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Crustaceans – Jointed Appendages for locomotion and feeding. Ashton Mouton 2432509 Dept. of Biodiversity and Conservation Biology University of the Western Cape. A Brief Description of Crustaceans.

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Crustaceans jointed appendages for locomotion and feeding l.jpg

Crustaceans – Jointed Appendages for locomotion and feeding

Ashton Mouton


Dept. of Biodiversity and Conservation Biology

University of the Western Cape

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A Brief Description of Crustaceans

  • Crustaceans are a large group of arthropods that are treated as a subphylum and are found in marine, freshwater and terrestrial environments although they are mostly found in aquatic ecosystems.

  • They have three distinct body divisions that include the head, the thorax and abdomen or when there is no clear distinction between the head and thorax then it's called the cephalothorax.

  • The most important groups found abundantly of the crustaceans are the copepods, barnacles, malacostraca (Craps, shrimps, lobster and krill), branchiopoda.

  • Groups that posses a well developed abdomen, usually have six specially adapted appendages for locomotion of which 5 are called swimmeret (pleopod) and one pair called the uropod

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Subphylum: Crustacea

Class: Branchiopoda






The Scientific Classification of Crustaceans

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Crustacean Composition

The exoskeleton is divided into a number of plates and cylinders

the jointed appendages are described as the point where the exoskeleton remains flexible and thin at the junction of the plates and cylinders Many of the crustacean's appendages are biramous

They have a hardened exoskeleton that contains calcium carbonate.

The head bears a pair of compound eyes and three pairs of mouth parts

a pair of mandibles and two pairs of maxilla used for handling food.

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There are three different kinds of appendages in crustaceans that allow their appendages to be diverse, which are the cylindrical walking legs, biramous appendages and the leaf like limbs. (Kaestner A (1970)The first sets of appendages are the biramous appendages that consist of a protopodite with two branches (Kaestner A (1970)The cylindrical walking legs bear a resemblance to that of other arthropods, which have one set of articles that belong to either the protopodite or endite if present, which are used for locomotion or holding onto its prey and rarely used for swimming in super order, Portunidae and Munnopsidae(Kaestner A (1970)The leaf-like appendages are only fond in the Branchiopoda and the Phyllocaridae and function like leaf-limbs that are adapted to do include swimming, respiration and filter current production (Kaestner A (1970)

Three Limb types

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Figure 1 shows the biramous appendage

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The Evolution of Crustaceans

The study of the diversity of crustacean limbs was made possible by the results of molecular and genetic modules of Drosophilia and mice that were made available(Panganiban et al 1995).

  • The two genes that are the main focus of the development of appendages on different segments are the ultrabithorax (Ubx)and the abdominal-A (abd-A) in crustaceans(Panganiban et al 1995).

  • The appendages that assist in feeding are called the maxilliped and do not express the Ubx/abd-A genes during early embryological development(Panganiban et al 1995).

  • Branchiopods have preserved many ancestral characters like the lack of maxillipeds (Panganiban et al 1995).

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The Evolution of Crustaceans (continue)

  • Copepods have one maxilliped present but the appendage has evolved separately from the maxilliped found in theMalacostracans(Panganiban et al 1995).

  • Therefore the gene expression responsible for the change in the morphology of limbs through evolution can represent the change of the maxilliped in some crustaceans through the mutation of the Ubx/abd-A expression; therefore it is reasonable to say that the altering patterns of Ubx/abd-A genes can form part of the developmental foundation of the evolution of crustacean appendages(Panganiban et al 1995)

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The Body Parts of crustaceans

  • The body of each crustacean is divided into three different groups, which contain the preoral two pairs of antennae, the mouthpart and the trunk appendages(Kaestner A (1970).

  • The trunk appendage is further divided into the thoracopods and pleopods. The first three thoracopods are transformed into accessory mouthparts that have strong endites, basal articles and less developed branches(Kaestner A (1970).

  •  When there is many pairs the modifications tend to be more similar in the posterior end and are then called maxilliped while the other limbs are called walking legs (perepods) (Kaestner A (1970).

  • Occasionally the grouping of the trunk somites match the distribution of the limbs, this results in many thoracopods transforming into maxilliped while the fusion of the head and thoracomeres to form the cephalothorax, examples are Isopods, Amphipods, Mysidacea and Cumacea(Kaestner A (1970).

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Figure 2 shows the different body appendages and body shapes

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The appendages found at the thoracic region are transformed into maxilliped to be used for feeding; their articles frequently allocate thorns on the inner surface, which help in the movement of two pairs of protopodites or endites and are analogous to the labium of insects(Kaestner A (1970).

The thoracic region may not bear modified appendages like in most Malacostracan but the pereopods are modified to appear like walking legs and in other crustaceans these limbs could be modified and used for swimming if there are large exopodites present (Kaestner A (1970).

In the branchiopoda the appendages found at the thorax are biramous with two parallel branches while the Ostracods have only two pairs of legs, which are highly specialized (Kaestner A (1970).

Crustaceans have a constant feeding activity and will undergo certain times of fasting during development, which occurs through molting (Sanchez-Pazza et al 2004). Molting involves different stages with different feeding behaviors and requires sufficient energy from the food available to crustaceans (Sanchez-Pazza et al 2004)

Thoracic Appendages

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Abdominal Appendages

  • Malacostracans are the only crustaceans that have pleopods, which are used for swimming and are therefore covered by setae furthermore their branches are possibly alike (Kaestner A (1970).

  • However they may also respire through these appendages by creating respiratory currents that serve has gills.

  • The males first two pairs of appendages form into gonopods, which are copulatory appendages The uropods are the last pair of the pleopods found in the Malacostracans and is joined with the telson to form the tailfan, which increase the thrusting action that the abdomen creates when moving (Kaestner A (1970).

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The integument is a membranous structure that contains various layers to protect the body of crustaceans

The hypodermis secretes a layered chitinous membrane or cuticle and the epicuticle protects it (Kaestner A (1970).

The integument in larger crustaceans may be used as ventral skeletal system to provide support for the continuous growth of these crustaceans (Kaestner A (1970).

Chromatophores are responsible for the different colors available in crustaceans, which are caused by these soluble pigments found in the cuticle (Kaestner A (1970).


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These consist of all the crustaceans that have eight thoracic somites six or seven abdominal somites and a few species have a abdomen that has a furca (Kaestner A (1970).

The appendages have pleopods that are found on the abdomen and the pleopods are divided into uropods.

Malacostracans can be characterized by having larger complex morphologies that are more advanced than other crustaceans, larger and heavier exoskeletons and are larger in size (Kaestner A (1970).

The species that are the most economically important are found in this group, which contain species like the Euphausid, shrimps, lobsters and crabs. Shrimps, lobsters and crabs fall in the order Decapoda and they are characterized by having a carapace that is fused to the thoracic metameres that extend to each side of the legs, which encloses the gills within the branchial chambers (Kaestner A (1970).

The appendages consist of three maxilliped while the other is walking legs but the first pereopods is structurally modified to be cheliped that is used to protect itself or handling prey (Kaestner A (1970).

The Malacostranans

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Figure 3 shows the different Malacostracans that are edible for humans

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Most crustaceans have hardened exoskeletons that can be preserved in rocks and have.

Fossils of crabs have been found in rocks that date back to the Cretaceous period, as well as those of the Cenozoic era.

Although soft shelled crustaceans have a poor fossil record.

This includes the barnacles and the shrimps

Crab fossils are found in rocks like the Gault clay that date back to the Cretaceous period, where these crustaceans lived on the bottom of sea or in reefs

History of Crustaceans

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The Anastraca are mostly the fairy shrimps that are constantly swimming at a slow pace with he venter twisted upwards, therefore they are found swimming just below the sea surface and only occasionally are found at the bottom of the sea bed.

They do not have maxillae but the locomotory limbs have a leaf-like appearance that enables the body to be pushed forward as well as by contracting and extending the trunk rapidly they can dash themselves off.

These crustaceans are filter feeders that rely on plankton, small suspended organic particles on plant and larger animals that create currents, which release any stubborn particles attached to these examples.

Food is caught by creating waves by rapidly vibrating the limbs that attract food to the mouth region where the small particles are sucked up into.

Feeding and Locomotion

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Figure 4 shows what the different appendages are used in the order Malacostraca

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The Cirripedia (barnacles), these crustaceans are either sedimentary or symbiotic and they all occur in marine habitats (Kaestner A (1970).

The body is consists of a head, thorax and abdomen region that enclosed in a bivalved carapace. Some Cirripedia maintain their primitive body order by still having six somites on the thorax and the abdomen by having five somites (Kaestner A (1970).

All Copepods are floaters and therefore rely on the currents to keep them afloat, if there were no currents available, they would sink and die.

In many tropical and Mediterranean species the setae on the appendages underwent specialized modification to increase resistance (Kaestner A (1970).

In the order Cyclopidae where the swimmers are found, many features have been modified to allow these crustaceans to remain longer suspended, for example the featherlike appearance of the caudal rami of Calocalanus (Kaestner A (1970).

Feeding and Locomotion (Continue)

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Parasitic Copepods have swollen unsegmented bodies and the legs are either reduced or lost due to evolutionary processes but once they are removed from the host they will be unfit to survive because they cannot swim or are capable of floating (Kaestner A (1970).

Pennella balaenopterae is the largest parasitic copepod, which is found on the finback of whales and a total body length of 32cm.

The living fossils of the Copepods are the free-living cyclopoid and harpacticoid Copepods although parasitic forms would have existed much earlier because of the occurrence of cysts found on Jurassic echinoids (Kaestner A (1970).

Parasitic Crustaceans

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These figures show two parasitic crustaceans

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A rise in global temperature may effect the distribution of crustaceans because they are exothermic organisms or their prey may have different migration patterns that will affect them, the higher the temperature the more difficult it will be for the crustacean to take in oxygen because of poor ventilation and insufficient aerobic capacity of mitochondria at low temperatures. .

” In a cause and effect hierarchy, the progressive increase in oxygen limitation at extreme temperatures may even enhance oxidative and denaturation stress.” (Panganiban et al 1995)

Tropical storms can affect the abundance of microscopic crustaceans by changing the frequency occurrence

If the climate were to change rapidly, most of the larger crustaceans would be heavily affected by it but the microscopic crustaceans especially the crustaceans that live in the sediments would be less affected.

Are changes possible due to climate change?

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Kaestner A (1970) Invertebrate Zoology, volume 3, John Wiley & Son Inc, university of Munich, pg 523

Sanchez-Paza A, Garcý F,Carren OC, Muhlia-Almaza A,. Peregrino-Uriarteb A B, Herna ndez-Lo J, Yepiz- G (2004) Usage of energy reserves in crustaceans during starvation: Status and future directions, Centro de Investigaciones Biolo´gicas Del Noroeste (CIBNOR), Unidad Hermosillo, Centenario Norte #53 Col. Prados Del Centenario, Hermosillo, Sonora C.P. Mexico


  • Panganiban G, Sebring A, Nagy L, Caroll S, Science, (1995) The development of Crustacean Limbs and the evolution of arthropods, Vol. 270, No.5240 pp1363-1366

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