“This is a medium sized, burrowing species that can attain a length of 15 cm (6 in). In the field, freshly excavated individuals are usually distinctly U-shaped. The body tapers toward the bluntly rounded mouth and narrows more drastically toward the stiff anal cone. Because of the relatively thick body wall and a dense layer of
ossicles, the skin is rigid and rough. Cylindrical tube feet are found along the midbody, and conical
papillae near the ends. The tube feet are arranged in two distinct rows along the radii and scattered over the interradial areas, but they are largest and most numerous on the ventral surface. The mouth is surrounded by 10 stout, bushy tentacles, of which the ventral two are the smallest. Surrounding the anus are five
calcareous plates, one at the end of each radius; anterior to each plate are one to five large, conical papillae. The numerous body wall ossicles consist of buttons, baskets, rods, and perforated plates. The heavily knobbed buttons are irregular and variable in length. The tiny baskets are shallow and carry seven to nine marginal teeth. Large perforated plates and rods are found in the tube feet. In both the anterior and posterior regions, there are numerous, large, perforated plates with a smooth to heavily knobbed surface. They are seldom found in the middle portion of the body, where buttons and baskets prevail. Unfortunately, the characteristic baskets, which are invaluable for unequivocal identification, may be completely lacking in some specimens, apparently
resorbed with age. Most individuals are a mottled gray, brown, or olive green, but some are nearly uniformly tan or black. The radial areas usually are lighter than the interradial areas, giving specimens a striped appearance. In live
T. gemmata, the tips of the tube feet may appear red, because of the presence of hemoglobin containing cells in the water vascular system” (Heller, Miller, Pawson, Kier 263)
