1. Molluscs and Arthropods
Lab #12
Molluscs and Arthropods

2. Phylum Mollusca 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

3. Class Gastropoda 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
abalone

4. Class Gastropoda 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

5. 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

6. Subclass Pulmonata

7. Class Bivalvia = the Clam

8. labial
palps
anterior
adductor
muscle

9. foot
mantle

12. Class Cephalopoda = the squid

13. 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

14. Subphylum Chelicerata Class Arachnida
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
Subphylum Chelicerata Class Arachnida
only a few scorpions are toxic to humans – Androctonus (northern Africa)
- Centuroides (Mexico, Arizona and New Mexico)
chelicerae
reproduction involves a complicated “dance” that lasts several hours
development of a scorpion requires 1.5 years until maturity

15. Class Arachnida 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
Class Arachnida
Opiliones
Acarina

16. 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

17. 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

18. 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)
Class Arachnida
mating involves complex behaviors involving tactile, chemical and visual signals

19. Subphylum Crustacea Class Malacostraca = the crayfish

21. Crayfish dissection External Anatomy
1 – uropods
2 – telson
3 – abdomen
4 – cephalothorax
5 – cephalic groove
6 – walking legs
7 – cheliped
8 – eye
9 – rostrum
a - antennae
Crayfish dissection External Anatomy

22. 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)

23. 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

24. 1st pair of swimmeret is larger in the male – for sperm transfer
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
1 = uropods
2 = pleopods or swimmerets
3 = walking legs or periopods
4 = cheliped (1st walking leg)
5 = 1st swimmeret
6 = antennae

25. 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
Female
1 – swimmeret
2 – male genital opening
3 – 1st pair of swimmerets - clasper
4 – 7 – walking legs
8 – base of the first pair of walking legs
1 – swimmeret
2 – seminal receptacle
3 – walking leg #5
4 – walking leg #4
5 – female genital opening
6 – walking leg #2

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

27. 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.
Female crayfish

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

29. Crayfish internal anatomy
digestive gland

31. 1 – walking legs
2 – gills
3 – cephalic groove
4 – 3rd pair maxilloped
5 –cheliped
6 – right eye
7 – rostrum
8 – right long antenna

32. 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).

33. Class Branchiopoda primarily live in freshwater
sea monkey
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
daphnia
water flea
fairy shrimp

34. 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

35. Subphylum Myriapoda terrestrial
Class Diplopoda
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 Chilopoda

36. 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

37. 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

38. Subphylum Hexapoda = Insects

40. Grasshopper External Anatomy

42. Grasshopper Internal Anatomy
Dorsal view

43. gastric caecae below
the crop
ovaries
hindgut/intestine
Malphigian tubules
ovipositor
Tracheae
Ventral view

45. 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