I've never heard that before. Is that due to rules of the Latin language? (assuming it is Latin) I know some languages have different forms for masculine and feminine nouns, but I wasn't aware that would translate into the scientific names of the species.
That is incorrect. Either one is not correct. It is Lasiodora cristata. The gender issue is something called gender declination. In other words, specific epithets ("species names") must be of the same gender linguistically as the genus name. In general, genera whose names end in a "a" are female and their species names must then also be female. However, there are many examples, particularly in theraphosid taxonomy, where a genus name that ends with an "a" is treated as masculine. This generally happens because of the original usage of the author of the genus. A good example is the well known genus Brachypelma. This genus appears to have a feminine name, but it is treated taxonomically as masculine. Therefore, you have species such as Brachypelma albopilosum and Brachypelma auratum. The "um" suffix is masculine and if "Brachypelma" were treated as feminine as the final "a" might lead you to assume, those species would be albopilosa and aurata, respectively. If some future taxonomist moved these two species to an existing or new genus whose name was treated as feminine the specific epithets would change to albopilosa and aurata. Another good example is Stromatopelma calceatum. This species has sometimes been referred to in print or in the trade as "Stromatopelma calceata" because the authors (reasonably) assumed that "Stromatopelma" is feminine and "corrected" the specific epithet to also be feminine. However, Stromatopelma is considered masculine and therefore "calceatum" is correct. As someone who is also well versed in reptile taxonomy, I have often wondered why I find so many more apparently masculine or feminine generic names used "oppositely" in theraphosids than in herps.
Those threads were very interesting (and even amusing: I love when one individual refers to taxonomists as taxidermists!). But this is another example of the different needs of the hobbyist and the scientist. Whether or not the species depicted in the photos by Betty, Atrax, and others are indeed the "true" Lasiodora cristata that it is what it is sold as in the US and the question was regarding whether to use the masculine or feminine specific epithet, not whether the spider in the trade is accurately identified and belongs in the genus Lasiodora. But since my interests go beyond the trade and into the scientific I find the information Martin pointed out to be of great interest and I am eager to look into the matter further. Thanks.