Arthropods

This slides focused only to Class Arthropoda

1. An  arthropod  is an  invertebrate   animal  having an  exoskeleton  (external  skeleton ), a segmented body, and jointed  appendages . Arthropods are members of the  phylum   Arthropoda  (from  Greek   árthron , " joint ", and pous  ( gen.   podos ), i.e. "foot" or " leg ", which together mean "jointed leg "), and include the  insects ,  arachnids , and  crustaceans .

2. Arthropods are   invertebrates  with  segmented  bodies and jointed limbs. The limbs form part of an  exoskeleton , which is mainly made of α- chitin , a derivative of  glucose .  One other group of animals, the  tetrapods , has jointed limbs, but tetrapods are  vertebrates  and therefore have  endoskeletons . DESCRIPTION

3. Phylum called Arthropoda (arthropods) is the largest and most successful of the animal phyla. All arthropods have segmented bodies divided into a head, jointed legs and abdomen. DESCRIPTION

4. Arthropods are characterized by their jointed limbs and  cuticles , which are mainly made of α- chitin ; the cuticles of crustaceans are also  biomineralized  with  calcium carbonate . The rigid cuticle inhibits growth, so arthropods replace it periodically by  moulting . DESCRIPTION

5. They are important members of marine, freshwater, land and air  ecosystems , and are one of only two major animal groups that have adapted to life in dry environments; the other is  amniotes , whose living members are  reptiles ,  birds  and  mammals . DESCRIPTION

6. Head _______________________ Thorax _______________________ Abdomen SEGMENTATION

7.     = Body    = Coxa (base)    = Gill branch //   = Gill filaments   = Leg branch Structure of a   biramous   appendage [13] SEGMENTATION

8. Basic arthropod body structure = heart = gut = brain, nerve cord,  ganglia O = eye INTERNAL ORGANS

9. Arthropod bodies are also segmented internally, and the nervous, muscular, circulatory, and excretory systems have repeated components .  Arthropods come from a lineage of animals that have a  coelom , a membrane-lined cavity between the gut and the body wall that accommodates the internal organs.

10. Arthropods have open  circulatory systems , although most have a few short, open-ended  arteries . The heart is typically a muscular tube that runs just under the back and for most of the length of the hemocoel .

11. Arthropods have a wide variety of respiratory systems. Small species often do not have any, since their high ratio of surface area to volume enables simple diffusion through the body surface to supply enough oxygen.

12. Living arthropods have paired main nerve cords running along their bodies below the gut, and in each segment the cords form a pair of  ganglia  from which  sensory  and  motor  nerves run to other parts of the segment . The brain is in the head, encircling and mainly  above  the  esophagus . It consists of the fused ganglia of the acron and one or two of the foremost segments that form the head.

13. The stiff  cuticles  of arthropods would block out information about the outside world, except that they are penetrated by many sensors or connections from sensors to the nervous system. Head of a   wasp   with three ocelli (centre), and   compound eyes   at the left and right SENSES

14. Their vision relies on various combinations of  compound eyes  and pigment-pit  ocelli : in most species the ocelli can only detect the direction from which light is coming, and the compound eyes are the main source of information, but the main eyes of  spiders  are ocelli that can form images and, in a few cases, can swivel to track prey.

15. Chemical sensors provide equivalents of  taste  and  smell , often by means of setae. Pressure sensors often take the form of membranes that function as  eardrums , but are connected directly to nerves rather than to  auditory ossicles . The  antennae  of most hexapods include sensor packages that monitor  humidity , moisture and temperature

16. Compsobuthus werneri  female with young (white) REPRODUCTION

17. A few arthropods, such as  barnacles , are  hermaphroditic , that is, each can have the organs of both  sexes . However, individuals of most species remain of one sex all their lives . A few species of  insects  and  crustaceans  can reproduce by  parthenogenesis .

18. Aquatic  arthropods may breed by  external fertilization , internal fertilization , where the  ova  remain in the female's body and the  sperm  must somehow be inserted All known terrestrial arthropods use internal fertilization, as unprotected  sperm  and ova would not survive long in these environments . On the other hand, many male   terrestrial  arthropods produce  spermatophores , waterproof packets of sperm, which the females take into their bodies.

19. The nauplius larva of a  prawn Most arthropods lay eggs, but scorpions are  viviparous : they produce live young after the eggs have hatched inside the mother, and are noted for prolonged maternal care.

20. CHARACTERISTICS OF ARTHROPODS

21. The segmented bodies are arranged into regions , called tagmata (e.g., head, thorax, abdomen ). The paired appendages (e.g., legs, antennae) are jointed . They posses a chitinous exoskeletion that must be shed during growth. CHARACTERISTICS

22. A hard outer body covering called an exoskeleton. They have bilateral symmetry. The nervous system is dorsal (belly) and the circulatory system is open and ventral (back) Specialized mouth parts. Segmented body CHARACTERISTICS

23. EXOSKELETON SPECIALIZED MOUTH PARTS JOINTED LEGS COMPOUND EYES SEGMENTED BODY CHARACTERISTICS

24. MAJOR CLASSES OF LIVING ANTHROPODS

25. The major Classes of living arthropods are as follows with one example each: Class Arachnida - spiders Class Crustacea - crabs Class Diplopoda - millipedes Class Chilopoda - centipede Class Insecta or Hexopoda - insects Class trilobites are an extinct group of arthropod

26. Trilobites   (meaning "three lobes") are a well-known fossil group of  extinct  marine  arthropods  that form the  class   Trilobita . Trilobites form one of the earliest known groups of arthropods . Kainops invius , early  Devonian Paradoxides  sp., late  Cambrian TRILOBITES

27. Class trilobites are an extinct group of arthropods that lived in the seas of the world for about 380 Mya (million years ago), from the Precambrian 610 Mya to around the end of the Permian 230 Mya . Trilobites finally disappeared in the  mass extinction  at the end of the  Permian  about  250   million years ago . The trilobites were among the most successful of all early animals, roaming the oceans for over 270 million years. [2]

28. Trilobites had many life styles; some  moved over the sea-bed  as  predators ,  scavengers  or  filter feeders  and some  swam , feeding on  plankton . Most life styles expected of modern marine arthropods are seen in trilobites, with the possible exception of  parasitism  (where there are still scientific debates).

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30. Class Arachnida  (uh- rak �- nid -uh),  spiders, ticks, mites, scorpions and others . This is a diverse class which belongs to a subphylum of the Arthropoda known as the Chelicerata . ARACHNID

31. Chelicerata are characterized as having two distinct body regions, a cephlothorax and an abdomen. Chelicerates have six pairs of appendages, the first two pairs being mouthparts and the following four pairs being legs . They do not have antennae .

32. The first pair of mouthparts are the chelicerae (sing., chelicera). They are three-segmented and pincher-like. The second pair of mouthparts are the six-segmented pedipalps. They may appear leg-like (spiders) or claw-like (scorpions).

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34. CHILOPODA Class Chilopoda  (chi-lo- po �- da ), the  centipedes .� Two tagmata (head and trunk ) One pair of antennae with 14 or more segments One pair of legs per trunk segment

35. Mouthparts: one pair of mandibles and two pairs of maxillae Appendages on the first trunk segment are clawlike poison jaws or fangs with which centipedes paralyze their prey. The class name refers to the lip- like appearance of the fused bases of these appendages. Eyes may be present or absent.

36. Centipedes are elongate and flattened.� They are usually found in somewhat protected places, such as in leaf litter, in the soil, under bark, or in rotten logs .  One species is commonly found in houses and other buildings .

37. Centipedes are predatory and feed on insects, spiders, and other small animals.�� The larger centipedes can bite humans, but the bite is not serious and is no more painful that the sting of a bee or wasp.� The common small centipedes of Nebraska are harmless to man. Overall, centipedes are beneficial natural enemies of insects.

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39. DIPLOPODA Class Diplopoda  (dip-low- po �- da ), the  millipedes .� Two tagmata (head and trunk) ��� One pair of antennae , usually having seven segments ��

40. Two pairs of legs on most trunk segments  (30 or more pairs total) Mouthparts: one pair of mandibles, and one pair of maxillae Eyes are usually present

41. Millipedes are usually cylindrical (sometimes slightly flattened).� Except for the first three trunk segments, each segment has two pairs of short legs.� Millipedes are found in damp places such as the soil, leaf litter, or under logs and stones.

42. Most millipedes are beneficial scavengers of decaying plant material.� A few attack living plants and are sometimes pests.� Even fewer are predacious. Millipedes do not bite man, but many give off a foul-smelling fluid containing hydrogen cyanide which can be strong enough to kill insects placed in a jar with a millipede

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44. INSECTA Class Insecta  (in�- sec- ta ),  the insects .��   Three tagmata (head, thorax and abdomen)� One pair of antennae��������������������������������� Three pairs of legs �������������������������������������������������

45. May have wings, either one or two pairs Insects are the most abundant life form now known to science.� Around 1,000,000 species have been described and named.� That is more than all the other known animals put together.

46. The subphylum  Hexapoda  (from the  Greek  for  six legs ) constitutes the largest (in terms of number of species) grouping of  arthropods  and includes the  insects  as well as three much smaller groups of wingless arthropods:  Collembola ,  Protura , and  Diplura  (all of these were once considered insects). The Collembola ( or springtails ) are very abundant in terrestrial environments.  Hexapods  are named for their most distinctive feature: a consolidated thorax with three pairs of legs. Most other arthropods have more than three pairs of legs.

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