Classification of Arthropoda with Identification Characters for Each Sub-Phylum and Class

Arthropods are classified into five sub-phylum and each then subdivide into classes (a total of 16 classes according to recent classification of animal taxa).

Classification of Arthropods

I.   Sub-phylum: Trilobitomorpha (extinct arthropods)

Class 1: Trilobita

II.   Sub-phylum: Chelicerata (spiders, horseshoe crabs)

Class 1: Arachnida
Class 2: Merostomata
Class 3: Pycnogonida

III.  Sub-phylum: Myriapoda (centipedes, millipedes)

Class 1: Chilopoda
Class 2: Diplopoda
Class 3: Pauropoda
Class 4: Symphyla

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IV.  Sub-phylum: Crustaceae (crabs, prawns, shrimps)

Class 1: Branchiopoda
Class 2: Remipedia
Class 3: Cephalocarida
Class 4: Maxillopoda
Class 5: Ostracoda
Class 6: Malacostraca

V.   Sub-phylum: Hexapoda (insects)

Class 1: Insecta
Class 2: Entognatha

Identifying Characters of Arthropodas

I. Sub-phylum: Trilobitomorpha: General characters:

Ø  Primitive arthropods
Ø  Extinct forms
Ø  Abundant during Paleozoic era
Ø  Body is divided into three lobes, hence the name trilobitomorpha
Ø  Body is divided into a median and two lateral lobes by a longitudinal axial furrow
Ø  Body division: head, abdomen and pygidium (pygidium = posterior body part of some insects and members of extinct trilobites. It is separated from the thorax by articulation. Pygidium contain anus and in females it also contains the ovipositor)
Ø  Head bears a pair of antenna and eyes
Ø  Eyes were compound
Ø  Appendages biramous
Ø  Structural differentiation of body parts absent

.

II. Sub-phylum: Chelicerata, General characters

Ø  Presence of chelicerae (chelicerae is the modified anterior most appendages)
Ø  Cephalothorax or prosoma with anterior six segments
Ø  Abdomen or opisthosoma with thirteen segments
Ø  Abdomen is divided into mesosoma and metasoma
Ø  Antennae completely absent

Sub-phylum Chelicerata includes three classes

.

III. Sub-phylum: Myriapoda, General characters

Ø  Includes centipedes and millipedes
Ø  All are terrestrial arthropods
Ø  Usually contain many legs
Ø  Single pair of antennae
Ø  Eyes simple
Ø  Mouth part lies on the underside of head
Ø  Upper lip of mouth with epistome and labrum
Ø  Lower lip of mouth with a pair of maxillae
Ø  A pair of mandibles present
Ø  Mandibles lie inside the mouth
Ø  Breath through spiracles that connect tracheal system similar to insects
Ø  Excretion through malpighian tubules

Sub-phylum Myriapoda includes four classes

.

IV. Sub-phylum: Crustacea, General Characters:

Ø  Usually marine aquatic arthropods
Ø  Head and thorax fused to form cephalothorax
Ø  Cephalothorax usually covered by single large carapace
Ø  Two pair of antennae (only arthropod with two pairs of antennae)
Ø  5 pairs of cephalic appendages
Ø  Cephalic appendages: first pair antennules, second pair antennae, third pair mandibles, fourth pair first maxillae and fifth pair second maxillae
Ø  Thoracic and abdominal appendages are biramous
Ø  First pair of antennae (antennules) are uniramous
Ø  Respiration through gills
Ø  Excretion by green glands or antennal glands
Ø  Sense organs: antennae, statocysts and eyes
Ø  Eyes are compound
Ø  Paired gonopores
Ø  Development usually indirect (direct forms also present)

Ø  Larval stage is called nauplius

Sub-phylum Crustacea is divided into six classes:

.

V. Sub-phylum: Hexapoda, General characters:

Ø  A large taxa, includes insects and a small group of wingless arthropods
Ø  Body plan: 3 parts, head, thorax and abdomen
Ø  Head with six segments
Ø  Thorax with three pairs of jointed legs (hence the name hexapoda)
Ø  Head bears a presegmental acron
Ø  Acron bears compound eyes

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Ø  Head segments are very closely fused
Ø  Appendages absent in segment 1 and 3
Ø  Segment 2 bears a pair of antennae
Ø  Segment 4 bears mandibles for crushing the food items
Ø  Segment 5 bears maxillae for chewing
Ø  Segment 6 bears the labium which forms the lower lip of mouth
Ø  Mouth lies between the fourth and fifth segments
Ø  Thorax composed of three segments, each with a single pair of legs
Ø  Each leg with single walking branch composed of five segments
Ø  Abdomen usually with 11 segments
Ø  Abdominal appendages are absent or extremely reduced
Ø  Abdomen contains most of the internal systems such as respiratory, excretory and reproductive systems
Ø  Respiration through tracheae
Ø  Excretion through malphigian tubules
Ø  Development always indirect
Ø  Larval stage present, which undergo complete metamorphosis

Sub-phylum Hexapoda is divided into two classes

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