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How to Know if a Sea Urchin Is Male or Female?

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Sea urchins are amazing sea creatures. They belong to phylum Echinodermata, a taxonomic group that incorporates other sea creatures like sea stars, brittle stars, sea cucumbers and crinoids. Distinguishing between a female urchin and a male is a major challenge since they have closely similar physical characteristics. Nevertheless, the differences may be told via dissection or microscopic viewing.


By observing the difference in reproduction you can tell a male from a female sea urchin without employing dissection method. This is because sea urchins reproduce externally. However, to succeed in observing sea urchins reproduce you will require a magnifying object. After the female lays eggs, which are jelly-encased, the male spreads milky sperm on them. The fertilized egg mass increases in size and divides. This begins a series of binary cell division, each time the number of eggs increasing by double, until the number of cells is 64 or thereabout, when a ciliated larva comes out of the membrane. This happens in a matter of hours.

Gonad Fatty Acids

A careful analysis of the content of the gonad fatty acids present in the female sea urchin's ovaries and the male's testes indicate differences that can determine gender. A study carried out in the south coast of Spain with two sea urchins species, Arbacia lixula and Paracentrotus lividus, showed remarkable difference in the fatty acids composition of the ovaries and testes between the two species. Both exhibited higher levels of 16:0, 14:0,18:2n-6, 18:3n-3, 18:4n-3 and 16:1n-7 in ovaries than in testes, while 22:5n-3, 18:0, 20:4n-6 and 22:1n-9 were found to be in lower levels in the ovaries than in the testes. The variations probably had something to do with the composition required by females and males for gametogenesis.

Gonad Appearance

Laboratory technicians have dyed gametes secreted by the gonads in the laboratory with a goal of discovering the sex-revealing colors. They not only revealed the sex colors but also discovered that the degree of lightness in the gametes could also tell the sex of the urchin, too. While the red and yellow colors are found to increase in females, these colors reduce in males. However, lightness increases in males and decreases in females giving their distinct distinguishing factor.

Gonad Moisture

A study on the moisture content of female and male gonads of the sea urchins indicates that females' have lower moisture content than males'. Proof of this is observed in the calculation of a factor called gonad index, in which males exhibit higher marks than females. It is calculated by dividing gonad wet weight by body wet weight and multiplying by 100. Males always exhibit a higher gonad wet index than their female counterparts.