Chapter 20: Crustaceans

What is the Latin root of the word "crustaceans"?

"shell."

How many species of crustaceans have been described so far?

Around 67,000 species; crustaceans control the water

pairs of antennae do crustaceans have?

Two pairs of antennae.

mouthparts in crustaceans?

One pair of mandibles.

pairs of maxillae do crustaceans have?

Two pairs of maxillae.

respiratory organs in crustaceans

Gills.

How many segments do crustaceans typically have?

A large number of segments, which is ancestral to the group.

What is the cephalothorax in crustaceans?

Some thoracic segments are fused with the head

What is the hard covering many crustaceans have?

carapace

What is the composition of the covers crustaceans' bodies?

The cuticle is made of chitin, protein, and calcium carbonate.

characteristic of the cuticle at joints in crustaceans?

soft and thin at the joints to allow movement.

a dorsal plate covers segment not enclosed by carapace

called a tergum.

transverse bar that covers each segment of a crustacean

called a sternum.

Where do female crustaceans deposit sperm?

in the gonopores for sperm deposition

Exites and Endites

respectively lateral and medial processes, an epipos is a specialized exite modified as a gill

Uropod

tail fin

What is the hemocoel in crustaceans?

is a persistent blastocoel

type of muscles are found in crustaceans?

have striated muscles oriented in antagonistic groups.

function of flexor muscles in crustaceans?

draw a part towards the body

function of extensor muscles in crustaceans?

extend the part outward

How does gas exchange occur in small crustaceans?

occurs across thin areas of the cuticle.

How does gas exchange occur in larger crustaceans?

have gills, usually internal, very delicate

What type of circulatory system do crustaceans have?

Open system, hemolymph returns to venous sinuses, valves in arteries prevent backflow

What affects the color of crustacean hemolymph?

Depending on respiratory pigment, may be colorless, reddish, or bluish

Dorsal heart

chief propulsive organ of circulatory fluid

What type of excretory system do crustaceans have?

have a pair of tubular antennal or maxillary glands, depending on where they open.

How is nitrogenous waste excreted in crustaceans?

is excreted across the cuticle and gills.

Nervous & Sensory Systems in Crustaceans

• Similar to annelids.

• Brain consists of a pair of supraesophageal ganglia.

• Connects to the subesophageal ganglion to innervate the face.

Sensory Organs in Crustaceans

• Eyes: Made of ommatidia, creating a mosaic or apposition image.

• Statocysts: Contain statoliths for balance.

• Tactile Hairs: For touch perception.

Sexes & Copulation in Crustacean

Most have separate sexes.

Highly specialized structures for copulation.

Parthenogenesis on Crustacean

Some parthenogenetic

Egg Brooding

Most brood their eggs

Development

Some have direct development

others mutliphasic life cycles

Larval Stage

Ancestral and most widely occurring larvae is a nauplius

Molting Process on Crustacean

The process of shedding the cuticle for growth or because of wear

Structure of the Cuticle on Crustacean

Epicuticle: outermost, lipid impregnated protein

Procuticle: bulk of cuticle, several layers

Endocuticle: innermost

Principal Layers on Crustacean

Chitinous principal layer

Uncalcified membranous layer

Instars on Crustacean

Intermolt phases

Separation of Old Procuticle

separates from epidermis

Premolt Phase in Crustaceans

new exocuticle secreted

molting fluid dissolves endocuticle

Discarding Old Layers in Crustaceans

Old epicuticle and exocuticle are discarded

New Cuticle Formation in Crustaceans

is stretched and unfolded.

endocuticle secreted

Environmental Stimuli in Crustaceans

Molting is usually triggered.

X-Organ Function in Crustaceans

stop the production of molt inhibiting.

Y-Organ and Molting Hormone in Crustaceans

Promotes release of molting hormone from the Y-organs, which lie near mandibles, initiate molting

Androgenic Glands in Crustaceans

Found in some males, but not females.

Lead to development of secondary sexual characteristics in males.

Feeding Specialization on Crustacean

show great feeding specialization, but all use a fundamental set of mouthparts.

Feeding Types on Crustacean

Predators: Eat larvae, worms, other crustaceans, snails, and fish.

Scavengers: Consume detritus and dead animals.

Suspension Feeders: Filter plankton and bacteria.

Crayfish Stomach

have a two-part stomach with a gastric mill.

gastric mill shreds food

Mantis Shrimp

Specialized digit for piercing or smashing prey.

Pistol Shrimp

Chelae can be cocked like a hammer.

second fastest animal motion recorded.

Overview Class Remipedia

Only about ten species

Body Structure Class Remipedia

25 to 38 trunk segments, all identical.

Paired, biramous swimming appendages.

Antennules and Feeding Class Remipedia

Antennules are biramous.

Maxillae and maxillipeds are prehensile and adapted for feeding.

Cephalocarida Overview

9 species

2 to 3 mm long

Habitat & Anatomy class Cephalocarida

Live in sediment

• No eyes

• No carapace

• No abdominal appendages

Limbs class Cephalocarida

Thoracic Limbs: All similar

Second Maxillae: Similar to thoracic limbs

Reproduction class Cephalocarida

True hermaphrodites

Eggs and sperm released through a common duct

Overview Class Branchiopoda

10,000 species

• Anostraca: fairy shrimp

• Notostraca: tadpole shrimp

• Diplostraca: water fleas

Anatomy & Habitat Class Branchiopoda

Flattened, leaflike phyllopodia (serve as respiratory organs)

Mostly freshwater

Life Cycle & Ecological Role Class Branchiopoda

Many species have complex life cycles with extensive periods of dormancy

Important components of food webs

Overview Class Maxillopoda

10,000 species

• Five cephalic segments

• Six thoracic segments

• Four abdominal segments (reductions are common)

Unique Features in Class Maxillopoda Nauplii

a maxillopodon eye

Subclasses Class Maxillopoda

1. Mystacocarida: Tiny, only 10 species

2. Copepoda: Copepods, very diverse

3. Tantulocarida: Only 12 species, recently described

4. Branchiura: Mostly fish ectoparasites

5. Pentastomida: Formerly a phylum, wormlike

6. Cirripedia: Barnacles (considered awesome)

Overview Subclass Mystacocarida

Less than 0.5 mm long

Only 10 species

Habitat Subclass Mystacocarida

Live in interstitial spaces in sand

Found worldwide

Overview Subclass Copepoda

Very abundant

Usually less than 2 mm in length

Retain their nauplius eye into adulthood

Limbs Subclass Copepoda

Single pair of uniramous maxillipeds

Four pairs of flattened, biramous, thoracic swimming appendages

Fifth Pair of Legs Reduced

Habitat & Behavior Subclass Copepoda

Habitat: Most are free-living, but many are parasitic

Development: Usually direct; some parasitic species have specialized multiphasic life cycles

Overview Subclass Tantulocarida

Only described in 1983

About 12 species

Smaller than 0.2 mm

Antennae Subclass Tantulocarida

One pair of antennae on sexual females

Abdomen Subclass Tantulocarida

Juveniles have six or seven abdominal segments

Life Cycle & Behavior Subclass Tantulocarida

Have both a parthenogenetic and sexual life cycle

Tantulus larvae penetrate the host's cuticle via a mouth tube

During metamorphosis to an adult, the abdomen and all thoracic limbs are lost

Overview Subclass Branchiura

Small group of mostly fish ectoparasites

Have sucking mouthparts

Anatomy Subclass Branchiura

Carapace: Broad, shieldlike carapace

Eyes: Compound eyes

Thoracic Appendages: Four biramous thoracic appendages

Abdomen: Short, unsegmented abdomen

Second Maxillae: Modified as suction cups

Life Cycle Subclass Branchiura

No nauplius stage, young resemble adults

Overview Subclass Pentastomida

130 species

Tongueworms (wormlike parasites)

Up to 13 cm

Mostly lung parasites of vertebrates

Anatomy Subclass Pentastomida

Transverse rings make them look segmented

Nonchitinous, highly porous cuticle; molted periodically during larval stages

Sometimes have five short protuberances on the anterior end

Simple, straight digestive system

No circulatory, excretory, or respiratory organs

Reproduction & Life Cycle Subclass Pentastomida

Separate, with females usually larger than males

Larvae: Ovoid, tailed, with four stumpy legs

Life Cycle: Very complex, with intermediate hosts

Overview Subclass Cirripedia

Barnacles

• Sessile as adults

Anatomy Subclass Cirripedia

Carapace: Surrounds the body and secretes a shell of calcareous plates

Head: Reduced

Abdomen: Absent

Thoracic Legs: Long, many jointed cirri with hairlike setae

Cirri: Extended between plates for filter feeding

Reproduction & Development Subclass Cirripedia

Most hermaphroditic, with internal fertilization

Free-living cyprid larvae; attach by their first antennae

Metamorphose into the adult form

Fun Fact Subclass Cirripedia

Barnacles have the longest penis relative to body size of any animal!

Overview Order Isopoda

Have invaded terrestrial habitats as well as very deep water

Dorsoventrally flattened

No carapace

Sessile compound eyes

Anatomy & Limbs Order Isopoda

Maxillipeds: The first pair of thoracic limbs

Thoracic Limbs: Other limbs lack exopods

Development & Life Cycle Order Isopoda

Usually direct

A few parasitic forms have complex life cycles

Overview Order Amphipoda

Body Shape: Resemble isopods, but compressed laterally

Gills: Located in the typical Malacostracan thoracic position

Limbs Order Amphipoda

Thoracic and abdominal limbs differ in function

Development Order Amphipoda

Direct, with no metamorphosis

Overview Order Euphausiacea

About 90 species, known as the krill

3 to 6 cm long

Carapace Order Euphausiacea

Fused with all thoracic segments, does not entirely enclose the gills

Limbs Order Euphausiacea

No maxillipeds, but have thoracic limbs with exopods

Bioluminescence in Order Euphausiacea

due to an organ called a photophore

Ecological Importance Order Euphausiacea

Very important to marine food webs

Overview Order Decapoda

About 18,000 species

Limbs Order Decapoda

Three pairs of maxillipeds

Five pairs of walking legs

• modified to form chelae (claws)

Largest Arthropod

The Japanese spider crab, which can reach up to 4 meters in size