I Befre Yu Read Have yu seen a drawing r picture f a knight in armr? What is the purpse f armr? On the lines belw list the advantages and disadvantages f wearing a heavy suit f armr. As yu read this sectin abut arthrpds, ntice the similarities between a knight's armr and a feature f arthrpds. I Read t Learn What is an arthrpd? Lcate Infrmatin Underline every heading in the reading that asks a questin. Then, highlight the answers t thse questins as yu find them. Reading Check 1. What are the advantages f jinted appendages? A typical arthrpd is a segmented, celmate invertebrate animal. A celm is a fluid-filled cavity cmpletely surrunded by mesderm. Arthrpds have bilateral symmetry, an exskeletn, and jinted structures called appendages. An exskeletn is a hard, thick uter cvering. An appendage (uh PEN dihj) is any structure, such as a leg r an antenna that grws ut f the bdy f an animal. In arthrpds, appendages are adapted fr a variety f purpses. There are appendages fr walking, sensing, feeding, and mating. Arthrpds are the earliest knwn invertebrates t have jinted appendages. Jints allw mre flexibility in animals that have hard, rigid exskeletns. Jints allw pwerful mvements f appendages. Jints allw appendages t be used in many different ways. Fr example, the secnd pair f appendages in spiders is used fr mating. In scrpins, the secnd pair is used fr seizing prey, d Hw des an exskeletn prvide prtectin? Arthrpds as a grup have been successful partly because they have exskeletns. The exskeletn is made f prtein and chitin (KI tun). In sme species, the exskeletn is a cntinuus cvering ver mst f the bdy. In ther species, it is made f separate plates held tgether by hinges. The exskeletn prtects and supprts internal tissue and prvides a place fr the attachment f muscles. In many species that live n land, a waxy layer n the exskeletn prtects against water lss. In aquatic species,.the exskeletn may be reinfrced with calcium carbnate. 338; Chapter 2 8 READING ESSENTIALS
Characteristics f Arthrpds, cntinued»*- "' j 1 What are the disadvantages f an exskeletn? One disadvantage f an exskeletn is that it is a relatively heavy structure. The larger an arthrpd is, the thicker and heavier its exskeletn must be t supprt its larger muscles. The weight f the exskeletn limits the size f arthrpds. Sme land dwelling and flying arthrpds have adapted by having thinner, lighter exskeletns. A thinner exskeletn ffers less prtectin but allws the animal t fly r jump. ^ Anther disadvantage is that the exskeletn des nt grw. An exskeletn must be shed peridically. Shedding the ld exskeletn is called mlting. Befre an arthrpd mlts, a new, sft exskeletn frms under the ld ne. When the new exskeletn is ready, the animal cntracts muscles and takes in air r water. This causes the animal's bdy t swell. The ld exskeletn splits pen and the animal sheds it. The new exskeletn is sft. Befre it hardens, the animal puffs up as a result f increased bld circulatin t all parts f the bdy. Many insects and spiders als increase in size by taking in air. The new exskeletn hardens in a larger size, allwing sme rm fr the animal t cntinue grwing, ci Mst arthrpds mlt fur t seven times in their lives befre they becme adults. During mlting, they are at risk frm predatrs. While the new exskeletn is sft, arthrpds cannt prtect themselves frm danger. Many species hide r remain mtinless fr a few hurs r days until the new exskeletn hardens. Hw is fusin related t mvement and prtectin? Mst arthrpds are segmented but they d nt have as many segments as wrms. In mst grups f arthrpds, segments have becme fused int three bdy sectins head, thrax, and abdmen. In ther grups, even these segments may be fused. Sme arthrpds have a head, but the thrax and abdmen are fused. Others have a head fused with a thrax, and an abdmen. A fused head and thrax is called a cephalthrax (se fuh luh THOR aks). d Fusin f the bdy segments is related t mvement and prtectin. Less fusin means mre mvement, but less prtectin. Beetles and sme ther arthrpds that have separate head and thrax sectins are mre flexible than thse with fused sectins. Shrimps, lbsters, and crayfishes have a cephalthrax, which prtects the animal but limits its mvement. 2. What limits the size f arthrpds? 3. What happens befre an animal mlts? Reading Chec 4. Name the three bdy sectins f mst arthrpd grups. READING ESSENTIALS Chapter 28 339
Characteristics f Arthrpds, cntinued Tracheal tubes are inside the bdy, thereby reducing water lss thrugh the respiratry surface while carrying air clse t each cell. Gills, with their large surface area, enable a large amunt f bld-rich tissue t be expsed t water cntaining xygen. What kinds f respiratry structures d arthrpds have? Arthrpds are quick, active animals. They crawl, run, climb, dig, swim, and fly. In rder t have xygen delivered quickly t the cells, they need efficient respiratry structures. Three types f respiratry structures have evlved in arthrpds: gills, tracheal tubes, and bk lungs. Aquatic arthrpds use gills t get xygen frm the water and release carbn dixide int the water. Land arthrpds either have a system f tracheal tubes r bk lungs. Mst insects have tracheal (TRAY kee ul) tubes, a netwrk f hllw air passages that carry air thrughut the bdy. Muscle activity helps pump the air thrugh the tracheal tubes. Air enters and leaves the tracheal tubes thrugh penings n the thrax and abdmen called spiracles (SPIHR ih kulz). Mst spiders and their relatives have bk lungs, air-filled chambers that cntain leaflike plates. The flded membranes increase the surface area f tissue expsed t air. The stacked plates f the bk lungs are arranged like pages in a bk. Bk lungs are flded membranes that increase the surface area f bld-rich tissue expsed t air. 5. Hw ants cmmunicate? What senses d arthrpds have? Arthrpds use antennae t detect mvement, sund, and chemicals with great sensitivity. Antennae are stalklike structures that allw arthrpds t detect changes in the envirnment. Antennae als are used fr sund and dr cmmunicatin. Ants and ther arthrpds are able t cmmunicate with each ther by phermnes. Phermnes (FER uh mhnz) are chemical dr signals given ff by animals."fr an ant t cmmunicate the presence f fd t anther ant, the first ant releases a phermne. Antennae sense the dr, which signals t the secnd ant that fd is present. Phermnes signal animals t engage in a variety f behavirs. Sme are used in scent trails. Others are imprtant fr mating behavir, d 340 Chapter 2 8 READING ESSENTIALS
Sectin Characteristics f Arthrpds, cntinued Accurate visin is imprtant t arthrpds. Mst arthrpds have ne pair f large cmpund eyes and three t eight simple eyes. A simple eye is a visual structure with nly ne lens that is used fr detecting light. A cmpund eye is a visual structure with many lenses. Each lens registers light frm a tiny prtin f the field f view. The ttal image that is frmed is made up f thusands f parts. The multiple lenses f a flying arthrpd, such as a dragnfly, help it t analyze a fast-changing landscape during flight, ci Arthrpds have well-develped nervus systems. The nervus system prcesses infrmatin cming in frm the sense rgans. The nervus system cnsists f a duble ventral nerve crd, an anterir brain, and several ganglia. Arthrpds have ganglia that have becme fused. These ganglia act as cntrl centers fr the bdy sectin in which they are lcated. 6. What is^he difference betweeira simple eye and a cmpund eye? What are ther arthrpd bdy systems? Arthrpd bld is pumped by a heart in an pen circulatry system. Vessels carry bld away frm the heart. The bld flws ut f the. vessels, bathing the tissues f the bdy. Bld returns t the heart thrugh pen bdy spaces. Arthrpds have cmplete digestive system. They have a muth, stmach, intestine, anus, and varius glands that prduce digestive enzymes. The muthparts f mst arthrpds include ne pair f jaws called mandibles (MAN duh bulz). The mandibles are adapted fr hlding, chewing, sucking, r biting the different fds eaten by arthrpds. 1 Sand flies and ther insects that feed by drawing bld have piercing blades r needlelike muthparts. The rlled-up sucking tube f mths and butterflies can reach nectar at the bases f lng, tubular flwers. The spnging tngue f the husefly has an pening between its tw fbes thrugh which fd is lapped. READING ESSENTIALS Chapter 2 8
Sectin Characteristics f Arthrpds, cntinued Mst arthrpds that live n land get rid f wastes thrugh Malpighian (mal PIH gee un) tubules. In insects, the tubules are all lcated in the abdmen. Malpighian tubules are attached t and empty direcdy int the intestine. The muscular system is well-develped in arthrpds. In human limbs, muscles attach t bnes. In arthrpd limbs, the muscles attach t the inner surface f the exskeletn. An arthrpd muscle attaches t the exskeletn n bth sides f the jint. Reading Check 7. Name three arthrpd systems discussed in this sectin. Hw d arthrpds reprduce? Mst arthrpd species have separate males and female's and reprduce sexually. Fr land species, fertilizatin is usually internal. Fr aquatic species, fertilizatin is usually external. A few species, such as barnacles, are hermaphrdites, animals with bth male and female reprductive rgans. Sme species, such as bees, ants, aphids, and wasps, exhibit parthengenesis. Parthengenesis (par thuh nh JE nuh sus) is a frm f asexual reprductin in which a new individual develps frm an unfertilized egg, ri Reprductive diversity has cntributed t the success f arthrpds. There are mre arthrpd species than all ther animal species cmbined. I After Yu Read Mini Glssary appendage (uh PEN dihj): any structure, such as a leg r an antenna, that grws ut f an animal's bdy bk lungs: gas exchange system fund in sme arthrpds where air-filled chambers have plates f flded membranes that increase the surface area f tissue expsed t air cephalthrax (se fuh luh THOR aks): structure in sme arthrpds frmed by the fusin f the head and thrax cmpund eye: in arthrpds, a visual system cmpsed f multiple lenses; each lens registers light frm a small prtin f the field f view, creating an image cmpsed f thusands f parts Malpighian (mal PIH gee un) tubule: in arthrpds, tubules lcated in the abdmen that are attached t and empty waste int the intestine mandibles (MAN duh bulz): in mst arthrpds, muthparts adapted fr hlding, chewing, sucking, r biting varius fds mlting: in arthrpds, the peridic shedding f an ld exskeletn parthengenesis (par thuh nh JE nuh sus): type f asexual reprductin in which a new individual develps frm an unfertilized egg phermnes (PER uh mhnz): chemical signals given ff by animals simple eye: visual structure in arthrpds that uses ne lens t detect light spiracles (SPIHR in kulz): in arthrpds, penings n the thrax and abdmen thrugh which air enters the trachea! tubes tracheal (TRAY kee ul) tubes: hllw passages in sme arthrpds that transprt air thrughut the bdy 3 I O Chapter 28 READING ESSENTIALS