Arthropods: Unique Characteristics and Adaptations

• Entomology I is an introduction to insects, and is course BIOL 355.
• Dr. (Mrs.) Sandra Abankwa Kwarteng from the Department Theoretical and Applied Biology, College of Science, teaches the course.

Taxonomic Hierarchy

• Insects belong to the Kingdom Animalia.
• They are further classified into the Phylum Arthropoda, and Class Insecta.

Arthropod Features

• Arthropods are segmented invertebrates with bilateral symmetry, making up over 82% of all living things.
• The arthropod head features mouthparts for feeding and various types of eyes.
• Arthropods possess compound eyes and ocelli, which are simple photoreceptors composed of a single lens with sensory cells, unlike compound eyes, ocelli do not produce complex images.
• The compound eye is hexagonal in shape, with each facet seeing part of an image, which the brain combines into a mosaic.
• The thorax is the middle body region, where legs and wings attach.
• The abdomen is the posterior end, housing digestive structures and reproductive organs.
• The exoskeleton of arthropods provides support and protection for soft tissues.
• It slows water loss for terrestrial animals.
• The exoskeleton provides a place for muscle attachment and is made of chitin.
• Arthropod appendages are adapted for feeding, mating, sensing, walking, and swimming.
• Uniramous appendages have a single branch.
• Biramous appendages feature two branches

Arthropod Characteristics

• Arthropods must shed their outer coverings in order to grow, in a process referred to as molting.
• Arthropods have a complete digestive system, including a mouth, gut, anus, and digestive enzyme-producing glands.
• Some arthropods have piercing or sucking mouthparts, known as Chelicera
• Some arthropods have biting or chewing mouthparts, known as Mandibles
• Arthropods obtain oxygen using gills, tracheal tubes, or book lungs.
• Their circulatory systems transport nutrients and remove wastes using open circulation, where blood is pumped by the heart.
• The excretory system includes the anus and Malpighian tubules for terrestrial arthropods and insects, which remove nitrogenous wastes and solutes from the hemolymph.
• Green glands are used by aquatic arthropods.
• Antennal glands are located near the base of larger antennae and help to eliminate ammonia waste.
• Many arthropods possess a tympanum, a flat membrane used for hearing.
• Among invertebrates, only arthropods have a sense of hearing that has independently evolved in several systematic groups.
• Arthropod tympanums are located on the antennae, forelegs, abdomen, or wings.
• Pheromones influence the behavior of other animals of the same species.
• Arthropods reproduce sexually via dioecious internal fertilization in terrestrial and some aquatic species, or external fertilization in some aquatic species.
• Arthropods undergo metamorphosis, either complete (egg-larva-pupa-adult) or incomplete (egg-juvenile-adult).
• Arthropods play ecological roles as predators, prey, parasites/vectors, food sources, agricultural pests, and pollinators.
• Some arthropods can produce honey and silk.

Class Arachnida

• Arachnida includes spiders and scorpions with mouthparts outside the head
• They have eight legs in the adult stage, breath by book lungs and do not posses jaws, antennae, or wings.
• Arachnids are largely opportunistic eaters, exhibiting carnivore feeding habits and tend to live a solitary lifestyle.
• Their bodies are divided into a cephalothorax, also known as prosoma, and an abdomen, also known as opisthosoma.
• Spiders and scorpions are found on every continent in almost every terrestrial habitat.
• Only a few arachnids possess economic importance (mites and ticks), some transmit diseases to humans, other animals, and plants.

Class Crustacea

• Crustaceans possess five pairs of walking legs and typically have a cephalothorax with a crusta, stalked compound eyes, antennules, and antennae.
• Examples include lobsters, and these arthropods have hard exoskeletons and mandibles to bite and grind food.
• Gills are the main respiratory organs for most crustaceans.
• Many crustaceans are food for humans with, smaller species being preyed upon by fishes and even whales.

Class Chilopoda

• Chilopoda includes Centipedes
• They have a flattened, segmented body with paired legs on each segment, with fully equipped adults having between 15 and 177 pairs.
• The antennae are used as sensory appendages.
• Centipedes are nocturnal and move fast for their size with a head with maxillae and mandibles, two antennae, compound eyes or ocelli.
• The first pair of legs are modified into forcipules, or venom claws.
• Large tropical species can kill humans, eating small arthropods, earthworms, and snails.

Class Diplopoda

• Diplopoda includes Millipedes
• They have two paired appendages per trunk segment, totaling around 100-300 pairs of legs and live worldwide.
• Millipedes are herbivores, primarily consuming dead vegetation and decaying plant material, and roll into a ball for both desiccation prevention and defense.
• Containing a gut running from mouth to anus and using separate sexes.
• Females laying eggs that are sexually fertilized by the male.
• The eggs may either be laid in a nest guarded by the female or laid one at a time and then left.

Class Insecta

• Insects are the most successful land animals and may have wings.
• Insects are externally made up of three tagmata: head, thorax, and abdomen.
• The head contains a pair of antennae, compound eyes, and ocelli.
• The thorax includes prothorax, mesothorax, and metathorax.
• The abdomen comprises 10 to 11 segments.
• Insects contain spiracles that lead to a tracheal system.
• Insects can walk, swim, run, or jump.
• Cockroaches can reach speeds of 5 kilometers per hour.
• Fleas can jump as far as 100 times their size.
• Trachea open to spiracles for respiration.
• Aquatic insects use gills for gaseous exchange.
• Insects have an open circulatory system and use Malpighian tubules responsible for the removal of waste.
• Insects may be ectotherms or endotherms.
• Insects have General Adaptability.
• They can live in environments of temperatures from -50°C (artic) to more than 40°C in hot springs.
• Insects have the ability to adapt to a wide range of food.
• Every species of plant is fed on by at least one species of insects.
• Insects feed on vertebrates and decomposing matter.
• These organisms are made up of cuticular protein called chitin.
• The exoskeleton is light in weight and gives strength, rigidity and flexibility to the insect body.
• The exoskeleton consist of hard plates called sclerites connected by soft membranous regions which allow flexibility where required.
• Their size enables many populations to exist on very small quantities of food.
• Insects can easily hide from predators by using microhabitats and ecological niches and require less energy and time to complete development.
• The exoskeleton structural mechanism is the waxy coating and most insects do not excrete liquid water; they reabsorb water from their waste products.
• During Enteronephric, the uric acid is excreted with faeces so there is no water loss, and this is well suited for water conservation.
• They have different types of appendages is due in part by the variety of insect species posses various that posses various forms of mouthparts to be able used to feed on a wide variety of substances.
• High fecundity is an insects egg-laying capacity.
• This rate helps increase the population at a faster rate.
• Insects reproduce both sexually as well as parthenogenetically
• Insects grow and go through in structure and function can be very different
• Insects for many insect species, the immature and adults feed on different food, for example a caterpillar feeds on plant matter while an adult butterfly feeds on plant nectar

Abundance of Insects

• There is much variation in insects,size and shape.
• There are over one (1) million described species of insects.
• Insects comprise of 75% of the all animal species has been named and described.
• Insects are divded up into 32 orders by Taxonomic Classification
• Insecta: Has largest Oder, being the Coleoptera, 125 with 125 families with around 500,000 species, with being thirty percent) of insects described belong to the Order Coleoptera butterflies,bees with
• Some of the largest insects, the (Titanus giganteus), (Deinacrida heteracantha), (Phryganistria chinensis)
• Some of the smalles insects include a parasitic Dicopomorpha echmepterygis wasp

Explore the features of arthropods, from exoskeletons to appendages. Learn about the unique characteristics, ecological success, and classification of arthropods and insects. Discover how jointed appendages provide terrestrial advantages and how ocelli differ from compound eyes.