Arthropods Tang Hiu Man(22) 6S Arthropods Tang Hiu Man (22) 6S

Kingdom Animalia Arthropods 節肢動物 Crustaceans 甲殼動物 Myriapods 多足動物 Arachnids 蜘蛛類動物 Insects MolluscsAnnelidsVertebrates

Introduction An arthropod is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages （附屬肢體）invertebrateanimal Largest group of invertebrate( ＞ 1 million species) Occupy ＞ 80% of all the animal species Largest number of species Has individuals occupying the greatest variety of habitats consists of repeated segments, each with a pair of appendages

Features All consists of chitinous( 角質素的 ) exoskeleton (cuticle) and jointed legs, some may have wings (eg. Butterflies, dragonflies) Consists of repeated segments, each with a pair of appendages Internal organs are also built of repeated segments Highly versatile (enabled them to become the most species-rich animals in most environment ) vision relies on various combinations of compound eyes

1.Crustaceans( 甲殼 ) Have biramous( 二肢 ) appendages Shrimp crab Barnacle 藤壺 water flea

2.Myriapods( 多足 ) have many body segments, each bearing one or two pairs of legs. centipede 蜈蚣 millipede

3.Arachnids( 蜘蛛類 ) presence of chelicerae( 螫肢 ), appendages just above / in front of the mouth. spider mite scorpion

4.Insects with six thoracic legs Butterfly bee beetle dragonfly

Cuticle (chitinous exoskeleton)  Reduce water lost by evaporation  Act as a protective layer against bacterial invasion & mechanical injury  Provide a rigid framework to support the body on land  The presence of joints between segments of legs allow rapid locomotion to take place  Provide large surface area for muscle attachment that produces force for locomotion  The thoracic( 胸的 ) cuticle with wings to make flight possible  With colour for camouflage( 保護色 )

Wings  They enable insects to fly so that: a. Insects can get their food & escape from their enemies quickly, thus flight facilitates survival. b. Insects can disperse themselves & thus reduce the problem of overcrowding.

Jointed Legs  Allow walking  A pair of strong & muscular hind legs( 後腿 ) allow rapid hopping( 跳 ) for long distance during escaping from enemies or catching preys

Small size  Reduce the competition for food & space  Reduce body weight to facilitate flight  Insects can easily hide themselves in crevices( 縫隙 )

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Modification of Jointed Appendages Jointed appendages can be modified Jointed appendages can be modified Can become many different structures for different functions Can become many different structures for different functions eg. appendages on head → eg. appendages on head → antennae( 觸角 ), palps( 觸鬚 ) for sensory functions antennae( 觸角 ), palps( 觸鬚 ) for sensory functions Appendages on thorax & abdomen( 腹 ) → Appendages on thorax & abdomen( 腹 ) → walking, swimming, transferring sperms walking, swimming, transferring sperms

Breathing Aquatic (crustaceans) gill terrestrial Tracheal system (insects & myriapods) Book lungs 書肺 (arachnids)

Gill Book lung Tracheal system

Reproduction terrestrial : internal fertilization terrestrial : internal fertilization Aquatic : external fertilization except scorpion (lay eggs) Aquatic : external fertilization except scorpion (lay eggs) A few: have organs of both sexes (eg. barnacles) have organs of both sexes (eg. barnacles) Parthenogenesis( 單性生殖 )(reversible) Parthenogenesis( 單性生殖 )(reversible)

Reference production_and_development production_and_development production_and_development production_and_development Advanced-level Biology for Hong Kong Advanced-level Biology for Hong Kong AL Biology Book 3 Ecology AL Biology Book 3 Ecology

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