Arthropods Arthropods Phylum Arthropoda make up the largest

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 Ca. CO 3 – 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=Daz 8 nkh-p. WM&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/Shutter. Stock, 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, filter-feeders • Include salps, holoplanktonic sessile

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