graptolite

 
Pronunciation: /ˈgraptəlʌɪt/

noun

  • a fossil marine invertebrate animal of the Palaeozoic era, forming mainly planktonic colonies and believed to be related to the pterobranchs.
    • Class Graptolithina, phylum Hemichordata

Origin:

mid 19th century: from Greek graptos 'marked with letters' + -lite: so named because of the impressions left on hard shales, resembling markings with a slate pencil