Phylum Arthropoda

Species of Phylum Arthropoda have segmented bodies, exoskeletons made of chitin, and jointed appendages. Arthropods are highly diverse and inhabit various environments, playing important roles in ecosystems as predators, pollinators, scavengers, and more.

General Charaderistics:

1) Habitat: These are free-living, aquatic (fresh water/marine) or terrestrial and some are parasitic form also.

2) Organisation: These species exhibit organ level system level of organization.

3) Germ Layer: They are triploblastic animals.

4) Symmetry: Body is bilaterally symmetrical.

5) Coelom: They possess true coelom which is reduced and act as haemocoel (blood cavity).

6) Digestion: Digestive system is complete with mouth and anus. Digestion is extracellular.

7) Respiration: Respiration through gills or trachea or book lungs. Haemocyanin is the usual respiratory pigment.

8) Excretion: Excretion through Malphigian tubules or Coxal gland or Green gland or Maxillary gland.

9) Circulation: Circulatory system is open type. Blood vessels open within haemocoel.

10 Locomotion: Presence of paired jointed appendages (segmental) helps in locomotion.

11) Reproduction: Reproduce sexually, sexes are separate. Fertilization internal in terrestrial but external in aquatic species. Parthenogenesis also seen in some members.

12) Development: Development may be direct or indirect.

13) Tagmatization: Body divided into – Head, Thorax and Abdomen. Cephalothorax (Head+Thorax) also seen.

Example: Limulus sp. (Horse shoe crab); Scorpio sp. (Scorpion); Aranea sp. (Spider) ; Nymphon sp. (sea spider); Palaemon sp. (Prawn); Cancer sp. (Crab); Julus sp. ; Apis indica ; Periplaneta sp. (Cockroach) etc.

Classification of Arthropoda

There are four subphylum in phylum Arthropoda.

Subphylum 1: Trilobita
Subphylum 2: Chelicerata
Subphylum 3: Crustacea
Subphylum 4: Uniramia

Subphylum 1: Trilobita:

Habitat: Extinct marine arthropods.
Shape: Body more or less oval and flattened from above downwards.
Body Parts: Body is divided into three regions- (i) Head/Cephalon; (ii) Thorax/Trunk; (iii) Pygidium
Eye: Presence of a pair of compound eyes laterally.
Carapace: Head and pygidium covered by unjointed calcareous exoskeleton called Carapace.
Antennae: A pair of many jointed antennae represent the pre-oral appendages.
Leg: Each leg has 8 segments.

Example: Holmia sp.

Subphylum 2: Chelicerata or Arachnomorpha

Habitat: Found in Marine or Terrestrial forms.
Body: Body is divided into two parts- (i) Cephalothorax (Prosoma) (ii) Abdomen (Opisthosoma).
Chelicerae: First pair of appendages on the first segment is called Chelicerae used for feeding.
Pedipalp: A pair of pedipalp present on 2nd segment.
Eye: Median simple eyes present mostly. Compound eyes present in few cases along with simple eye on lateral side.
Antennae: Absent
Development: Development usually direct.

Example: Limulus sp. (Horse Shoe Coab), Scorpio sp. (Scorpion). Nymphon sp. (Sea Spider), Pycnogonum sp.

Subphylum 3: Crustacea:

Habitat: Mainly aquatic, mostly marine, many fresh-water and some are terrestrial.
Body: Body divisible into 3 regions- Head, Thorax and Abdomen.
Eye: A pair of compound eyes present.
Antennae : Two pairs of antennae are a distinguishing feature among crustaceans.
Cephalic Appendages: One pair of Mandibles and two pairs of Maxillae.
Carapace: Carapace covers all or part of the body.
Respiration: Respiration takes place either by gills or by general surface of the body.
Excretion: Excretion through antennal gland (Green gland) or shell gland (Maxillary gland).
Biramous: Appendages are typically biramous.
Development: Development includes a larval form, ‘Nauplius’.

Example: Palaemon sp. (Prawn); Carcinus sp. (True crab)

Subphylum 4: Uniramia:

Habitat: Mainly terrestrial, few are aquatic animals.
Eye: Compound eyes present. Many species lack eyes.
Antennae: One pair of antennae present.
Cephalic Appendages: One pair of mandible and two pair of maxillae. Mandibles are unjointed without palp.
Respiration: Respiration through trachea.
Excretion: Excretory organ is Malphigian tubules.
Uniramous: Appendages are uniramous, unbranched.

Example: Scutigera sp. ; Pauropus sp.; Spirobolus sp. ; Apis indica ; Musca domesticus ; Locusta sp. etc.

Phylum Annelida Phylum Mollusca