Essay Example on The life cycle of echinoids is simple Reproduction









The life cycle of echinoids is simple Reproduction is strictly confined to adult stages that generally involve the spawning of eggs and sperm freely into the seawater followed by the external fertilization Kelly 2000 Most echinoids are free spawners that produce a vast number of small yolk poor eggs that develop into planktonic feeding larvae known as echinopluteus in response to environmental factors that signal the availability of suitable benthic habitat Mc Edward et al 2007 During spawning the gonads release large quantities of eggs and sperm into the water for the increased chance of survival in the marine environment Bolton et al 2001 When sperm are added to the water the outer gelatinous layer around the egg dissolves and the sperm become attached to the jelly coat Tamaru et al 2010 A fertilization membrane lifts from the surface of the egg after about 3 minutes stretching the jelly layer and leaving a perivitelline space Zygotes were classified with the formation of the fertilization membrane around the circumference of the egg Kelly 2000 Said membrane started to form within 8 minutes after insemination With the penetration of the sperm it was pushed forward by its microtubules towards the center of the egg Rahman et al 2009 

When the egg s cortical layer is reached by the sperm exchange of genetic material happened and cytoplasmic movements are increased Before the first cleavage to happen the membrane stopped the vibration the cell surface becomes regular and hyaline layer thickened Sarifudin et al 2016 In most species the hatched egg turns into a planktonic larva Poulin Feral 1996 Development biologists investigated the early embryonic development through the cleavage stages blastula formation gastrulation and larval morphogenesis Mc Edward et al 2007 Blastula stage emerged as the end of the cleavage stages This stage forms an epithelial monolayer surrounding with a central spherical blastocoel whose cells in between one another during the further development Spiegel and Howard 1983 Numerous microvilli are present in the exterior apical ends of the apical ends which are tightly rooted in the apical lamina Hall and Vacquier 1982 As the development continues the blastula cells become resistant to small sugar molecules from the external environment Moore 1940 At this point it breaks the envelope allowing the embryo to hatch and become a free swimming blastula Several yolk vesicles are enclosed in the peripheral layer and deposited in the ectoderm during the later development of the embryo Hardin 1987 Followed by gastrula wherein gastrulation triggers a different pattern of motility to the developing embryo and dramatic decrease of the overall rate of mitotic divisions are noted Gustafson and Wolpert 1967 1963 With about 1000 cells the epithelium of the vegetal pole of the embryo flattens and thickens to form the vegetal plate in the animal pole Spiegel and Howard 1983 In the larval stage the echinoid is developing into a juvenile 

The developmental patterns are determined by three factors mode of nutrition habitat and type of morphogenesis Mc Edward et al 2007 Planktotrophic larvae develop from their eggs which uses a portion of energy to metamorphose Larvae with higher feeding concentration tend to develop and metamorphose quickly into bigger juveniles compared to their siblings that are less fed Reitzel et al 2005 Epithelial red pigmented cells were not present in the ventral oral region of the embryo at prism stage During the course of the complete development of prism larva the surface of the embryo was covered by cilia with an apical tuft on the anterior pole and a ciliated ring around the anus Rahman et al 2012 After this stage the two armed larvae will develop as lecithotrophic larvae that depend on the nutrition coming from the yolk The echinopluteus is complex the pelagic larva that generally possesses eight anterior directed arms that bear the ciliated feeding structure that is supported by calcareous skeletal rods Okazaki 1975 It develops a complete functional gut and mostly feeds on suspended particulate matter Burke 1987 Nerves are distributed along the ciliated band and in the esophagus for swimming and feeding coordination

Burke 1978 Strathmann 1971 Mackie et al 1969 and possess a neuropil a dense network of interwoven nerve fibers which controls the metamorphosis that is located at the anterior end of the oral hood Burke 1978 The internal cavity of the larvae is mostly filled with gel like blastocoelic space Strathmann 1971 Its body form is very diverse due to variation in the number and relative sizes of the larval arms Pearse Cameron 1991 However all echinoplutei share the same larval body plan that is defined by body symmetry morphogenetic axes coelomic organization nervous system vestibule and metamorphic fates of larval structures Mc Edward Miner 2007 Normally larval stage takes one 1 month but this varies to the species Emlet et al 1987 Its development includes growth and elaboration of the larval body to the formation of the rudiment of the juvenile echinoid in preparation for the induction of settlement and metamorphosis to juvenile adult Its post metamorphic development includes growth and sexual maturation to become a reproductive adult Mc Edward et al 2007

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