Arthropoda

• Arthropoda can either be considered as a monophyletic clade of genetically diverse but evolutionarily linked species or an artificial, polyphyletic grouping of similar taxa evolving multiple times from different pre arthropod ancestors
• Approximately 900,000 species have been recorded, with probable as many more remain to be described
• Arthropods


  • Insects
  • Spiders
  • Scorpions
  • Pseudoscorpions
  • Centipede
  • Crabs
  • Lobsters
  • Brine shrimps

  
• Arthropods


  • The distinguishing feature is the presence of a jointed skeletal covering composed of chitin (a complex sugar) bound to protein
  • They 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
• Arthropod Great Diversity and Abundance


  • 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
• 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 Antarctica
• Brine shrimp 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 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


  • Head often fused with thorax to form cephalothorax covered dorsally by carapace
  • 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


  • Branchipoda
  • Cephalocarida
  • Maxillopoda
  • Malacostraca
  • 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
  • Nervous system and sensory system are simple
  • Gathered food particles are pushed into a ventral food groove that leads to the mandibles, then the Mouth and, in turn, a complete gut
  • Gas exchange can occur across the body wall
  • 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 Branchipoda


  • 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 Malacostraca


  • Largest subclass of crustacea including most crabs, lobster, shrimps, crayfish, krill, sow bugs and beach flies
  • Large marine and fresh water crustacean
  • 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
• Maxillopods


  • 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)
• Malacostrata


  • Largest subclass of crustacea including most crabs, lobster, shrimps, crayfish, krill, sow bugs and beach flies
  • Large marine and fresh water crustacean

  
• Thorax


  • Comprises eight segments
  • Abdomen six segment, rarely seven
• Exoskeleton


  • Head unite with few or more thoracic segment to form cephalothoracic carapace
• They appear to be confined to the Southern Hemisphere
• Superorder Syncarida "mountain shrimps"


  • They lack a carapace but have exopodites on all thoracic limbs
  • Eyes are sessile or stalked or completely absent
  • The exopod is in the shape of a whip
  • They live in freshwater lakes and streams