Arthropods and Panarthropoda

• Arthropods are protostomes in the Ecdysozoa group and share characteristics with mollusks and annelids.
• Protostome development is regulated by early embryonic division, leading to segmented bodies and jointed appendages in arthropods.
• Arthropods are the most diverse animal group, with over a million species, thriving due to segmented bodies, exoskeletons, and specialized appendages.

Panarthropoda

• Panarthropoda includes arthropods, onychophorans (velvet worms), and tardigrades (water bears).
• Shared features include segmented bodies, jointed appendages, and an exoskeleton, all suggesting a common ancestor.
• This group’s diversity ranges from microscopic tardigrades to large predatory spiders.

Arthropoda

• Arthropoda subgroups include Chelicerata, Myriapoda, Crustacea, and Hexapoda.
• Chelicerata includes arachnids and horseshoe crabs, characterized by chelicerae (pincer-like mouthparts) and lacking antennae.
• Myriapoda includes millipedes and centipedes, known for having many body segments and legs.
• Crustacea includes crabs, lobsters, shrimp, and crayfish, often having two pairs of antennae and specialized appendages.
• Hexapoda includes insects, recognized by three body segments and three pairs of legs.

Arthropoda: Chelicerata

• Chelicerates have chelicerae for feeding and two main body regions: cephalothorax and abdomen.
• Unlike other arthropods, chelicerates lack antennae but possess sensory structures like compound eyes or setae.
• Chelicerates include spiders, scorpions, ticks, mites, and horseshoe crabs, adapting to terrestrial environments with varied feeding and respiratory structures like book lungs or tracheae.

Arthropoda: Chelicerata: Arachnida

• Arachnids feature a cephalothorax, housing eyes, chelicerae, and walking legs, and an abdomen containing internal organs.
• Chelicerae are modified into pincers or fangs for feeding and defense.
• Pedipalps are used for sensation, prey handling, or reproduction.
• Respiratory systems include book lungs or tracheae.
• Spiders produce silk using spinnerets for web construction.

Arthropoda: Myriapoda

• Myriapods include millipedes and centipedes, both having many body segments.
• Millipedes are detritivores with two pairs of legs per segment, generally slow-moving and nocturnal.
• Centipedes are carnivorous predators with one pair of legs per segment, typically fast-moving and active during the day.

Arthropoda: Crustacea

• Crustaceans include crabs, lobsters, shrimp, and crayfish.
• They are characterized by a chitinous exoskeleton, often reinforced with calcium carbonate.
• Crustaceans have two pairs of antennae, three or more pairs of legs, and specialized appendages for various functions.
• These arthropods are found in aquatic and terrestrial environments.

Arthropoda: Crustacea: Crayfish

• Crayfish are freshwater crustaceans found in lakes, rivers, and ponds.
• The carapace is the hard outer covering protecting the cephalothorax.
• The cephalothorax combines the head and thorax, housing mouthparts and legs.
• The abdomen is a segmented tail section used for movement, and for carrying eggs in females.

Crustacean Appendages: Crayfish

• Chelipeds are large pincers used for capturing prey, defense, and communication.
• Walking legs consist of five pairs that aid movement on surfaces.
• Swimmerets are small abdominal appendages that assist in swimming and carrying eggs in females.
• Antennae and antennules are sensory organs that detect food, predators, and environmental changes.

External Structure of a Crayfish: Lateral View

• The carapace covers the cephalothorax.
• The visible abdomen ends in a tail fan (uropods and telson) used for rapid swimming.

External Structure of a Crayfish: Dorsal and Ventral View

• Dorsal view displays the carapace and segmented abdomen, with the carapace providing protection.
• Ventral view shows legs, swimmerets, and mouthparts, with ventral openings for digestive and excretory systems.

Food and Feeding Mechanisms of Crayfish

• Crayfish are omnivores that consume decaying organic matter, detritus, aquatic plants, and small invertebrates.
• Chelipeds capture and manipulate food.
• Mandibles chew and break down food.
• Maxillipeds handle food and pass it to the mouth.

Digestive Systems of Crayfish

• Food passes through the mouth and is chewed by mandibles.
• The esophagus moves food to the stomach, divided into a cardiac stomach for grinding and a pyloric stomach for enzyme breakdown.
• Nutrient absorption occurs in the midgut.
• The hindgut reabsorbs water, and waste is expelled through the anus.

Circulatory Systems of Crayfish

• Crayfish have an open circulatory system.
• Hemolymph is pumped by a heart into body cavities where it bathes organs.
• Hemolymph returns to the heart through sinuses.

Respiratory and Excretory Systems of Crayfish

• Respiration occurs through gills in the gill chamber under the carapace, extracting oxygen and expelling carbon dioxide.
• Excretion happens via green glands near the antennae base, filtering waste from the blood and expelling it through ducts.

Nervous and Sensory Systems of Crayfish

• The central nervous system (CNS) includes a brain above the esophagus and a ventral nerve cord along the abdomen.
• Compound eyes provide vision.
• Antennae detect chemical cues.
• Setae provide touch and taste.
• Statocysts maintain balance.

Reproductive Systems of Crayfish

• Males transfer sperm to females using specialized pleopods.
• Females produce eggs in ovaries, which are fertilized externally.
• Females carry fertilized eggs on their abdomen until they hatch into larvae.

Molting and Growth of Crayfish: Ecdysis

• Crayfish undergo ecdysis (molting) to grow.
• The old exoskeleton splits, and the crayfish emerges.
• A new, soft exoskeleton hardens gradually.

Ecdysis of Crayfish

• During ecdysis, crayfish discard their old exoskeleton and form a new one underneath.
• Crayfish are vulnerable during molting and hide until the new exoskeleton hardens.

Crustacea: Crayfish Life Cycle

• The crayfish life cycle includes eggs, larvae, juveniles, and adults in a direct cycle.
• Eggs are laid by females and fertilized externally.
• Larvae hatch from eggs as small versions of adults.
• Juveniles grow through molting, developing into adults.
• Adults mature and reproduce.

Reproduction and Life Cycles of Crayfish

• Crayfish reproduce sexually, with males transferring sperm to females during mating.
• After fertilization, females carry eggs on swimmerets until they hatch into larvae.
• Growing crayfish molt and develop into adults, continuing the cycle.

Life Cycles of Crayfish

• Eggs are laid and fertilized externally.
• Larvae are small and planktonic, developing into juveniles.
• Juveniles continue to molt and grow.
• Adults are capable of reproduction and mating.