Good Example Of Marine Invertebrate Phylum Essay

Marine invertebrate phylum

The term invertebrates refers to a speciose group of animals that includes over 1.5 million of known species. Zoologists believe there are at least 5 million undescribed species that belong to 32 phyla. There are two subkingdoms: Prometazoa and Eumetazoa. Prometazoa includes various primitive organisms which bodies do not have the differentiated typical tissues (two phyla). Eumetazoa is more numerous and their bodies have the tissues that specialize on certain functions (Brusca, Brusca & Haver, 2006).
Invertebrates differ by their body structure and life conditions, which are the adaptations to the environment. The paper describes the most significant evolutional adaptations: food acquisition, predation avoidance, locomotion, reproduction, and development.
Placozoa, which is the primitive phyla, has a few species. The typical representative is a Trichoplax adhaerens. It feeds with bacteria, algae, and flagellated protozoa. The Trichoplax adhaerens has developed two feeding mechanisms: pinocytosis (cell drinking) and phagocytosis. The movement is realized with cilia, and the body form constantly changes. The alimental behaviour depends on the quantity of food available. If there is sufficient quantity of food, the animal becomes plain and the movement activity decreases. However, if the concentration of food substrate is low, the organism actively moves and changes its form. Placozoa has developed sexual and asexual reproduction (body division and budding). The advanced specie among Placozoa is Spongia (Porifera), which developed a neuroskeleton. The specie forms colonies for the efficient food acquisition (Brusca et al., 2006).
Coelenterata is famous for its evolutionary adaptation mechanism for predators offence and defence. These are the specific sting cells for effective hunting. The organisms are also able to adapt to toxic environment by reducing its body size to sphere, and expanding their tentacles in favourable environment. The species of this group have cells organized in tissues. For instance, corals (Anthozoa), have the enteric cavity divided into septa, while the enteric cavity of some other species is branched inside the tentacles (as in Scyphozoa).
The next evolutional step is the bilateral symmetry that is observed with Bilateria and Platyhelminthes (flat worms) that have developed the mesoderm (in addition to endoderm and exoderm). The evolutionary adaptaions are realized as improvement of sensorium, organs of equilibrium and smell.
Rotifera and Rotatoria have the ciliary formation on the front part of the body used for feeding and movement in water media. The organisms have an adaptation to the attached way of life. A muscular leg attaches to the substrate with a specific cementing solution.
Nemathelminthes are characterized with the primary body structure with the internal organs. The evolution has advanced the digestive organs divided into three sections for the enhanced food assimilation (Brusca et al., 2006).
The parasiticus species depict the reverse evolution, as simplification of the body form. They also have cupules and hamus for the extended stay in a bowl of a host organism. Annelidas have evolved numerous adaptations, namely body and internal organs segmentation. In case some segment is injured, Annelida loses it and can regenerate later (Schiedges, 1979). The organs of the senses have also been developed, namely smelling and touch, as for a marine specie Polychaeta that is able to orientate and analyze it in a quick manner.
The limbs of Arthropoda are divided into segments that allows them moving smoothly by bending them in various dimensions. Insecta have developed ability to breathe and swim under water. Arthropoda have several muscle groups and an additional mechanism for sight, the small eyes spread all over the body, including limbs. This adaptation allows gathering information by fragments, and thus instantly respond to dangerous conditions, as predators attacks (Brusca et al., 2006).
Echinodermata are famous for their unique movement, namely the ambulacral system. The ambulacral system is a branch system filled with liquid, which composition is close to marine water. The ambulacral system is united to the environment through the petrosal channel. The numerous ambulacral limbs branch of the radially located ambulacral channels, and each limb has the muscular alveole that is meant to lengthen the limb. In addition, the ambulacral system takes part in breathing and food acquisition: a sea star is able to open a shell-fish (Forcucci & Lawrence, 1986).
Shell-fish have the protecting testa covering the body. The immantle is covered with epidermis; the immantle organs are located inside, namely the depature routes of the reproductive, digestive, and excretory systems. The specific movement of Cephalopoda is realized via reaction motion: water enters the immantle cavity, and as the immantle muscles contract, water is thrown away via modified limb part, which causes the reaction motion. The shell-fish moves backwards. Cephalopoda developed lingual ribbon that acts as a grater for food blending. Lingual ribbons are meant to scrape down the algae and bacteria from stones and other surfaces (Brusca et al., 2006).
Marine invertebrate phyla have gone through numerous evolutionary stages and have developed various modifications to survive in the environment. These include specific organs for movement, reproduction and senses, tissues, body forms, behavioural and life strategies.

References

Brusca, R. C., Brusca, G. J., & Haver, N. J. (2006). Invertebrates. Sunderland, Mass: Sinauer Associates.
Forcucci, D. & Lawrence, J. M. (1986). Effect of low salinity on the activity, feeding, growth and absorption efficiency of Luidia clathrata (Echinodermata: Asteroidea), Marine Biology, 92(3), 315-321.
Schiedges, K. L. (1979). Reproductive biology and ontogenesis in the polychaete genus Autolytus (Annelida: Syllidae): Observations on laboratory-cultured individuals.
Marine Biology, 54(3), 239-250.