Promachocrinus
... that Promachocrinus is unusual among crinoids in having ten pairs of arms?
... that <i id="mwBDs"><b id="mwBDw"><a href="./Promachocrinus" id="mwBD0" rel="mw:WikiLink" title="Promachocrinus">Promachocrinus</a></b></i> is unusual among <a href="./Crinoid" id="mwBD4" rel="mw:WikiLink" title="Crinoid">crinoids</a> in having ten pairs of arms?