Lab 3 (Annelids and Echinoderms)

Question 1

What are the classes to the Phylum Annelida?

Answer 1

Class Polychaeta
Class Oligochaeta
Class Hirudinida

Question 2

Explain the basics to the Phylum Annelida

Answer 2

• Have adapted to marine, freshwater and terrestrial habitats
• Usually elongate, worm like animals
• Cross section would reveal a roughly tubular shape and a well muscled body wall
• Segmented bodies
• Metamerism is taken ti an extreme, where the internal and external structures are repeated nearly identically in each metamere
• Their coeloms are divided by septae (formed from peritoneum), which isolate the metameres internally
• Between each pair of septae is a fluid filled compartment that generates hydrostatic pressure, which contributes to locomotion
• This advanced skeleton combined with well developed muscles, makes for animals very proficient in coordinated digging, creeping and swimming movements

Question 3

What are metameres?

Answer 3

Repeated, homologous body segments

Question 4

What is metamerism?

Answer 4

The repetition of the homologous body segments

Question 5

Explain the basics to the class Polychaeta

Answer 5

• Clamworms
• Found only in oceans, living in burrows dug in sand or debris of shallow waters
• They are nocturnal, emerging from their burrows to hunt and prey on smaller organisms at night

Question 6

What is the support of the clamworms?

Answer 6

• The entire body is covered in a thick cuticle, which offers structural support and protection from the environment

Question 7

What is the feeding/digestion of the clamworms?

Answer 7

• Head is at the anterior end of the animal
• The head is comprised of two main regions
  1) the posterior region of the head is the peristomium (Contains the mouth and lacks the appendages found on the segments of the trunk. At rest, the mouthparts are typically converted and not visible)
  2) Posterior end the last segment is the anus
• The chitinous jaws indicate that this animal is a predator

Question 8

What is the sensory of the clamworms?

Answer 8

• The anterior region of the head is called the prostomium and can be recognized by the presence of numerous sensory structures
• The four eyes are small and dark coloured
• One pair of antennae is found at the anterior end of the prostomium, between the larger palps
• Long tentacles also line either side of the prostomium
• The antennae, tentacles and palps are used for touch and taste
• On the posterior end of the animal is a pair of cirri
• There are other sensory cirri on each of the appendages

Question 9

What is the locomotion of the clamworms?

Answer 9

• Every segment anterior to the peristomium has a pair of bristly lobed appendages (these are called parapodia)
• As individual parapodia undergo circular motions one at a time in a wave like fashion down the length of the body, the clam worms moves forward
• The entire body is well muscled and can undulate (this increases the speed at which the animal moves)
• The distal end of each lobe of the parapodium is equipped with a bundle of hair like bristles or setae
• A thick long chitinous spine called an aciculum is deeply embedded in each lobe, reaching all the way to the muscular body wall at the proximal end
• The acicula provide structural and mechanical support for the parapodia; the muscles to which they are attached are responsible for thrusting the acicula outward as the animal moves
• Cirri on either side of the lobes, are tactile sensory structures

Question 10

What is the respiration of the clamworms?

Answer 10

• The large combined surface area of the highly vascularized parapodia is where most gas exchange takes place

Question 11

What is the reproduction of the clamworms?

Answer 11

• They are dioecious and reproduce sexually but externally

- Mature clamworms leave their burrows in swarms and release their gametes into the water

Question 12

Explain the basics of the class oligochaeta

Answer 12

• Few setae
• Posses a structure called a clitellum
• Earthworms are common clitellates
• They are found in moist, rich soil
• Mostly nocturnal
• Forage for food at night
• Consume large amounts of soil, from which they extract nutrients from live and decaying plant material

Question 13

What is the external (general) of the earthworms?

Answer 13

• A segmented and metameric animal
• Covered by a thick cuticle
• It is rounded on one side and slightly flattened on the other (the latter is the ventral side)
• First four segments at the anterior end comprise the head (the first is the peristomium)
• The last segment (at the posterior ) bears the anus
• Thickened, saddle like clitellum is closest to the anterior end
• In mature worms, this structure secretes egg capsules into which eggs are laid

Question 14

What is the peristomium?

Answer 14

It contains the mouth, just like that of the Polychaeta

Question 15

What is the feeding/digestion of the earthworms?

Answer 15

• From the mouth (buccal cavity), food enters a thick, muscular pharynx and then moves into the esophagus
• Food then passes into a large, thin walled crop (similar to a stomach) where it is stored before it is passed to the muscular gizzard.
• Physical digestion (grinding) of the food takes place within the gizzard
• Ground up food is further digested and absorbed in the intestine (which runs posteriorly for the rest of the length of the body); solid waste is then finally passed out the anus

Question 16

What is the excretion of the earthworms?

Answer 16

• Each side of the body wall of each segment also contains a nephridium
• Essentially it is a “mini kidney” that is involved in waste excretion

Question 17

What is the circulatory/respiration of the earthworms?

Answer 17

• The esophagus is surrounded by the dark, circular aortic arches of the heart
• They have a closed circulatory system
• There are no respiratory organs; the slimy skin of the worm and its requirement for a damp environment are indications that it can diffuse oxygen and carbon dioxide directly through its skin into tiny capillaries underneath
• The dorsal vessel running along the top of the gut is muscular and is the main “pump” in the circulatory system
• The aortic arches of the heart ensure that blood flows into the ventral vessel and the capillaries on the ventral side

Question 17

What is the circulatory/respiration of the earthworms?

Answer 17

• The esophagus is surrounded by the dark, circular aortic arches of the heart
• They have a closed circulatory system
• There are no respiratory organs; the slimy skin of the worm and its requirement for a damp environment are indications that it can diffuse oxygen and carbon dioxide directly through its skin into tiny capillaries underneath
• The dorsal vessel running along the top of the gut is muscular and is the main “pump” in the circulatory system
• The aortic arches of the heart ensure that blood flows into the ventral vessel and the capillaries on the ventral side

Question 18

What is the reproduction of the earthworms?

Answer 18

• They are monoecious
• Cross fertilization occurs during copulation
• The male seminal vesicles (where sperm are stored and where they mature before copulation) are the most prominent reproductive organs and are found lying on either side of the esophagus
• The testes (where sperm is produced) are concealed inside the vesicles
• Lateral to and slightly beneath the anterior lobes of the seminal vesicles are 2 pairs of round seminal receptacles (these are female organs that store sperm after copulation)
• The ovaries (where eggs are produced) and the sperm ducts (through which sperm are voided from the body) are beneath the posterior lobes of the seminal vesicles
• During copulation, sperm are ejected from the sperm ducts of one animal and are taken up into the seminal receptacles of the other
• The clitellum secretes a cocoon, or egg case, which is slipped off the anterior end of the worm
• As the cocoon passes over the genital pores, eggs and sperm are released into it (fertilization occurs here)
• The cocoon is then deposited on the ground and the young hatch in a few weeks

Question 19

What is the nervous/sensory of the earthworms?

Answer 19

• The ventral nerve cord lies below the intestine

- It runs the length of the body and connects to the cerebral ganglia in the head (found lying on top of the pharynx)

Question 20

What is the movement/locomotion of the earthworms?

Answer 20

• The outer margins of the body are lined with two layers of muscle
• The outer layer consists of circular muscles that wrap around the body (contractions change the body’s circumference)
• Underneath, longitudinal muscles run from the head to tail (contractions shorten the body)
• Setae on the ventral surface of the animal grip the soil as it pulls itself forward

Question 21

Explain the basics of the class hirudinida

Answer 21

• Leech
• Predaceous blood suckers that attach themselves to a host during feeding
• Freshwater animals (they feed on the blood of amphibians and mammals)
• Leech saliva contains anticoagulants that prevent blood form clotting and analgesics (that keep the host from being aware of its activity)
• Still used for medicinal purposes, such as to reduce blood in hematomas and promote blood flow at surgical sites
• They have segmented bodies
• Each segment is subdivided into 1 to 5 smaller segments called annuli
• The clitellum is only visible when the leech is fully reproductive (the pale segments on the upper portion of the body constitute the clitellum)
• The internal anatomy is similar to that of the earthworm

Question 22

What is the feeding of the leeches?

Answer 22

• The anterior end possess the oral sucker, which bears the mouth
• the mouths of many species of leeches are equipped with numerous tiny sharp teeth to grasp the prey and promote blood flow
• The head bears many specialized sensory cells used to locate prey, including chemoreceptors and in many cases eye spots (ocelli)

Question 23

What is the locomotion of the leeches?

Answer 23

• The posterior end end bears the caudal (tail) sucker
• The caudal sucker is not involved directly in feeding
• It helps anchor the animal and assists in locomotion
• To move, the oral sucker attaches and the body contracts
• the caudal sucker then attaches, and the body extends forward and the oral sucker attaches anew

Question 24

What is the reproduction of the leeches?

Answer 24

• The male and female genital pores may be visible on the ventral surface
• Leeches are monoecious
• They reproduce like earthworms (cross fertilization and the production of cocoons via the clitellum)

Question 25

What are the classes to the Phylum Echinodermata?

Answer 25

Class Asteroidea
Class Echinoidea
Class Holothuroidea

Question 26

What is the Phylum Echinodermata?

Answer 26

• Exclusively marine animals
• Sea starts, sea urchins, sand dollars, sea cucumbers
• Spiny skin
• Dermal endoskeleton of calcareous plates and spines, which are fused into a full body armour in some animals
• Deviate from the bilateral body plan
• The larvae (immature stage) of echinoderms are bilaterally symmetrical
• Adults display pentaradial symmetry
• Adult echinoderms have no posterior or anterior sides, only oral and aboral surfaces
• They possess a water vascular system, a type of hydraulic system with canals that channel water into tiny tube feet, which are used in movement and feeding
• They have no head, a poorly developed nervous system with no centralized brain, no true circulatory system, mediocre locomotory abilities, no segmentation and gas exchange is through the skin

Question 27

Explain the basics to the class Asteroidea

Answer 27

• Sea stars
• They have a star shaped body
• Commonly reside in rocky intertidal zones; others live at great depths
• Some are particle feeders, but most are predators of slow moving prey such as molluscs, corals, and other echinoderms

Question 28

What is the external (general) of the sea stars?

Answer 28

• The body consists of a central disk and five arms
• On the distal end of each arm are tiny tentacles and an eyespot (these are sensory, tactile and visual)
• The mouth is an opening at the centre of one side of the body. This is oral surface
• There are tube feet along the ambulacral groove on the oral surface of each arm
• The central disk is in the middle of the aboral surface
• On one edge of the disk, there’s a small, round, whitish, porous madreporite (it will be near the junction where two of the arms meet)
• The madreporite is the surface through which sea water enters the water vascular system

Question 29

What is the structure/defence of the sea stars?

Answer 29

• There are white, hard, calcareous spines extruding through the skin
• These are extensions of dermal ossicles

Question 30

What is the feeding/digestion of the sea stars?

Answer 30

• The stomach fills the central disk and has two sections
• The uppermost section (on the aboral side) is the pyloric stomach
• From the pyloric stomach, a duct extends into each arm, where it connects with the pyloric cecae (these are digestive glands, essentially the liver), which are the large, dark, conspicuous organs on each arm
• A short intestine leads from the pyloric stomach to the rectum; the anus pomes to the aboral side of the central disk
• Below the pyloric stomach is the much larger second section, the cardiac stomach
• When eating its favourite food (bivalves), the sea star uses it arms to hold the valves if its prey open and near its mouth
• The sea star then everts its stomach and pokes it between the opened valves (enzymes released from the pyloric cecae begin to digest the soft tissues of the prey)
• Partly digested material is drawn into the stomach, where digestion is completed (muscles then bring the stomach back to its normal position inside the central disk)
• Solid waste is ejected from the anus
• There are no kidneys or kidney like structures in these animals

Question 31

What is the reproduction of the sea stars?

Answer 31

• With the digestive glands removed, there will be a pair of gonads visible in each arm
• They are paler, softer and usually shorter than the cecae
• Sea stars are dioecious
• Each gonad opens to the exterior via a tiny duct and genital pore on the surface of the central disk (masses of eggs and sperm are released and fertilization occurs externally)

Question 32

What is the movement/locomotion of the sea stars?

Answer 32

• The arm (once dissected) should display 2 rows of very small,, transparent, round ampullae (they are divided by a bony ambulacral ridge and are directly connected to the tube feet)
• If the ambulacral ridge is removed, the ampullae are shown (which are connected to a single radial canal, which in turn connects to a ring canal which encircles the stomach)
• The madreporite is connected to the ring canal
• These structures are all part of the water vascular system
• Water makes it way through the plate, into the canals and into the ampullae
• Contractions of the ampullae force water into the tube feet, making them elongate
• The ends of the tube feet are cup shaped (if they come in contact with a hard surface, suction force allows them to attach)
• Individual feet are not very strong, but working together, the suction can be used to pull the animal forward at a rate of about 15cm per min

Question 33

Explain the basics to the class Echinoidea

Answer 33

• Sea urchins
• They lack arms, and their body is enclosed in a globose shell (test) of interlocking calcareous plates that is covered in moveable spines
• They bear pentaradial symmetry, dermal endoskeleton and water vascular system

Question 34

What is the external (general) of the sea urchins?

Answer 34

• Mostly herbivores
• They scrape algae from rock surfaces, munch on leaves or trap drifting plant material
• They have long spines (which may have broken on your dried specimen) that offer substantial protection from many types of predators
• The tube feet all originate from rows of pores in the ambulacral region
• Both the spines and the tube feet are involved in locomotion
• The mouth is on the oral surface and the anus on the aboral surface

Question 35

Explain the basics of the class Holothuroidea

Answer 35

• Sea cucumbers
• It has elongated, tubular, leathery, bumpy body and no arms
• They have pentaradial symmetry and a dermal endoskeleton
• Slow moving, bottom dwelling scavengers that feed on plankton and organic debris

Question 36

What is the movement/locomotion of sea cucumbers?

Answer 36

• The flattened side contains three ambulacral regions with well developed tube feet
• The other side is rounded, and has the other two ambulacra, with smaller tube feet
• The flattened, well footed side is that which moves along the substrate

Question 37

What is the feeding/digestion of sea cucumbers?

Answer 37

• The mouth, an opening at the oral surface, is encircled by tentacles
• These extensible tentacles are modified tube feet and are therefore also part of the water vascular system
• Some species use their tentacles for filter feeding (others use them to shovel mud and sand directly into the mouth)
• The anus is found at the opposite end, on the aboral surface

Question 38

What is the support/defence of sea cucumbers?

Answer 38

The hard endoskeleton of the sea cucumber is not visible to the naked eye (the skin is embedded with tiny calcareous dermal ossicles)