Transcript Urechis caupo
Phylum Annelida: summary of
Name from Latin annulus meaning a ring.
Vermiform. Possess tissues and organs.
Muscular gut with mouth and anus.
Body divided into segments.
Outer epithelium with clumps of bristles (except in forms
with suckers). May be covered with a cuticle.
Body wall muscular with both circular and longitudinal
Closed circulatory system.
Nervous system with supraoesophageal ganglion,
circum-oesophageal ring and ventral nerve cord.
Nephridia responsible for most excretion
The annelids (L. annelus: a little ring) are the
Annelids are coelomate, protostomes and the
body is metameric being composed of serially
repeated segments or metameres.
Each segment is separate from the next
segments being divided by partitions or septa.
each segment are components of
most organ systems such as the
circulatory, nervous and excretory
there is a degree of redundancy in
annelids so that if a segment is damaged it
need not be fatal.
evolution of segmentation is the great
evolutionary innovation of the annelids.
allows annelids to make
more precise body movements than
organisms that have a hydrostatic
skeleton, but lack segmentation e.g. the
Because the coelom is divided by septa the
force of muscle contraction in a segment is not
transmitted throughout the body, but instead is
confined to the single segment.
Thus, one segment may elongate while the
adjacent one contracts and this allows the
animal to make fine, controlled movements.
With the exception of the leeches, the coelom is
filled with fluid and acts as a hydrostatic
Annelids possess circular and longitudinal
muscles and this enables individual segment to
be elongated or contracted.
Crawling is achieved by alternating waves of
contraction by circular and longitudinal muscles
passing down the body (peristalsis).
Because they have fine control of movement
annelids have evolved a relatively sophisticated
Most annelids are burrowing forms and as an
adaptation to this lifestyle bear short chitinous
bristles called setae on each segment. The
setae enable the annelid to gain traction against
the side of the burrow.
other annelids longer hair-like setae
assist the animal in swimming.
the annelids that live in burrows or in
tubes the setae help to prevent the animal
from being pulled out.
occur worldwide being found in
the sea, freshwater, and in the soil.
feed on organic matter in the mud or
soil, by filtering suspended particles from
the water, act as predators, or suck blood.
The typical annelid body has a two part head
made up of a prostomium and a peristomium, a
series of segments, and a terminal pygidium
which contains the anus.
Neither the head nor the pygidium are
considered true segments. In growth, new
segments form anterior to the pygidium. If an
annelid is cut in two the posterior segments can
are approximately 12,000-15,000
species of annelids divided into 4 classes:
Polychaeta: polychaete worms
polychaetes are the largest of the
annelid classes and include more than
10,000 described species, most of which
are marine. Morphologically very diverse.
name “poly” “chaete” refers to the
numerous chaetae or bristles they
have a well differentiated
head that has sense organs including eyes
and cirri (short tentacles), jaws (in
predatory forms), or a fan for filter feeding.
segments bear parapodia, which are
lobed structures used in swimming,
crawling, or for anchorage in tubes.
Parapodia also serve as gills.
Polychaetes follow one of two basic lifestyles being
either sedentary/sediment burrowing (“sedentary”) or
active hunting (“errant”) species.
Sedentary polychaetes usually exhibit variation in the
structure of segments. All are filter-feeders or deposit
Sedentary polychaetes burrow in mud and soil or build
their own tubes from which they filter feed.
Tubes may be made from calcium carbonate, a secreted
paper-like material, or sand grains.
of the sedentary polychaetes, which
inhabit burrows or build tubes, are filter
feeders and consume plankton or detritus.
such as fanworms extend long,
modified feathery crowns of stiff prostomial
tentacles to feed. Ciliary action draws in
food, which is trapped in mucus and
delivered down grooves to the mouth.
A number of families of sedentary polychaetes
burrow in soft sediments either swallowing
sediment or scraping it of bacteria, algae, fungi
and other live material.
Many functionally resemble oligochaetes and
have reduced parapodia, lack prominent sense
organs and have well developed circular muscles
Some have soft prehensile tentacles they use
collect food particles.
polychaetes such as lugworms
are very common on estuaries.
make burrows in the sand and
consume large quantities of sand. After
they’ve extracted the digestible material
the remaining material is defecated and
forms a characteristic pile outside the
Lugworm (two images above) from
Above right Lugworm casts.
are an important source of food
for wading birds.
forms of polychaetes such as
Nereis have a muscular pharynx equipped
with jaws that can be quickly everted to
Bobbit worm a predatory polychaete.
polychaetes typically can crawl
rapidly using their parapodia.
are active hunters that can sqeeze
through small spaces (e.g. in coral,
crevices, etc.) is search of prey.
consume any other invertebrates
that they can catch and dismember.
are over 3000 species of
oligochaetes, the most familiar of which
are the earthworms.
terrestris, the common
earthworm, grows from 4-12 inches, but
tropical forms may reach 12 feet in length.
burrow in rich, damp soil and
leave their burrows at night to eat
vegetation and to breed.
play a significant role in soil
fertility by aerating the soil with their
burrows, adding vegetable material, and
mixing subsoil and topsoil.
Darwin studied earthworms and published a book on
their effects on soil.
He estimated that an earthworm eats its own weight in
soil daily and that in an acre of land 10-18 tons of dry soil
passed through their guts annually.
Earthworms consume dead organic material and partially
digest it, the waste passing out of them containing
nutrients valuable to plants and supplemented with
nitrogenous wastes from the worm.
In addition to the earthworms there are many
freshwater species, most of which burrow in silt
and mud or creep along the bottom, although
some live among submerged vegetation.
Freshwater forms usually are smaller than
terrestrial and have more conspicuous setae.
Most respire through their skins, but some have
gills. Most are algae or detritus feeders.
like all annelids, have a
double circulatory system as both the
coelomic fluid and circulatory system are
used to carry food, wastes and gases.
blood system is closed, with the
dorsal blood vessel being the main
The excretory organs are called nephridia and
there is a pair in each segment, each of which
occupies parts of two successive segments.
A ciliated funnel (the nephrostome) opens just
anterior of an intersegmental septum and from
this a tubule leads into the posterior segment
and forms a series of loops that are closely
surrounded by blood vessels.
tubule eventually opens to the outside
via an aperture called a nephridiopore.
system works by cilia drawing
coelomic fluid into the nephrostome and
selective reabsorbtion of salts and water
occurs in the loops leaving only a dilute
urine to be excreted to the outside.
Reproduction in earthworms
are hermaphroditic and mate
by aligning their ventral surfaces together.
Each worm’s clitellum (thickened section
of some midbody segments) secretes
mucus, which holds the two worms
Sperm is exchanged and stored in a
Reproduction in earthworms
After sperm has been exchanged the worms
separate and each secretes a cocoon around its
clitelleum. The cocoon slides along the body
and picks up eggs and sperm.
Fertilization occurs within the cocoon as does
later embryonic development.
As the cocoon slides off the worm its ends seal.
Young worms emerge several weeks later.
are more than 500 species of
leeches, most of which are freshwater
have anterior and posterior
suckers which they use in locomotion.
With the exception of one group, leeches
lack septae and their coelom is largely
filled with connective tissue and muscle.
Many leeches are carnivorous, but leeches are
best known as blood-sucking ectoparasites.
The leech penetrates its host using its jaws or
proboscis and sucks blood with its powerful
To ensure blood continues to flow the leech
secretes a powerful anticoagulant (hirudin) in its
World’s largest leech
hundreds of years leeches were used
for blood letting, in the belief that too much
blood caused a variety of medical
being discarded as a medical tool
leeches are again being used by
reattachments of severed digits and in
the case of skin grafts, because the blood
vessels are damaged, pooling of blood
often threatens to kill the attached tissue.
however, can remove the
pooling blood safely allowing time for veins
Medicinal leech feeding
pogonophorans (or beardworms)
were formerly considered to be a phylum,
but now are considered to be derived from
were first discovered during deep
sea dredging in 1900 off Indonesia, but
since then about 80 species have been
identified in seas worldwide.
similar to tube dwelling polychaetes,
the first pogonophorans were considered
to be a separate group because they lack
a complete gut and appeared not to be
The lack of segmentation proved to be illusory.
Pogonophorans live buried in the mud and their
lower ends were broken off when collected
In 1964 complete pogonophorans were dredged
up and it was discovered that the posterior end
of pogonophorans (called the opisthosoma) is
segmented and bears setae.
siboglinids live in the mud and silt of
the seafloor usually at depths > 200m.
body is divided into a short forepart,
which bears tentacles, a long, slender
trunk, and the small segmented
opisthosoma. The body is covered with a
cuticle and has setae on the trunk and
Because siboglinids have no mouth or complete gut it’s
unclear how they obtain nutrition.
They absorb some nutrients in the water through their
tentacles, but most energy apparently is derived from a
mutualistic association with chemoautotrophic bacteria.
The bacteria oxidize hydrogen sulfide to produce energy
and live in an expanded section of the midgut called a
trophosome. There is no foregut or hindgut.
The Echiura (from Greek -- echis: a viper and ura: a tail) are
worms that are closely related to the Annelids.
Like annelids thay have a trochophore larva, but differ from
the annelids in being unsegmented.
They are widely distributed in shallow marine benthic habitats.
Possess a characteristic extensible proboscis (used in
feeding on detritus) and a set of small hooks or spines on the
Echiurans live in permanent burrows in soft sediments. Most
are unselective detritus feeders
Urechis caupo the “innkeeper worm” is a common
inhabitant of mudflats along the coast of California.
It builds and lives permanently in a U-shaped burrow and
it uses a mucus net secreted by its proboscis to trap
plankton in water it draws through its burrow.
Urechis is called the "innkeeper worm" because many
marine organisms, such as small crustaceans,
polychaete worms and fish, live commensally inside its
Urechis caupo the Innkeeper worm
The Phylum Sipuncula (from Latin: meaning
“little pipe”) consists of approximately 250
species of benthic, marine worms, most from 1530 cm in length.
Sometimes referred to as the “peanut worms”
most burrow in sand or silt or occupy crevices or
empty mollusc shells or worm tubes.
The body is unsegmented and divided into an
anterior introvert and a posterior trunk.
Like the Echiurans the sipunculids are generally
non-selective deposit feeders and they use the
tentacles surrounding the tip of the introvert to
They produce a trochophore larva similar in
structure to that of the annelids.