The word mollusk comes from a Latin word meaning “soft”, which refers to the soft mantle that covers the mollusks, which then secretes the enzymes to form the calcium carbonate shell that protects their boy. The phylum Mollusca are invertebrates containing some sort of a calcium-carbonate shell to cover their soft mantle which secretes the enzymes that make up this shell. Mollusca is one of the most diverse phyla in the world, only second to insects.
The earliest mollusk species that date back all the way to the Cambrian time period (about 542 million years ago) include chitons and conchifers. Most of the fossils that have been found are extremely small, only about 1-5 mm. The oldest known cephalopods, which include squids, octopi, and cuttlefish, date back to much later times, in the Late Cambrian era, which ended around 488 million years ago. The fossil record gives very little evidence to prove how mollusks came about and evolved into what they are today. Because of the little evolutionary evidence, scientists have turned to comparative molecular biology. Biologists have inferred from studies that Phylum Mollusca and Phylum Annelida, which consists of segmented worms, share a common ancestor. The strongest evidence that they share a common ancestor is found in their embryonic stages. They both have pear-shaped larva called trochophore in the first stage of development. In both phyla, these larva have cilia that project from either end of the trochophore and encircle the middle. These cilia function by propelling trochophore through the water and drawing food into their mouths. Trochopheres that are free-swimming also aid in the dispersal of other marine mollusks. However, terrene mollusks and many marine-living annelids devel...
... middle of paper ...
...ability of a mollusk’s muscular foot to grasp things, such as food, has been adapted into what are now the tentacles of an octopus or squid. The calcium-carbonate shell found in most mollusks is a variety of sizes, shapes, and colors, but most of them have a single function: to protect the mollusk’s soft mantle and to prevent predators from eating them.
Works Cited
Campbell, Dana, and Jennifer Hammock. "Mollusca — Details." Encyclopedia of Life. Encyclopedia of Life, n.d. Web. 13 Mar. 2014.
Foster, Bethney. "Mollusk Life Cycle." EHow. Demand Media, 26 Aug. 2009. Web. 25 Mar. 2014.
Salvini-Plawen, Luitfried Von. "Mollusk (animal Phylum)." Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 25 Mar. 2014.
"Phylum Mollusca." Phylum Mollusca. N.p., n.d. Web. 25 Mar. 2014.
"Mollusk." - New World Encyclopedia. N.p., 30 Apr. 2006. Web. 29 Mar. 2014.
Because of its size and abundance, T. californicus is commonly regarded as the insect of the sea. This creature is generally very small, from 1-3 mm in size as adults. They are cylindrically shaped, and have a segmented body (head, thorax, abdomen) though no noticeable division between body regions (Powlik 1966). Each segment of the body has a pair of legs. They use their 'legs' to propel themselves through the water in short rapid jerks. They have 2 pairs of long feathered antennae, a chitin us exoskeleton and a single eye in the middle of their head, this simple eye can only differentiate between light and dark.
There is no doubt that arthropods are an extremely successful group of animals, with an estimated 5-10 million species worldwide[1], and this can be attributed to having an exoskeleton; it provides many benefits, such as protection from parasitism and other threats. However, one major disadvantage of having an exoskeleton is the limitations that an inelastic cuticle can place on growth. The exoskeleton provides protection, but when freshly moulted the animal is soft and vulnerable, as well as having limited mobility and use of appendages; many seek shelter before moulting[2]. There are similarities and differences between the moult cycles of all the arthropods, however only crustaceans and insects will be discussed here.
Crustaceans belong to the Arthropoda Phylum, which includes critters like ants, spiders, and centipedes. I know! Crazy to think that a delicious crab is in the same group as a spider! But they share similar characteristics. For starters, members of the Arthropoda Phylum do not have a backbone like you and me, so they are called __invertebrates__. And, as mentioned earlier, their skeleton is external, which is referred to as an __exoskeleton__.
Flatworms belong to the phylum Platyhelminthes. They have the simplest body plan of all bilaterally symmetrical animals. They are called flatworms because their bodies are compressed. The mouth is the only opening into the digestive cavity the flatworms have. Food is taken in through this hole and wastes are discharged also through this hole. Flatworms have a well-defined nervous, muscular, excretory, and reproductive system. The flatworm distributes the food it digests through a digestive tube that branches throughout all of its body parts. The fact that the worm’s body is flat serves many purposes. It allows the worm to hid in small spaces, to fit into the opening of other animals if the worm is parasitic, and it means that all the cells are close enough to the surface for exchange of oxygen and carbon dioxide with the environment (Meinkoth 399).
Liubicich, D.M., et al. 2009. Knockdown of Parhyale Ultrabithorax recapitulates evolutionary changes in crustacean appendage morphology. PNAS 106 (33): 13892-13896
They are invertebrates (spineless animals) and are cousins of anemones and jellyfish. When thousands of these animals are grouped together, they are referred to as coral colonies. Each coral "tree" or "mound" is one colony of coral polyps. A polyp has a sac-like body and an opening or mouth encircled by stinging tentacles called cnidae.
to the lobster and crab. Their closest living relative today is the horseshoe crab.The name
Fox, R. 2001. Invertebrate Anatomy OnLine: Artemia Franciscana. Lander University. http://webs.lander.edu/rsfox/invertebrates/artemia.html, retrieved February 13, 2011.
The Burgess Shale Fauna is a fauna that was constructed based on a group of fossils that were initially found, in the Burgess Shale area in the Canadian Rockies (Gould, 1989). They are a very important group of fossils as “modern multicellular animals make their first unprotected appearance in the fossil record some 570 million years ago” through this group (Gould, 1989, pp. 24). Moreover the Burgess Shales are known to have preserved the soft parts of animals enabling us to get a better understanding of life at the time.
Soft corals are grouped in the phylum Cnidaria, class Anthozoa, and order Alcyonacea. Their distinguishing characteristic is that their polyps always bear eight tentacles which are on both edges fringed by rows of pinnules (Fabricius and De’ath, 2002). The common name “soft coral” comes from the fact that they have no massive external skeleton as compared to the more commonly studied hard corals.
With its abundance of genera, the Burgess Shale is one of the world’s most important fossil fields. It’s discovery in 1909 led to over 100 years of paleontological study in the Canadian Rockies, a majority of which has been carried out in two quarries known as the Walcott and Raymond quarries (Hagadorn, 2002). Though he was originally in search of trilobites in the Burgess Shale Formation, paleontologist Charles Walcott also discovered a diverse group of soft- and hard-bodied fossils, from algae and sponges to chordates and cirripeds (Hagadorn, 2002). Soft-bodied fossils are incredibly rare due to their delicate structure and susceptibility to decay, so it is hard-bodied fossils that more regularly occur in fossil findings. However over 75,000 soft-bodied specimens have been found in the Burgess Shale formation (Hagadorn, 2002). These specimens are preserved in layers of shale formed from deposits of fine mud. One of the most significant species discovered is the Pikaia gracilens. Believed to be an early chordate, the Pikaia gracilens existed very close to the beginning of the evolutionary path that ultimately lead to humans (McGraw-Hill Encyclopedia, 2006).
Arthropods are animals belonging to the phylum Arthropoda, which is the largest of all phyla in the Animal Kingdom, with more than one million species, making them almost 80% of the whole kingdom. These include insects, arachnids, crustaceans and many more, most of which are quite small, the biggest being the Japanese Spider Crab with a leg span of 3.5 meters and the smallest being the microscopic Plankton.
First of all, an octopus is a cellapod. Which means it has a soft body, and no bones. An octopus also has eight arms, large useful eyes, and suction cups. ( Octopuses and Squid, page 6 by: Tori Miller.) All of these traits are mostly used for hunting. Eight arms come in handy when your prey is fast and can get away easily, large eyes are useful when you need to see in the dark or the depths of the ocean, and suction cups are used when they need to grab hold of something.( Octopuses Squid, page 14.) ( National Geographic, Octopus Facts.) Octopuses have blue blood caused by copper and bag like bodies. When born they're 1/4 of an inch and don't rely on...
The world we live in today is full of an exceptional variety of animals. The time it took to conclude to the various sorts of species seen today has been throughout a period of millions of years. The vast majority of these animals are accredited to evolutionary advancements. When the environment changes, organisms have become accustomed to changing to fit their environment, to ensure their species does not die off. These physical changes have resulted in different phyla, ranging from basic structures, like sponges to advance systems, like that of an octopus.