What is a Caridina shrimp?

Before focusing on Caridina, it would be a good idea to explain what a shrimp actually is. Firstly, it is important to note that not all organisms colloquially termed a ‘shrimp’ are true shrimp, such as the mantis shrimp, which is actually a stomatopod (Stomatopoda). Scientifically, a true shrimp is any species that falls under the infraorder Caridea (caridea, ‘shrimp’). These species share morphological adaptations that make them more hydrodynamic and suited to swimming, collectively known as the ‘Caridoid facies’ (carid, ‘shrimp’; –oid, ‘like’),which can be summarised as follows:

  • Solid carapace covering the thoracic segments
  • Movable, stalked eyes
  • Biramous antennule
  • Scale-like exopod of antenna
  • Oar-like, natatory exopods on thoracic appendages
  • Long, segmented, flexible abdomen
  • Tail fan for backward swimming and steering formed by paddle-like branches (uropods) of sixth abdominal appendages and terminal telson
  • Abdomen, packed with powerful musculature
  • Most internal organs excluded from abdomen, except hindgut and nerve cord
  • Five pairs of paddle-like abdominal limbs (pleopods) used in forward swimming

Shrimp are not defined by the Caridoid facies, however, as most species under the superorder Eucarida (eu, ‘true’; carida, ‘shrimp’) exploit these characteristics. Also, some true shrimp may have lost these characteristics by natural selection, and other closely related orders may have similar morphologies.

Caridina shrimp are organisms under the genus Caridina, and are all true shrimp. Below is a table on the full scientific classification of a Caridina species Caridina caerulea, demonstrating the morphology that accompanies each taxon of classification. The physical characters up to ‘Caridea’ are therefore characteristics usually present in all shrimp.

Taxonomic Rank  Classification  Physical characters
 Domain  Eukaryota Cells contain membrane-bound structures (organelles).
 Kingdom  Animalia  Cells lack cell walls; Multicellular with few exceptions; Heterotrophic; Motile in some form.
Phylum  Arthropoda  Lack vertebrae; Segmented body; Jointed limbs; Chitinous exoskeleton.
 Subphylum  Crustacea  Biramous limbs; Nauplius larvae.
 Class  Malacostraca 19-20 segments: cephalon (5), thorax (8), abdomen (6-7).
 Subclass  Eumalacostraca 19 segments:  cephalon (5), thorax (8), abdomen (6).
 Superorder  Eucarida Capace fused to all thoracic segments; Stalked eyes.
 Order Decapoda  10 legs; Full carapace.
 Suborder Pleocyemata  Eggs incubated on female’s pleopods.
 Infraorder Caridea  2nd abdominal somite overlaps adjacent; 2 pairs of chelate pereiopods; Complex larval stages; Lamellar gill structure.
 Superfamily Atyoidea  Mature form inhabits freshwater, few exceptions.
Family Atyidae  Chelae have brushes of setae.
 Genus Caridina  (Mainly in subtropical and tropical freshwater habitats).
 Species Caridina caerulea  Full species description.

References:

Bauer R. T., (2004). Remarkable Shrimps: Adaptations and Natural History of the Carideans. Chapter 1, pg 3 – 6. University of Oklahoma Press.

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