1. 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

2. 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

3. Evidence of Arthropoda
KEY
segmentation
jointed appendages
exoskeleton

4. 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

6. 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

7. Barnacles are crustaceans!

8. The wonderful world of crustaceans!
Amphipods have a curved body that is flattened sideways
Isopods are dorsoventrally flattened
Shrimps, lobsters and crabs are decapods; all have ten legs made up of 5 pairs of appendages 1
2-5

9. Molting Arthropods must molt, or shed, their exoskeleton as they grow
Most arthropods are small because the rigid exoskeleton puts limitations on their size
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11. 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

12. 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)!

13. © Steffen Foerster Photography/ShutterStock, Inc.
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.

14. 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

15. 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

16. 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

17. Phylum Echinodermata

18. Sea urchins have a round, rigid test
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

19. Sea Urchin (class Echinoidea)

20. 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

21. 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!

22. 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?

23. 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

24. Urochordates (sea squirt)

25. 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)

26. Phylum Chordata, Subphylum Cephalochordata
All four characteristics of chordates are present throughout entire life

27. Phylum Chordata, Subphylum Cephalochordata