thecae is theca's Plural Form

theca

US 
UK 
  • n.膜;【植】药室;孢蒴;鞘
  • Web孢子膜;海蕾化石
Plural Form:thecae  
n.
1.
【植】药室;孢蒴
2.
鞘;壳;囊;膜;(珊瑚的)外壁