vertebrate 復習

頭が２つあるサメの胎児についての記事からです。

An egg-laying shark joins the rare creatures in nature that have been found with two heads

For the first time, scientists have seen an egg-laying (oviparous) shark embryo with two heads.

It belongs to the species Galeus atlanticus, otherwise known as the Atlantic sawtail catshark.
This species now joins the list of real life two-headed creatures found in nature, which BBC Earth looked at in depth in October 2016.
The embryo was not easy to spot. It was hidden amongst 797 others, which the scientists had stored for medical research in their laboratory in Malaga, Spain.
Both sharks had a mouth, two eyes and even two brains. They also had two hearts, stomachs and livers, but shared an intestine. The two were attached below the gills.
Though other two-headed sharks have been found, they all belonged to species of shark that give birth to live young, such as the bull shark foetus discovered in 2013.
It is not known whether this two-headed shark would have survived if it had been born. Though, as the researchers write in the Journal of Fish Biology: "It is known that, although with a low incidence, two-headed conjoined twins occur in all major groups of vertebrates."
http://www.bbc.com/earth/story/20161027-a-shark-embryo-has-been-found-with-two-heads

取り上げる単語は"vertebrate"です。

LDOCEで調べてみると、"a living creature that has a backbone"とありました。

『ジーニアス英和辞典』第4版(大修館)でも確認してみると、「脊椎(背骨)のある、脊椎動物の」とあり、名詞でも使われます。

このサメの胎児は、互いにエラの下の部分から繋がっており、口や目、脳、心臓、肝臓、胃などはそれぞれ２つずつありますが、腸は１つしかないそうです。(Akim)