Original description: Test wide, subconical to subcylindrical in shape, with well-developed horn. Cephalis and thorax sparsely perforated with short ridges, covering with layer of microgranular silica. All but final post-abdominal chamber gradually increasing in width and length as added. Final post-abdominal chamber decreasing in width. Abdomen and post-abdominal chambers consisting of square to rectangualr pore frames with long costae superimposed between everyone or two rows of pore frames. Costae with short, transverse elements.
Original remarks: Hsuum gratum n. sp. differs from H. acutum n. sp. by having a wider subconical test, and by having thinner, more regular costae on the earlier chambers.
Etymology: Gratus-a-um (Latin, adj.) pleasing.
Full reference: K. Y. Yeh. 1987. Taxonomic Studies of Lower Jurassic Radiolaria from East-Central Oregon. National Museum of Natural Science Special Publications 2:1-169
Sister taxa: Hsuum acutum, Hsuum altile, Hsuum amabile, Hsuum arabicum, Hsuum arenaense, Hsuum belliatulum, Hsuum brevicostatum, Hsuum cuestaense, Hsuum feliformis, Hsuum lucidum, Hsuum lupheri, Hsuum matsuokai, Hsuum maxwelli, Hsuum mclaughlini, Hsuum mirabundum, Hsuum modicum, Hsuum mulleri, Hsuum optimum, Hsuum parasolense, Hsuum parvulum, Hsuum plectocostatum, Hsuum robustum, Hsuum rosebudense, Hsuum rutogense, Hsuum tamanense
Type specimen: NMNS (000087). Its type locality is Suplee-Izee area, OR-600A, which is in a Toarcian marine tuff/limestone in the Hyde Formation of Oregon.
Ecology: passively mobile planktonic omnivore