Crustacea Study Guide PDF

# Subphylum: Crustacea ## Objectives: By the end of this Unit, the students will be able to: 1. Know the habitat of Arthropoda. 2. Enumerate the specific characters of Arthropoda. 3. Describe similarities and differences in morphology which indicate phylogenetic relationships. 4. Classify phylum Art...

# Subphylum: Crustacea ## Objectives: By the end of this Unit, the students will be able to: 1. Know the habitat of Arthropoda. 2. Enumerate the specific characters of Arthropoda. 3. Describe similarities and differences in morphology which indicate phylogenetic relationships. 4. Classify phylum Arthropoda. 5. Distinguish between the classes and orders of Class Crustacea. 6. Describe the external and internal organs and the biology of some crustacean animals (Ex: Prawn). 7. Know the economic importance of *Crustacea*. 8. Learn how to search literature from the internet and digital library to write scientific essays on this study. ## Invertebrates - Are animals that lack (without) a backbone. - Account for 95% of known animal species. ## Phylogenetic Tree The attached image shows a phylogenetic tree of animal kingdom showing the relationships between different phyla. - The tree starts from multicellularity evolving from ancestral protists. - The phyla are organized based on their body symmetry and coelom development. - Most of the phyla except *Porifera* and *Cnidaria* are bilaterally symmetrical and triploblastic. - *Porifera* and *Cnidaria* have radial symmetry and are diploblastic. - *Platyhelminthes* and *Nematoda* are acoelomate with no coelom. - *Mollusca* and *Annelida* are pseudocoelomate. - *Echinodermata* and *Chordata* are deuterostomes with the blastopore opening to the anus. - *Arthropoda* is a protostome with the blastopore opening to the mouth. ## Protostomes vs. Deuterostomes The attached image shows a diagram of the difference in the development of protostomes and deuterostomes. - Protostomes have a blastopore that develops into the mouth and an anus that opens separately. - Deuterostomes have a blastopore that develops into the anus and a mouth that opens separately. ## Phylum *Arthropoda* 1. **Etymology:** *Phylum Arthropoda* means: - *arthro-* = joint - *pod* = leg, foot 2. Huge group, is the most largest phylum of all living organisms, both in number of species and in number of individuals, over one million species of insects alone. Represent, 84% of all animal species are arthropods. 3. Found nearly in all habitats of the biosphere. They are adapted for life on land, in soil, in fresh, brackish or marine waters, in air and on or in the bodies of animals as well as plants. 4. They have *bilaterally symmetrical*, *triploblastic*, and *metamerically segmented* bodies. 5. Arthropods are segmented coelomates (Schizocoelomata) that have an exoskeleton and jointed appendages. 6. Their appendages are modified for many different functions. 7. The body of an arthropod is completely covered by the cuticle, an exoskeleton made of chitin. 8. When an arthropod grows: - It molts its exoskeleton in a process called ecdysis. 9. Their features are: - Tough exoskeleton. - Jointed appendages. - Segmented bodies. 10. The arthropods diversity are success due to their segmentation, hard exoskeleton, and jointed appendages. ## *Arthropoda* Body Structure The attached image shows a diagram of a crustacean body. - The body is divided into a head, thorax and abdomen. - The head has a carapace that protects the head. - The thorax has a pair of antennae and a pair of mandibles for feeding. - The abdomen has a telson and a pair of uropods. ## Exoskeleton The attached image shows a diagram of the layers of exoskeleton. 1. **Exoskeleton:** - Chitin - Flexible - Hard - Water proof - The exoskeleton consists of three layers: - **Epicuticle:** Oily and waxy. - **Exocuticle:** Chitin and protein. - **Endocuticle:** Chitin only. 2. The exoskeleton is secreted by the epidermis, which is a layer of living cells. 3. The exoskeleton has the following functions: - Support. - Locomotion by acting as a lever system. - Mechanical protection. - Retards evaporation in air and osmosis in water, helping with water balance. ## Organ Systems *Arthropods* are *metazoa* with an *organ-system* level of organization. ### Digestive System - Arthropods have a complete digestive system (tubular alimentary canal with mouth and anus). The mouth is not terminal and has movable appendages. The anus is terminal. - The alimentary canal has three regions: - **Foregut:** Ectodermal. - **Midgut:** Endodermal. - **Hindgut:** Ectodermal. - Arthropods have diverse feeding habits and can be carnivorous, herbivorous, or omnivorous. ### Respiration - Arthropods have a variety of specialized organs for gas exchange. - **Gills** are found in aquatic/marine arthropods. - **Tracheal systems** are found in most terrestrial arthropods. - **Book lungs** and **Book gills** (modified gills) are found in spiders and scorpions. ### Circulatory System - Arthropods have an open circulatory system. - **Hemolymph** is circulated into the body cavity surrounding the tissue and viscera. It contains blood and is called *haemocoel*. - The circulatory system is open with dorsal heart, arteries and blood sinuses, but no veins. - The dorsal heart pumps hemolymph over the brain. - Arteries pour the blood into a large spaces called sinuses (dorsal, ventral and two lateral sinuses). - Ostia (holes) in the sides of the heart let hemolymph in to go around again. ### Excretion Excretion can be performed by: 1. **Green gland** or **coxal gland** in crustaceans. 2. **Malpighian tubules** in spiders and insects. 3. Excretion involves the removal of *nitrogenous compounds* resulting from cellular metabolism. ### Nervous System - The nervous system is highly developed and resembles those of annelids. - It consists of: - Brain with nerves around the esophagus. - Paired ventral nerve cords. - Segmental ganglia, which often fuse into 1-2 ganglia in each *tagma*. - Arthropods have modified sense organs: - Statocyst, chemical receptors, compound eyes, mouth, antennae and legs. - *Arthropods* have mechanisms for protection: - Sting, pincers, and nasty chemicals. ### Muscular System - Arthropods have a well developed muscular system composed of striated muscles. - Muscles do not form a continuous layer with the body wall. I.e. The muscle layer does not contribute to the formation of the body wall. - Muscles are segmentally arranged in bundles to move specific segments. - Flexor and adductor muscles are present. ### Reproduction - Sexes are usually separate with paired *gonads* and a *gonoduct*. - Usually internal or external fertilization occurs with males shedding a small packet of sperm that the female picks up. ### Development - **Molting** is the process by which arthropods shed their exoskeletons. - Development usually includes varying degrees of metamorphosis. - **Metamorphosis** is regulated by *hormones*. - **Incomplete metamorphosis** includes larval stages where eggs hatch into different types of larvae that then metamorphose into young animals. - **Complete metamorphosis** does not include larval stages. Eggs hatch directly into young animals. ## Differences between *Arthropoda* and *Annelida* 1. A distinct head (cephalization) in all *Annelida* forms, with well-developed sense organs like compound eyes, statocysts and auditory organs for quick response. 2. The body of an arthropod is completely covered by the cuticle, an exoskeleton made of chitin. 3. *Annelida* have bundles of striated muscles for moving particular parts. *Arthropoda* have jointed appendages for locomotion. 4. *Annelida* have special respiratory organs, such as gills, tracheae and book-lungs in the majority of forms. ## Classification of Phylum *Arthropoda* Arthropods are classified according to: 1. Presence of *mandible* 2. Presence of *chelicerae* 3. Presence or absence of *antenna* They are divided into two subphylas: 1. **Mandibulata:** With *mandibles*. 2. **Chelicerata:** With *chelicerae*.