Transcript Marine Invertebrates_7c (Arthropods, Echinoderms, Chordates)

Arthropods
• Arthropods (Phylum Arthropoda) make up the
largest phylum of animals
– 3 out of every 4 animals are arthropods
• The largest group of Arthropods are the
insects, which are rare in the sea
• The overwhelming majority of Arthropods in
the ocean are crustaceans (class Crustacea)
– Shrimp, lobster, crabs, copepods, barnacles
Phylum Arthropoda
• Arthropod means “jointed foot”
• Jointed appendages such as legs and
mouthparts
• Body is segmented and bilaterally-symmetric
• Arthropods possess a tough, external
skeleton, or exoskeleton
– Composed of chitin
– Secreted by underlying tissue, must molt or shed
Evidence of Arthropoda
KEY
segmentation
jointed appendages
exoskeleton
Phylum Arthropoda, Subphylum Crustacea
• The majority of marine arthropods are
crustaceans (subphylum Crustacea)
• Crustaceans are distinguished from other
Arthropods by their possession of a pair of
biramous (two-parted) limbs, and by a
nauplius larval stage
– Includes barnacles, shrimp,
krill, crabs, lobsters, and
copepods
http://www.earthlife.net/inverts/crustacea.html
Phylum Arthropoda, Subphylum Crustacea
• Crustaceans are specialized for life in the
water
– Most possess gills to obtain oxygen
– Chitinous exoskeleton reinforced with CaCO3
– Two pairs of antennae
Barnacles are crustaceans!
The wonderful world of crustaceans!
Amphipods have a curved body Isopods are dorsoventrally flattened
that is flattened sideways
Shrimps, lobsters and crabs
are decapods; all have ten
legs made up of 5 pairs of
appendages
1
2-5
Molting
• Arthropods must molt, or shed, their
exoskeleton as they grow
• Most arthropods are small because the rigid
exoskeleton puts limitations on their size
afcd.gov.hk
serc.si.edu
http://movingspaceproductions.com/view.php?video=Daz8nkh-pWM&feature=youtube_gdata_player&title=Molting+horseshoe+crab
serc.si.edu
Other Marine Arthropods
• Other than crustaceans, there are relatively
few marine Arthropods
• Horseshoe crabs are not crustaceans, and
belong to subphylum Chelicerata
– Largely extinct; only five living species
– Horseshoe-shaped carapace* that encloses a body
with six pairs of legs
*shield-like structure that covers anterior portion of
Arthropods
Phylum Arthropoda,
Subphylum Chelicerata
• Chelicerae are pointed appendages which are used
to grasp food
• Subphylum Chelicerata includes sea spiders (class
Pycnogonida) and arachnids (class Arachnida)!
Horseshoe Crabs
• Horseshoe crabs belong to class Merostomata
(“thigh mouth”)
• Appendages used for feeding at one end, and
for swimming/locomotion at the other
• Critically important
in coastal marine
food webs
– Why?
© Steffen Foerster Photography/ShutterStock, Inc.
Horseshoe crabs
• Oldest record of horseshoe crab fossils date
back 450 million years ago
• Horseshoe crab blood contains hemocyanin to
carry oxygen; blue
• Blood contains amebocytes which release a
clotting factor when
exposed to bacteria
– Used to detect
contamination in
medications
http://www-tc.pbs.org/wnet/wp-content/blogs.dir/3/files/2008/06/590_crash_blood.jpg
Echinoderms
• Sea stars, sea urchins, and sea cucumbers
belong to phylum Echinodermata (“spiny
skin”, “hedgehog skin”)
• Exclusively marine
• Adult echinoderms possess pentamerous
symmetry; in which the body is arranged in
five parts around a central axis
– No dorsal, ventral, anterior or posterior end; oral
and aboral ends only
Phylum Echinodermata
• Echinoderms have an internal skeleton, or
endoskeleton covered by a bumpy, sometimes
spiny, tissue layer
• Echinoderms have a network of water-filled
canals connected to muscular tube feet,
which extend when filled with water
• The vascular system connects to the outside
environment via the madreporite on the
aboral surface
Phylum Echinodermata
Types of Echinoderms
Sea stars can
regenerate
missing body
parts
Brittle stars have long,
flexible arms; most
abundant group of
Echinoderms
Sea urchins have a round,
rigid test
Sea Urchin (class Echinoidea)
Types of Echinoderms
Sea cucumbers are worm-like;
elongated along the oral-aboral
axis, as if pulled/stretched from
the mouth and anus
Crinoids use outstretched,
feathery arms to capture food
particles from the water; includes
feather stars and sea lilies
Chordates without a backbone
• The Chordates (phylum Chordata) contain
three major groups or subphyla:
– Urochordata
– Cephalochordata
– Vertebrata
• Precursors to the vertebrates are found in
Urochordata and Cephalochordata; 2 small
groups of marine invertebrates which share a
phylum with us!
Phylum Chordata
• During at least part of their development, all
chordates share the following four
characteristics:
– A dorsal, hollow nerve cord
– Gills, or pharyngeal slits
– A notocord, a flexible rod for support
– A post-anal tail
Ontogeny recapitulates phylogeny?
Phylum Chordata, Subphylum Urochordata
• Tunicates (subphylum Urochordata) exhibit all
four characteristics of other chordates during
embryonic development only
– No tail in adults
• Exclusively marine
• Include sea squirts,
sessile filter-feeders
• Include salps, holoplanktonic
Urochordates (sea squirt)
Phylum Chordata,
Subphylum Cephalochordata
• Lancelots (Subphylum Cephalochordata)
exhibit all four characteristics of chordates
throughout their entire lives
• Filter-feeders; use their gill slits to capture
food particles
• Differ from vertebrates, in that their
notochord is not surrounded and protected by
a vertebral column (bone)
Phylum Chordata,
Subphylum Cephalochordata
All four characteristics of chordates are
present throughout entire life
Phylum Chordata,
Subphylum Cephalochordata