In the morning giant regularly twisted head of insect? (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

AM (abbreviation for Latin ante meridiem = before noon = in the morning) + alternate letters (regularly) of G [i] A [n] T , all reversed (twisted). A guess-and-check because I’d never heard of it. Wikipedia says it’s a part of a segmented animal, for example an insect, where a number of segments are grouped together to form a functional part such as its head or abdomen. I’ll be surprised if I ever need to know that in future.