What type of symmetry does a starfish have

The maximum value 1. Suppose a starfish is a five-pointed star and the distance between the center and bottom of an arm is 1, which is h. Through software simulation, we adjusted the ratio until the five-pointed star figure aligned with the real starfish, ultimately obtaining the distance from the endpoint of arms and the center as 3. Thus the length of an arm H was 2. According to our calculation using data from starfish Table 2 , the center of gravity of an intact starfish lies at the coordinates, 0.

We calculated the center of frequency with frequentness of action in a plane analytic fashion. We then assigned the frequency of action of each arm to the centroid of the unit, shown as the point U in Fig.

The center of frequency was then obtained from averaging the centers of the five units. If the distance between the center and the bottom of an arm is equal to 1 and the distance between the center and the endpoint of an arm is equal to 3. The blue, yellow, green and red planes represent the symmetric planes of turning-over, crawling, fleeing and average, respectively. Anterior and posterior directions are as shown. Table 3 shows the experimental data from 1, starfish.

The center of frequency in the turning-over experiment was located at the coordinates 0. The center of frequency is not the same with the origin point, v-test, 0. The symmetric plane is shown in blue in Fig. Table 4 shows the experimental data from starfish. The center of frequency in the crawling experiment was located at the coordinates 0.

The symmetric plane is shown in yellow in Fig. Table 5 shows the experimental data from starfish. The center of frequency in the fleeing experiment was located at the coordinates 0. The symmetric plane is shown in green in Fig. Turning-over is a difficult action for a starfish. Crawling represents the propensity of the starfish to use its body when it is free moving. Fleeing represents the organism's emergency response when it is in danger.

These three experiments show the symmetric plane in three ways, so the three centers of frequency can be averaged: 0. The average plane is shown in red in Fig. Fleeing occurs when a starfish is in danger, determining whether it will survive. The starfish must use its body to move quickly, and its fleeing behavior strongly reflects its bilateral propensity. Turning-over is difficult to execute, and the starfish must also efficiently use its body.

Therefore, this behavior also reflects its bilateral propensity quite clearly. Finally, crawling is performed when the starfish is freely moving, so this exhibits the lowest bilateral propensity. The plane of bilateral symmetry should lie approximately where the red line is i.

Thus we hypothesize that during movement adult starfish tend to take as front the direction of the Anterior end in the embryonic development, and take as rear the Posterior end. Even though we know from the statistically studied behavior that starfish are bilaterians , the adult starfish only retains a slight mechanism of bilateral symmetry, and we can only roughly identify the location of the symmetric plane.

As with the orientation of the starfish's movement, Arm 5 obviously moves much less in the backward direction i. The direction of Arm 5 can, therefore, be considered anterior, and the direction in between Arm 2 and Arm 3 can be considered posterior Fig.

From our behavioral research, we can conclude that starfish behave as bilaterians. Our findings can be generalized to all classes of echinoderms except for the sea cucumber. In other words, during their evolution from the Cambrian era to present, some bilateral symmetry has persisted in adult echinoderms. It is also likely that other systems match this bilateral symmetry, such as the nervous system, the sensory organs and the motor system. Animals tend to move in the anterior direction, instead of posterior or other directions.

Sense organs and the nervous system also tend to concentrate at the anterior side. Because starfish are more likely to move toward Arm 5, it is possible that their sensory organs are focused there as well. Nerve ganglions may also be more developed around this direction, and the nervous system in the central disk might concentrate towards this direction.

The essence of the radial symmetry of echinoderms is an adaption to their benthic habitat niche. The sensory organs of starfish are not highly developed, nor can they move very fast.

Starfish tend to act more like radial animals so that they can be open to stimuli from all directions and move evenly toward different directions. But when they are in danger, they tend to use their bodily functions efficiently and behave more bilaterally.

This remnant of their bilaterally symmetric ancestors may have benefited echinoderms during evolution. Concentration of their sensory organs and nervous system helps echinoderms observe and react to their environment more intensively, especially for tracing prey and detecting enemies.

Concentration of their motor system helps to save energy and move faster. Additionally, their propensity for motion makes it more convenient to pursue prey and run away from natural enemies.

Partial bilateral symmetry facilitates several difficult actions. Echinoderms resemble the octopus to some extent, appearing like a radial animal, while actually having bilateral behavioral mechanisms and the corresponding physical characteristics.

Our results provide evidence that echinoderms have retained bilateral tendencies from the Cambrian era to the present, and this likely has some kind of adaptive significance. This work has implications for research on the evolution, embryonic development, behavior and fossil research of echinoderms and deuterostomes.

We wish to thank the 2 referees for their helpful suggestions for improving the manuscript. Competing Interests: The authors have declared that no competing interests exist. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. National Center for Biotechnology Information , U. PLoS One. Published online Jan Hector Escriva, Editor. Author information Article notes Copyright and License information Disclaimer.

Received Jun 19; Accepted Nov Copyright Ji et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited. This article has been cited by other articles in PMC. Abstract Echinoderms take many forms of symmetry. Introduction There are six classes of echinoderms: Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, Holothurioidea and Concentricycloidea.

Materials and Methods Materials Asterias amurensis is a very common species of sea star in East Asian coastal areas. Open in a separate window. Figure 1. The madreporite is shown by Point A. Table 1 Numbering systems. Weighing All weights were measured on analytical balances that were accurate to at least 0. Figure 2. The five-pointed star conforms to the real starfish's shape. Behavioral experiment The following experiments were conducted in calm seawater, and the starfish used were all healthy and sound.

Figure 3. The turning-over process is shown from Step 1 to 6. Figure 4. Crawling action of the starfish. Statistical Methods 1 Treatment of mass during statistics process During the statistics of mass, we compare the five arms of the starfish within itself, which means each starfish was designated with the same weight 5 and contributed the same to the sum weight.

Results The center of gravity in a bilateral animal is supposed to lie on the plane of bilateral symmetry. Center of gravity During calculation, we assumed that the central disk was homogeneous. Table 2 Relative weight of each arm Standard Deviation. Share Tweet Email. Go Further. Animals Wild Cities This wild African cat has adapted to life in a big city.

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Begin typing your search term above and press enter to search. Press ESC to cancel. Skip to content Home Ethnicity Are starfish have bilateral symmetry? Ben Davis February 6, Are starfish have bilateral symmetry?

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