Insect Abdomen: Appendages found on the abdomen

Insect abdomen is the third functional region of insect body. It is located behind the thorax and contains 6-10 segments. There are various types of appendages arise from the abdomen.

Cerci

Located close to anus.

-Blattodea: simple and jointed cerci

Via ediacaran.mech.northwestern.edu

-Orthoptera: simple and not jointed cerci

-Dermaptera: Sclerotized, forceps like cerci

Dermaptera forcep like cerci via gallurapestcontrol.com

-Thysanura: Long filamentous cerci

Long filamentous cerci of Thysanura

-Ephemeroptera larvae: Wing like cerci that helps to move forward in water.

Wing like cerci -Ephemeroptera larva

Styles

Can be seen in Cockroach and Lepisma. It is regarded as the vestige of the walking limb.

via microscopy-uk.org.uk

Median caudal filament

This is a thread like projection arising from he center of the last abdominal segment between the cerci.

Abdominal Prolegs

Can be seen in Lepidopera.

via entomology.umn.edu

Abdominal Gills

These are respiratory organs and found in nymphs of some aquatic insects.

Cornicles

These are located dorsally on the abdomen as paired secretory structures.

      

Female External Genitalia

Ovipositors are used for oviposition and it is formed by the modification of 8-9 abdominal segments. Thysanura, Orthoptera, Thysanoptera and some Hymenoptera insects contain true ovipositors.

Ovipositor places egg inside caterpillar 

Egg is released (naturecloseups.com)

-The ovipositor is modified as a poison injecting sting ( Wasps, bees..etc)

via amazingnature.us

-Hind end of the abdomen is extended to work as an ovipositor

Male genitalia

Modification of 9^th abdominal segment makes the copulatory organ of males which is consist of aedeagus and pair of lateral claspers to grasp and hold the abdomen of the female during mating. 

Moulting and cuticle formation of insects

Hormones such as Ecdysone and bursicon play an important role during the events in moulting.

Apolysis

·         Epidermal cells divide and change their shape.

·         These cells separate from the inner surface of the old endocuticle and leave out the sub-cuticular space.

·         This space is consisting of moulting fluid, proteinase and chitinase.

·         These enzymes are inactive in this stage.

Formation of the epicuticle

·         Cuticulin is deposited below the moulting fluid and above the epidermis.

·         This forms the new Cuticulin layer.

·         Inner protein epicuticle is deposited under the Cuticulin layer.

Deposition of new procuticle

·         Deposition of procuticle occurs beneath the Cuticulin layer.

·         After the deposition enzymes in the moulting fluid activate and digest the old endocuticle.

·         Only a thin layer of the old endocuticle is left out.

·         This layer is called as Ecdysial membrane. These lines are located in the median lines of head and thorax.

·         Weak lines appear along this Ecdysial layer.

·         Wax secretion occurs on to the surface of the new cuticle.

Ecdysis

·         Moulting fluid and digested old endocuticle are absorbed.

·         Intake of the air and muscular contractions cause the insect’s body to swell.

·         This leads the old exoskeleton to split open along the weak lines.

·         Insect draws itself out.

·         All parts of the old cuticle are shed.

·         This old cuticle is called as cast skin.

Expansion of the new procuticle

·         New cuticle is soft and pale.

·         At this moment new procuticle expands before it hardens.

Hardening and darkening of cuticle

·         Hardening of the cuticle is known as sclerotization.

·         This forms sclerites which are rigid plates of exoskeleton.

·         It also darkens the cuticle. This is known as tanning.

Deposition of the new endocuticle

·         New endocuticle deposits after the moulting and tanning.

Internal gill structures of aquatic vertebrates

INTERNAL GILLS

·         Pouched gills: in agnathans – lamp rays

·         Septal gills: in chondrichthyes

·          Aseptal gills: in osteichthyes

Pouched gills

·         Large sac like branchial pouches which are lined with primary gill lamellae.

·         Water goes through mouth àpharynx àpore shaped internal gill slitsàbranchial pouches.

·         Water leaves the branchial pouches through pore shaped external gill slits.

Septal gills

·         Branchial pouches are narrow chambers.

·         Between the branchial chambers, para branchial chambers are present with external gill slits. External gill slits are small and slit shaped.

·         Distal tips of the interbranchial septa can act as valves to close the external gill slits.

·         Gill lamellae runs along the interbranchial septa towards the body surface.

·         Internal gill slits rise from the pharynx and run into each branchial chamber.

Aseptal (non-septal) gills

·         Operculum covers the gills.

·         A single large opercula cavity is present with one valved external gill slit.

·         Interbranchial septa are greatly reduced.

·         Therefore gill lamellae extend freely into the opercula cavity.

(diagram: http://people.eku.edu)

Comparative anatomy of the animal body covering

INVERTEBRATE BODY COVERING

Protozoan body covering

·         Plasma membrane acts as the body covering.

·         Some have an additional gelatinous outer layer.

·         Some have a complex body covering called Pellicle. Ex:- Paramecium

Pellicle

·         Two membranes are present as outer alveolar membrane and outer alveolar membrane.

·         Between those two an alveolar cavity is present.

·         Some have cilia in the pellicle.

Poriferan body covering

·         Thin.

·         Two types of epidermis.

-          Pinacoderm: outer epidermis. Single layer of Pinacocytes. Pinacocytes are scale like falttened cells.

-          Choanoderm: inner epidermis. Single layer of choanocytes. Choanocytes are oval shaped cells with a flagellum on each.

·         Between those to lies the mesoglea or mesenchyma.

·         It’s a jelly like layer consist of spicules and amoebocytes, enclosing a central cavity called spongocoel.

·         Spicules supply strength and amoebocytes give rise to new cells.

·         Ostia are located on the wall.

Cnidarian body covering

·         Similar to that of Poriferan.

·         Outer epidermis: Cuticle is present.

                             Consist of small cubicle cells.

·         Inner gastrodermis: Mainly consist of columnar epithelial cells.

·         Mesoglea: Jelly like layer.

Platyhelminthes, nematode, annelid and arthropod body covering.

·         Single layer epidermis is present.

·         Cuticle is present on the epidermis.

·         Some arthropods have an inner layer of dermis.

VERTEBRATE BODY COVERING

·         Body covering is called as skin.

·         It has a multilayered structure.

·         Consist of two layers as epidermis and dermis.

Epidermis

·         Multilayered.

·         Avascular.

·         Forms structures such as feathers, claws, scales…etc.

·         From top to bottom of the epidermis;

-          Stratum corneum: Dead keratinized cells are on the surface.

-          Stratum germinativum

-          Basal lamina.

Dermis

·         Fibrous connective tissue with blood vessels, nerves and sensory receptors.

·         Fish scales are derived from the dermis.

Fish skin

·         Relatively thin.

·         Derivatives of the skin;

-          Scales: Bony scales derived from dermis.

             Bone cells come into the dermis and secrete scales. Afterwards they leave. Dentine and enamel layers are later deposited on those scales.

-          Melanophores: Star shaped cells that lie under the epidermis.

-          Glands

                                                                                     I.            Mucous glands: unicellular mucous producing glands. Mucous reduce friction when swimming. Produce mucous cocoon to protect from predators and heat in dry seasons. Also prevent invasion of bacteria.

                                                                                  II.            Poison glands: produce poisonous substances.

                                                                               III.            Light emitting glands: aids to attraction, species recognition and avoid predators.

Amphibian skin

·         Thin, moist skin.

·         Can breathe through the skin.

·         Derivatives of the skin

-          Glands

                                                                         I.            Mucous glands: keep the skin moist

                                                                      II.            Granular poison glands: parotid and parotoid glands.

-          Chromatophores: present in epidermis and dermis. Gives colorization.

·         No scales except for some species.

Reptilian skin

·         Thick, dry skin.

·         Stratum corneum is hardened with dead keratinized cells.

·         Can observe two layers in the epidermis.

-          Outer epidermal generation

-          Inner epidermal generation

·         Therefore they can shed scales or called as molting.

·         Scent producing glands are present in some.

·         No mucous glands.

Bird skin

·         Thin but horny scales are on legs and feet.

·         Claws and beak present.

·         Derivatives of the epidermis:

-          Feathers

                                                                 I.            Contour feathers: Cover the body.

                                                              II.            Flight feathers: Cover the wings. Large and stiffer.

                                                           III.            Down feathers:  lie beneath the contour feathers. Fluffy barbs.

                                                           IV.            Bristle feathers: Short and stiff but the barbs are absent.

·         Stratum corneum is not keratinized like in mammals.

·          Dermis lacks ossification.

·         Glands: mainly secrete lipids.

-          Uropygial gland: Single, branched alveolar gland located above the base of the tail. Produces fatty and waxy secretion. This is later spread over feathers to make waterproof.

-          Wax glands: lie in the external ear canal

Mammalian skin

·         Thick epidermis.

·         Transitional layers can be seen between stratum corneum and stratum germinativum.

·         Stratum corneum is thick and forms foot pads in many mammals.

·         Glands:

-          Sebaceous glands: alveolar branched glands that produce oil and wax.

-          Sweat glands: tubular coiled glands.

-          Mammary glands