The phylum Mollusca is large and diverse, encompassing ten different classes of animals. The animals are most commonly recognized as one of three different types: the bivalves, the univalves, and those without shells (or with very small internal shells, ex. slugs). Bivalves are mollusks with two shells such as clams and oysters. Univalves are animals with one shell such as a snail. Mollusks without shells include squid, banana slugs, and octopi.
Some mollusks are terrestrial, occurring in most environments on earth, while others live in the water for some or all of their life. Many of the most popular mollusks are marine species because they are pretty and some are caught for food or jewelry. Some of the qualities that define a mollusk are definite organs (mainly heart, gonads, and kidneys), a complete digestive tract, and a muscular foot. Although their bodies are not segmented, they do have two definable parts: the head and the foot. Their shells are made of calcium carbonate. The shells are very decorative on the inside for many marine species, and the outside for many snails. Most mollusks have at least two stages of life and their second stage (or adult phase) is often marked by bearing a shell.
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Polyplacophora are more commonly referred to as chitons. They look ancient, like a trilobite of the ocean. Their body is an elongated dome with eight overlapping plates and they are usually as big as a quarter. Making their living on algae, they are commonly found in intertidal areas as they cling to the rocks, but usually they are camouflaged very well with cryptic coloring.
Those animals with two shells are conveniently all lumped together in class Bivalvia. They don’t have a formal eating structure, so they filter food by siphoning it from the water with gills between their two valves. Their organs, including their nervous system, are all located between the two shells and they have a muscular foot that can stick out. This foot is used for locomotion, attaching to rocks, or both. Bivalvia is diverse and includes animals like the oyster, which give us pearls by covering bits of sand that come into their system with the calcium carbonate that they use for their shells. The waters surrounding Point Reyes are a popular spot for collecting oysters and clams.
The class Scaphopoda are known as tusk shells and found in marine environments world wide. They look like elephant tusks that are 15cm long, and they feed on the bottom of the sea. Most likely, these animals occur at our Seashore, but the chances of seeing them are extremely unlikely.
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Gastropoda is the most widespread class within Mollusca. It is estimated to have as many as 75,000 species and undoubtedly many of its species occur at Point Reyes. The gastropods are univalve animals and can be terrestrial, freshwater, or marine and include snails, abalones, limpets. Their name is from Greek roots with gaster referring to stomach and poda referring to feet. This makes sense because their major two body parts are their head region (with most of their organs) and their muscular foot. This separation also comes from a process which also defines a gastropod called torsion. Torsion occurs during their development into an adult; their internal organs twist 180 degrees and results in the separation of its organs from its foot. Although the gastropods have some similarities, they are for the most part extremely varied and because they all live in very different places, they eat very different things.
The abalone is by far Point Reyes most famous specimen of Gastropoda. It is a beautiful marine snail that at one time was extremely abundant along the coast. Currently, there are very stringent restrictions on the collection of abalones in northern California. The banana slug is one of the most commonly spotted Gastropods at Point Reyes.
Most intelligent and softest are the easiest way to describe the cephalopods. The creatures of Cephalopoda have lost their shells, and compensate with a far more developed brain. Also, they have an overdeveloped muscular foot, which is turned into arms or tentacles. Its flagship members are octopus, squid, cuttlefish, and nautilus. Besides being able to make a living in difficult places, they are able to defend themselves in unusual ways. Most are able to change color and texture rapidly to match surroundings, and are also able to shoot an ink cloud to make a getaway.
Point Reyes Seashore has the Red Octopus (Octopus rubescens), but like may inhabitants of the sea, it is almost never seen. They do live in intertidal areas, but spotting one is extremely rare and if you do, it is safest to not touch the animal. Another common cephalopod is the common squid, but don't expect to see this one either. They only will come towards the shore area to breed and then die.
Text by Kristen Truchinski
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Cassandra Brooks interviews Amy Henry, an intern looking for Black Abalones in the Golden Gate National Recreation Area and Point Reyes National Seashore.
- 4 minutes, 34 seconds
- Credit / Author:
- Cassandra Brooks/Pacific Coast Science and Learning Center
- Date created:
The Natural Laboratory Podcast Script:
Searching for the Endangered Black Abalone in Northern California
This is the Natural Laboratory, a podcast exploring science for Bay Area National Parks. I'm Cassandra Brooks
Black Abalone is one of seven abalone species found in California's intertidal waters. This small abalone, with a smooth dark shell, has succumbed to the same fate as most abalones: overfishing. Commercial fisheries for Black Abalones began in 1968 and by the 1990s landings plummeted to zero.
But fishing wasn't the only culprit. Black Abalones have gotten sick, really sick with withering syndrome. This disease, caused by a bacterial infection, halts the abalone's production of digestive enzymes. No longer able to digest food, the abalone must consume its own body mass.
The disease was first recognized in the mid 1980s and has since decimated Black Abalone populations by up to 99% in some regions. As a result, Black Abalones have been classified as critically endangered by the IUCN.
Thus far, Southern California populations have been especially hard hit by withering syndrome. Yet little is known about the status of Northern populations.
[Interview with Darren Fong]
Darren Fong: We got a request from the federal agency, National Marine Fisheries Service for information about the status and trends of Black Abalone in our park. We actually had no information to provide them because we never did any surveys for that species within our park.
Cassandra Brooks: That's Darren Fong, Aquatic Ecologist with the Golden Gate National Recreation Area. Per request, Fong set out with interns Amy Henry and Kari Eckdahl looking for Black Abalones in the Golden Gate National Recreation Area and Point Reyes National Seashore. Here's Amy Henry.
[Interview with Amy Henry]
Amy Henry: Well no large-scale survey has been done of Black Abalone north of San Francisco Bay before or even in the Bay Area. Black Abalone have never been particularly common in this area, but no one has ever been out and surveyed these sites before. So although we know that they are rare, we don't know how rare. The data and information that we are collecting is going to provide information for future studies, for the studies of these endangered species, and will lead to better legislation and how to protect them.
CB: So far, they've found Black Abalones, but not very many of them and none with withering foot syndrome. But these surveys are just the first step.
CB: Part of their challenge is getting down to the rocky and sometimes treacherous intertidal, where the abalones live.
AH: So the sites we've been surveying have been identified using Google Earth and a project a few years back called “The Coastal Biophysical Inventory.” This project identified areas of rocky coastline where abalone could possible live. So basically all we know about a site beforehand is that it is rocky. We interviewed Park Rangers from the local area to find out about the best trails to get down to sites. Sometimes this requires a rope to climb down crumbly steep cliffs, sometimes we get there and it doesn't look like good abalone habitat at all and we are sorely disappointed.
AH: We're also working at very early in the morning hours. The timing of our surveys have to be going with the low tides, and they have to be negative tides, below zero tides. Some of these occur at 4:30 in the morning. We have woken up at 3 am before and taken a hike out in the dark with flashlights where we think there are spooky creatures behind every turn.
CB: To Amy and Kari all the early mornings and scrambling over cliffs have been worth it.
AH: The park service really has a mission that you can get behind. You can really support and know that the work you are doing is for the benefit of all the citizens of America and California and to protect it for future generations. Even for our small little piece of protecting Black Abalone, is a really beautiful creature that I never appreciated before, never knew much about before. And hopefully because of our work, we will be able to show it to our children in the future and say we had a piece in protecting this animal from going extinct.
CB: With the Pacific Coast Science and Learning Center, I'm Cassandra Brooks.