Arthropoda characters & classification

ARTHROPODA
INTRODUCTION
GENERAL CHARACTERS
CLASSIFICATION

1. ARTHROPODA Arthropods were first studied by Aristotle . Von- sie -Bold coined the Name Arthropoda Arthropoda , animals having jointed appendages or legs. Arthro = Jointed; poda = foot Bilaterally symmetrical, triploblastic , metamerically segmented , haemocoelomic , protostomes , invertebrates having head, thorax and abdomen, a chitinous exoskeleton and jointed legs and appendages.

2. Introduction Most successful phylum on the Earth that has ever existed. The phylum includes such animals as spiders, insects, shrimps and craps among many others that can be found in a wide range of environments from the ocean floor to the mountain peaks. Largest class- Hexapoda / Insecta Largest order- Coleoptera Chitinous exoskeleton- prevents dessication and helps in attachment of muscles Ecdysis / moulting

3. General characters Cosmopolitan in distribution found in aquatic, terrestrial and aerial forms.  Some are ectoparasitic and vectors of disease. Body have jointed appendages or legs (which are modified to different structures to perform different functions like jaws, gills, walking legs, paddle) . There may be 3 pairs, 4 pairs, 5 pairs, many pairs. Body is triploblastic . Bilaterally symmetrical. Organ system level of organization. Body is divisible into head, thorax and abdomen. Tagmosis

4. General characters This is the first group to develop a true head, which contains sense organs and feeding organs specialized for their particular habitats. Body is covered with chitinous exoskeleton. Sclerites , tergum , sternum and pleura, ecdysis / moulting to facilitate growth They are haemocoelomate . Coelom i.e. body cavity is filled with blood or fluid. Head bears a pair of compound eyes and antenna. Locomotion takes place by jointed appendages. Swimming, creeping, burrowing, running, flying can be accomplished with the jointed appendages

5. General characters Digestive system is complete, straight and well developed. forgut , midgut and hindgut, foregut and hindgut covered internally by cuticle, midgut by endoderm The mouth bears mouth parts for ingestion of foods. Mouths are modified for chewing, biting, sponging, piercing, siphoning. Respiration takes place by general body surface or gills (in Crustaceans) or trachea ( in insects, diplopoda and chilopoda ) or booklungs ( Arachnida ) and book gills (in king cobra).

6. General characters Circulatory system is of open type i.e. do not have blood vessels and enters directly into the body chambers. The blood / Haemolymph is colorless. In crustaceans it is blue due to haenocyanin . Heart is dorsal to haemocoel Excretion takes place through Malphigian tubules (in terrestrial form) or green glands or coxal glands (in aquatic forms). NOTE: Aquatic forms are ammonotelic , terrestrial forms are uricotelic . Nervous system is of annelidian type, which consists of brain and ventral nerve cord. Sensory organ include antennae, sensory hairs for touch and chemoreceptor, simple and compound eyes, auditory organs (in insects) and statocysts (in crustacean).

7. General characters Muscles are striated, very few non striated Unisexual i.e. sexes are separate. Sexual dimorphism can be seen in some Fertilization is internal or external. They are either oviparous or ovoviviparous. Development may be direct or indirect. Parthenogenesis can be seen in some insects Life history includes one to many larval forms and a metamorphosis

8. Phylum Arthropoda – Six Sub-Phyla Tardigrada Pentastomatida Trilobitomorpha or Triolobita Picnogonida or Pantopoda Chelicerata Mandibulata Of these six phyla now Tardigrada , Pentastomatida and Picnogonida are included under minor phyla Consequently only three sub phyla are discussed here. Classification of arthropoda

9. I.Sub -phylum- trilobita Extinct marine arthropods – fossils found inn Cambrian period Body – head, trunk and pygidium Body is protected by chitinous plates- exoskeleton Body is oval divided into three lobes by longitudinal furrows A pair of many jointed antennae are present on head Four pairs of biramous appendages Trunk appendages are also biramous and chitinous gnathobase was attached to each leg Respiration by gill like structure Larva – Protaspis Examples : Triarthrus , Agnostus

10. II. SUB-PHYLUM- CHELICERATA Terrestrial or marine animals Body – Prosoma or Cephalothorax(6 segments) and Opisthosoma(13 segments) Devoid of antennae Cephalothorax bears six pairs of appendages 1 st pair- Chelicerae, 2 nd pair- Pedipalpii remaining four pairs of walking legs At the hind end of opisthosoma- a telson is present Second abdominal segment bears genital aperture covered by genital operculum. Median ocelli are present Respiration by book lungs Excretion by malphigian tubules and coxal glands. Sexes are separate and development is direct Chelicerata includes– Merostomata , Arachnida

11. 1.Class- merostomata Marine animals Prosoma bears a pair of compound eyes Opisthosoma is divided into mesosoma and metasoma Prominent caudal spine is present Mesosoma has 4-5 pairs of appendages Respiration through gills It includes two sub-classes i ) Xiphosura and ii) Eurypterida

12. Sub class: xiphosura Cephalothorax is dome shaped/ convex shaped Two pairs of eyes present on dorsal side of cephalothorax Mouth is on ventral side surrounded by six pairs of appendages In the abdomen mesosoma is 6 segmented and metasoma is unsegmented and is like a long spine called telson Coxal glands – excretory organs Example : Limulus ( K ing crab)

13. Sub-class- eurypterida It includes fossil animals which had stout bodies Examples : Eurypterida and Pterygotus

14. Class- arachnida Terrestrial animals Body – cephalothorax and abdomen Exoskeleton is made of chitin Simple eyes are present. Compound eyes when present are degenerated Prosoma/cephalothorax bears chelicerae and strong pedipalpi , four pairs of walking legs Antennae are absent Respiration is by book lungs or tracheal tubes Take only liquid food Sexes are separate. Divided into Nine orders.

15. Sl.No Orders Examples 1 Scorpionida (Scorpions) Palamnaeus , Buthus 2 Araneida (Spiders) Lycosa ( hunting spider), Cteniza (trap door spider) 3 Pseudoscorpionida Chelifer , Garypus 4 Solifuga Galeodes 5 Palpigrada Eukoenenia 6 Pedipalpida Mastigoproctus 7 Phalangida Oligolophus , Gaddo 8 Podogona Cryptocellus 9 Acarina (Ticks & Mites) Ixodes (Tick), Sarcoptes (Mite)

16. Sub-phylum- mandibulata Animals with mandibles Aquatic or terrestrial animals Body is made of two parts- head and trunk. Trunk in some cases may be divided into thorax and abdomen Appendages include 1or 2 pairs of antennae and walking legs Compound eyes and simple eyes are present Respiration by gills, trachea or skin It includes four classes Crustacea Chilopoda Diplopoda Insecta / Hexapoda

17. Class- crustacea Marine animals. Some live in fresh water and others in damp places Live independently or as parasites or as symbiotic animals Body – head, thorax and abdomen (cephalothorax in some) Five pairs of cephalic appendages –antennules, antennae, mandibles and two pairs of maxilla A pair of stalked compound eyes Eight pairs of thoracic and six pairs of abdominal appendages are also seen

18. Class- crustacea Exoskeleton is made of plates or sclerites . The cuticle is in the form of thin membrane between sclerites Respiration is by gills Circulatory system consists of heart , arteries and haemocoelomic spaces Excretion is by antennal glands Sexual dimorphism is present Free swimming Nauplius stage in the life cycle

19. Crustacea is divided into six sub-classes Sl .No Sub – class Examples 1 Branchiopoda Daphnia(water flea) Apus 2 Ostracoda Cypris 3 Copepoda Cyclops , Diaptomus 4 Branchyura Argulus , Dolops 5 Cirripedea Barnacles ( Lepas , Balanus ) 6 Malacostraca Squilla , Palaemon , Cancer(Crab)

20. Class- chilopoda ( opisthogoneata ) Commonly called centipedes Body dorsoventrally flattened Head is formed by 6 segemnts and trunk by many segments Nocturnal animals live in humid places Head bears two pairs of maxillae and a pair of legs in each segment of trunk except last two First pair of legs of the trunk bear poisonous claws into which poisonous glands open Genital openings are present between the penultimate legs. Gonads are dorsal to the gut. Respiration by tracheal tubes. Examples: Scutigera , Scolopendra

21. Class- diplopoda ( progoneata ) Commonly called millipedes- have numerous legs. Each segment with two pairs of legs Each segment has two pairs of ganglia, two pairs of spiracles and two pairs of ostia Vegetarians and nocturnal. Body is cylindrical and divisible into 5 segmented head and a large number of body segments. Maxillae unite to form a special structure called gnathochilarium . Besides maxillae head bears a pair of antennae and a pair of mandibles also Gonads are ventral to alimentary canal and are unpaired but gonoducts are paired Poisonous glands and claws are absent. Examples: Julus , Spirostreptus

22. Class- insecta / hexapoda Commonly called hexapods Body is divisible into head, thorax and abdomen Head is made of 6 segments . Externally segmentation is not seen Head bears a pair of antenne , a pair of mandibles, two pairs of maxillae and a pair of compound eyes Thorax is divisible into three segments- Prothorax, mesothorax and metathorax Two pairs of wings and three pairs of jointed legs in the thorax

23. Class- insecta / hexapoda Abdomen is without appendages A pair of well developed salivary glands help in digestion Excretion – Malphigian tubules associated with gut Tracheal respiration Sexual dimorphism, development is direct/indirect with larval and pupal stages

24. Hexapoda is divided into two sub- classes. They are Sub classs - Apterygota ( Ametabola ) Sub-class- Pterygota Wings are absent Wings are present. In some they are secondarily absent Metamorphosis is absent Metamorphosis is present Examples : Lepisma , Campodea , Podura etc Examples : Dragon fly, Mantis, Locust, Cimex , Cockroach, Butterfly etc.