General character and classification of Arthopoda.

General characters of Arthropoda.

Some of the general characters of Arthropoda are as follows.

• Organ-system level of body organization.
• Body bilaterally symmetrical, triploblastic and metamerically segmented.
• Appendages jointed, usually one pair to a somite, and with varied functions as jaws, gills, legs, etc.
• True coelom reduced and largely replaced by a blood-filled haemocoel.
• Muscles mostly striated, usually capable of rapid constriction.
• The exoskeleton of dead chitinous cuticle that is shed at intervals, called ecdysis or moulting, for growth and development.
• Body division into the head, thorax, and abdomen. Head and thorax often fused to form a cephalothorax.
• The digestive system completes with mouth and anus.
• Mouth part adapted for various modes of feeding.
• The circulatory system opens with a dorsal often many-chambered heart, arteries and blood sinuses or haemocoel.
• The respiratory system by general body surfaces, gills, trachea or book-lungs.
• Excretory organs are green glands or Malpighian tubules.
• The nervous system typically annelidan, with a dorsal brain, connected with a nerve ring to a double ventral nerve cord.
• Sensory organs comprises of eyes (simple and compound), chemo-and tactile receptors, and balancing and auditory organs.
• Parental care well marked.
• Sexes usually separate (dioecious). Reproduction usually internal. Oviparous or ovoviviparous.
• Development direct or indirect with one or many larval stages. Parthenogenesis in some.

Classification.

Arthropoda is a much heterogeneous group including a variety of divergent views concerning their phylogeny. Because of this reason no definitive system of classifying this phylum exists. The classification adopted here is a synthesis of several views so that the large and diverse phylum may be conveniently grouped. Seven subphyla are recognised in the following classes. Of these, only Trilobitomorpha, Chelicerata and Trilobitomorpha includes a number of extinct classes only.Onychophora, Tardigrada and Pentastomida show only doubtful or superficial relationships with other arthropods, so that some book treat them as independent minor phyla.

Subphylum I. Trilobitomorpha

(Gr., tri, three + lobos, lobe + morphe, form

1. Fossil trilobites. Mostly marine and bottom-dwellers. Cambrian to Permian.
2. Body three-lobed, due to 2 longitudinal furrows.
3. Biramous appendages on all segmented except the last one.
4. Head distinct. Probably one pair of antennae.

Example: Triarthus, Dalmanites.

Subphylum II. Chelicerata

(Gr., chele, claw + keros, horn + ate, group)

1. Body divided into an anterior cephalothorax (prosoma) and a posterior abdomen (opisthosoma).
2. Pro somatic appendages 6 pairs. The first pair of preoral chelicerae with claws, followed by posterior and 4 pairs of walking legs.
3. Antennae and true jaws absent.

Class 1. Merostomata

(Gr., meros, high + stoma. mouth

1. Marine ith median simple and lateral compound eyes.
2. 5to 6 pairs of abdominal appendages with book-gill.
3. Abdomen ending in a sharp telson or spine.
4. Excretion by coxal glands. No Malpighian tubules.

Subclass 1. Xiphosura

(Gr., xipos, sword + aura, tail)

1. Cephalothorax with large extended, convex, horseshoe-shaped carapace.
2. Abdomen unsegmented with a long terminal telson.

Example: Limulus

Subclass 2. Eurypterida

(Gr., eurys, broad + pteryx, wing).

1. Extinct marine, giant water scorpions.
2. Cephalothorax small. Carapace plain, not extended.
3. Abdomen 12-segmented and narrowed behind.

Examples: Eurypterus, Pterygotus.

Class 2. Arachnida

(Gr., arachna, spider)

1. Terrestrial or aquatic. Eyes simple. No compound eyes.
2. Cephalothorax ith 2 chelicerae, 2 pedipalps and 4 pairs of walking legs.
3. Respiration by tracheae, book-lungs or both.

Order 1. Scorpionida (=Scorpiones)

1. Elongated, fair-sized true scorpions.
2. Metasoma ending in a telsion and poison sting.
3. Respiration by 4 pairs of lungs.

Example: Buthus, Palamnaeus.

Order 2. Pseudoscorpionida (= Chelonethida)

1. Tiny false scorpions.
2. Abdomen 11-segmented, without sting and telson.
3. Chelicera 2. jointed, with comb-like serrations.

Example: Chelifer, Microcreagris.

Order 3.Araneae

1. True spiderProsoma and opisthosoma without visible segments and joined by a narrow pedicel.
2. Opisthosoma three pairs of spinnerets.
3. A flagellum on each chelicera of male, for sperm transfer.

Example: Galeodes.

Order 4. Solifugida (=Solifugae)

1. False spiders, sun spiders or wind spiders.
2. A flagellated on each chelicera of male, for sperm transfer.

Example: Galeodes.

Order 5. Palpigradi

1. Small-sized microwhip scorpions. Without eyes.
2. Opisthosoma 11-segmented, ending in a large 15-jointed telson or flagellum.

Example: Koenenia.

Order 6. Pedipelpi (=Uropygi)

1. Elongated whip scorpions with 1 pair of eyes.
2. Pedipalps large, heavy, with a terminal pincer.

Example: Mastigoproctus.

Order 7. Amblypygi (= Podogna)

1. Flattened scorpion-spiders or taillers whip scorpions.
2. Abdomen 12-segmented, without flagellum.

Example: Charinus.

Order 8. Ricinulei (Podogna)

1. Rare, small, tick-like, heavy- bodies arachnids.
2. Third pair of legs in the male from copulatory organs.

Example: Ricinoides.

Order 9. Opioliones (=Phalangida)

1. Spider-like Harvest-men, Harvest-spiders or daddy longlegs.
2. Scent glands under the carapace.

Example: Phalangium.

Order 10. Acarina

1. Ticks and mites. Free-living or parasitic.
2. Largest arachnid orders with 20,000 species.

Examples: Sarcoptes.

Subphylum III. Mandibulate

(L., mandibula, mandible+ate, group)

1. Compound eye common.
2. Body division into heads thorax, and abdomen.

Class 1. Crustacea

(L. crusta,shell)

1. Head often joined w ith thorax to form a cephalothorax.
2. Sexes usually separated.

Subclass 1. Cephalocarida

1. Antennae short. Eyes absent.
2. Hermaphrodite.

Example: Hutchinsoniella.

Subclass 2. Branchiopoda

1. Primitive, small sized, mostly freshwater.
2. Antennules and 2nd maxillae reduced or absent.

Order 1. Anostraca

1. Fairy shrimps with 19 or more trunk segments.
2. Carapace absent.

Examples: Artemia.

Order 2. Notostraca

1. Tadpole shrimps with 25-45 trunk segments.
2. Eyes sessile. Styles joined.

Examples: Apus, Lepidurus.

Order 3. Diplostraca

1. Eyes fused, sessile.
2. Styles unjointed, claw-like.

Examples: Daphnia, Cyzicus.

Subclass 3. Ostracoda

1. Trunk appendages 2 pairs, leg-like.
2. Antennules and antennae large, used in swimming.

Order 1. Myodocopa

1. Carapace with antennal notches.
2. Antennae biramous, enlarged at base.

Example: Cypridena.

Order 2. Podocopa

1. Carapace unnotched. Trunk appendages 2 pairs.
2. Antennae uniramous clawed at tips.

Example: Cypris.

Order 3. Platycopa

1. Carapace unnotched.
2. Antennae uniramous.

Example: Cytherella

Order 4. Cladocopa

Carapace unnotched. Antennae biramous.

Example: Polycope.

Subclass 4. Mystacocarida

1. Primitive. Body microscopic.
2. A single median eye.

Example: Derocheilocaris.

Subclass 5. Copepoda

1. Body small, made of heads thorax and abdomen.
2. Antennules long. Antennae smaller.

Example: Cyclops.

Subclass 6. Branchiura

1. Body dorso-ventrally flattened.
2. First maxillae modified into suckers.

Example: Dolops.

Subclass . Cirripedia.

1. Barnacles. Adult sessile, attached or parasitic.
2. Abdomen rudimentary with caudal styles.

Order 1. Thoracica

1. Non-parasitic. With or without a stalk, Hermaphrodite.
2. Thoracic appendages 6 pairs, cirriform.

Example: Lepas.

Order 2. Acrothoracica

1. Sessile. Bore into mollusca shells or corals.
2. Unisexual.

Example: Alcippe.

Order 3. Ascothoracica

parasitic in echinoderms and corals.

Example: Synagoga.

Order 4. Apoda

Parasitic without mantle and appendages.

Example: Proteolepis.

Order 5. Rhizocephala

Adult parasite, degenerate, sac-like.

Example: Sacculina.

Subclass 8. Malacostraca

1. Body large sized. Typically made of 19 segments.
2. Abdomen end in a telson. No caudal styles.

Order 1. Nebaliacea

Abdomen segment 7 instead of 6.

Example: Nebalia.

Order 2. Mysidacea.

Body elongated. Uropods from fantail.

Example: Mysis

Order 3. Cumacea

Head and thorax generally enlarged. Abdomen enlarged.

Example: Cumopis

Order 4. Isopoda

Head and 1 or 2 thoracic segments from cephalothorax. Gills and heart abdominal.

Example: Oniscus

Order 5. Amphipoda

Sand hoppers. Body laterally compressed.

Example: Cyamus.

Order 6. Stomatopoda

Mantis shrimps. Body flattened. Abdomen large, broader than cephalothorax.

Example: Squilla.

Order 7. Decapda

Shrimps, crayfishes, prawns, crabs, etc.

Suborder (a) Natantia

Body laterally compressed. Rostrum prominent.

Example: Prawn, Shrimp.

Suborder 2. Reptantia

Body dorsoventrally flattened. Rostrum short or absent.

Example: Crayfish.

Class or group 2. Myriapoda

(Gr., myrios, ten thousand + podos, foot)

1. Exclusive terrestrial, air-breathing mandibulate arthropods.
2. Body worm-like made of the head and elongated trunk with many similar leg-bearing segments.
3. Respiration by trachea. Spiracles arranged segmentally.
4. Sexes separated, Gonad single. Gonoducts paired.
5. Excretion by 1 or 2 pairs of Malpighian tubules.
6. Body worm -like, made of the head and elongated trunk with many similar leg-bearing segments.

Class 3. Insecta

( L.insectus, cut or divided)

1. Body made of head (six fused segments), thorax (3 segments) and abdomen (up to 11 segments.)
2. Head with compound eyes (1pair), antennae (1 pair) mandible (1pair) and maxillae (2 pairs).
3. Mouth parts modified for different feeding habits.
4. Thorax with 3 parts of jointed legs and 1 or 2 pairs of wings which may be absent.
5. Respiration by tracheae. Spiracles lateral.
6. Excretion by Malpighian tubules.
7. Unisexual. Fertilization internal. Development usually with metamorphosis.

Subclass 1. Apterygota

1. Primitively, wingless insect.
2. Little or no metamorphosis.
3. Abdomen with cerci and style-like appendages.

Order 1. Protura

1. No antennae, true eye and metamorphosis.
2. Abdomen with 11 segments plus a telson.

Example: Acerentulus.

Order 2.Collembola

1. No eyes,trachea,Malphian tubules, and metamorphosis.
2. Abdomen 6 segmented, with a springing organ.

Example: Achorutes.

Order 3. Thysanura

1. Body covered by minute silvery scales.
2. Antennae long.Mouth parts chewing.

Example:Lepisma

Subclass 2. Ptergota (Metabola)

1. Wings present. Secondary lost in same.
2. Metamorphosis complete or incomplete.

Division (a) Exopterygota (Heterometabola)

1. Well, developed external or buds.
2. Metamorphosis gradual. Young stages are lymph.

Order 1. Orthoptera

Wings two pair. Foreign straight and leathery. Hindwings membranous and folded at rest.

Example: Romalia and Poecilocerus.

Order 2. Isoptera

Wings 2 pairs. Held flat on black . Or wingless.

Example: Termites or white ants.

Order 3. Dermaptera

Mouth part chewing. Forceps -like cerci at the tip of the abdomen for offence and defence.

Example: Forficula.

Order 4. Ephemeroptera

Wings 2 pairs, membranous. Forewings longer and triangular. Hindwings smaller and rounded.

Example: Ephemera.

Order 5. Odonata

Wings 2 pairs, membranous. Eyes very large.

Example: Dragonflies, Damselflies.

Order 6. Plecoptera

Wings 2 pairs, membranous, longer than a body.

Example: Isoperla

Order 7. Psocoptera (=Corrodentia)

Wingless or drawings larger than hindwings.Example Booklice.

Order 8. Mallophaga

Wings absent. Body small. Head large. Mouth parts chewing. Eyes degenerate. Legs clasping.

Order 9. Anoplura(=Siphunculata)

No wings. Body broad, flat, Head small.Mouth parts piercing and sucking.

Example: Pediculus (Human louse).

Order 10. Thysanoptera

Wings 2 pairs, similar, fringed with hairs.

Example: Thrips.

Order 11. Hemiptera

Wings 2 pairs or wingless. Forewings thickened at base, membranous at tip (hemelytra).

Example: Bedbug.

Order 12. Homoptera

Wingless or 2 pairs of uniform membranous wings.

Example: Cicadas Aphids.

Division (b) Endopterygola (Holometabola)

1. Wings develop internally in pupal case.
2. Metamorphosis complete with larval and pupal stages.

Order 1. Neuroptera

1. Wings large, membranous, ith much veined.
2. Antennae long. Mouth parts chewing. Cerci absent.

Example: Crysopa.

Order 2. Celeoptera

1. Forewings leathery. Hindwings membranous folding.
2. Antennae variously modified. Mouth parts chewing.

Example: Beetles.

Order 3. Mecoptera

1. Wings long, similar, narrow, membranous.
2. Mouth parts chewing, on a prolonged beak.

Examples: Panorpa.

Order 4. Trichoptera

1. Wings long, hairy, folded roof-like over the abdomen.
2. Antennae long. Mouth part rudimentary.

Example: Caddisflies.

Order 5. Lepidoptera

1. Wings membranous, covered with overlapping scales.
2. Mouth parts sucking, coiled under the head.

Example: Butterflies.

Order 6. Diptera

1. Wings 1 pair. Hindwings as knob-like halters.
2. Mouth parts piercing-sucking or sponging.

Example: Musca.

Order 7. Hymenoptera

1. Wings 2 pairs, similar, membranous. On each side hooked together during flight.
2. Mouth parts sucking or chewing. Ovipositor of female usually forms a piercing sting.

Example: Apis.

Order 8. Siphonaptera

1. Small. Laterally flattened. Secondarily wingless.
2. Mouth parts piercing sucking. Legs long leaping.

Example: pulex.

Reference:

Agrawal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordahttp://www.encyclopedia.com/topic/Arthropoda.aspxn

E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L.,Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.