Practical Lab 3 Kingdom Animalia - Invertebrates

Body Plan in Higher Animals

• During the early stages of an animal's development, the growing embryo forms three distinct layers of cells - the germ layers

• Ectoderm: covers the embryo surface, develops into the animal’s skin (outermost layer) and, in some types of animals, also forms the central nervous system

• Endoderm: the innermost layer, lines the primitive gut, and gives rise to the lining of the digestive tract and its out-pocketings like the liver and lungs of vertebrates

• Mesoderm: between the ectoderm and endoderm, forms the muscles and most of the other organs between the gut and outer covering of the animal

Body Plan in Higher Animals

• There are three ways bodies can be organized around the cellular (germ) layers.

• 1) The simplest organization (seen in the flatworms - Platyhelminthes) is the acoelomate body plan.

• In this body plan, there is no cavity between the digestive tract and outer body wall, this space is filled with mesodermal parenchyma cells

Body Plan in Higher Animals

• 2) The pseudocoelomate body plan (seen in roundworms – Nematoda)

• This body plan has a fluid filled cavity called the pseudocoelom, between the digestive tract and outer body wall.

• There is a layer of mesoderm underneath the outer body wall.

• But there is no mesoderm surrounding the organs so the cavity is not completely lined by mesoderm.

• The internal organs of pseudocoelomate animals are found free the pseudocoelom.

• This arrangement is known as a “tube-within-a- tube” body plan.

Body Plan in Higher Animals

• 3) The coelomate body plan (seen in Earthworms)

• Coelomates have the body cavity (the coelom) completely lined by mesoderm.

• There is a layer of mesoderm underneath the outer body wall and there is another layer surrounding the organs

• The two layers of mesoderm connect dorsally and ventrally to form mesenteries that suspend the internal organs in the coelom.

Phylum Nematoda - Roundworms

• Roundworms have two morphological advances that flatworms don’t have:

• 1) In addition to their digestive cavity, roundworms have a body cavity called a pseudocoelom consisting of a fluid-filled space between the outer body wall and digestive tract.

• 2) They have a complete digestive tract with a
  mouth and an anus.

Phylum Nematoda (Roundworms) - Ascaris lumbricoides

• The larger animals, with straight tails, are females.

• The thinner animals, with hooked tails, are males

• At the anterior end, the mouth is surrounded by three lobes (lips) of tissue

• At the posterior end, locate the anus.

• Normally, the three lobes (lips) can be used to help you distinguish the anterior from the posterior end of the animal

Phylum Nematoda (Roundworms) - Ascaris lumbricoides

• Locate the muscular pharynx, just behind the mouth

• The intestine will appear as a thin ribbon-like structure that extends from the mouth to the anus

Feeding and Digestion in Nematoda (Roundworms)

• The mouth opens into a muscular pharynx, a pump to bring food from the mouth into the intestine

• From the pharynx, the intestine travels the length of the body to the anus (the intestine starts from the pharynx, a part of the throat, and extends all the way down through the body until it reaches the anus, where waste is expelled)

Respiration and Circulation in Nematoda

• Nematoda live in interstitial spaces of aquatic sediments and soils

• this means that these animals mostly live in the tiny spaces between grains of sand, mud, or soil in water or on land.

Reproduction in Nematoda

• Males and females live in the intestines of humans where they graze on the intestinal contents

• Eggs are excreted with feces, and if they contaminate food, they can be ingested by another host. The larvae hatch in the new host's intestine and burrow through the intestinal walls, entering the bloodstream. From there, they travel to the lungs. In the lungs, they burrow through the air sacs (alveoli) and move up the trachea and down the esophagus. Sometimes, the larvae go the wrong way and crawl up the esophagus, exiting through the nose

Female Ascaris sp. (Phylum Nematoda - Roundworms)

• A genital pore may be visible

• The genital pore is connected to a short vagina.

• The vagina divides into two uteri.

• At the end of each uterine segment, a thin oviduct can be seen, followed by the ovaries.

• Eggs are produced by meiosis within the ovaries, and move along the oviducts to the uterus.

• Fertilization of the eggs occurs in the uterus.

Male Ascaris sp. (Phylum Nematoda - Roundworms)

• The anus serves both an excretory and a reproductive function in males.

• The copulatory spicule (a hook-like appendage used to hold the female’s genital pore open) should be seen at the edge of the anus.

• At the posterior end of the intestine is the cloaca (which is connected to the anus on the outside).

• The cloaca is a common collecting area for fecal material from the intestine and spermatozoa from the seminal vesicle (the thick organ connected to the intestine at the cloaca)

Male Ascaris sp.

• The thick tubes associated with the seminal vesicle are the sperm ducts or vas deferens.

• The finest of the threads are the testes.

• Sperm cells are produced in the testes, and they mature as they move along the vas deferens to the seminal vesicle.

• During copulation, the sperm enter the cloaca before being deposited in the female.

• Nematode sperm are unusual because they are amoeboid, not flagellated.

Phylum Annelida (Earthworms)

• Annelids include a variety of marine, freshwater, and terrestrial worms including leeches and earthworms.

• The most distinctive feature is the division of their bodies into rings or segments (Latin annullus = little ring).

• This type of body segmentation is called metamerism

Phylum Annelida

• metamerism is evident in the external features of the worms, which accounts for their common name, the segmented worms.

• most annelids also show internal metamerism with the division of the body into compartments by regularly repeated septa (walls) and by the repetitive arrangement of organs and organ systems

Phylum Annelida

• Annelids are more advanced than Nematodes (roundworms).

• They have a true coelom, fully lined with a layer of mesodermal epithelium called the peritoneum.

• They have a more centralized nervous system and a closed circulatory system.

• Most annelids also have setae, which are small, bristle-like appendages.

• The Phylum Annelida is subdivided into four classes: Oligochaeta, Polychaeta, Hirudinea, and Archiannelida (OPHA)

External Anatomy of the Earthworm (Lumbricus terrestris)

• The most noticeable feature is the clitellum, on the dorsal surface.

• The clitellum produces a mucus sheath that surrounds the worms during mating and makes the cocoon within which fertilized eggs are deposited.

• The anterior of the animal is more cylindrical than the flattened posterior and is the closest to the clitellum.

External Anatomy of the Earthworm (Lumbricus terrestris)

• The ventral surface of the earthworm is usually a lighter colour than the dorsal surface.

• The mouth is located on the ventral surface of the first segment while the anus is found at the end of the last segment

• Bristle-like setae: used for locomotion.

Internal Anatomy of the Earthworm - Digestive System

• The muscular pharynx (food ingestion) is at the anterior end.

• This is followed by a tube-like esophagus which terminates in a crop (the wider organ).

• The crop serves as a storage stomach

Internal Anatomy of the Earthworm - Digestive System

• The gizzard is posterior to the crop

• The crop is soft and thin and the gizzard is muscular (soil is ground up and churned within the gizzard).

• The gizzard is followed by a long intestine in which digestion and absorption occur

• On the dorsal surface of the intestine is the typhlosole which increases surface area for absorption

Internal Anatomy of the Earthworm - Excretory System

• Nephridia are the excretory organs and remove fluids and wastes from both tissue fluids and blood.

• A network of blood capillaries surrounds the nephridia and works in the exchange of materials, removal of wastes, and re-absorption of water and other useful materials.

• This exchange occurs between the nephridia and the blood.

• The nephridia leads to a bladder and materials exit the body through a small nephridiopore

Internal Anatomy of the Earthworm - Respiratory and Circulatory Systems

• All annelids live in moist environments, most are aquatic.

• Even the earthworm can survive only in damp soil

• Internal transport in annelids is performed by the coelomic fluid which is moved around by contractions of the body wall musculature and, in the most segmented worms, by a closed circulatory system.

• To enhance the capacity of the blood or coelomic fluid to carry oxygen, these fluids may contain respiratory pigments.

• In the annelids the respiratory pigment is hemoglobin, which can either be contained within cells or be in solution in the blood

Internal Anatomy of the Earthworm - Respiratory and Circulatory Systems

• There are five pairs of pseudohearts surrounding the esophagus: The pseudohearts look like black rings on the dissected specimen.

• The blood in the dorsal vessel flows anteriorly (forward).

• It is pumped downward by five pairs of the pseudohearts to the ventral blood vessel.

• The blood in the ventral blood vessel flows posteriorly

Internal Anatomy of the Earthworm - Reproductive System

• Earthworms are hermaphrodites with male and female reproductive organs present in each individual, but they cross fertilize.

• Two earthworms mate by attaching at their clitella and exchanging sperm, and then they separate.

• The received sperm cells are temporarily stored in sperm receptacles while the clitellum secretes a mucous cocoon.

• The cocoon slides along the worm, picking up the eggs, which are produced in ovaries, and then the stored sperm.

• Finally, the cocoon slips off the worm's head. The embryos develop within the cocoon

Internal Anatomy of the Earthworm - Reproductive System

• The reproductive structures of the earthworm start at segment nine.

• The seminal receptacles (bulb-like organs in segments nine and ten) are where sperm cells received from another worm are stored.

• Three pairs of whitish seminal vesicles (segments 9-12) should also be very visible.

Internal Anatomy of the Earthworm - Reproductive System

• Sperm are produced within testes located inside the seminal vesicles and transferred to the male genital pore or gonophores through the vas deferens

• The female reproductive structures consist of a pair of ovaries (segment 13) connected to the female genital pore or gonophores via a series of small passageways
  

External Anatomy of the Clamworm - Phylum Annelida (Nereis sp.)

• The clamworm is a marine organism, living in sediment

• They have segmented bodies and each segment has a parapodia

• Protruding from the parapodia are many setae from which the class derives its name (poly-many, chaeta-setae)

Internal Anatomy of the Clamworm - Digestive System

• It is carnivorous (Lumbricus is herbivorous)

• The mouth and jaws are retractable and are used to capture small animals

• The mouth opens into the muscular pharynx, which leads to the esophagus

• Lateral to the esophagus are two esophageal caeca (singular, caecum).

• Posterior to the esophagus is the stomach-intestine.
  

Internal Anatomy of the Clamworm - Respiratory and Circulatory Systems

• Each body segment of the clamworm has a pair of lateral parapodia.

• They can be used as legs in crawling or as oars for swimming.

• The parapodia have a large surface area, are well vascularized with blood vessels, and are the major sites of gas exchange

• The movement of the parapodia keeps fresh water with a high oxygen concentration constantly moving over the respiratory surface.

• Parapodia can be considered primitive gills

Phylum Arthropoda

• Arthropods can be found literally anywhere

• Their success is due to a rigid external skeleton and jointed appendages (arthro = jointed; poda = foot) that are used for locomotion, feeding, reproduction, defence, and sensing the environment

External Anatomy of the Crayfish - Phylum Arthropoda (Cambarus sp.)

• The body is divided into an anterior cephalothorax (fused head and thorax) and a posterior abdomen

• The chitinous exoskeleton protects the crayfish from predators.

• Because the exoskeleton surrounds the body, it must be molted periodically to allow for growth.

• Until the new skeleton hardens, the animal is helpless.
  

External Anatomy of the Crayfish (Cambarus sp.)

• The carapace covers the cephalothorax.

• The rostrum is an anterior, pointed extension of the head.

• A pair of stalked eyes is located on the lateral side of the rostrum.

• One pair of antennae is located on the head as well.

• The mouth is located on the ventral side of the body, between the mandibles

• The abdomen consists of several segments and is terminated by the telson

• The appendages are modified to serve many functions: feeding, walking, and swimming.

External Anatomy of the Crayfish (Cambarus sp.)

• The male and female crayfish have an equal number of appendages.

• However, in male crayfish the first two pairs of swimmerets have been modified.

• They are elongated and can be brought together for the transfer of sperm from the male to the seminal receptacles of the female.

• In female crayfish, all of the five pairs of swimmerets are of the same size and are used for swimming
  

Internal Anatomy of the Crayfish - Digestive System

• The large yellowish digestive gland, occupies much of the posterior part of the cephalothorax and secretes enzymes and stores food.

• The mouth leads via a short esophagus to the large stomach which occupies most of the anterior region of the cephalothorax.

• Open the stomach and locate the chitinous teeth that form the gastric mill (used to grind food).

• The intestine runs from the stomach through the abdomen ending at the anus.

Internal Anatomy of the Crayfish -
Osmoregulatory and Excretory System

• Because of their diversity of form and lifestyle, arthropods show considerable variety in many of their organs, including the excretory system.

• We will examine two common arthropod excretory systems, which function in both osmoregulation and waste removal

• 1) Green glands found in aquatic arthropods

• 2) Malpighian tubules found in terrestrial groups

Internal Anatomy of the Crayfish -
Respiratory and circulatory Systems

• Aquatic arthropods generally have gills for respiration except for a few extremely small species that lack special respiratory structures.

• Observe the "feathery" gills

• Note that the carapace covers the gills except at the anterior and posterior ends of the gill chamber.

• Water that contains oxygen is driven through the chamber and over the gills by the second pair of maxillae (known as “gill bailers”).

• The gills are well vascularized for gas exchange
  

Internal Anatomy of the Crayfish -
Respiratory and circulatory Systems

• Arthropods have an open circulatory system with a prominent heart receiving blood from the hemocoel and pumping it into vessels for distribution to the body.

• Depending on the type of respiratory organ the arthropod has, the circulatory system may or may not be important in the transport of oxygen to the body tissues.

• In animals where blood is not important for the circulation of respiratory gases, no respiratory pigment may be present. (e.g., insects)

Internal Anatomy of the Crayfish - Reproductive System

• The gonads (testes or ovaries) are lateral to the anterior portion of the intestine

External Anatomy of the Grasshopper - Romalea sp.

• The grasshopper belongs to the Class Insecta, which is characterized by having three body regions (head, thorax, and abdomen), one pair of antennae, and six legs

• Romalea has 10 abdominal segments and the terminal abdominal segment has the reproductive genitalia.

• The terminal segment of males is blunt, whereas that of females is modified to lay eggs and is called an ovipositor

Internal Anatomy of the Grasshopper - Digestive System

• The esophagus, conveys chewed food from the pharynx into a large storage organ, the crop.

• Digestive glands called the gastric caecae are attached to the stomach

• The gastric caecae produce enzymes that are
  secreted into the stomach to aid in digestion

Internal Anatomy of the Grasshopper - Digestive System

• Because most of the digestive tract is lined with chitin (except the stomach and crop) digestion and absorption take place mainly in the stomach.

• The digestive tract continues as the intestine, a thin tube without accessory structures.

• It leads to the short rectum which opens to the exterior via the anus.

• The hair-like tubules lying over the intestine are Malpighian tubules, the excretory organs

Internal Anatomy of the Grasshopper - Osmoregulatory and Excretory Systems

• Malpighian tubules: serve as excretory organs in such terrestrial arthropods as insects, centipedes, millipedes and arachnids.

• Wastes enter the tubules and are removed via the hindgut

Internal Anatomy of the Grasshopper - Reproductive System

• The gonads are dorsal to the intestine, in the region of the Malpighian tubules

• In the male, each of the two testes is composed of a series of slender tubules (follicles) and they are located above the intestine

• Each testis is joined to a longitudinal vas deferens. The vas deferens is joined to a single ejaculatory duct to which accessory glands are attached

Internal Anatomy of the Grasshopper - Reproductive System

• In the female, each ovary is composed of several tapering egg tubes which produce the ova

• Each ovary is joined to an oviduct leading to the vagina, to which a pair of accessory glands and a single spermatheca is attached.

• The latter organ is used to store sperm received at copulation