20. Crustaceans

8/3/2019 20. Crustaceans

1/57

Crustaceans

Chapter 20


2/57

Subphylum Crustacea

Crustaceans,

subphylum

Crustacea typically

have biramous,branched,

appendages that are

extensively

specialized forfeeding and

locomotion.


3/57

Subphylum Crustacea

Crustacea is

divided into 5

classes.

Currentmolecular

phylogenies do

not support the

monophyly of allclasses.


4/57

Subphylum Crustacea - External

Features

Secreted cuticle is made of chitin, protein, and

calcareous material.

Heavy plates have more calcareous deposits -

joints are soft and thin, allowing flexibility.

Dorsal tergum and ventral sternum are plates

on each somite lacking a carapace.

Anterior end is a nonsegmented rostrum andthe posterior end is the unsegmented telson.


5/57


6/57

Subphylum Crustacea

Crustaceans are the onlyarthropods that have two pairsof antennae.

They also have a pair ofmandibles (jaw-likeappendages) and two pairs ofmaxillae on the head.

Each body segment usually has

one pair of appendages. Ancestrally biramous except for the

first antennae.


7/57

Subphylum Crustacea -

Appendages

Members of Malacostraca andRemipedia have appendages on eachsomite.

Other classes may not bear appendages onabdominal somites.


8/57

Subphylum Crustacea -

Appendages

Appendages have become specialized by

evolving into a wide variety of walking legs,

mouthparts, swimmerets, etc. from

modification of the basic biramous appendage.


9/57

Subphylum Crustacea

The ancestral condition in arthropods is

to have many body segments.

Fewer segments and increasedtagmatization is the derived condition.


10/57

Subphylum Crustacea - Internal

Features

Muscular and nervous systems and

segmentation exhibit metamerism of

annelid-like ancestors.

Hemocoel - persistent blastocoel that

becomes filled with blood.

Coelomic compartments remain as end

sacs of excretory organs and gonads.


11/57

Subphylum Crustacea - Muscular

System

Striated muscles make up a major

portion of crustacean body.

Most muscles arranged as antagonisticgroups.

Flexors draw a limb toward the body and

extensors straighten a limb out.


12/57

Subphylum Crustacea - Muscular

System

Abdominal flexors of a crayfish allow it to

swim backward.

Strong muscles located on each side ofstomach control the mandibles.


13/57

Subphylum Crustacea - Respiratory

System

Smaller crustaceansmay exchangegases across thinner

areas of cuticle. Larger crustaceans

use featherlike gillsfor gas exchange.

Bailer of 2ndmaxilla draws waterover gill filaments.


14/57

Subphylum Crustacea - Circulatory

Open circulatory system Dorsal heart - single-chambered

sac of striated muscle.

Valves in the arteries preventbackflow of hemolymph.

Hemolymph conducted to gills, ifpresent, for oxygen and carbondioxide exchange.

Hemolymph may be colorless,reddish, or bluish.

Hemocyanin (blue) and/orhemoglobin (red) are respiratorypigments.

Contains ameboid cells thatmay help prevent clotting.


15/57

Subphylum Crustacea - Excretory

System Antennal ormaxillary glands are

called green glands in decapods.

End sac of antennal gland has a

small vesicle and a spongy labyrinth.

Labyrinth connects by an excretorytubule to dorsal bladder that opens

to exterior pore.

Resorption of salts and amino acids

occurs as the filtrate passes the

excretory tubule and bladder.

Mainly regulates the ionic and

osmotic composition of body

fluids.


16/57

Subphylum Crustacea - Excretory

System

Nitrogenous wastes are excreted across

thin areas of cuticle in the gills.

Freshwater crustaceans constantlythreatened by over-dilution with water.

Gills must actively absorb Na+ and Cl-.

Marine crustaceans have urine that is

isosmotic with blood.


17/57

Subphylum Crustacea - Nervous

System

Pair ofsupra-esophageal ganglia connects to eyes and twopairs of antennae.

Neuron connectives join this brain to the subesophagealganglion.

Supplies nerves to mouth, appendages, esophagus, and

antennal glands. Double ventral nerve cord has a pair of ganglia for each somite

to control appendages


18/57

Subphylum Crustacea - Sensory

System

Eyes and statocysts are the largest sensoryorgans.

Tactile hairs occur on the body, especially on

chelae, mouthparts and telson. Chemical sensing of taste and smell occurs in

hairs on antennae and mouth.

Statocyst opens at base of first antenna in

crayfish. Statocyst lined with sensory hairs that detect

position of grains of sand.


19/57

Subphylum Crustacea - Sensory

System Compound eyes are made of

many units called ommatidia.

Cornea focuses light down thecolumnar ommatidium.

Distal retinal, proximal retinal,and reflecting pigment cellsform a sleeve around eachommatidium.

Each ommatidium detects arestricted area of objects, a

mosaic, in bright light. In dim light, the distal and

proximal pigments separateand produce a continuousimage.


20/57

Subphylum Crustacea - Diversity of

Reproduction

Barnacles are monoecious but generally

cross-fertilize.

In some ostracods, males are scarce and

reproduction is by parthenogenesis.


21/57


Reproduction

Most crustaceans brood eggs in brood chambers, in

brood sacs attached to the abdomen, or attached to

abdominal appendages.

Crayfishes develop directly without a larval form.


22/57


Reproduction

Most

crustaceans

have a larva

unlike the adult

in form, and

undergo

metamorphosis.

Gulf shrimp


23/57


Reproduction The nauplius is a common

larval form with uniramousfirst antennae, and biramoussecond antennae andmandibles that all aid in

swimming. Appendages and somites are

added in a series of molts.

Metamorphosis of a barnacleproceeds from a free-

swimming nauplius to acypris larva with a bivalvecarapace and finally to asessile adult with plates.


24/57

Subphylum Crustacea - Ecdysis

Ecdysis is necessary for a

crustacean to increase in size

the exoskeleton does not

grow. Physiology of molting affects

reproduction, behavior, and

many metabolic processes.

Underlying epidermis

secretes cuticle.


25/57


Molting animals grow in the intermolt phases, orinstars.

Soft tissue increases in size until there is no spacewithin the cuticle.

When body fills the cuticle, animal is in the premoltphase.

Molting occurs often in young animals and may ceasein adults.


26/57


Hormonal Control of Ecdysis:

Temperature, day length, or other stimuli

trigger central nervous system to begin

ecdysis.

Central nervous system decreases

production of molt-inhibiting hormone by the

X-organ. Promotes release of molting hormone from

the Y-organs which promotes ecdysis.


27/57

Subphylum Crustacea - Endocrine

Functions

Removing eyestalks accelerates molting

and prevents color changes to match

background.

Hormones from neurosecretory cells in

eyestalk control dispersal of cell pigment.


28/57

Subphylum Crustacea - Feeding

Habits

Same fundamental mouthparts in variouscrustaceans are adapted to a wide arrayof feeding habits.

Suspension feeders generate watercurrents in order to feed on plankton,detritus ,and bacteria.

Predators consume larvae, worms,

crustaceans, snails, and fishes. Scavengers eat dead animal and plant

matter.


29/57

Subphylum Crustacea - Feeding

Habits

Crayfishes have a two-part stomach.

Gastric mill grinds up food in 1st

compartment.


30/57

Class Remipedia

Only 10 described species inClass Remipedia.

All found in caves connected tothe sea.

Primitive features include 2538

segments with similar, paired,biramous, swimmingappendages.

Antennules also biramous.

Maxillae and maxillipeds areprehensile and specialized for

feeding. Swimming legs are directed

laterally rather than ventrally as isfound in copepods andcephalocarids.


31/57

Class Cephalocarida

Only 9 species described inClass Cephalocarida.

Live in coastal bottomsediments from intertidal

zones to 300 meters depth. Thoracic limbs and 2nd

maxillae are very similar.

Lack eyes, a carapace, andabdominal appendages.

True hermaphrodites andunique in discharging eggsand sperm through sameduct.


32/57

Class Branchiopoda

Includes three orders:

Anostraca fairy

shrimp and brine shrimp,

no carapace. Notostraca tadpole

shrimp, carapace forms

a large dorsal shield.

Diplostraca waterfleas carapace

encloses body but not

head.


33/57

Class Branchiopoda

Phyllopodia legs that serve as

respiratory organs.

Legs may be used for filter feeding and

locomotion as well.

Mostly freshwater forms.


34/57

Class Branchiopoda

Water fleas (like Daphnia) produce

females parthenogenetically in summer.

Males are produced when unfavorable

conditions arise and overwintering

fertilized eggs are produced that are

resistant to cold and desiccation.


35/57

Class Ostracoda

Ostracods are enclosed in a two part

carapace and look a bit like a clam.

Marine or freshwater. Mostly benthic.


36/57

Class Maxillopoda

axillopods generally

have 5 cephalic, 6

thoracic, and 4

abdominal segmentsplus a telson.

Reductions common.

The nauplius of

maxillopods has a

maxillopodan eye

unique to this group.


37/57

Class Maxillopoda Subclass

Copepoda

Planktonic crustaceansinclude many species ofcopepods (subclass

Copepoda) which are amongthe most numerous of allanimals.

They lack a carapace.

Retain the simplemaxillopodan eye in adults.

Antennules used in swimming.

Very diverse.


38/57


Copepoda

Parasitic forms highly modified and reduced -often unrecognizable as arthropods.

Free-living copepods may be the dominantconsumer.

Marine copepod Calanus is most abundantorganism in zooplankton by biomass.

Cyclops and Diaptomus important elements offreshwater plankton.

Some free-living copepods are intermediatehosts of human parasitic tapeworms andnematodes.


39/57


Tantulocarida

Subclass Tantulocarida

- only recently

described.

Approximately 12species.

Tiny copepod-like

ectoparasites of deep-

sea benthic

crustaceans.


40/57


Branchiura

Members of thesubclass Branchiuralack gills.

Most areectoparasites ofmarine andfreshwater fish.

510 mm long. Development is

direct.


41/57


Pentastomida

Subclass Pentastomida -tongue worms.

Consist of about 90species of parasites of

vertebrate respiratorysystems.

Most infect reptile lungs,a few infect air sacs ofbirds or mammals.

Range from 1 to 13 cm inlength.

Chitinous cuticle regularlymolted.


42/57


Cirripedia

Barnacles subclass cirripedia are a

group of mostly sessile crustaceans whose

cuticle is hardened into a shell.


43/57


Cirripedia

Their legs are long,

many jointed cirri that

extend out through the

calcareous plates tofilter feed.


44/57


Cirripedia

Barnacles are

hermaphroditic.

Most hatch as a nauplius

larva then become a cypridlarva (resembles the

ostracod Cypris).

Cyprids attach to the

substrates and beginsecreting calcareous plates.


45/57


Cirripedia

Parasitic forms may have a kentrogon

stage that injects cells into the hemocoel

of host.


46/57


47/57

Class Malacostraca

alacostracans

usually have a

head with 5 fused

segments, athorax with 8

segments and an

abdomen with 6.

Anteriorrostrum

Posteriortelson


48/57

Class Malacostraca Order Isopoda

Order Isopoda including pill bugs. Only truly terrestrial crustaceans.

Also have marine and freshwater forms.

Dorsoventrally flattened, lack a carapace, and

have sessile compound eyes.

Compressed dorsoventrally.


49/57

Class Malacostraca Order

Amphipoda

OrderAmphipoda many marine, terrestrial& freshwater forms.

Amphipods resemble isopods: Lack a carapace, have sessile compound eyes,

and one pair of maxillipeds. However, they are compressed laterally.

Development is direct.


50/57

Class Malacostraca Order

Euphausiacea

OrderEuphausiacea contains approximately 90species.

Includes important ocean plankton called krill.

Most are bioluminescent with a light-producing organ

called a photophore. Form a major component of the diet of baleen whales

and of many fishes.

Eggs hatch as nauplii.


51/57


52/57

Class Malacostraca

Harder, heavy plates in larger crustaceans

due to calcareous deposits in addition to

chitin.

The carapace covers much or all of thecephalothorax.


53/57

Phylogeny

Remipedia appear to be the most

primitive of Crustacea.

Two pairs of uniramous limbs on each

segment.

One theory is that each modern somite

represents two ancestral somites that

fused together, forming the biramousappendage.


54/57

Adaptive Diversification

Crustaceans are unquestionably the dominant

arthropod in marine environments.

They also share dominance in freshwater

environments with the insects. The class Malacostraca is most diverse and

members of Copepoda are most abundant.


55/57

Classification

Class Remipedia

Class Cephalocarida

Class Branchiopoda Order Anostraca

Order Notostraca

Order Cladocera

Ph l d Ad ti


56/57

Phylogeny and Adaptive

Diversification

Class Ostracoda

Class Maxillopoda

Subclass Copepoda Subclass Tantulocarida

Subclass Branchiura

Subclass Pentastomida

Subclass Cirripedia

Ph l d Ad ti


57/57

Phylogeny and Adaptive

Diversification

Class Malacostraca

Order Isopoda

Order Amphipoda

Order Euphausiacea

Order Decapoda

Documents

20. Crustaceans