Arachnida and general life-cycle of arthropods

ClassificationSubphylum: Chelicerata-Body: Prosoma(6) and Opisthosoma(12)

A pair of chelicerae on the 1st prosomal segment

One pair of pedipalps + 4 pairsof walking legs

Three classes: 1.Arachnida 2. Merostomata 3. Pycnogonida

Class: Arachnida- spiders, scorpions, ticks, mites, etc.

Order- Acarina- ticks(hard and soft ticks, mites)

Class- Arachnida

• two body segments - cephalothorax and abdomen

• legs (4 pairs)

• 1 pair of chelicerae (used to grasp food)

• no antennae,No wings

• Mouthparts (palps, chelicerae and hypostome) are

borne on capitulum

• head is not distinct

• all are terrestrial

• Respiration is through lung hooks or trachea in Terrestrial forms ,through skin in parasitic form and trough gills in aquatic form

• sexes are separate: oviparous or viviparous

• mostly they are free living and some as parasite

• Ticks – parasites Mites – free-living & parasites

The main character of this group are the prosoma and opisthosoma.

The gnathostoma (capitulum) bears 3 structures that make up the mouthparts: the hypostome(toothed median structure), a pair of chelicerae(1st pair of appendages), and the pedipalps(2nd pair of appendages and has teeth)Mouthparts of the Acari are modified for specialized feeding

The pedipalps grasp a skin, while the chelicerae cut through it; the hypostome is thrust into the wound and the teeth anchor itself.

During feeding, the pedipalps either bend outward as the chelicerae and hypostome penetrate the flesh or remain rigidly and intimately associated with the hypostome during skin penetration; the pedipalps serve as counter-anchors while the tick is attached to the host

INSECTA ARACHNIDA

• Large mouth• ill developed sucking pharynx• Presence of antenna• Presence of wing • body divided into head thorax and

abdomen• no poisonous claw

• 3 pairs of legs• Segmented abdomen

• small or minute mouth • well developed sucking pharynx• no antenna• no wing• body divided into cephalothorax

and abdomen• presence of poison clawwith

which they paralyzed their prey before sucking its body fluid

• 4 pairs of legs(except larval stage)• No segmented abdomen

The general life cycle of arthropods and its

development stages

Metamorphosis

METAMORPHOSIS- The transformation of an immature insect from a larva to a pupa to an adult

ECDYSIS- Shedding of skin one or more times during growth

Types of metamorphosis

• Ametabolous metamorphosis-without metamorphosis- eg- silverfish

• Gradual metamorphosis

• Incomplete metamorphosis

• Complete metamorphosis

Gradual metamorphosis:

• Immatures are called nymphs.

• Change in form is gradual

• obvious changes involving development of external wing pads

• differences in color or markings.

• Nymphs and adults generally share the same habitat.

• e.g. grasshoppers ,crickets and true bugs

Complete metamorphosis (Holometabolous)

• Immatures are called larvae and pupae.• Butterflies, moths, beetles, flies, ants, bees mosquitoes and flea• Larvae do not resemble adults. • Wings and other adult features ………..an immobile pupal stage. • Immatures and adults may or may not share habitats. • Immatures are adapted for feeding • Adults are adapted for reproduction and dispersal. The adults inside the first instar is called as “imago”• Instar: The insect itself between molts "third instar (larva)"

LARVAIn the holometabolan type of insect the Larva has a head, horax and abdomen which bears five pair of fleshy hooked legs called prolegs

Types of larva:

1. Oligopod - these are characterized by presence of more or less well developed thoracic legs and the absence of abdominal appendages.. E.g Ladybird beetle Rhinocerusbeetle

2. Protopod: emerge in embryonic development and have imperfectly segmented abdomen It occurs in some parasitic forms of insects. Eg; Grubs of parasitic hymenoptera

3. Polypod: They have well defined segmented body with small thoracis legs and a number of abdominal pro- legs.Eg; Cater pillar(larvae of moth and butterflies

4. Apodous: Thet are degenerated type of larvae which are legless,robust,C- shaped or spindel shaped.

Its is called maggot in housefly

PUPA-It is resting, inactive stage of the holometabolous insects and transitional phase

during which the wings are developed and the insect attain matured sexual organs

Types- Based on shape or attachment of appendages

• Obtect type

The pupae have appendages which are firmly pressed against the body and the pupa is highly chitinized. Eg; moth pupa.

• Exarate pupa

Appendages are not glued to the body and uncovered after casting. All oligopod larvae turn in to exarate pupae. Eg ; Coleoptera, Hymenoptera.

• Coarctate pupa

The last larval skin is changed in to a pupal case.Pupal case is dark, brown, barrel shaped, smooth with no apparent appendages. Eg; Housefly., cocoons in silkworm

Incomplete Metamorphosis(Hemimetabola)

• Immatures are called naiads. • e.g. cockroach grasshopper, lice and bugs. • Immatures do not closely resemble adults • naiads have tracheal gills. • transition to adult form is gradual • Nymphs and adults dwell in different habitats

The many diverse orders of insects have three different types of life cycles. These life cycles are called "metamorphosis“ because of the changes of shape that the insects undergo during development.

Life cycle of Acarina