[This diary was originally posted to Daily Kos on August 25, 2006.]

The Bay Scallop (Aequipenctin irradians) is a Molluscan maverick. The species has succeeded by breaking or bending the rules of bivalvery at almost every turn. Think Han Solo, Zaphod Beeblebrox and Captain Hilts from "The Great Escape" all stuffed between two calcareous shells.

The shells are identical (actually mirror images of one another) except for the color. The top shell is darker, often with bands of alternating brown and cream. The bottom shell is white. Both shells are strongly ribbed, with up to twenty raised lines radiating from the base. Scallops cannot dig as clams do, so the dark top shell helps it to camouflage as it sits on the dark, muddy bottom. Weeds and sponges grow on it as well, completing its disguise.

Arthropods, including crustaceans, insects and arachnids, are by far the largest group of animals that exist on Earth, comprising over 80% of all known species of animals. And the single largest land-dwelling arthropod is the coconut crab (Birgus latro). Found on tropical islands in the Pacific and Indian oceans, these monsters may reach a leg span of well over six feet.

Squid are free-swimming mollusks, and like their close relatives the octopods, they are intelligent, predatory, fast-growing and have a depressingly short life span usually lasting merely a year.

The long-finned squid (Loligo pealei), one of about forty species that occur worldwide, is most abundant in the Atlantic and is the animal you are most likely eating when you order calamari. It grows to a little over a foot in length and, like all squid, have ten tentacles surrounding the mouth. These are used to capture prey and transfer them into the beak-like mouth.

While beachcombing it's not uncommon to come across the strange thing pictured above mixed in among the various beach debris.  This is the empty egg case, or "Mermaid's Purse", of a Skate.

Fish are divided into two main groups: the cartilaginous fish, which include sharks, skates and rays, and the bony fish, which include nearly all of the rest of the fishes found in both fresh and salt water.  The bony fish have a skeleton made of calcium, like those of birds and mammals.  The cartilaginous fish have a skeleton made of cartilage.

Unlike most bony fish, which shed hundreds or even thousands of unprotected eggs into the water, cartilaginous fish produce only a few young and protect them inside a leathery egg case.  Most female sharks keep the egg case inside their bodies and give birth to live young.  Skates, rays and some types of sharks, however, lay a couple of egg cases on the ocean floor and leave them to develop alone.

Generally the introduction of a non-native species of plant or animal into an ecosystem is a destructive event. Whether they be rabbits or poisonous cane toads introduced to the Australian outback or kudzu spreading through the American south, these organisms out-compete, consume or displace native fauna and flora. The introduction of these exotics, whether brought to foreign shores by accident or intentionally, is by definition due to human activity.

This is part III on hermit crabs. Hermit Crab Basics is here, and hermit crab reproduction is here.

Tonight I’d like to focus on hermit crab symbionts. Symbiosis is a relationship between unrelated species of animals. There are several different types, ranging from parasitism, where one species benefits and the other is harmed, to mutualism, where both species benefit from the relationship. With hermit crabs, symbiotic relationships tend to be mutualistic, meaning that although the relationship isn’t neccessary for the the survival of either species, it is nonetheless beneficial to both parties. I’d like to take a look at three symbiotic examples here.

As we saw last week in the diary Hermit Crab Basics, hermit crabs have abandoned a crustacean's typical total exoskeleton body coverage in exchange for the security of living inside an old univalve shell. The advantage of this strategy is that it can shed the portion of the exoskeleton covering the front part of its body without having to endure that dangerous "soft-shell" stage other crabs have to deal with. As I mentioned, one disadvantage is the crab must periodically find new, larger shells as it grows. As we shall see here, there are other obstacles this animals must contend with as well.

Hermit crabs are found all over the world in shallow waters and are one of the more familiar coastal animals. Although they have an exoskeleton, as all crustaceans do, this protective covering only surrounds the head, legs and claws. To protect the soft rear part of the body they must find a suitable shell to crawl into.

[This diary was first posted to Daily Kos on August 11, 2006.]

Sea urchins are Echinoderms, spiny-skinned animals related to starfish and sea cucumbers. Echinodermata is a rather small phyla of animals and is unique in that virtually all members of this group are strictly marine.

They also, as a group, employ nearly every type of feeding method exhibited by animals. Sea stars are predators, crinoids are filter feeders, as are some sea cucumbers. Many types of sea cucumbers are deposit feeders (swallowing sand, digesting the organic material and passing the undigestible bits). Sea urchins alone are mainly herbivores.  The animal above is my local Purple Sea Urchin (Arbacia punctulata).

Last Friday you guys voted overwhelmingly for Hermit Crab Basics as this week’s MLS topic. Unfortunately I’ve been dealing with the flu all week so I haven’t been up for doing the research. I’ll tackle that next week. Tonight I’d like to show you my newest marine acquisition, which was brought in just a few hours ago by a friend of mine who has been fishing rock crabs for about thirty years. This is the first albino he’s ever seen.

(Last week’s diary was called Cassiopeia, about the upside-down jellyfish, and is here if you missed it.)

In Greek mythology, Cassiopeia was the beautiful and vain wife of Cepheus, an Ethiopian king. Cepheus and Cassiopeia had a daughter, Andromeda, who was to be wed to the hero Perseus. Cassiopeia, at the last minute, decided to promise Andromeda to Agenor, a son of Poseidon.

Agenor arrived at the nuptials with an army, intending to kill Perseus and take Andromeda for himself. If you remember, Perseus is the guy who slayed the Gorgon. As Agenor’s army approached, Perseus retrieved the Medusa’s head and turned the army, including Cassiopeia, into stone. Poseidon decided to place Cassiopeia, along with Cepheus, in the heavens as constellations. However, as punishment for her vanity he placed her in the night sky sitting in a chair that revolved around the North Star so that she would spend half of all eternity upside down.

Most people know the sand dollar as the dried, white "shell" found in craft stores and gift shops. What you are seeing is simply the test, or skeleton, of a once living animal. Sand dollars are related to sea stars and sea urchins, and share many of those other animals’ characteristics, including a ventral mouth, tube feet and spines.

Thirty-three years ago a young upstart director named Steven Speilberg made what is now viewed as the first summer blockbuster movie. This film made stars of Richard Dreyfuss, Roy Scheider and Robert Shaw, who played the fantastic trio of characters named Hooper, Brody and Quint. But the real star was "Bruce", the mechanical fish named after Speilberg’s lawyer, whose job it was to bring to life Peter Benchley’s killer great white shark that terrorized the fictional town of Amity, New York.

All snails belong to the phylum Gastropoda (literally "stomach-footed"). Nearly all are covered with a single spiral shell. Given that there are around 75,000 species around the world, plus several thousand more extinct forms known from their fossils, there is obviously going to be quite a bit of variation in this group of univalves. Including some that are completely shell-less, such as land and sea slugs, and others whose shells are so rudimentary that they are barely noticeable. So I’ll be using some pictorial examples that I hope will illustrate some of the basic common features.

Algae are the dominant photosynthetic organisms found in marine ecosystems. They may be tiny planktonic organisms, comprised of merely a single cell, or clusters or strands of a few dozen cells. These microscopic types are known as microalgae. Macroalgae are the more familiar types, commonly referred to as seaweeds. I’ll be dealing mainly with the latter here.

[This diary was originally posted to Daily Kos on August 4, 2006. New Marine Life Series content will be back next Friday with the new year.]

So, what do clams have to do with tree rings?

Dendrochronology is the study of past events using growth rings in trees.  In some ways it's actually more a study of ecological history than biology (or put better, a study of history using biology).  When viewed in cross section the rings of a tree can be clearly seen and its past growth can be measured as new cells are laid down by the cambium tissue layer just beneath the bark.

[This diary was first posted to Daily Kos on July 28, 2006. Original essays will resume after the New Year.]

Most of you are at least somewhat familiar with the life cycle of Salmon in the Pacific Northwest. Born in rivers and streams far inland, the newly hatched young float downstream toward the ocean where they live out most of their lives in salt water. Each year a mass migration occurs where adults battle their way upstream and over waterfalls back to their fresh water nursery grounds where they spawn, die and become bear food. Fish that do this are called anadromous.

Here in my New England backyard lives another species of fish, the American Eel (Anguilla rostrata), which does the opposite. Known as catadromous fish, they are born in salt water, spend their lives in freshwater rivers and lakes and then return to the ocean to spawn.

What’s this grey squirrel got to do with marine life? Stay with me for a second. Countershading is a form of camouflage used by many open water fish, although it is also commonly seen in many terrestrial creatures as well. Basically it is just a color pattern found on animals where the dorsal surface is dark and the ventral surface is light colored.