Phylum Arthropoda: Crustacea & Muscular Systems - Biosciweb.net

Phylum Arthropoda: Crustacea & Muscular Systems 10.1 

Lab #10 -- Biological Sciences 102 – Animal Biology 

The large lineage of crustaceans, insects, and myriapods 

that possess mandibles, or jawlike appendages, instead of 

chelicerae are often called mandibulate arthropods. They 

have, in addition to mandibles, at least one pair of antennae 

and a pair of maxillae on the head. 

Until recently crustaceans, insects, and myriapods 

(millipedes and centipedes) were all placed in a single 

subphylum, Mandibulata, of the phylum Arthropoda 

because all possess mandibles. However, a growing body of 

opinion among zoologists contends that the mandibles of 

the crustaceans and the mandibles of insects and 

myriapods are not homologous but are the result of 

convergent evolution from separate origins. Consequently 

crustaceans are now placed in a separate subphylum, 

Crustacea, and insects and myriapods are grouped in the 

subphylum Uniramia. 

Decapoda by Haeckel 

Body Plan Features Characteristic of Members of the Subphylum Crustacea: 

‣ gills for respiration 

‣ two pairs of antennae 

‣ two pairs of maxillae on the head 

‣ usually one pair of appendages on each body segment 

‣ some appendages of present-day crustaceans are biramous (two-branched) 

Body Plan Features Retained by Arthropods (seen in previously studied phyla): 

‣ bilateral symmetry 

‣ eucoelomic (true coelom) 

‣ high degree of cephalization = well developed head with sensory organs 

‣ specialized segmentation (metamerism) = tagmata 

‣ triploblastic structure (endoderm, mesoderm and ectoderm) 

‣ all organ systems are present 

Body Plan Features Characteristic of Members of the Phylum Arthropoda: 

1. developed striated muscle for rapid movement 

2. an exoskeleton, or cuticle, containing the tough nitrogenous polysaccharide chitin for 

support and protection 

3. gills and a very efficient tracheal system for gaseous exchange 

4. greater specialization of body organs, especially specialization of form and function 

among the appendages 

5. "open" circulatory system 

A hermit crab – a crustacean arthropod, 

not a mollusc



Phylum Arthropoda 

Classification 

Subphylum Trilobita (tri'lo-bi'ta) (Gr. tri, three, + lobos, lobe). Trilobites. All extinct forms; 

Cambrian to Carboniferous; body divided by two longitudinal furrows into three lobes; distinct 

head, thorax, and abdomen; biramous (two-branched) appendages. 

Subphylum Chelicerata (ke-liss'uh-ra'ta) (Gr. chele, claw, + keras, horn, + ata, group 

suffix). Eurypterids, horseshoe crabs, spiders, and ticks. First pair of appendages modified 

to form chelicerae; pair of pedipalps and four pairs of legs; no antennae, no mandibles; 

cephalothorax and abdomen usually unsegmented. 

See Lab #10 for more detailed taxonomy of the Subphylum Chelicerata 

Subphylum Crustacea (crus-ta'she-a) (L crusta, shell, + acea, group suffix). About 45,000 

species. Crustaceans. With gills; body covered with carapace; exoskeleton with limy salts; 

appendages currently considered biramous and variously modified for different functions; 

head with two pairs of antennae. 

Class Remipedia (about 10 species that dwell in caves connected to the sea) 

Class Cephalocarida (about 10 species; only true hermaphroditic arthropods) 

Class Malacostraca (about 20,000 species) 

Order Decapoda (shrimps, lobsters, crabs, crayfish = about 18,000 species) 

Order Isopoda (dorsoventrally flattened; pill bugs or roly-polies = Armadillidium, 

kelp lice, etc.) 

Order Amphipoda (laterally flattened; beach hoppers = Orchestia, etc.) 

Order Euphausiacea (krill; look like small shrimp with external exposed gills) 

Class Branchipoda (have ventral phyllopodia - “leaf-like appendages” - for respiration; 

fairy shrimp, brine shrimp, tadpole shrimp, water fleas) 

Class Ostracoda (have a bivalve carapace; only two trunk appendages; mussel shrimp 

or seed shrimp) 

Class Maxillopoda (Copepoda, Tantulocarida, Branchiura, Cirripedia) 

Subclass Copepoda (copepods) 

Subclass Thecostraca (barnacles & about 100 species of small crustaceans that 

are parasites of cnidarians and echinoderms) 

Infraclass Cirripedia (barnacles; gooseneck, acorn & buckshot barnacles) 

Order Rhizocephalans such as Sacculina are crab parasites 

Subphylum Myriapoda Myriapods. All appendages uniramous; head appendages consisting 

of one pair of antennae, one pair of mandibles, and one or two pairs of maxillae. 

Subphylum Hexapoda Hexapods. 

Class Insecta (in-sek'ta) (L. insectus, cut into). About one million species. Insects. 

Body with distinct head, thorax, and abdomen; thorax usually with two pairs of 

wings; three pairs of jointed legs. Example: lubber grasshopper, Romalea. 

See Lab #12 for more detailed taxonomy of the Subphyla Myriapoda and Hexapoda.



Muscular Systems: Types of Muscle Cells 

Muscles are specialized organs comprised of cells that are both electrically excitable (they can 

conduct action potentials) and contractile. This contractibility allows muscles to move the 

bones found in appendages or against a hydrostatic skeleton as well as to manipulate internal 

organs and structures. The cell structure of skeletal cells that control body movements is 

different from that of the smooth muscle cells that operate in the digestive, cardiovascular, 

respiratory, reproductive, etc. organ systems. Cardiac muscle cells have specialized 

connections for electrical conduction (gap junctions) and protein connections between cell 

membranes (desmosomes) which are critical to the normal functioning of the heart and the 

effective pumping of blood. 

muscle fiber = elongated multinucleate skeletal muscle cell 

Muscles are made of specialized fibrous cells that contain the specialized muscle protein fibers 

(actin and myosin among others). These fibers are packed together into myofibrils which in 

turn are packed together to form a muscle. We will review the basic functional unit of muscle 

called a sarcomere later in lecture. 

Three Basic Tvpes of Muscle Tissue: 

Some types are not found in some animals 

1. Skeletal muscle = moves bones/skeleton, voluntary respiratory organs, eyes, mouth, etc. 

‣ skeletal muscle fibers are long, cylindrical multinucleate muscle cells or fibers (they 

form a syncitium) 

‣ skeletal muscle is striated 

‣ under voluntary control 

2. Smooth muscle = circle the digestive tract, blood vessels, respiratory, reproductive and 

urinary ducts; make up parts of many internal organs 

‣ smooth muscle cells are long, tapering strands that are not multinucleate 

(=uninucleate) 

‣ smooth muscle is not striated 

‣ under involuntary control 

3. Cardiac muscle = heart muscle only 

‣ cardiac muscle is composed of the fast acting, uninucleate muscle cells that make 

up the heart 

‣ cardiac muscle is not striated 

‣ under involuntary control 

‣ due to specialized connections between cardiac muscle cells called intercalated 

disks, the cells which make up a chamber of the heart can beat in unison for the 

efficient pumping of blood. Intercalated disks contain cell-to-cell connections called 

gap junctions and desmosomes 

motor neurons = neurons that innervate skeletal muscle fibers 

motor unit = a motor neuron can divide and form neuromuscular junctions with several 

(sometimes thousands) of skeletal muscle fibers. The motor neuron plus the skeletal muscle 

fibers it innervates make up a motor unit. When a motor neuron fires, all of the muscle fibers 

that it innervates will contract.



LAB PROCEDURE 

NAME: 

LAB SCORE: 

Refer to the textbook and Internet for illustrations, diagrams, and 

additional information about crustaceans. 

Observation of Living Specimens 

Subphylum Crustacea 

Class Branchiopoda (branciopods) – see slide presented by instructor 

‣ Observe the specimens and/or diagrams of a branchiopod. 

‣ Record the descriptive information requested at the end of the lab for this species. 


Class Maxillopoda 

Subclass Copepoda (copepods) – see slide presented by instructor 

‣ Observe the specimens and/or diagrams of the copepod, Cyclops. sp. 




Subclass Thecostraca 

Infraclass Cirripedia 

‣ Observe the specimens and/or diagrams of the gooseneck barnacle, 

Polycipes polymerus 






‣ Observe the specimens and/or diagrams of one member of the genus, Balanus. 



Class Malacostraca (19 body segments) 

Order Amphipoda (amphipods) 

A caprellid (skeleton shrimp) 

An amphipod 

‣ Observe one of the specimens and/or diagrams of an amphipod on display. 



Class Malacostraca 

Order Isopoda (isopods) 

‣ Observe one of the specimens and/or diagrams of an isopods on display. 


‣ If available, observe the terrestrial isopod, Armadillidium vulgare on display. 

Realize that this animal commonly known as the "pillbug" or “rollie-pollie” is a 

crustacean and not an insect.





Order Decapoda (shrimps, lobsters and crabs) 

‣ Observe one of the specimens and/or diagrams of on display of each of the following 

infraorders (as available). 


Infraorder Caridea 

(shrimp) 

‣ What does the word Caridea mean (what is its etymology)? 

Infraorder Astacidea 

(crawfish & clawed lobsters), the crayfish, Procambarus, sp. 

‣ What does the word Astacidea mean (what is its etymology)? 

Infraorder Palinura 

(spiny lobsters) such as Panulirus interuptus 

‣ What does the word Palinura mean (what is its etymology)? 

Infraorder Anomura 

(crabs with antennae lateral to eyes) 

a hermit crab such as Pagurus sp. or Isocheles sp. 

a Galatheid crab such as Petrolisthes sp. or. Pachychelis sp. 

a Hippid crab such as Emerita sp. or Blepharipoda sp. 

‣ What does the word Anomura mean (what is its etymology)? 

Infraorder Thalassinidea 

(mud or ghost shrimp) such as Callianassa sp. 

‣ What does the word Thalassinidea mean (what is its etymology)? 

Infraorder Brachyura 

(Crabs with antennae between the eyes) such as Cancer sp. 

‣ What does the word Brachyura mean (what is its etymology)?



DISSECTION 


Order Decapoda 

Procambarus, sp. (Crayfish) 

Obtain a living crayfish. Observe the movements and behavior of your specimen. 

‣ Which crayfish appendages are involved in respiratory movements? 

‣ Which legs are involved in walking? 

‣ What is the apparent function of the antennae? 

‣ How does the crayfish right itself – describe the righting response? 

‣ When the crayfish flexes its tail rapidly in the water, what function does it 

serve? 

‣ In what direction is the animal propelled when it does this movement? 

‣ What chela (pincer) muscles are strongest, those which close pincers or those 

that open them? 

‣ What are the advantages of an exoskeleton? 

‣ What are the disadvantages of an exoskeleton?



‣ Examine the external anatomy of the crayfish on both the dorsal and ventral 

sides and be able to identify the following structures: 

External Morphology 

‣ cephalothorax 

‣ abdomen 

‣ carapace 

‣ telson 

‣ rostrum 

‣ uropods 

Paired Appendages 

‣ antennae 

‣ antennules 

‣ chelipeds 

‣ four pairs of walking legs 

‣ pleopods (swimmerets) 

‣ thoracic and cephalic feeding appendages (maxillopeds and mandibles) 

‣ Which of these appendages are cephalic? 

‣ Which of these appendages are thoracic? 

‣ Is your crayfish a male or a female? 

After you have completed your study of the live specimen, place it in boiling water, and 

after a brief period, remove it and allow to cool. Hold the crayfish and cut through the 

back of the carapace along the dotted line indicated (see pg. 11.9). Cut through the 

thoracic region just internal to the branchiostegal line. If the crayfish is about to molt, 

there will be a thin sheet of unhardened chitin inside the hardened exoskeleton. This 

should be stripped off with forceps. 

Next, cut along the dotted line indicated on pg. 11.9 to remove the left branchiostegite 

and reveal the gills. After observing the gills, and removing them, cut along the dotted 

lines indicated on pg. 11.9 to remove the side wall of the thorax and the head.



Internal Structures to Identify on the Crayfish (you may find others) 

‣ heart (as visible) 

‣ stomach 

‣ gastric mill (“little teeth” in the stomach) 

‣ gastroliths (if present in the stomach) 

‣ gills (lateral sides of thorax) 

‣ green glands (whitish and circular; at the very anterior ventral portion inside the 

head at the base of the antennae) 

Did you find gastroliths during your dissection? 

If so, briefly describe their appearance and texture. 

‣ What is the function of the gastroliths? 

‣ Why might marine crustaceans lack gastroliths? 

‣ What types of molecules and ions comprise the exoskeleton of most crustaceans?


Lab #10 -- Biological Sciences 102 – Animal Biology





SPECIMEN STUDY/DISSECTION 



Crab 

On the COOKED or a LIVE crab displayed in the lab, identify the external structures listed 

below. 

Scientific name of crab specimen: 

Infraorder of crab specimen: 

External Structures to Identify on the Crab 

‣ cephalothorax (covered by the carapace) 

‣ abdomen (broad in females, narrow in males) 

‣ four pairs of walking legs 

‣ telson 

‣ rostral teeth 

‣ chelapeds 

‣ chelae 

‣ walking legs 

‣ Is your specimen a male or female? 

‣ Carefully lift the abdomen of the crab. 

‣ If male, are any abdominal appendages present? What might these be used for? 

‣ If female, are there any eggs being held and roughly how many eggs? 

‣ Crayfish have a green gland. Some crabs also have a green gland. 

What is the function of the green gland? 

‣ Which pairs of legs are chelate (biramous or bifurcated, like pincers)?



‣ How does this compare with your observations of the crayfish? 

‣ Where are the gills located in a crayfish? 

‣ Where are the gills located in a crab typically? 

Your instructor will be coming around to each group to assist you and ask you 

to identify the structures listed in preparation for the invertebrate lab practical. 

‣ Place your crayfish specimen in the waste container provided. 

‣ Rinse your dissecting tray and clean your supplies and return them.





Living Specimens Data 


Class Branchiopoda (branchiopods) - see slide presented 

by instructor 

Scientific name: 

Common name: 

Notes & observations to help you remember and distinguish this group/species: 



Subclass Copepoda (copepods) – see slide 

presented by instructor 


Common name: 






Common name: 

Is there a stalk present in this species? 

Notes & observations to help you remember and distinguish this group/species:







Common name: 

Is there a stalk present in this species? 




Order Amphipoda 


Common name: 

Is this specimen dorso-ventrally or laterally flattened? 




Order Isopoda 


Common name: 








Infraorder Caridea 


Common name: 



Infraorder Astacidea, the crayfish, Procambarus, sp. 


Common name: 

Notes & observations to help you remember and 

distinguish this group/species: 

Infraorder Palinura such as Panulirus interuptus 


Common name: 

Notes & observations to help you remember and distinguish 

this group/species: 

Infraorder Anomura, a hermit crab such as Pagurus sp. or Isocheles sp. 


Common name: 




Infraorder Anomura, a Galatheid crab such as Petrolisthes sp. or. Pachychelis sp. 


Common name: 


Infraorder Anomura, a Hippid crab such as Emerita sp. or Blepharipoda sp. 


Common name: 


Infraorder Thalassinidea such as Callianassa sp. 


Common name: 


Infraorder Brachyura such as Cancer sp. 


Common name: 






Order Euphausiacea (krill) 


Common name: 



Homework – use the Internet to help you answer these questions: 

‣ This is a nauplius larva of a crustacean. Briefly describe 

and/or draw a flowchart diagram to show the lifecycle of a 

decapod. Be sure to include the names of specific larval 

stages. 

Nauplius larva



Sacculina are crab parasites 

‣ To what class and order do the Sacculina crab 

parasites belong? 

‣ Briefly describe and/or draw a flowchart diagram to 

show the lifecycle of the Sacculina crab parasite. 

Be sure to include the names of specific larval 

stages. 

‣ In which class and order does the mantis shrimp belong? 

‣ Briefly describe how mantis shrimp (stomatopods) capture their prey.



LABORATORY NOTES: 

Copepoda by Haeckel

Phylum Arthropoda: Crustacea & Muscular Systems - Biosciweb.net

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