Invertebrate Lecture 6 PDF

# Phylum Arthropods ## **Classification of Phylum Arthropoda (Mind Map)** - **Phylum Arthropoda** - **Sub-Phylum - I** - **Trilobitomorpha** - **Trilobiza : (extinct)** - **Sub-Phylum - II** - **Chelicerata** - **Arachnida: Spiders, Scorpions**...

# Phylum Arthropods ## **Classification of Phylum Arthropoda (Mind Map)** - **Phylum Arthropoda** - **Sub-Phylum - I** - **Trilobitomorpha** - **Trilobiza : (extinct)** - **Sub-Phylum - II** - **Chelicerata** - **Arachnida: Spiders, Scorpions** - **Merostomata: Horseabow crabs** - **Pycnogonida: Sea spiders** - **Sub-Phylum - III** - **Myrlapoda** - **Chilopoda: Centipedes** - **Diplopoda: Millipedes** - **Pauropoda:** - **Symphyla** - **Sub-Phylum - IV** - **Crustacea** - **Branchiopoda: Brine shrimp** - **Remipedias: Blind crustaceana** - **Chephlocaridai: Horseshoe shrimp** - **Maxillopoda: Barnacles** - **Ostracoda: Seed shrimps** - **Malacostraca: lobsters, crabs, shrimp** - **Sub-Phylum - V** - **Hexapoda** - **Insecta: Insecta (Winged insects)** - **Entognatha (Wingless insects)** ## **Subphylum Chelicerata** - Body divided into 2 regions: - Prosoma / Cephalothorax (fused head & thorax). - Abdomen. - Lack jaws. - Have 6 appendages & no antennae. - First pair of preoral chelicerae with claws, followed by postoral pedipalps and 4 pairs of walking legs. ### **Class Arachnida:** - **Spiders** - **Ticks** - **Scorpions** ## **Subphylum Chelicerata** - **Cephalothorax (prosoma)** - Fused head and thoracic region - Sensory, feeding, locomotion - **Abdomen (opisthosoma)** - Contains digestive, reproductive, excretory, and respiratory organs ## **Subphylum Chelicerata** - **Appendages attached to cephalothorax** - Pair of chelicerae (pincer-like feeding appendages) - Pair of pedipalps (usually sensing or feeding) - Four pairs of legs (5 in horseshoe crabs) ## **Subphylum Chelicerata** - Usually has eyes - Never has antennae - Most suck liquid food from prey ## **Class Arachnida** - **Special features to know** - All arachnids are carnivores. Most eat insects. - No antennae - Many have 8 simple eyes. - Use coxal glands and/or Malpighian tubules for nitrogenous waste/excretion - Have book lungs (folds of body wall to form lungs) - Air intake tubes: trachaea, which open to outside via spiracles - Dioecious (separate male/female individuals) ## **Spider body parts** - Unlike an insect, the spider's body is in two sections. ## **Spider body parts** - Two body regions: cephalothorax and abdomen - Have 4 pairs legs attached to their thorax - A pair of chelicerae (fangs) - A pair of palps. Function as sense receptors, short arms, and pincers (in scorpions). - Cephalothorax joined by a slim waist (pedicel) to the, the abdomen second body section ## **The cephalothorax** - The cephalothorax is covered above by a hard cuticular plate (carapace) - On the outside of the cephalothorax are: - The simple eyes - usually eight (sometimes six) - The mouthparts - two large jaws with their piercing fangs (the chelicerae) - The pedipalps - that help with food handling, touch and taste sensing and, in male spiders, are modified as mating organs. - The legs - four pairs of jointed legs with two to three terminal claws ## **The abdomen** - On the outside of the abdomen are: - The book lung covers - to protect the delicate organs inside - The gonopore or genital opening - from which eggs or sperm are released is placed in the genital groove between the front pair of book lungs. In most female araneomorph spiders there is another separate, plaque-like mating opening, the epigynum. - The spinnerets (silk spinning organs) - usually four or six in number. ## **Spinneret** - Spinnerets are tubular or conical structures and silk is produced in liquid form at the tip. When exposed to the air the silk forms a filament and the spider or insect draws out the silk into a thread. - The silk is then used to create a web or covering for a cocoon. ## **The abdomen** - On the inside of the abdomen are: - The book lungs - the breathing organs. - Small openings called spiracles lead into air filled cavities into which the thin, leaf-like lamellae of the book lungs project - like rows of book pages. - Silk glands - to produce the liquid protein that makes the silk - Reproductive organs (ovary or testes). ## **Scorpion** - Scorpions are poisonous, ovoviviparous arthropods, found in tropical and subtropical countries. - They are predaceous carnivores, preying mostly on insects and spiders. - They are secretive, hiding by day in cracks, crevices and burrows or under stones, etc. ## **Scorpion** - The body of scorpion has three divisions, namely prosoma (cephalothorax), mesosoma (pre- abdomen), and metasoma (post - abdomen). - Each region is six segmented ## **Scorpion** - Prosoma is covered dorsally by carapace, and ventrally by sternum. - On the carapace are two or three pairs of lateral eyes and a pair of median eyes. ## **Scorpion** - Ventrally, prosoma bears the mouth and six pairs of appendages, namely a pair of chelicerae, a pair of pedipalps and four pairs of walking legs. - Chelicerae are small and chelate. - Pedipalps are large, chelate and pincer-like. ## **Scorpion** - Mesosoma made of 6 segments - Genital operculum: first mesosomal segment - Pectines: second segment - These are used for exploring the ground and for recognition of sex. - Stigmata: 3rd, 4th, 5th and 6th pre-abdominal segments bears a pair of stigmata or spiracles, which lead into book-lungs. ## **Scorpion** - Metasoma - It consists of 6 distinct cylindrical segments, each enclosed within a complete chitinous ring. - The last metasomal segment bears the anus on its post-ventral side and a stinging apparatus or telson. ## **Scorpion** - Scorpions are predatory carnivores. - They seize the prey by their pedipalps, paralyse, them by injecting venom, and tear them to pieces by chelicerae. - They are slow-eaters. - The respiratory organs are book- lungs. - Excretory organs include a pair of Malpighian tubules and a pair of coxal glands. - Eyes are simple, vision is feeble. - Sexes are separate. - Newborn ones are carried on mothers back for nearly a week. - They grow by periodic moulting. ## **How Does it Protect Itself?** - Scorpion has two very large pinchers that are not very strong. - They use the pinchers to hold it prey and then sting it quickly with the stinger on the end of the tail. - These scorpions are very aggressive, and their venom can kill a human. - They can also camouflage themselves in their natural habitat. ## **How Does it Get Food? What Does it Eat?** - The scorpion grabs its prey with their pinchers and sting them quickly. - In their natural habitat they feed mainly on crickets, bugs and other small rodents and lizards.