Polychaetes and others
PLEASE READ and do feather dusters during this lab. Also look at
any spoon or peanut worms available and then do errant
polychaetes.
Most segmented worms found in marine environments represent a major
evolutionary branch of annelids--Class Polychaeta. The name means "many
bristles." The bristles, or setae, project from side flaps called "parapodia."
Parapods have a variety of shapes -- adaptations for different habitats and
life-styles. Species living in rocky environments have leg-like parapods used
in walking. In burrowing species, parapodia function as digging paddles. In
some worms the parapodia are short and combine with peristaltic
contractions to move the worm through the mud. In others, the parapodia
contract following their power stroke, streamlining the worm for passage
through the mud.
Sedentary Polychaetes
Sedentary polychaetes are usually adapted to living permanently in tubes or
burrows; some attach themselves to rocks or piers. Many sedentary
polychaetes, like the lugworm, Arenicola, live in burrows in sand or mud. The
majority, however, are tube builders. Tubes of different species vary greatly
in their composition and structure. They may be composed of sand, shell, or
other particles held together with mucus, or made entirely of organic
substances secreted by the worm that harden on contact with water. The
tubes may be straight, branched, spiraled, or U-shaped. Most are permanently
attached to a substrate, and the worm seldom or never ventures outside;
however, the tube worm Cistenides moves about the seafloor, dragging along
its delicate tube of sand grains. Sedentary polychaetes have greatly modified
head regions for specialized feeding habits. Many are adapted for feeding on
organic matter deposited on the ocean floor. For example, the lugworms have
a simple, thin-walled, jawless proboscis, which is used to draw sand into the
gut, where organic matter is removed. Other worms have feeding tentacles
that extend from the tube opening and creep along the mud or sand, picking
up organic deposits. Still others of the Sedentaria are filter feeders: the
beautiful feather-duster worms have a crown of feathery, ciliated tentacles
that extend from the tube opening to sweep small planktonic organisms from
the water. The tentacles are quickly withdrawn if the animal is startled. The
parapodia are reduced in the sedentary polychaetes, and the setae of many
tube-dwelling forms are hooked to help the worm hold itself to the wall of its
tube.
We have living representatives of the tube dwelling polychaetes. The
Sabellids are commonly known as "fanworms" or "feather duster"
worms due to a colorful appearance of a maroon or red-colored
tentacular branchial crown. They are indirect deposit-feeders. They have
no proboscis. While feeding they spread out their branchial crowns to trap
suspended particles and to sweep with their long mobile palps picking up
deposited material (filter-feeding). Only suitable sized particles are ingested
while others are rejected at the mouth. The more primitive sabellids
members making temporary mucus tubes and creep around actively. They
move either forward or backwards and they have 2 pairs of eyes, one at the
head and the other at the pygidium. Typical ones are tubiculous, relying
entirely on suspended food particles and living in tough tubes lined with
muco-protein and covered with mud, sand and general debris. The large ones
never leave their tubes and are associated with shallow water but smaller
ones are able to move around. and are common in deep seas.
1. Obtain a feather duster worm and place in a dish of sea water (Salt
water only please). Allow it to acclimatize to its new environment.
Study its feeding device under the stereoscope. A. Include a movie or
several photographs of its filter feeding in your notebook.
Worm in tube
The particles that land on the grooves can be
sorted with respect to size.
2. There may be other sedentary worms available for you to observe.
Obtain photographs. and compare the morphology of at least one other
specimen to the feather duster worms. Pay particular attention to the
head, which will tell you how these animals feed. For example, some
sedentary worms have long tentacles with groves on them. These act as
the “feathers” of a feather duster worm. The food particles are moved
along by cilia in these grooves toward the mouth.
An example of another type of sedentary worm we may have in the lab.
Spirorbis
In this genus and in the family Spirorbidae all species live in permanent
calcareous tubes cemented to algae, shells, or rocks. These have cemented
themselves to our filter in the large 60-gallon tank.
Obtain a few specimens of this microscopic worm and place them in a small
Petri dish so they can acclimatize to their new conditions. Be prepared to
watch them for a few minutes so you can see them unfurl their tentacular
crown.
Terrebellids or cirratulids (spaghetti (many feeding tentacles) or hair
worms (one pair of feeding tentacles))
We have hair worms in our tank. You can have your instructor put some
food in the tank and watch their feeding tentacles protrude in response .
Some of these also came in with the Bryosoans. We will see if we can
either scrap some off of our tank walls or see if those that came in with
the bryozoans are still alive, so that you can crack the tubes and so see
more of the external anatomy.
Terebellids are very complex animals, and have a body that may be
divided into three regions, a head, thorax, and abdomen. The head is
specialized for feeding and respiration, the thorax for moving in the
tube, and the abdomen for the digestion of food.
Cirratulids have a much more uniform body than do the terebellids.
Each segment looks much like the next, and while a head is present, the
remainder of the worm’s body is not divided into sections. There is
neither a thorax nor an abdomen. Additionally, the cirratulids found in
aquaria do not live in tubes but are found living free in the sediments
below the surface.
Errant Polychaetes
Errant polychaetes include actively crawling or swimming forms, which may,
however, also spend time in burrows or crevices, or under rocks on the
seashore. A familiar errant polychaete is the clamworm, Nereis, widely used
as bait. Errant polychaetes swim, crawl over the ocean bottom, or tunnel
through surface sediments. Many are predators on small invertebrates; some
are scavengers. In most the first few body segments bear sensory projections
called cirri, while the remaining body segments bear conspicuous leg like
appendages called parapodia. The parapodia, along with undulations of the
body, propel the worm in crawling and swimming; parapodia are tipped with
bundles of setae, usually made of chitin. Most errant polychaetes have welldeveloped head regions, which bear eyes, sensory tentacles, and a specialized
organ, the nuchal organ, thought to detect chemicals. The anterior end of the
gut often forms a protrusible structure, the proboscis, sometimes equipped
with strong chitinous jaws and used in feeding. The setae of some
polychaetes, e.g., the tropical fireworm, are composed of calcium carbonate
rather than chitin and are hollow. These brittle setae are easily broken off and
contain a toxin that produces a painful reaction in humans. In the
scaleworms, a series of overlapping scales form a covering over the animal's
upper surface. In the sea mouse these scales are completely covered by long,
slender, feltlike setae projecting from the parapodia.
3.. We will not know what representative of errant polychaetes we will have
until we prep Wednesday night and see what our supply houses have sent us.
We will also spend some time looking for representatives in our tanks.
Generally errant polychaeates are unwelcomed guests in our tanks, and so we
do not really encourage their presence. a. Please compare the overall
locomotion, morphology and any anatomy that may be apparent to that
seen in the earthworm or Lubirculus. Wear gloves when handing these
specimens, may have hairs on their body that can irritate your skin.
Obtain videos of any specimen in which you can clearly see circulation
and locomotion. You can try feeding your specimens. Please remember
to record your observations in your journal.
Other annelids???
4. Spoon worms.
Echiurans were included in the Annelida until recently. Your textbook is very
conservative and still includes them as class of Annelida. Even by those that
consider them a separate phylum, they are still considered close relatives of
the annelids. The body of an echiuran lacks annelid-type segmentation, but
the distinctive free-swimming trochophore larval stages of echiurans and
polychaetes are very similar. Your teaching instructor will set up the dish of
spoon worms under the microscope. a. Every one should take time to watch
these animals move and attempt to bury themselves again. b, If you are lucky
they may feed for you. Try fish food first, but black worms or liver may also
work. Watching that spoon unfold is a sight you will not forget. Please
remember to record your observations in your journal. Spoon and peanut
worms are animals you many never again encounter in your lives.
5. Peanut worms
Sipuncula -- These animals, which are commonly called "peanut worms"
because some have the general shape of shelled peanuts, are not particularly
well studied. Only about 320 species have been formally described, all marine
and mostly from shallow waters. While some (like the specimen of Sipunculus
shown below) burrow into sand and mud, others (like this unidentified
species from French Polynesia) live in crevices in rocks, or in empty shells.
Still others bore into rock. For instance, sipunculans have no trace of
important annelid characters such as segmentation and chaetae (bristles).
The characters they do share with annelids (e.g. worm shape, introvert,
trochophore larva) are not restricted to annelids and sipunculans, but are
much more general. These animals are now placed in a separate phylum, but
were once considered aberrant annelids. Now some believe they may even
be more closely related to mollusks. a. Obtain a peanut worm and watch it
move and feed. If possible take photographs or video its introvert.
Please remember to record your observations in your journal.
Spoonworm.
Peanut worm.