Invertebrates have very different life histories than vertebrates Invertebrates have very different life histories than vertebrates. Sea stars release gametes (eggs and sperm) into the water where they fertilize (combine) and develop into tiny drifting larvae that will eventually settle on the ocean floor to grow into an adult. Sea stars have separate sexes. The adults are in one habitat (benthic) while the larvae are in another (as plankton in the water). http://www.flickr.com/photos/64476710@N00/5122412952/ 1

What do you think this might be What do you think this might be? This is the larval form of the seastar we just saw– it is called an echinopluteus. Eventually this organism will sink to the bottom of the ocean and grow to be a sea star. http://www.flickr.com/photos/draco_cd/1177501949/ 2

These barnacles also release gametes (eggs and sperm), which combine and develop into tiny drifting larvae that will eventually grow and settle on rocks and grow into an adult barnacles. The adults are in one habitat while the larvae are in another (as plankton in the water). http://www.flickr.com/photos/modomatic/2394983702/ 3

What do you think this organism is What do you think this organism is? This is a larval form of a barnacle– a nauplius. In time, it will grow bigger and sink to the bottom, where it will settle on a rock and grow to be a barnacle. http://www.flickr.com/photos/draco_cd/1177077389/ 4

This red urchin releases gametes (eggs or sperm), which combine with sperm or eggs from another urchin to produce tiny drifting larvae that will eventually grow and settle on the ocean floor to grow into an adult. The adults are in one habitat (benthic) while the larvae are in another (as plankton in the water). http://www.flickr.com/photos/kightp/5601911457/ 5

What do you think this is What do you think this is? This is the larval form of a sea urchin, called a pluteus. This pluteus will grow bigger and sink to the bottom and grow to be an adult urchin. 6

Now we will learn about the life cycle of a crab! This is an adult crab. If we flip her over… http://www.flickr.com/photos/9428166@N03/2689687946/ 7

We see that she is carrying a large brood of eggs! http://www.flickr.com/photos/jaycollier/744506931/ 8

The eggs develop into a larval stage called zoea The eggs develop into a larval stage called zoea. They are weak swimmers, so they are called plankton! They move around in the water column and try to eat food. http://www.flickr.com/photos/meanandpinchy/225807890/ 9

Here is a drawing of a zoea Here is a drawing of a zoea. The zoea drift around and eat food so they can grow. After some time, they molt and become a new shape… http://www.mesa.edu.au/friends/seashores/crab_reprod.html 10

They turn into megalopa– another kind of plankton They turn into megalopa– another kind of plankton. The megaolopa look more like crabs. They continue to drift around in the ocean as plankton, eating and growing until they are ready to metamorphose into a juvenile crab. http://www.padillabay.gov/macroalgaeOnCrabs.asp 11

This is another drawing of a crab megalopa http://www.mesa.edu.au/friends/seashores/crab_reprod.html 12

The planktonic megalopa metamorphoses into a benthic juvenile crab The planktonic megalopa metamorphoses into a benthic juvenile crab. The crab sinks to the bottom, where it will remain for the rest of its life, eating and growing bigger with every molt. http://www.flickr.com/photos/draco_cd/2591582260/ 13

MOLTING Molting is the process a crustacean undergoes to grow. It grows a new shell (slightly bigger, but soft and folded up a bit) under its old shell, and grows enough to squeeze open its old shell and leave it behind, wearing its new (slightly bigger) shell. It pumps in water to fill out its new shell as it hardens. Now the crab has some room to grow into its new shell! http://www.serc.si.edu/education/resources/bluecrab/molting.aspx 14

Plankton Neckton Benthic Just as a reminder: Plankton are ocean drifters– they are weak swimmers at the mercy of ocean currenty Neckton are ocean swimmers- they swim strongly enough to control where they go in the ocean Benthic organisms live on or in the ocean bottom. The larval crab is plankton. The adult crab is a benthic animal. Many marine animals live in (and need) different habitats in their lives! Benthic 15