Download mantle cavity

Kingdom Animalia
Last day…
introduction to animals
& their characteristics
…covered early branches the
Porifera (prob. monophyletic),
Ctenophora & Cnidaria, the
Acoela, and started the
Lophotrochozoa
Began looking at phylum Platyhelminthes – the Flatworms
- ~20,000 spp.?
- also acoeolomate & triploblastic, but usually more complex
than Acoela
covered Class Turbellaria…
- mostly free-living, marine, a few freshwater
- glide or swim
- reproduce by fission, or sexual reproduction by
hermaphrodites
Class Monogenea – monogeneans
- external parasites of fish (or hippo) with relatively simple
life cycles
Class Trematoda – Trematodes, or flukes
- mostly internal parasites of a wide range of animals
- have oral sucker near mouth & ventral sucker to attach
- complex multinucleate covering helps fool immune system,
resist digestive enzymes
Fasciolopsis
intestinal fluke
Have complex life cycles with intermediate hosts (often a
mollusc) & different types of larvae
- most hermaphroditic, but Schistosoma has males & females
- schistosomiasis caused by blood fluke in intestinal or
bladder veins, affects 200 million people
Class Cestoda – tapeworms
- specialized parasites, mostly of vertebrates (including us)
- scolex (‘head’) w. suckers & sometimes hooks to attach in
intestines
- no mouth or digestive system, just
absorb nutrients
- long ‘body’ of proglottids, mostly
contain sex organs, detach &
pass out in feces
Phylum Rotifera – rotifers – 1,800 spp.
- tiny (0.5 – 2 mm) animals of aquatic or moist habitats,
but w. complex bodies w. organ systems, e.g. alimentary
canal w. mouth & anus, ‘jaws’ for grinding
- has pseudocoelom
- one class reproduces via unfertilized eggs producing only
females, apparently for > 35 million years?
The lophophorates: 3 phyla actually have lophophores:
crown of ciliated tentacles, draws water & food in
- these phyla sessile, lack definite head, have U-shaped
alimentary tract & true coelom
We look at 2 of those 3 phyla…
Phylum Ectoprocta – the bryozoans (‘moss animals’)
- 4,500 spp.
- normally colonial, individual zooids not fully independent
- filter-feeders, retractable lophophore
- most marine, may be reef-builders
(hard exoskeleton), but some
freshwater spp. (9 in IL)
Pectinatella
magnifica
Phylum Brachiopoda – Brachiopods or ‘lamp shells’
- resemble tiny clams, but on stalk & w. lophophore inside
- 2 halves of shell are dorsal & ventral (not lateral)
- only in marine waters
- scarce today (~335 spp.), but
abundant in Palaeozoic
Move into group of phyla with trochophore larvae – first:
Phylum Mollusca – the Molluscs (clams, snails, squids, etc.)
- huge phylum (93,000 spp.?) of varied form, but same basic
body plan: shell-secreting mantle covers visceral mass
(w. major organs), foot for locomotion, digging)
- mantle cavity houses gills, anus, etc.
Eight? living classes, but 4 most diverse are:
Class Polyplacophora – Chitons
- oval body, dorsal shell w. 8 plates (but body unsegmented)
- foot for locomotion, and used as suction cup
- like many molluscs, have rasping radula
- use it to scrape algae off rocks
Class Gastropoda – snails and slugs
- marine (most), fresh-water or terrestrial, by far the largest
class (about 70,000 species)
- head present, eyes on tentacles
- terrestrial snails lack gills, respire through lining of
mantle cavity
- embryo undergoes torsion during development: body twists
up to 180°, bringing anus & mantle cavity over head
- distinct from coiling of shell
Most gastropods herbivorous, but some predatory
- radula modified to scrape flesh, bore holes in shells or as
‘harpoon’
- cone shells harpoon fish with fast-acting venom
- complex venom used as pain-killer, & may have other uses
Class Bivalvia – clams, oysters, mussels, scallops…
- shell with 2 halves, hinged mid-dorsally (so a left
valve & a right valve)
Bivalves have no distinct head, & no radula
- mantle cavity has gills for gas exchange & feeding
- suspension feeders, and mostly sedentary
- some burrow or move slowly w. foot, & scallops
use ‘jet propulsion’ by rapidly opening/closing shell
- some bivalves
have eyes &
sensory tentacles
at edge of mantle
- giant clams may
weigh > 220 kg,
colorful due to
algal symbionts
Class Cephalapoda – squids, octopuses, nautiluses
- active predators with tentacles to grab prey, beak to bite &
toxic saliva
- well developed eyes, and regarded as very intelligent for
invertebrates
- jet propulsion from siphon
Chambered nautiluses have shell, but shell reduced &
internal in squids, often absent in octopuses
Some squids quite large (Humboldt Squid – to 1m for mantle)
- but giant squid (rarely seen alive) to 2.25 m for mantle,
perhaps 13 m to ends of tentacles
…and Colossal Squid is largest invertebrate
- only +/- complete specimens immature?, but adults
estimated to reach 14 m
- more robust body, relatively shorter tentacles, so weight
at least 495 kg
Last of the lophotrochozoans…
Phylum Annelida – segmented worms (‘little rings’)
- 16,500 spp. in marine, freshwater & damp soil habitats
- divided into 2 classes?
Class Oligochaeta – Earthworms
- bristles or chaetae along side are sparse (4 pairs/segment)
- tunnel through soil, consuming dirt
& organic material, eliminating
waste as ‘castings’
- ganglia above & below
pharynx connect to
ventral nerve cord
- hermaphrodites, clitellum
produces ‘cocoon’ for
shed eggs & sperm
- some may regenerate after
fragmentation
Leeches
- formerly separate class, now seem to be part of Oligochaeta
- mostly fresh-water, a few terrestrial or marine
- famous for blood-sucking but many are predators
- have 2 suckers for attachment, but no chaetae or parapodia
- blood suckers use anesthetic secretion, then anti-coagulant
- still used medicinally to drain blood & anti-clotting drug
Class Polychaeta – the Polychaetes (‘bristle worms’)
- each segment has pair of parapodia w. many chaetae
- locomotion, & often function as gills
- mostly marine, bottom crawlers or tube dwellers, some
drift or swim
Some annelids famously big…
- Giant Gippsland Earthworm – to 3 or 4 m long?
- a South African sp. may be larger (report of 6.7 m)
- giant reef bristle worms average 1m, but up to near 3 m,
or more??
- and they have jaws!!
Have worked our way
through Lophotrochozoa,
sister group is the Ecdysozoa
- perhaps the most successful
animals of all?
Ecdysozoa identified as a monophyletic group by genetic
data, but do share trait of ecdysis: shedding old covering
& secreting new one to increase in size
- includes 9 phyla, but
2 much more diverse
than others…
Phylum Nematoda – Nematodes, or roundworms
- unsegmented round bodies, usually small (but up to 1 m)
- covered by tough cuticle
- ubiquitous, in aquatic habitats, soil, & in other organisms
- 25,000 spp. described, but might be 500,000, or 1,000,000
- pseudocoelomate, & no circulatory system
- usually separate sexes & internal fertilization, zygote can
withstand harsh conditions
- most nematodes free-living, feed on wide range of live &
dead food, important in nutrient cycling
- but many spp. are crop pests (often attacking roots) or
parasites of many species, including humans
- e.g. Trichinella spiralis from raw pork causes trichinosis
And now the big time! Phylum Arthropoda – Arthropods
- by far the biggest phylum, ~2/3 of all described spp.
are arthropods (~1,000,000 spp.)
In number of individuals & broad distribution, most
successful of all animal phyla
- likely related to body plan of phylum
- plan includes segmented body (but specialized in regions)
- hard exoskeleton
protects, supports
& prevents
dessication
- jointed appendages
for mobility
- exoskeleton composed of a cuticle covering entire surface,
composed of chitin (a polysaccharide) & protein
- provides attachment points for muscles
Arthropods have well-developed sensory organs: eyes,
simple or compound, olfactory/taste receptors,
antennae for touch & smell
- well cephalized
- have various
organs for gas
exchange, e.g.
spiracles leading
to branched
tracheal system
in insects
Aquatic arthropods usually have gills with extensive surface
area for gas exchange
Arthropods have open circulatory systems: hemolymph
pumped by heart through arteries, but empties into sinuses,
the hemocoel
- not a coelom (true coelom is small in arthropods)
- hemolymph flows around organs, then returns to heart via
valved pores
4 subphyla in Arthropoda, starting w. Cheliceriformes
- named for chelicerae: claw-like feeding appendages, used
as pincers or fangs
- most of ~100,000 spp. are arachnids – spiders, ticks, mites,
scorpions, harvestmen & sun spiders
- cheliceriforms also include horseshoe crabs & perhaps
sea spiders
Cheliceriforms have body w. cephalothorax & abdomen
- no antennae, but most have simple eyes
- 6 pairs of appendages start w. pedipalps – sensory, feeding
& reproduction
- then chelicerae & 4 pairs of walking legs
- respiration
using book
lungs