Internal Anatomy

Musculature

A typical caridean possesses particularly strong muscles located mostly in the pleon or abdominal segments (Wicksten , 2010). These muscles allow the shrimp to escape a potential predator rapidly with a ‘tail flick’ propelling the shrimp backwards. In commercially harvested carideans it is these muscles that are consumed.

The musculatures of the pleopods in A. strenuus are relatively weak in comparison to the burrowing Crangonidae and other Alpheidae shrimp species as A. strenuus only uses them for swimming and moving sediment as apposed to excavating deep tunnels (Banner & Banner, 1982).

The major chelae, which produces the snapping sound signature to alpheid has a different muscular structure to the minor chelae. Surprisingly, the major chelae appears to be of a slower contracting type with most muscle fibers uniformly large in diameter while the minor chelae has a three part arrangement with large fibers located centrally with two regions of smaller diameter fibers on either side producing rapid contractions of the claw (Mellon, 1999).   

Nervous system

Located anteriorly is a cerebral ganglion from which branch optic, antennal and antennular nerves as well as a ventral nerve chord (Wicksten, 2010).

There are many sensory organs associated with carideans most of which are only visible via electron microscope. A prominent sense organ is the eyes consisting of a pigmented cornea and an eyestalk (peduncle). More cryptic sensory organs include statocysts located within the cephalic region usually in the first antennae of most alpheid shrimp are used for balance (Wicksten, 2010). The second antennae function as touch sensitive organs but may also have chemoreception for long distances (Wicksten, 2010). Chemoreception by touch also occurs in the dactyls of the thoracic appendages and inner mouthparts known as ‘taste’ (Wicksten, 2010)

Digestive system

The opening of the oral cavity is covered by protective ‘double door-like’ structures called labrum covered in setae to prevent large unwanted particles entering the mouth and to stop food escaping (Felgenhauer & Abele, 1985).

Carideans also possess an esophagus, which enters a two-chambered stomach. The stomach consists of a cardiac stomach where food is ground and sorted while the pyloric stomach where setae prevent large particles entering the midgut until they are further broken down (Felgenhauer & Abele, 1985). The midgut extends almost the entire length of the pleon, which is the distasteful ‘vein’ in commercially consumed species of carideans (Wicksten, 2010). Finally the there is a short section of hindgut before the anus, which is located on the ventral side of the telson (Wicksten, 2010)

Circulatory system

A. strenuus like all crustaceans have an open circulatory system lacking in capillaries  (Wicksten, 2010). The blood or hemolymph consists of amebocytes, clotting agents and a pigment called hemocyanin (Wicksten, 2010).

The heart, located beneath the posterodorsal portion of the carapace receives hemolymph via five pairs of ostia and leaves through a single artery which them branches to supply the visceral mass and appendages (Wicksten, 2010).

Respiratory system

Phyllobranchiate gills are located in chambers on either side under the carapace (Wicksten, 2010). Water enters the gill chambers anteriorly, sides and rear propelled via the scaphognathites of the second maxillae and exit next to the mouth (Wicksten, 2010). Gas is exchanges across a thin, permeable membrane of the gill lamellae (Wicksten, 2010).

Excretory system

Excretory pores and antennal glands are located on the second antennae excrete nitrogenous waste mainly as ammonia (Wicksten, 2010).

Reproductive structures

A. strenuus are gonochoristic and express sexual dimorphism with the females generally being slightly larger than the males (Banner & Banner, 1982). Males possess a pair of testes located dorsally to the hepatopancreas while females have paired tubular ovaries dorsal to the cardiac stomach (Wicksten, 2010).

The sperm of a typical caridean are often thumbtack shaped and are aflagellate (Kim et al, 2003).