Athropoda

• PHYLUM ARTHROPODA


  Jointed Appendages
• Arthropoda can either be considered as a monophyletic clade of genetically diverse but evolutionarily linked species.
• Arthropoda can be considered an artificial, polyphyletic grouping of similar taxa evolving multiple times from different pre arthropod ancestors.
• About 84 percent of all known species of animals are members of this phylum.
• Arthropods are represented in every habitat on Earth and show a great variety of adaptations
• Approximately 900,000 species have been recorded, with probable as many more remain to be decribed
• Arthropods


  • Insects
  • Spiders
  • Scorpions
  • Pseudoscorpions
  • Centipede
  • Crabs
  • Lobsters
  • Brine shrimps
• Several types of arthropods live in aquatic environments and others reside in terrestrial ones; some groups are even adapted for flight.
• Arthropods


  • The distinguishing feature is the presence of a jointed skeletal covering composed of chitin (a complex sugar) bound to protein
  • The non-living exoskeleton is secreted by the underlying epidermis
  • Arthropods lack locomotory cilia, even in the larval stages, probably because of the presence of the exoskeleton
  • The body is usually segmented, and the segments bear paired jointed appendages, from which the name arthropod ("jointed feet") is derived
  • Like annelids, they are basically metameric, with new segments arising during development from a specific budding zone at the rear of the animal
  • In modern members there is a fusion and modification of different regions of the body for highly specialised functions
  • The specialisation of groups of segments, known as tagmatisation (tagma): Is seen in the body divisions of insects and arachnids
• Arthropod Great Diversity and Abundance


  • A Versatile Exoskeleton / cuticle
  • Segmentation and appendages for efficient locomotion
  • Air is piped directly into cells
  • Highly developed sensory organs
  • Complex behavious patterns
  • Reduced competition through metamorphosis
• Many other crustaceans live in the sea at depths exceeding 4,000 metres (around 13,100 feet), while the insect collembolans and jumping spiders have been found on Mt. Everest at heights exceeding 6,700 metres (around 22,000 feet).
• Minute copepods (typically less than 1 millimetre long) are among the most abundant animals on Earth, especially in marine surface waters.
• Minute crustaceans inhabit underground waters in many parts of the world, and deserts support a large arthropod fauna, especially insects and arachnids.
• Collembolans and the oribatid mites are among the permanent inhabitants of Antartica.
• Brine shrip are found in some saltwater lakes, and beetles, mites, and various crustaceans have been taken from hot springs.
• Arthropods are the only invertebrates capable of flight.
• Classification of Arthropods


  • Subphylum Chelicerata
  • Subphylum Trilobitomorpha (trilobites)
  • Subphylum Crustacea
  • Subphylum Myriapoda
  • Subphylum Hexapoda
• Subphylum Trilobitomorpha (trilobites)


  • Head (or cephalon) composed of 5 segments bearing a pair of antennae and compound eyes
  • Oval, flattened body composed of cephalon, thorax and pygidium, each segmented
  • Dorsal surface molded longitudinally into 3 lobes; each segment bears a pair of similar, branched appendages
  • Marine
  • More than 4,000 fossil species known
• Trilobite orders


  • Agnostida
  • Redlichiida
  • Corynexochida
  • Lichida
  • Odontopleurida
  • Phacopida
  • Proetida
  • Asaphida
  • Harpetida
  • Ptychopariida
• Subphylum Chelicerata


  • Body divided into prosoma (cephalothorax) and opisthosoma (abdomen)
  • No antennae
  • First pair of appendages consists of chelicerae flanking the mouth
  • In most chelicerates the other prosomal appendages are a pair of pedipalps and four pairs of legs
• Class Merostomata (Horse shoe crab)


  • Large marine chelicerates with book gills on the underside of the opisthosoma
  • Prosoma covered by a dorsal carapace
  • Opisthosoma bears a long terminal spine
  • Three body segments: prosoma, opisthosoma, and telson
  • Ten eyes on the top of the prosoma and six pairs of appendages on the underside of the prosoma
  • Five pairs of appendages are for walking and one pair of chelicera help the horseshoe crab move food into its mouth
  • The telson or tail is attached to the opisthosoma and is used for steering and flipping the crab over
• Orders of Merostomata


  • Xiphosura (horseshoe crabs, 4 species)
  • Eurypterida (Gigantostraca), which is extinct and includes 200 fossil species from the Paleozoic Era
• Class Arachnida (scorpions, spiders, ticks, mites)


  • Chiefly terrestrial
  • Book lungs and/or tracheae as gas exchange organs
  • Opisthosoma (abdomen) segmented or unsegmented externally and broadly or narrowly joined to the prosoma
  • About 70,750 species; Size: 0.25 mm–l8 cm
  • Prosomal appendages consist of 1 pair of chelicerae, 1 pair of pedipalps, and 4 pairs of legs
  • Gonopore always on the lower side of second abdominal segment
• Orders of Arachnida


  • Acari: (Acariformes and Parasitiformes) mites and ticks
  • Amblypygi: whip-spiders
  • Araneae: spiders
  • Opiliones: harvestmen
  • Palpigradi: micro-whip scorpions
  • Pseudoscorpiones: pseudoscorpions (False Scorpions)
  • Ricinulei: hooded tick-spiders
  • Schizomida: schizomids
  • Scorpiones: Scorpions
  • Solifugae: sun-spiders, camel-spiders, or wind scorpions
  • Uropygi or Thelyphonida: vinegaroons
• Class Pycnogonida (Sea spiders)


  • Mostly Marine
  • Narrow trunk of 4 to 6 segments
  • Greatly reduced abdomen
  • Cephalon (head) with proboscis bearing a pair of chelicerae, palpi, and egg-carrying legs
  • Commonly found crawling over sessile animals, such as hydroids and bryozoans
  • Usually 4 pairs of walking legs attached to lateral projections of the trunk
  • Tubercle with 4 eyes located dorsally between the first pair of legs
  • No gas respiratory organs
  • About 1,000 described species; 1 mm–10 cm

  
• The correct taxonomy within the Pycnogonida group is uncertain, and it appears that no agreed list of orders exists. All Families are considered part of the single order Pantopoda.
• Subphylum Crustacea (Crabs, shrimps,isopods, amphipods, krill, brine shrimp, copepods, barnacles)

  • Mainly aquatic, generally marine but few freshwater and few live in moist places
  • Generally free living but few are parasitic
  • Head bears a pair of compound eye and five pairs of appendages
  • Thorax and abdomen often with a pair of biramous appendages in each segments
  • Respiration either by gill or general respiratory surface
  • Sex usually separate & sexual dimorphism is common
  • Development includes metamorphosis with free larval stages
  • Coelom greatly reduced, it is in the form of haemocoel
  • Excretory organs are modified coelomoduct which may be either maxillary gland or antennary (green) glands
  • 44,000 described species distributed among 6 subclasses

  
• Subclasses of Crustacea


  • Class Branchipoda
  • Class cephalocarida
  • Class maxillopoda
  • Class malacostrata
  • Class Remipedia
• Class Branchipoda


  • A small body (0.25 mm - 10 cm long)
  • Simple mouth parts
  • Paired compound eyes, single simple eye
  • Leaflike or phyllopodous appendages, for feeding, locomotion, and respiration
  • Minimal body tagmosis
  • The nervous system and sensory system are simple, although some species vibrate their compound eyes to gather more visual information
  • Gathered food particles are pushed into a ventral food groove that leads to the mandibles, then the Mouth and, in turn, a complete gut
  • Since most branchiopods are small with a thin cuticle, gas exchange can occur across the body wall as well
  • The circulatory system includes a heart that pumps blood into an open body cavity or hemocoel
  • Undigested particles exit through the anus and nitrogenous wastes are eliminated through maxillary glands
• Orders of Branchiopoda


  • Phyllopoda (fairy shrimp, tadpole shrimp and brine shrimp)
  • Cladocera (Daphnia species)
• Class Remipedia


  • The first described remipede was the fossil Tesnusocaris goldichi (Lower Pennsylvanian), but, since 1979, at least seventeen living species have been identified with global distribution throughout the Neotropics
  • Their size is variable from 10–40 millimetres long and include a head and an elongated trunk of up to forty-two similar body segments
  • Swimming appendages are lateral on each segment, and they swim on their backs. They are slow-moving
  • They have fangs connected to secretory glands; it is still unknown whether these glands secrete digestive juices or poisonous venom, or whether remipedes feed primarily on detritus or on living organisms
  • They have a primitive body plan for crustaceans, and have been regarded as an ancestral crustacean group
  • The size and complexity of the brain suggests that Remipedia might be the sister taxon to Malacostraca, regarded as the most advanced of the crustaceans

  
• Class Cephalocarida


  • Horseshoe shrimp are small, 2-4 mm
  • Have an elongated body and a large head, the posterior edge of which covers the 1st thoracic segment
  • Eyes are absent and the 2nd pair of antennae is located posterior to the mouth, which is unique for the Crustacea
  • Maxillae are unspecialized. The 1st pair of maxillae is very small and the 2nd pair has the same makeup as the following thoracic legs
  • The mouth is behind the upper lip and mandibles occur on either side
  • There are 10 thoracic segments and the abdomen bears a telson but no other appendages

  
• Class Malacostrata


  • Largest subclass of crustacea including most crabs, lobster, shrimps, crayfish, krill, sow bugs and beach flies
  • Thorax comprises eight segments, abdomen six segment, rarely seven
  • Exoskeleton of head unite with few or more thoracic segment to form cephalothoracic carapace
• Orders of Malacostraca


  • Syncarida "mountain shrimps"
  • Mysidacea
  • Cumacea
  • Leptostraca
  • Isopoda
  • Amphipoda
  • Stomatopoda
• Class Maxillopoda


  • Generally small animals
• Mouth


  Behind the upper lip and mandibles occur on either side
• Thoracic segments


  • 10
  • Abdomen bears a telson but no other appendages
• Eg.


  • Hutchinsoniella macracantha
• Class Malacostrata (Soft shell)


  • 8 groups (Orders)
  • Largest subclass of crustacea including most crabs, lobster, shrimps, crayfish, krill, sow bugs and beach flies

  
• Crustacean


  • Large marine and fresh water
  • Thorax comprises eight segments, abdomen six segment, rarely seven
  • Exoskeleton of head unite with few or more thoracic segment to form cephalothoracic carapace