leech can swallow as much as ____________________ its
weight in blood
o Can take up to _____________________ to digest
o A leech can live for a _____________________ before it must feed again
How Annelids Fit into the World

Important in many habitats
o Aquatic species are food for many fish, crab, and lobster
o Earthworms perform an essential task in ___________________________
___________________

By constantly burrowing through the ground, they help
_______________________ the soil

Without the efforts of these annelids, the structure and fertility of
farm soils would degenerate quickly, lowering ________________
______________________