Editing Sand dollar (section)

== Sex and reproduction ==
During the month of August, the sand dollar will have had its highest gonad index, and in November and December is the time when sand dollars will spawn.<ref>{{Cite journal |last1=Cocanour |first1=Barbara |last2=Allen |first2=Kenneth |date=1967-01-01 |title=The breeding cycles of a sand dollar and a sea urchin |url=https://www.sciencedirect.com/science/article/abs/pii/0010406X67907499 |journal=Comparative Biochemistry and Physiology |volume=20 |issue=1 |pages=327–331 |doi=10.1016/0010-406X(67)90749-9 |issn=0010-406X}}</ref> Broadcast spawning is how sand dollars reproduce.

For animals like the sand dollar (an [[echinoderm]]) their main mode of reproduction is [[Spawning|broadcast spawning]].<ref>{{Cite journal |last1=Leuchtenberger |first1=Sara Grace |last2=Daleo |first2=Maris |last3=Gullickson |first3=Peter |last4=Delgado |first4=Andi |last5=Lo |first5=Carly |last6=Nishizaki |first6=Michael T. |date=2022-12-01 |title=The effects of temperature and pH on the reproductive ecology of sand dollars and sea urchins: Impacts on sperm swimming and fertilization |journal=PLOS ONE |language=en |volume=17 |issue=12 |pages=e0276134 |doi=10.1371/journal.pone.0276134 |doi-access=free |issn=1932-6203 |pmc=9714736 |pmid=36454769|bibcode=2022PLoSO..1776134L }}</ref> An adult sand dollar's gender cannot be determined directly by just looking at it. The only way to determine the gender of the animal is by the color of its gamete exudate. The gamete exudate is the fluid released into the water during the spawning of sand dollars. Yellow exudate will contain eggs and white exudate will contain sperm.<ref>{{Cite web |title=Inducing Fertilization and Development in Sand Dollars {{!}} Embryo Project Encyclopedia |url=https://embryo.asu.edu/pages/inducing-fertilization-and-development-sand-dollars |access-date=2025-04-13 |website=embryo.asu.edu}}</ref>

By completing reproduction through spawning, sand dollars will reproduce in groups which increases the chances of fertilization. Male sand dollars start spawning by releasing sperm through the accessory papillae or the [[Gonopore|gonopores]]. After roughly 10 minutes, spawning stops, and the sand dollar will cover itself with sand. After the male spawns, the sperm enters the female's egg, beginning fertilization.

After roughly 80 minutes of fertilization, cell division will begin to occur, also known as [[Cleavage (embryo)|cleavage]]. After cleavage, the cells become [[Blastulation|blastulae]] and then [[Gastrulation|gastrula]]. During the gastrula stage, the embryo's height decreases and the width slightly increases. After the gastrula stage, the larvae will begin the pluteus stage. At this point in a sand dollar's early stages of life, it will want to feed but cannot. The sand dollar [[Larva|larvae]] will have mouths that are able to open but cannot eat.

Along with wanting to feed, the larvae will have three identifiable body parts: an esophagus, stomach, and intestine. Though at the beginning of the pluteus stage, the larvae cannot feed, it will feed towards the end of the stage just before [[metamorphosis]]. The larvae will push out the forming juvenile sand dollar and begin metamorphosis. For sand dollars, this stage takes about an hour and thirty minutes for the larval tissues to regress. Since the larval tissues are in regress, the sand dollar will then start to undergo resorption of these tissues. After metamorphosis, the sand dollar will start to become a juvenile, developing a skeleton, teeth, and will begin to be able to feed themselves.<ref>{{Cite journal |last1=Vellutini |first1=Bruno C. |last2=Migotto |first2=Alvaro E. |date=2010-03-22 |title=Embryonic, Larval, and Juvenile Development of the Sea Biscuit Clypeaster subdepressus (Echinodermata: Clypeasteroida) |journal=PLOS ONE |language=en |volume=5 |issue=3 |pages=e9654 |doi=10.1371/journal.pone.0009654 |doi-access=free |issn=1932-6203 |pmc=2842294 |pmid=20339592|bibcode=2010PLoSO...5.9654V }}</ref>