Posted by Melda Research on May 8th, 2019
A transport system is very critical for a transportation system to reduce problems associated to surface-to-volume. Typically, the transport system of fluids is driven by cilia, muscles or both. Research has to be carried out to determine which character state, either cilia or muscle-drive fluid transport is plesiomorphic and which is derived. T
Character states for fluid transport systems for different animals
The figure 1 above which is a summary of reemerging consensus on animal phylogeny shows that the earlier-diverging metazoan animals namely sponges and placozoans and also protest out groups such as choanoflagellates use cilia in their transport systems. The later-diverging groups such as cnidarians, ctenophores, and bilaterians use both cilia and muscle in their transport systems. The filled circle in the figure above indicates the common ancestor of (Cnidaria+Ctenophora) + Bilateria. Despite extensive research on the origin of muscles in transport groups for the three groups, no research has been carried out on the functional biology of these animals. It is crucial to conduct functional studies to determine which is used for transport when both cilia and muscles are in existence. The cnidarians gastrovascular system is examined to illuminate further on the utilization of cilia and muscles in transportation systems.
In this paper cnidarians, contractile cells are considered to be myoepithelial. Cnidarians comprise of two clades namely the medusozoans (such as hydrozoans, cubozoans, staurozoans, and scyphozoans) and the anthozoans (such as hexacorals and octocorals). For many years, there has been extensive research on the movements of contractile stolon tips of the colonial hydroids. In hydractiniid hydroids, the movements of contractile stolon tips of the colonial hydroids correspond to a pattern of gastrovascular flow that has been shown by microscopy. A polyp shows a myoepithelial contraction that is followed by relaxation and hence leads to the driving of a cycle of sequentially bidirectional flow throughout the stolons. Every cycle takes a few minutes. The characteristics of the flow in the stolon include periods of inflow as well as the outflow in which the lumen expands and contracts, respectively. The rates of inflow are initially maximal, but as the lumen expands they decrease to a minimum. The flow rates are zero when the tip is fully grown. The outflow starts at low rates that increase as the lumen closes. The flow rates are at zero or minimal when the lumen is closed.
There has been little attention to the study of anthozoans except for pennatulacean octocorals. The flow in pennatulaceans is driven by both cilia and myoepithelial peristalsis. Existing research has suggested that there is a significant difference between the primarily myoepithelial contractions processes and exclusively ciliary action processes driving the hydroid and octocoral gastrovascular flow, as well as in the resulting patterns of flow. However, not all the questions have been answered. Does the data from hydractiniid hydroids include other colonial hydroids? To what extent do the measures from one genetic clone of P. parrini include other non-pennatulacean octocorals? Are octocorals that are closely related to P. parent the same as the distantly related ones? Are there consistent differences between octocorals and hydroids? (Harmata, et al., 2013). Quantitative measures of gastrovascular flow can be employed to provide answers to the questions. Studies of hydractiniid hydroids have indicated that these patterns are stereotypical within species and even within the same family. Therefore attention should be focused on measuring genetic lones from various species and families instead of different genetic clones from similar species. The existing phylogenetic framework should guide the choice of species as it assists to reduce the general concerns relating to animal transport systems. The figure 2 below shows schemata of the phylogenetic relationships of cnidarians, illustrating the affinities of the six study species.
schemata of the phylogenetic relationships of cnidarians, illustrating the affinities of the six study species
Harmata, K. L., Parrin, A. P., Morrison, P. R., McConnell, K. K., Bross, L. S., & Blackstone, N. W. (2013). Quantitative measures of gastrovascular flow in octocorals and hydroids: toward a comparative biology of transport systems in cnidarians. Invertebrate biology, 132(4), 291-304.
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