Lab #12

Molluscs and Arthropods

• Class Scaphopoda (300 species)– tooth shells, tusk shells– all are burrowing marine animals– most distinctive characteristic – conical shell open at both ends

• Class Monoplacophora– undivided arched shell– flat foot

• Class Caudofoveata– wormlike molluscs– live in vertical burrows on the deep sea floor– lack a shell or a foot

• Class Aplacophora (250 species)– “solenogasters”– lack a shell– may be closely related to the flatworms– most have a radula– surface dwellers on corals– carnivores

Phylum Mollusca

• Gastropod diversity– Subclass Prosobranchia (gill in front of heart): marine snails and abalone

• largest group• 20,000 species, mostly marine• few are freshwater and terrestrial• most are herbivores or deposit feeders• some are carnivorous – inject venom into their prey (fishes, other

molluscs or annelids) using a modified radula that is shaped like a harpoon

Class Gastropoda

abalone

• Gastropod diversity– Subclass Opisthobranchia (gill in back of heart): sea hares, sea slugs

• mostly marine• fewer than 2,000 species• shell, mantle cavity and gills are reduced or may be lost in this group• many species have nematocysts – acquire these from their cnidarian prey• foot may be modified for swimming

Class Gastropoda

• Gastropod diversity– Subclass Pulmonata

• 17,000 species• most are freshwater and terrestrial – snails and slugs• mostly herbivores• long radula for scraping plant material• mantle cavity is highly vascular and serves as a lung – open to the air

via a pneumostome

Class Gastropoda

Subclass Pulmonata

Class Bivalvia = the Clam

labialpalps

anterioradductormuscle

foot

mantlehttp://www.youtube.com/watch?v=YKTl5kwtjMc

http://iweb.tntech.edu/mcaprio/clam.htm

Class Cephalopoda = the squid

http://blog.tepapa.govt.nz/2008/04/29/dissection-of-giant-squid/

Arthropod Phylogeny

• Subphylum Chelicerata: first pair of appendages are pincerlike – Class Merostomata– Class Arachnida– Class Pycnogonida

• Subphylum Crustacea: head with two pairs of antennae; biramous appendages– Class Malacostraca– Class Branchiopoda– Class Maxillopoda

• Subphylum Hexapoda: body divided into head, thorax and abdomen; uniramous appendages on the thorax– Class Insecta

• Subphylum Myriapoda: body divided into a head and trunk; uniramous appendages– Class Diplopoda– Class Chilopoda

Phylum Arthropoda

• Subphylum Chelicerata: body divided into a prosoma and an opisthosoma; first pair of appendages are pincer-like and used for feeding– Class Merostomata – horseshoe crabs– Class Arachnida – scorpions, spiders, daddy long legs,

mites & ticks– Class Pycnogonida – sea spiders

Subphylum Chelicerata

Class Arachnida

chelicerae

• Order Scorpionida: scorpions– tropical to desert climates– are secretive and nocturnal– distinctive chelicerae that surround the mouth + a pair of

chelate pedipalps – opisthoma is divided into a pre-abdomen and a post-

abdomen (called the tail) – curves dorsally and anteriorly over the pre-abdomen when aroused

– tip of the tial is the telson with a sting – bulbular base that contains venom-producing glands and a hollow, sharp barb

only a few scorpions are toxic to humans – Androctonus (northern Africa)- Centuroides (Mexico, Arizona and New Mexico)

• reproduction involves a complicated “dance” that lasts several hours

• development of a scorpion requires 1.5 years until maturity

• Order Opiliones: daddy long legs or harvestman– body appears ovoid (unlike a spider)– many are omnivorous as opposed to carnivorous spiders

• Order Acarina: mites and ticks– great impact on human health and welfare– free-living forms are herbivores or scavengers – damage to crops– parasitic forms feed on blood and tissue fluids– some can be permanent ectoparasites– ticks are ectoparasites during the entire life history

Opiliones Acarina

Class Arachnida

Class Pycnogonida

• sea spiders• all are marine• most common in cold waters• live on the ocean floor• feed on cnidarian polyps and

ectoprocts• some feed through sucking

tissues through a proboscis

Class Arachnida• Order Araneae: 34,000 species of spiders (carnivorous)– prosoma: bears chelicerae with poison glands and fangs– pedipalps around the mouth are leglike

• are modified in the males for sperm transfer– opisthoma/abdomen: swollen and contains openings to the reproductive tract, book lungs and

trachea– end of the opisthoma – spinnerets - associated with silk glands – emits a protein as a liquid that

hardens with air as it is drawn out = web for prey capture– bite their prey to paralyze them – puncture the body with their chelicerae and inject venom

• suck out the blood first, then inject digestive enzymes to “liquefy” internal organs– few are toxic to humans – Black widow (Lactrodectus) and brown recluse (Loxosceles)

• mating involves complex behaviors involving tactile, chemical and visual signals

Phylum Arthropoda

• Subphylum Crustacea: mostly aquatic; head with two pairs of antennae; one pair of mandibles and two pairs of maxillae; biramous appendages– Class Malacostraca– Class Branchiopoda– Class Maxillopoda

Subphylum Crustacea Class Malacostraca = the crayfish

Crayfish dissectionExternal Anatomy

1 – uropods2 – telson3 – abdomen4 – cephalothorax5 – cephalic groove6 – walking legs7 – cheliped8 – eye9 – rostruma - antennae

Crayfish dissection– 8 paired appendages are present on the cephalothorax

• first two pairs = first and second antennae• third through fifth are associated with the mouth – crushing, tearing food

– the 3rd pair = mandibles– 4th and 5th = maxillae (#1 and #2)

• 6th through the 8th are called the maxillipeds – food handling– last two maxillipeds bear gills

antennules (1)antennae (2)mandible (3) second maxillae (4)first maxilliped (5), second maxilliped (6)third maxillipeds (7) walking legs or chelipeds (8)openings to the green glands (9)

• 1 = uropods• 2 = pleopods or swimmerets • 3 = walking legs or periopods• 4 = cheliped (1st walking leg)• 5 = 1st swimmeret• 6 = antennae

• appendages 9 through 13 are on the thorax – called walking legs (or periopods)– first pair (pair #9) is called the cheliped (4) – chelicera used in defense and capturing

food– remaining pairs are for walking/crawling along the sea floor

• 1 = uropods• 2 = pleopods or swimmerets • 3 = walking legs or periopods• 4 = cheliped (1st walking leg)• 5 = 1st swimmeret• 6 = antennae

• appendages 14 through 18 are on the abdomen – called swimmerets or pleopods (2)– 1st pair of swimmeret is larger in the male – for sperm transfer– abdomen is associated with the telson

» bears the anus which is flanked on either side by flattened biramous appendages called the uropods (1)

» flipperlike structure used for swimming

Male Female

1 – swimmeret2 – male genital opening3 – 1st pair of swimmerets - clasper4 – 7 – walking legs8 – base of the first pair of walking legs

1 – swimmeret2 – seminal receptacle3 – walking leg #54 – walking leg #45 – female genital opening6 – walking leg #2

» in females – eggs attach to the pleopods and the embryos brood on these “legs” until hatching

» in males – the first two pleopods (#10 and #11) are modified into gonopods or claspers for sperm transfer

Male crayfish

modified first swimmerets called gonopods (1)openings to each vas deferens (2) third (3), fourth (4) and fifth (5) walking legs

Male crayfish

Female crayfish

swimmerets (1) opening to the seminal receptacle (2)openings to the oviducts (3)third pair of walking legs (4). Note: These openings have been expanded to make them more visible.

Crayfish meat

abdominal flexor muscles (1) & abdominal extensor muscles (2) = MEATintestine (3), one of the fifth walking legs (4), carapace (7), uropods (5) and telson (7).

Crayfish internal anatomy

digestive gland

1 – walking legs2 – gills3 – cephalic groove4 – 3rd pair maxilloped5 –cheliped6 – right eye7 – rostrum8 – right long antenna

Internal anatomy

green glands (1) , compound eyes (2), the digestive gland (3), mandibular muscles (4), gills (5), abdominal extensor muscle (6), a portion of the fifth walking leg (7), and one of the third maxillipeds (8).

Class Branchiopoda

• primarily live in freshwater• all possess flattened, leaflike

appendages used in respiration, filter feeding and locomotion

• order Cladocera: water fleas– e.g. Daphnia– large carapace covers their body– sexual reproduction produces “wintering

eggs” that hatch in spring• order Anostraca: fairy shrimp and

brine shrimp– fairy shrimp live in temporary ponds that are

formed through thaws and rains– eggs are brooded by the female– after the female dies and the pond dries –

eggs encyst and enter a dormant stage– with water – hatch into larval stages– dormant embryos can be carried by wind

and rain

sea monkey

daphniawater flea

fairy shrimp

Phylum Arthropoda

• Subphylum Hexapoda: body divided into head, thorax and abdomen; five pairs of head appendages; three pairs of uniramous appendages on the thorax– Class Insecta

• Subphylum Myriapoda: body divided into a head and trunk; four pairs of head appendages; uniramous appendages– Class Diplopoda– Class Chilopoda

Subphylum Myriapoda

• terrestrial• 4 classes – characterized by a

body consisting of head and trunk plus uniramous appendages

• Class Symphyla• Class Pauropoda• Class Diplopoda: millipedes• Class Chilopoda: centipedes

Class Diplopoda

Class Chilopoda

Subphylum Myriapoda

• Class Diplopoda: millipedes– head with mandibles for chewing + two antennae– circular body with 11 to 100 trunk segments – each segment is actually two

segments fused together– two pairs of legs per segment – push against the substrate for locomotion– two ganglia, two pairs of ostia and two tracheal trunks per segment– feed on decaying plant material using mandibles

Subphylum Myriapoda• Class Chilopoda: centipedes

– nocturnal– head with maxillae and mandibles +

2 antennae + compound eyes or ocelli

– flattened body - 15 or more trunk segments each with one pair of legs per segment

– first pair of legs modified into forcipules or venom claws

• not seen in other arthropods– rest of the legs = maxillopeds– fast-moving predators – small

arthropods, earthworms and snails– bite can be annoying to humans

Subphylum Hexapoda = Insects

Grasshopper External Anatomy

Grasshopper Internal Anatomy

Dorsal view

gastric caecae below the crop

ovaries

hindgut/intestine

Malphigian tubules

ovipositor

Tracheae

Ventral view

Subphylum Trilobitomorpha• the fifth, extinct subphylum • trilobites• dominant form of life in the oceans 600 MYA• crawled along the substrate feeding on annelids, molluscs and decaying organic

matter• oval body – flattened and divided into three longitudinal regions• all body segments are articular – roll into a ball• appendages – two lobes or rami – called biramous• inner lobe - walking leg• outer lobe bears spikes or teeth – digging or swimming or as gills in gas exchange