External morphology : crab

 

External organization of crab

_Crab Body Structure_

·       Cephalothorax (fused head and thorax)

·       Abdomen (reduced, straight, symmetrical)

·       - Depressed carapace (dorsal)

Cephalothorax_

-         Dorsal carapace (flat, broad, oval)

-         Anterior and lateral margins: Semi-circular, spiny

-         Ventral side: Sternites, lines of fusion marked

_Cephalic Appendages_

-         Compound eyes (stalked, movable)

-         Antennae

_Cephalothoracic Appendages_

-         Antennule (small, paired, retractile)

-         Second antenna (small, paired, erect)

-         Mandible (paired, stout palp, non-serrated incisor processes)

-         4-5. First and second maxillae (prominent second maxillae with scaphognathites)

-         6-8. First, second, and third maxillipeds (whiplike exopodites, sword-shaped epipodites)

Thoracic Appendages_

-         Five pairs of walking legs:

-         First pair: Chelate (claw-like)

-         Second, third, fourth: Walking

-         Fifth pair: Modified as paddle (Portunid families)

_Maxilliped Structure_

-         Endites (inner branches)

-         Endopodite (inner limb)

-          Exopodite (outer limb)

-         Epipodite (outer branch)

-         Coxopodite (basal joint)

-         Ischiopodite (second joint)

*Walking Legs (Pereopods)*

-         Uniramous, jointed

-         Five pairs, with bases set apart on each side

-         First pair: Well-developed, powerful chela (major cheliped)

-         Other legs: Clawed, but not chelated

-         Functions: Food capture, defense, walking sideways

-         *Major Cheliped Structure*	-         Minor Cheliped Structure*
-         Coxa -         Basis -         Ischium -         Carpus -         5. Merus -         6. Manus (Propodus -         Pollex -         8. Dactyl	-         . *Coxa -         Basis -         Ischium -         Carpus -         Merus -         Manus -         Pollex -         Dactyl

*Aabdominal Appendages (Pleopods)*

-         Rudimentary

-         Six pairs, but sixth pair absent in both sexes

-         Male: Two pairs of copulatory stylets (1^st and 2^nd pleopods)

-         Female: Four pairs of pleopods form egg-carrying basket

*Abdomen*

-         Six-segmented, flap-like

-         Thinner than cephalothorax

-         Flexed in ventral side of cephalothorax

-         Anus at terminal end of last segment

*Key Features*

-         No swimmerets (locomotor appendages) in abdomen

-         Well-developed walking legs

-         Powerful chela (major cheliped) for food capture and defense

*Sex Identification in Crabs*

-         Separate sexes (male and female)

-         Identified using abdominal flap and appendages

*Male Crab Characteristics*

-         Abdominal flap: Pointed (triangular)

-         Narrow, thin abdomen

-         Two pairs of copulatory stylets (modified 1^st and 2^nd pleopods)

-         *Female Crab Characteristics*

-         Abdominal flap: Semi-circular (wide, rounded)

-         Broader, more rounded abdomen

-         Four pairs of pleopods forming an egg-carrying basket