alloscutum

See also: scutum

English

The alloscutum on this typical female hard tick is the black surface on the back, below the brown, large, shield-shaped scutum

After the tick has fed, the alloscutum has extended hugely and been stretched till it is smooth. The scutum is relatively less conspicuous, because it has not changed in size, whereas the tick has swollen as it engorged.
Note the folds in the skin of the alloscutum, that show where the muscles are attached, that enable the tick to roll over if it should fall on its back.

Etymology

From Ancient Greek ἄλλος (állos, “other”) and from Latin scūtum (“shield”).

Noun

alloscutum (plural alloscuta)

1. (zoology) the flexible part of the dorsal body wall behind the rigid scutum in a hard tick, particularly a female, — the alloscutum is the part of the body wall that must stretch to accommodate the blood that the tick swallows when it engorges in preparation for laying eggs.
   • 2008, Heinz Mehlhorn, Encyclopedia of Parasitology, →ISBN:

     Powerful muscle groups are also present in the alloscutum of the female, nymphal, and larval Ixodid ticks, through which the tick is able to redistribute the centre of gravity and regain an upright position when it falls into an upside-down position.