In Chapter 7, Shubin in describing the body building of the organisms and their similarty mentions the choanoflagellates in sponges. Going back to the Invertebrate unit, please discuss different phylums that exist in the unit (Porifera, Cnideria, Platyhelminthes, Nemotoda, Mollusca, Annelida, and Arthropoda) in terms of their body plan, embryonic developement and other physcial characteristics that distinguishes it from other phylums.
Kevin Jeon
Bboybyung@gmail.com
Porifera is a group of invertebrates that contains organisms such as sponges. The organisms contain radial symmetry. There are no specific tissues in Porifera, however, there are two layers of tissues that are separated by the mesohyl. Porifera are filter feeders as they filter calcium by digesting reefs and mollusks.
ReplyDeleteCnidaria, another group of invertebrates, consists of organisms such as corals and jellies. These invertebrates also contain radial symmetry. Cnidaria are diploblastic as they contain an endoderm and an ectoderm only. Cnidarians are protostomes as they form mouth to anus.
Platyhelminthes consist of organisms such as flatworms and tapeworms. These organisms contain bilateral symmetry and are triploblastic. They form head to anus which means they are protostomes. They are much different from the other groups of invertebrates as these organisms can be parasitic.
Mollusca is a group that consists of Gastropoda, bivalvia, and cephalophoda. In other words, snails, scallops, and squids. Mollusca’s contain bilateral symmetry and are protostomes. They are triploblastic.
Annelida is a group that consists of earthworms and other segmented worms. They contain bilateral symmetry and are protostomes. They are triploblastic as well as coelomate. The worms use their coelom as a hydrostatic skeleton to move.
Arthropoda is a group that consists of arachnida, crustacea, insecta, chilopoda, and diplopoda. They contain bilateral symmetry and are triploblastic. Arthropods, being the most numerous of the bunch, are also the most diverse as well.
Nematoda is another group that consists of roundworms and hookworms. They contain bilateral symmetry and are triploblastic. They form head to anus and are thus protostomes. They contain a pseudocoelom. They play the role of decomposers in the environment as they recycle nutrients.
Echinodermata is a group that consists of asteroidean, or star fish. They are triploblastic and form anus to head (deuterostome). They contain a thin skin that covers the exoskeleton. They also contain a water vascular system which helps them move as water rushes in and out of their body into hydraulic canals in their legs. Echinodermata’s also contain an open circulatory system and skin gills.
Sources:
Campbell (Chapter 33)
Shreeraj Patel
shreeraj.patel1@gmail.com
In Chapter 7, Neil Shubin discusses the importance of examining the various characteristics of Invertebrates, explaining how the observation of cells within a sponge are “useful in understanding the origin of bodies” (Shubin, 131). Shreeraj has already outlined various characteristics of the Invertebrate phyla, but I would like to add on several things that he missed for each phylum.
ReplyDeletePorifera:
An organism that is representative of phylum Porifera is a sponge. Organisms in the phlyum Porifera are suspension feeders. Sponges have thousands of pores which allow water to flow into their spongocoel, its central cavity. As a suspension feeder, they “capture food particles suspended in the water that passes through their body” (Campbell 670). A sponge has two layers of cells that are divided by a region called the mesohyl, which contains cells known as amoebocytes. Amoebocytes have several functions, and its main function is to gather food from the water that comes in, and to digest it for energy. Sponges have several different cell types. One specific example is flagellated choanocytes, which draw water through the pores and into the central cavity using the movement of its flagellum. The food particles trapped by the choanocytes allow phagocytosis by the surrounding amoebocytes, which transport the nutrients to other parts of the body which require the nutrients. They are Parazoan, meaning that they lack true tissues. Because they lack true tissues, their symmetry type are classified as neither radial nor bilateral. They are largely aceolomate, and can either perform asexual reproduction through budding or undergo sexual reproduction with hermaphroditic individuals. They fertilize externally, and develop externally by attaching to an object on the sea floor. They are largely sessile, and are heterotrophic.
Cnidaria:
An organism that is representative of phylum Cnidaria is a jellyfish. Organisms in the phylum Cnidaria are heterotrophic, and use cnidocytes to inject poision into their prey. Cnidarians mostly utilize a gastrovascular cavity which functions as the location at which the organism feeds and excretes. They are Eumetazoans, meaning that they have true tissues organized in the form of germ layers. They are radially symmetrical, and are acoelomate. Because they are not a part of a group of animals known as Bilateria, they are classified as neither protostome nor deuterostome. Cnidarians are dipoblastic, meaning that they solely have an endoderm and an ectoderm, and lacks the third germ layer, the mesoderm. They are polymorphic, meaning that they have both an asexual (polyp) stage and a sexual (medusa) stage. Because they live in an aquatic environment, Cnidarians fertilize largely fertilize externally and develop externally.
Platyhelminthes:
ReplyDeleteOrganisms that are representative of phylum Platyhelminthes are flatworms, tapeworms, and planarians. Organisms in phlyum Platyhelminthes are Eumetazoans. They are bilateral, meaning that they are highly cephalized and are mostly tripoblastic. Platyhelminthes are mostly aceolomates, and include species that are either free-living or parasitic. They reproduce either asexually by fission or sexually with hermaphroditic individuals. Because they live in a terrestrial environment, its offsprings undergo internal fertilization and external development.
Mollusca:
An organism that is representative of phlyum Mollusca is a clam. Organisms in phylum Mollusca are Eumetazoans and are bilateral. They are tripoblastic, and are also coelomates, meaning that they have a cavity lined by the mesoderm. A distinctive feature of phlyum Mollusca is that they have a muscular foot for locomotion, and a radula for feeding.
Annelida:
An organism that is representative of phlyum Annelida is an earthworm. Organisms in phylum Annelida are Eumetazoans, bilateral, coelomates, and are tripoblastic. Organisms in phylum Annelida use their coelom as a hydrostatic skeleton, and their seate for swimming and crawling through land. For digestion, they employ peristalsis to move food through its digestive tracts and have structures such as the gizzard and the pharynx to acquire and digest food.
Arthropoda:
Organisms that are representative of phylum Arthropoda are insects, crayfish, and centipedes. They are Eumetazoans, bilateral, coelomates, and are tripoblastic. They are known as the most successful phlyum out of all Invertebrates for their rich diversity in species.
Nematoda:
An organism that is representative of phylum Nematoda is a round worm. Animals in phylum Nematoda are Eumetazoans, bilateral, and are pseudocoelomates (meaning that they have a coelom lined by its endoderm). For locomotion, they employ longitudinal muscles that result in a whip-like movement. Round worms are often parasitic, as they absorb nutrients from its host.
Echinodermata:
An organism that is representative of phylum Echinodermata is a starfish. Organisms in phylum Echinodermata are Eumetazoans, are bilateral, are coelomate, and are tripoblastic. An important idea to note is that they are the only deuterostome out of all Invertebrate phyla, making their embryonic development unique. They employ tube feet and a madreporite for locomotion, but are largely sessile.
In summary:
An important idea to remember is that organisms in phylum Porifera are the only Parazoans, and therefore are neither bilaterally nor radially symmetrical. In addition, they do not have a true coelom since they lack true tissues, and are neither protostome nor deuterostomes.
Another rule to remember is that the rest are all Eumetazoans, and the only phylum with radially symmetry is phylum Cnidaria.
In addition, all phyla except Echinodermata, Porifera, and Cnidaria undergo spiral cleavage. Because Echinodermatas are deuterostomes, they are unique in that they undero radial cleavage.
Works Consulted:
Campbell Biology
AP Biology Lab Book
Your Inner Fish
http://en.wikipedia.org/wiki/Coelom
(Keigo Tanaka; tanakarus3@hotmail.com)