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Echinoderms have Bilateral Tendencies Chengcheng Ji, Liang Wu, Wenchan Zhao, Sishuo Wang, Jianhao Lv





Echinoderms take countless forms the symmetry. Pentameral the contrary is the major type and the other develops are obtained from it. However, the ancestors that echinoderms, which source from Cambrian period, were thought to be bilaterians. Echinoderm larvae room bilateral during their early on development. Throughout embryonic development of starfish and sea urchins, the position and also the developmental succession of every arm space fixed, implying an auxological anterior/posterior axis. Starfish also possess the Hox gene cluster, i beg your pardon controls symmetrical development. Overall, echinoderms are thought to have actually a bilateral developmental mechanism and also process. In this article, we concentrated on adult starfish habits to corroborate the bilateral tendency. We weighed their main disk and also each eight to measure up the place of the facility of gravity. Us then studied your turning-over behavior, crawling behavior and fleeing actions statistically to attain the center of frequency of every behavior. By joining the facility of gravity and also each center of frequency, we derived three behavioral symmetric planes. These behavior bilateral tendencies could be related to the A/P axis during the embryonic development of the starfish. The is really likely the the adult starfish is, to part extent, bilaterian since it screens some bilateral propensity and also has a definite behavior symmetric plane. The remainder the bilateral symmetry may have actually benefited echinoderms during their advancement from the Cambrian period to the present.

Citation: Ji C, Wu L, Zhao W, Wang S, Lv J (2012) Echinoderms have Bilateral Tendencies. Gimpppa.org ONE 7(1): e28978. Https://doi.org/10.1371/journal.pone.0028978

Editor: Hector Escriva, Laboratoire Arago, France

Received: June 19, 2011; Accepted: November 18, 2011; Published: January 11, 2012

Funding: This occupational was supported by the grant from the National herbal Science foundation of China (Project J1103520) and National simple Science foundation of China, (Education of ar Research, job 0830630). The funders had actually no function in examine design, data collection and also analysis, decision to publish, or ready of the manuscript.

Competing interests: The writer have claimed that no contending interests exist.


There are six classes that echinoderms: Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, Holothurioidea and Concentricycloidea. All are radial, except for the holothurians <1>, which evolved from a radial ancestor <2>. Among the actinomorphic echinoderms, most are pentameral animals <1>, <2>, and also the other symmetry creates are obtained from pentameral the contrary <3>–<5>.

The ancestors of echinoderms, which originated from the Cambrian era, were deuterostomes <6>. Since deuterostomes are all bilateral, we have the right to infer the the ancestors that echinoderms to be bilaterians <7>, <8>. To adapt to your benthonic habitat and also planktonic habitat niches, echinoderms progressed from bilateral symmetry first to asymmetry, climate to pentameral the contrary <9>–<11>.

Echinoderm larvae room bilateral during early breakthrough <12>, <13>. They an initial change right into asymmetry <14>, <15> then proceed to adjust into pentameral the contrary <11>, <16>. Larvae have actually an A/P axis that is established by the resolved developmental mode and also the absolute sequence in the embryonic development process <16>. During this process, tissues and also organs enhance the equivalent symmetry creates <16>, <17>.

The Hox gene family is recognized to manage symmetry advance and formation of the body axis in deuterostomes <18>–<21>. So, it is possible that the Hox genes in echinoderms manage the change from bilateral come radial symmetry <22>–<25>.

Despite regularly being studied, it is still not clear whether adult starfish retain their bilateral symmetry system to part extent. Jennings and also Cole learned the locomotion and righting of the starfish in Stylasterias forreri <26>, <27>. Jones etc. Learned the top arm during motion in Echinaster sepositus <28>. Kjerschow-Agersborg studied the physiological anterior end in Pycnopodia helianthodes <29>. Thorpe studied the orientation the locomotion in echinoderm <30>. O"Donoghue learned the migration behaviors of specific starfish <31>. Rodenhouse studied the morphology and behavior in Pteraster tesselatus <32>. Blacksmith studied the neural system and also behavior that starfish <33>.

To explore this question, us weighed starfish arms and main disks to determine their center of gravity and symmetric mechanism. Us then counted the number of times that starfish supplied each arm and statistically calculate their behavior symmetric plane. We concluded that starfish are slightly bilateral in behavior, and also they are, to part extent, bilateral animals.


Asterias amurensis is a very common varieties of sea star in east Asian coastal areas. We designated the eight opposite come the madreporite as arm 1, and the others follow clockwise successively in aboral see (Fig. 1). Our numbering device is different than the ahead ones, presented in Table 1 <34>.


All weights to be measured on analytical balances that were specific to at least 0.0001 g or 0.1 mg.

The place of the last pair of side pedicellaria in ~ the base of each eight was designated together the cutting heat (line together in Fig. 2). The eight of the dried starfish were reduced off and weighed. Because some starfish might regenerate a brand-new arm when it is broken, those v notably various arms were excluded. Due to the huge number that starfish supplied in this experiment, minor differences resulting indigenous inconspicuous regeneration deserve to be regarded as insignificant.

Line h, the distance in between the center and also bottom that the arm, is 1. Line H, the size of one arm, is 2.985. Heat L is the cut line. As soon as weighing, the eight were cut off along Line L. The main disk is the light-colored regular pentagon. We thought about the arms together cones, so allude G, the center of heaviness of an arm, lay in ~ H/4 of the triangle. We assumed the central disk to be homogeneous, so suggest O, the center of gravity of the main disk, put in the facility of the constant pentagon. The unit of action is the shaded part. A unit of activity contains one arm and 1/5 that the central disk near the arm. Allude U is the facility of heaviness in the airplane unit, and also we assigned the frequency of activity of each eight to it. Allude U is located at U = <(h×h×2/3)+H×(h+H/3)>/(h+H) = 1.6617.


After cut off every one of the arms, the intact central disk to be weighed (Fig. 2). Since the organs space within the central disk and also the organs room soft with irregular shapes, it was challenging to division the central disk into five equal parts and also weigh them precisely.

Behavioral experiment

The adhering to experiments were carried out in patience seawater, and the starfish used were every healthy and also sound. We lifted the starfish wholly, not simply with one single arm. No particular permits were compelled for the explained field studies.

1) Turning-over experiment.

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The starfish to be turned upside down and also left to turn back freely. Generally, the starfish firstly expanded its eight upwards, climate bent two nearby arms against the ground for support, stamped the ground v the opposite arm and lifted the various other two arms upwards on every side, finally the opposite arm lost its contact with the substrate and also the starfish turned over <35>, <36> (Fig. 3). In together cases, we taped the number of the stamping arm. Occasionally, they only bent one arm against the ground for support, stamped the ground v the opposite two arms and also lifted the other two arms upwards on every side. In these cases, we taped the 2 stamping arms and assigned every a weight of 0.5.