Her teacher, JH is applauded for encouraging her to write me the letter and for fostering Brianne's interest in science!
Our teachers asked us students to write to an expert on a topic, that we chose, and I chose to write mine on starfish. I chose starfish cause starfish are just a mystery; I want to learn more about starfish.I'm looking forward for your response on starfish, on the questions. Thank you I knew you were the right one to write to.
Food might be anything from organic slime to algae to animals that either don't move very much(such as mussels or clams) or may never move (such as sponges). Some, as we'll see below are fierce predators.
Although starfish/sea stars DO have something similar to eyes, they are not quite the same. There are organs on each of the armtips that permit starfish to sense light and perhaps heat.
Many special sensors lie on the top of their body that allows them to sense light. Many species are sensitive to light and will move off if it is too hot.
Note the GREEN ARROWS below! Those are where the "eyes" (technically called eye spots) are located.
Because the ocean is always "inside" them, they can "smell" or detect food immediately. They can detect anything good or bad that might be around them. This includes "smelling" bad things like poisons and uncomfortable things about the water (such as if it is freshwater -starfish only live in sea water). But they can also "smell" predators and prey immediately!
Many predators that feed on starfish can immediately be sensed by a starfish when their "smell" gets into the water. If a starfish doesn't like the smell, it will move away from it very rapidly..
If we enlarge the area in the blue circle to the box below...
We see all of those fuzzy patches between all of the white granules/spines. Those fuzzy patches are each a single finger shaped balloon like structure called a papula (plural is papulae). Those are the gills.
Each one of those patches can contain dozens of papulae, which are extended when the animal is comfortable and feels secure. Each of these permits the animal to collect oxygen for the starfish to breathe. They are generally found only on the top and side surfaces, generally not on the underside.
Starfish are members of the phylum Echinodermata. A phylum represents the largest natural grouping of different 'types' of animals. For example, phylum Mollusca includes squids, clams and snails and phylum Arthropoda includes insects, crabs, spiders and centipedes. Humans and mammals belong to the phylum Chordata-also called the chordates.
Echinoderms are the "spiny skinned" animals-and include starfish, their close relatives the brittle stars, sea urchins, sea cucumbers, and feather stars. Echinoderms are on the same "side" of the family tree of the animals but are quite distant from chordates (which includes the mammals).
Echinoderms have evolved in a VERY different way and in a much different direction than Chordates (mammals). And so, their biology is also much different.
Their reproductive/egg-laying biology is one example of how different they are..
Here is a video of a starfish from the tropical Pacific (in southern Japan). Not all starfish assume this unusual "standing on arm tips" pose..See those white threads being released by the animal??
This species is releasing reproductive cells-called gametes into the water.
Male and female gametes join together in the water and grow into a series of different small larval stages that eventually settle out and grow into an adult.
Here is video that shows the many different stages as they grow and develop...ultimately becoming an adult.
MOST times, eggs and baby starfish form in the ocean. BUT in some UNCOMMON cases there are species of starfish that will actually KEEP their eggs or juveniles until they grow to an adult size...
Again..this is NOT typical.. but it does happen. These eggs and juveniles are usually kept around the mouth...
9. Do starfish have brains? No, but...
So, starfish have what is called radial symmetry (specifically pentaradial or five part symmetry). That is, if you were to cut the animal in half it does not have an exact and opposite side.
The arms all project out from the middle the way that spokes on a bicycle wheel project from the middle.
As a result, there is no head or true central location where the nerves meet.
In its place, is what's called a radial nervous system. The nerves form a ring around the mouth in the disk and radiate out along the arms.
Although its not as apparently developed as the brain or nervous system in a human (or some other mammal) the behavior in sea stars is surprisingly complicated. Under time lapse cameras, biologists have observed that sea stars are capable of a great deal of behavior that one would not expect from such a seemingly simple nervous system!
10. Can you send a picture of a starfish?
I can do better than that! Click here and this will take you to the Flickr Photostream group for sea stars/starfish! And there are MANY different kinds to enjoy!
Click here and go to the Encyclopedia of Life's Asteroidea page to see more!
Whew! Okay. that's some good questions!
My thanks to Brianne and her teacher for these great questions!!
If they or any other students would like to get further clarification of if you have more questions, drop them in the comments below and I'll do my best to answer them by the end of the week! (answers will be in the comments)