Arthropoda - Kingdom: Animalia - SS1 Biology Lesson Note
Arthropoda is the largest and most diverse phylum in the animal kingdom, encompassing a wide range of organisms such as insects, spiders, crustaceans, and centipedes. Arthropods are characterized by their jointed appendages, segmented bodies, and exoskeletons.
Here are some key features and characteristics of Arthropoda:
1. Body Structure: Arthropods have segmented bodies divided into distinct regions, such as the head, thorax, and abdomen. The body is covered by a tough, external exoskeleton made of chitin, providing protection and support. The exoskeleton must be periodically molted to accommodate growth.
2. Jointed Appendages: Arthropods have specialized appendages, such as legs, antennae, and mouthparts, which are jointed and allow for a wide range of movements. These appendages serve various functions, including locomotion, feeding, sensory perception, and reproduction.
3. Exoskeleton and Molting: The exoskeleton of arthropods provides structural support and protection against predators and desiccation. However, it restricts growth, necessitating molting. During molting, the old exoskeleton is shed, and a new one forms to accommodate the growing body.
4. Segmentation: Arthropods display a high degree of body segmentation. Each segment often bears a pair of appendages, which may be modified for different purposes, such as walking, swimming, or grasping prey.
5. Respiratory System: Arthropods exhibit various respiratory mechanisms. Some have tracheal systems, which are networks of tubes that deliver oxygen directly to tissues. Others use gills for respiration in aquatic environments, while some rely on book lungs or spiracles for gas exchange.
6. Circulatory System: Arthropods have an open circulatory system, where the blood, called hemolymph, flows through interconnected spaces called hemocoel. The hemolymph bathes the organs and tissues directly, facilitating gas exchange and nutrient transport.
7. Sensory Organs: Arthropods possess a range of sensory organs, including compound eyes, simple eyes (ocelli), and antennae. Compound eyes consist of multiple light-detecting units called ommatidia, allowing for a wide field of vision. Antennae are often used for touch, taste, and smell.
8. Reproduction and Development: Arthropods exhibit diverse reproductive strategies, including sexual and asexual reproduction. They typically have separate sexes, although some species are hermaphroditic. Most arthropods lay eggs, but some undergo direct development without a larval stage.
Ecological Dominance: Arthropods are highly successful and occupy nearly every terrestrial and aquatic habitat on Earth. They play vital roles in ecosystems as pollinators, decomposers, predators, and prey. They have a significant impact on ecological processes and are essential for maintaining ecosystem balance.
Image from animalwised.com
The phylum Arthropoda is divided into several major groups or subphyla, each with its unique characteristics and diversity. Here are the main divisions or subphyla of Arthropoda:
Chelicerata: This subphylum includes arthropods with specialized mouthparts called chelicerae, which are used for feeding. Chelicerates are characterized by having two main body segments: the cephalothorax and the abdomen. Examples of chelicerates include spiders, scorpions, ticks, mites, and horseshoe crabs.
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1. Myriapoda: Myriapods are arthropods with numerous legs and elongated bodies. They are divided into two main groups: centipedes (class Chilopoda) and millipedes (class Diplopoda). Centipedes have one pair of legs per body segment and are predominantly carnivorous, while millipedes have two pairs of legs per body segment and primarily feed on decaying plant matter.
Figure 29 Image from nps.gov
2. Crustacea: Crustaceans are predominantly aquatic arthropods that inhabit marine and freshwater environments. They have a wide range of body forms, including crabs, lobsters, shrimp, crayfish, barnacles, and copepods. Crustaceans typically possess two pairs of antennae and branched appendages for feeding and locomotion.
Figure 30 Image from uh.edu
3. Hexapoda: Hexapods are arthropods with six legs, making them the most diverse and abundant group of arthropods. This division includes insects (class Insecta), which are characterized by their three body segments (head, thorax, and abdomen) and diverse adaptations for flight, feeding, and reproduction. Insects play crucial ecological roles as pollinators, decomposers, herbivores, and predators.
Figure 31 Images from dreamstime.com