For those wanting to know what the new Snapchat emoji symbols mean, there is several different things that they repersent and these emojis have replaced the âBest Friendsâ feature with Friend Emojis smilies.
(plural tetrads) 1  A group of four things. ( 2 chemistry) A tetravalent atom or radical. ( biology) Two pairs of sister chromatids (a dyad pair) aligned in a certain way and often on the equatorial plane during the meiosis process.
Ostracoderms (shell-skinned) refers to the armored jawless fishes of the Paleozoic. The term does not often appear in classifications today because it is paraphyletic or polyphyletic, and has no phylogenetic meaning.he microscopic layers of that shield appear to evolutionary biologists, like they are composed of little tooth-like structures.. Neil Shubin writes: Cut the bone of the [ostracoderm] skull openâ¦pop it under a microscope andâ¦you find virtually the same structure as in our teeth.