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Chapter 28: Arthropods Section 1: Introduction to Arthropods Introduction to Arthropods ________________________________ – animal having a segmented body, an exoskeleton containing chitin, and a series of jointed appendages; belong to the phylum Arthropoda o More than ________________________ species have been described o Vary enormously in size, shape, and habits Diversity and Evolution in Arthropods Arthropods are divided into _____________ subphyla: o _________________________ Oldest subphylum of arthropods ____________________________ were dwellers in ancient seas ______________________ o __________________________ ____________________________________ include spiders, ticks, mites, scorpions, and horseshoe crabs o __________________________ _________________________________ include such familiar (and edible) organisms as crab and shrimp o __________________________ __________________________________ include most arthropods: centipedes, millipedes, and all insects—including bees, moths, grasshoppers, flies, and beetles Form and Function in Arthropods All arthropods exhibit several key features o 3 most important features Tough _______________________________ Series of ______________________________________________ __________________________________________ o Other characteristics Brain located in dorsal part of head Ventral nerve cord Open circulatory system powered by a single heart The Arthropod Body Plan The _________________________________ is a system of external supporting structures that are made primarily of the carbohydrate ____________________ Provide excellent protection from physical damage ________________________________ o Prevents water loss Helps arthropods move efficiently and adapt to their environment Disadvantages o Cannot ________________ as the animal grows o Movement can occur only at the joints of the “armor” All arthropods have jointed appendages that enable them to move Over millions of years, appendages have evolved into marvelously versatile adaptations to different environments o _____________________________ o ______________ o ____________________________________ o ________________ o __________________________ All arthropods have segmented bodies Feeding Appendages enable these animals to eat almost any food you can imagine Exhibit every mode of feeding o ___________________________ Some eat any plant, others are more selective o ___________________________ Some catch and eat other animals, others feed on animals that are primarily already dead o ___________________________ External parasites drink blood or body fluids from animals, internal parasites passively absorb nutrients through body walls o ___________________________________ Use comb like bristles on mouthparts or legs to filter plants and animals from water o ___________________________________ Respiration Have evolved three basic types of respiratory structures—______________, _____________________________________________________, and _______________________________________ o Most have only one of these respiratory structures Aquatic arthropods have gills just under the cover of their exoskeleton Are formed from part of the same appendages that form mouthparts and legs Book gills (horseshoe crabs) and book lungs (spiders and their relatives) are unique to these arthropods ______________________________________________ are layered like the pages of a book Increase the surface area for gas exchange Tracheal tubes (terrestrial arthropods) From spiracles, long branching tracheal tubes reach deep into the animals’ tissues Supplies oxygen by _________________________ to all body tissues Work well in only small animals Internal Transport A well-developed heart pumps blood through an _______________ circulatory system When the heart contracts, it pumps blood through arteries that branch into smaller vessels and enter the tissues There the blood leaves the vessels and moves through spaces in the tissues called _________________________ Eventually, the blood collects in a large cavity surrounding the heart, from which it re-enters the heart through small openings and is pumped around again Excretion Undigested food becomes solid waste that leaves through the anus Most terrestrial arthropods dispose of nitrogen-containing wastes by using a set of ____________________________________________ o Bathed in blood inside the body sinuses o Remove wastes from the blood, concentrate them, and then add them to undigested food before it leaves via the anus Terrestrial arthropods may have small excretory glands by their legs instead of Malpighian tubules Aquatic arthropods dispose of cellular wastes by diffusing them from the body into the surrounding water o Also eliminate nitrogen-containing wastes through a pair of ____________________________________ located near the base of the antennae Are emptied to the outside through a pair of openings in the head Response Have well-developed nervous systems All have a ________________________ that consists of a pair of ganglia in the head Have a nerve cord with several other pairs of ganglia o Serve as local command centers to coordinate the movement of ____________________________________ Why insects can move after their heads are cut off Have simple sense organs such as statocysts and chemical receptors Have compound eyes that contain more than 2000 separate lenses that can detect color and motion Have well-developed sense of ___________________ o Receptors located on mouthparts, antennae, and legs Insect ears are found in strange places o Eardrums are normally located __________________________________ Sense organs help it detect and escape predators Some also have venomous stings and bites Some arthropods trick predators by _____________________________________ o Drop a claw or a leg Body part keeps moving to distract the predator while the rest of the animal scurries away Use visual trickery to fool predators Hide through _____________________________ Others imitate the warning coloration of poisonous or dangerous species— _________________________ Movement Have well-developed ___________________________________ that are coordinated by the nervous system Muscle generate force by _____________________________, then transfer that force to the _________________________________ At each joint, some muscles are positioned to flex the joint and other muscles extend to it o Allows arthropods to beat their wings against the air to fly, push their legs against the ground to walk, or beat their flippers against the water to swim Reproduction Reproduction is ______________________ Males and females produce sperm and eggs Fertilization takes place ______________________________________________ ____________________________ The male uses a special reproductive organ to deposit sperm inside the female EXCEPTION: In spiders and some crustaceans, the male deposits a small packet of sperm that the female picks up Growth and Development in Arthropods Exoskeletons present a problem in terms of ________________________ Arthropods must replace their exoskeletons with larger ones in order to allow their bodies to increase in size as they mature In order to grow, all arthropods must ________________, or shed, their exoskeletons o Controlled by ___________________________ When molting time is near, the epidermis digests the inner part of the exoskeleton and absorbs much of the chitin After it secretes a new exoskeleton inside the old one, an arthropod pulls completely out of its old skeleton o Often _______________ what is left of the old exoskeleton o Must then wait for the new exoskeleton to __________________ Can take a few hours to a few days Molt several times between hatching and adulthood In most cases, the process of growth and development involves __________________________________, or a dramatic change in form As the young grow, they keep molting and getting larger until they reach adult size Along the way, they gradually acquire the characteristics of adults Many insects undergo _____________________________________________ —a four stage process where the eggs of insects hatch into larvae that look nothing like their parents As they grow, they molt repeatedly When it reaches a certain age, it sheds its larval skin one last time and becomes a ________________ o During this stage the insects body is completely rearranged o After metamorphosis, the animal emerges as a fully grown adult with both internal and external body parts that are completely different from what it had before