Invertebrate Notes: 3Super phylum Arthropoda: Bilateral protostomesIt is the largest animal grouping. There are more than 1 million species of insects and perhaps 50 million species of arthropods.Characteristics:Arthropods are characterized by jointed appendages and an exoskeleton. The following are general arthropod characteristics.1) Exoskeleton: All arthropods have an
articulated (jointed) exoskeleton that is secreted by the underlying epidermis. The skeleton is made up of an outer (waxy) layer that is made of lipoproteins, a hardened middle layer, and a flexible inner layer. Both the middle and inner layer are made of chitin and proteins. The exoskeleton also extends inwards at both ends of the digestive tract, and in insects the exoskeleton lines the
trachea.The exoskeleton serves as protection against predators and is often waterproof. The exoskeleton is used for food grinders in the foregut, for wings, for tactile hairs, even for the lens of the arthropod eye.Muscles are attached to the various portions of the exoskeleton allowing for complex movement.The exoskeleton does not grow and must be discarded and reformed many times as the animal grows and develops. Molting is the discarding of the old exoskeleton. When the animal molts, an enzyme dissolves the inner layer of the old exoskeleton while a new (soft) one forms.Appendages in arthropods are very diverse. They can be modified for walking, feeding, sensory reception, copulation and defense.Arthropoda used to be a large phylum, but scientists have broken the Super phylum Arthropoda into four phyla:1) Chelicerata: which include horseshoe crab, sea spiders, spiders, mites, and scorpions. 2) Crustacea: are known as crabs, lobsters, shrimps, barnacles...3) Uniramia: include insects and four minor classes.4) Trilobita:, which are totally extinct.The complete digestive system includes specialized mouthparts.Mandible is the hard jaw, which crushes food.Chelicerae are fanglike appendages, which pierce the prey.Maxillae and Maxillary Palps can manipulate and hold food.Pedipalps in chelicerates and Maxillipeds in uniramians are also present for either walking or holding food.Excretory System:Insects have Malpighian tubules, which are located in the coelom and absorb nitrogenous wastes from the blood and pass it into rectum.Crustaceans have green glands, which are near the head and absorb
nitrogenous wastes from blood and pass then out of the body near the antennae.The circulatory system in arthropods is open.The blood circulates food and oxygen around the body. The beating heart pumps blood into the body cavity and the blood makes its way back to the heart.The
respiratory system in arthropods is very diverse.Gills are feathery looking and thin. The blood inside the gills take oxygen from water.Book gills are thin "pages" of tissue, which work like gills.Book Lungs are a series of page-like air sacs that take oxygen from air.Tracheal tubes have outside holes (spiracles) that lead to tracheal tubes, which end in tiny moist tubes (trachioles). Trachioles exchange gases with the body cells.Reproduction in arthropods. All members of this phylum have separate sexes. The male passes sperm to the female, and fertilization occurs inside female who lays eggs. Some insects develop through the process of metamorphosis. There are two types of metamorphosis:Incomplete: egg---> nymph---> adult (grasshopper)Complete: egg---> larva---> pupa---> adult (butterfly, fly)Hormones control metamorphosis.Nervous System: Arthropods contain a brain with ventral nerve chords and ganglia that run down the length of the body. The arthropods with compound eyes have special lobes of the brain devoted to
sound. The tympanum is a specialized organ to detect vibrations. Sensory hairs and bristles are also used.Phyla and Classes of arthropods:Phylum Chelicerata:These arthropods do not have antennae or mandibles. Their first appendages are chelicerae, which are pincers or fangs. The second pair of appendages are pedipalps that may have pincers, modified walking legs, or sensory organs. Posterior to the pedipalps are jointed walking legs. The head and thorax may be fused; this structure is named the cephalothorax. There are three classes of Chelicerates.1) Merostomata: 4 species of horseshoe crabs. Blood contains copper as the oxygen carrying molecule. This makes their blood blue which is called Hemocyanin.2) Pycnogonida: sea spiders.3) Arachnida: 57,000 species of spiders, ticks, mites, scorpions and daddy longlegs. These have 4 pairs of walking legs. The chelicerae are highly specialized. Pedipalps- spiders transfer sperm to female. Scorpions tears food. This is the bulk of Chelicerates.Spiders live on liquid diets. Prey are bitten and paralyzed. Enzyme from the midgut pours into torn tissue, which makes a broth. This is taken into the spider stomach. Chelicerates respire with book lungs or trachea. Chelicerates have a cephalothorax—a fused head and thorax region.The posterior abdominal surface of spiders has spinnerets, modified appendages from which a fluid protein is exuded the protein solidifies into silk.Phylum
Crustacea.There are 40,000 species of crustaceans, examples are crabs, crayfish, lobster, shrimp, prawns, barnacles, and daphnia. Members of this arthropod group have separate genders, with some exceptions. Crustaceans have a carapace, a heavy shield that arises from the head and covers the thorax. The abdomen consists of six distinct segments. Various appendages have specific functions; for example, the antennae (two pairs) are sensory organs while the mandibles crush food.Crustaceans respire with gills. They have appendages that move water over their gills. Smaller ones move gas by diffusion across thin layers of cuticle.The digestive tract includes a foregut and hindgut that are lined with cuticle tissue of the exoskeleton. Most food is absorbed through the midgut.They excrete using the green gland.Phylum Uniramias:A single pair of antennae and their unique mandibles identifies this group. Uniramians respire through trachea and excrete with Malpighian tubules. Insecta is the major class of terrestrial mandibulates. Chilopoda and Diplopoda are two of the remaining four smaller classes.Cl. Chilopoda: centipedes, characterized by one pair of appendages per body segment. They have poisonous claws that paralyze their prey and help in defense.Cl. Diplopoda: millipedes, which have two pairs of appendages per body segment. These eat decaying leaves and plant matter.Class Insecta:This is the largest class of arthropods, comprising seventy percent of all animal species on earth. Insects are the only invertebrates capable of flight. There are 26 orders of insects. The four largest are as follows:1) Diptera: two winged; flies, gnats, and mosquitoes.2) Lepidoptera: scale winged; moth and butterfly.3) Hymenoptera: membrane winged; ants, wasps, and bees.4) Coleoptera: shield-winged; beetles.Insect have the following characteristics: three body regions, three pairs of legs (on thorax), one pair of antennae, a set of complex mouth parts and two pairs of wings (not all insects have two pairs of wings—some have a modified set that acts as a cover (beetles), others have two that are hooked together (bees), others have one set of working wings and the other set is vestigial—there’s something there (looks like a really small drumstick) but it doesn’t act like a set of wings) .The digestive system of insects consists of a foregut and hindgut lined with cuticle. The stomach or midgut, in the abdomen, is the chief organ of absorption. The specific enzymes used in digestion depend on the insects' diet.Insect excretion is via Malpighian tubules. Nitrogenous wastes are eliminated in the form of dry uric acid crystals. This removes wastes from the blood (hemolymph) and dumps the waste into the
branch from the ganglia.The respiratory system is a network of cuticle-lined tubules. Air circulates to the various tissues and supplies the cells directly with oxygen. Water loss is regulated by the opening and closing of spiracles.Reproduction: Separate males and females. These two must get together, recognize each other and fertilize the eggs (usually internally). Some species advertise with colors, sounds, light or odors. Most mate only once in a lifetime (females want to make a good choice on mates). The females will lay her fertilized eggs near a food source.Behavior:Examples: Spiders build webs and catch prey, crickets chirping to find a mate; certain females produce chemicals (pheromones) to attract males.Social insects, bees, ants, and termites are a female
dominated society. The queen is the dominant and only fertile female. In the egg stage, the queen is fed 'royal jelly' to produce a fertile female. If two or more queens emerge simultaneously, they will fight to the and only one new queen will remain in the nest. A swarm is a mating flight where male drones will contribute to the queen's sperm bank. The queen lives for approximately five years, laying thousands of eggs.Workers are infertile females. Newly emerged workers are nursemaids, older workers are hive guards, and most mature workers are foragers. Like the queen, they have a stinger on the last abdominal segment.Drones are haploid males, which are produced from
unfertilized eggs. The only purpose of a drone is to mate with the queen and then it is driven from the hive and dies.Bees communicate distance and direction with the dance. For example, a waggle dance indicates distant flowers and a circle dance indicates nearby flowers.Insects undergo one of the two types of metamorphosis.1) Incomplete: The young are smaller forms of the adult. These smaller forms have different body proportions. The insects will molt a number of times until the adult is formed.2) Complete: The larval stage looks completely different from the adult form and usually has a different feeding strategy. The main job of the larva is to eat and grow. The main job of the adult is to mate and reproduce.
Phylum Echinodermata:
Echinoderms are deuterostomes (this makes them the most advanced invertebrate—evolutionarily). The cleavage pattern of deuterostomes occurs in a radial manner. The anus develops at or near the blastopore. The mouth forms secondarily elsewhere. The coelom is formed by outpocketing of the embryonic gut (enterocoelous). There are 7,000 species of echinoderms.
Phylum Echinodermata:
There are six classes in this phylum: 1) Class Crinoidea: sea lilies, feather stars. 2) Class Asteriodea: starfish.
3) Holothuroidea: sea cucumbers. 4) Ophiuroidea: brittle stars.
5) Echinoidea: sea urchins and sand dollars.
6) Concentricycloidea: sea daisies—discovered recently on waterlogged wood of the deep sea.
Characteristics of echinoderms: They are deuterostomes with
Radial symmetry as an adult. As larvae, echinoderms are bilaterally symmetrical. The larvae grow into adults with a five-part radial symmetry.
locomotion, feeding, and gas exchange.
Reproduction: Separate genders release sperm and egg into the water.
Representative echinoderm: Class Asteriodea: starfish
Body structure: There is a central disc from which radiate a number of arms. The interior skeleton bears projecting spines (for which the phylum is named). The skeleton is made up of tiny, calcium-containing plates (under the skin—first endoskeleton) that are held together by skin tissues and muscles.
The mouth is on the lower or oral surface of the central disk. Above the mouth is the stomach. When eating, the stomach everts out through the mouth and secretes enzymes that soften up the prey. The food is then taken up into the stomach.
Circulation: There is no circulatory system; the food is distributed by liquid in the body cavity. The coelom forms a complicated system of cavities and tubes. This arrangement helps provide for circulation.
Excretion: Echinoderms have no excretory organs. Nitrogenous wastes are collected by ameboid cells and passed out of the organism through skin gills. Skin gills are fingerlike projections that are protected by the spikes.
Respiration: Gases are exchanged through the skin gills.
Nervous System: There is no head or brain, but a nerve ring around the mouth and a nerve chord down each arm. These nerve chords have eyespots at the end. These eyespots are the only sensory organ of the echinoderm. However, the epidermis contains neurosensory cells that function in photoreception and chemoreception.
Reproduction: Sexes are separate, with paired gonads in each arm. The zygote develops into a dipleurula larva. Many members have remarkable regenerative powers.
A water-vascular system is used for locomotion. The water-vascular system (wvs) is unique to this phylum. This system consists of a modified coelomic cavity and creates hydrostatic support for the tube feet. A radial canal and a central ring interconnect these tube feet. At the end of each tube is a structure with which the foot attaches to the substrate. At the opposite of the foot there is a
muscular sac called the ampulla.
Water enters the sieve plate (madreporite) on the top-side (aboral) of the central disc, then moves down the stone canal to the ring, canal, out of the radial canals, and down each arm. The ampullae fill with water. When the ampullae contract, water flows out of the ampullae and into the foot, making it rigid enough to walk on. When the tube feet are placed on hard surface, contractions of the muscles at the base of each tube foot collectively exerts enough force to pull the starfish
Digestion: Food enters the mouth and moves into the stomach, then to the digestive glands in each arm, and finally to the liquid in the body cavity for distribution. When the starfish eats, the stomach everts through the mouth and squeezes through small openings. The enzymes from the stomach digest the soft tissue of the prey.
Other Echinoderms:
Class Ophiuroidea: Brittle Stars—long and flexible. Their tube feet lack suckers.
Class Echinoidea: In sea urchins and sand dollars arms are not present, but five paired rows of tube feet are on the bottom through the hardened skeleton. These organisms also have hardened spikes.
Class Crinoidea: Sea Lilies/Feather Stars. They crawl about with their long and flexible arms and are suspension feeders.
