Echium simplex (Tower of jewels), herbaceous biennial plant up to 3 m in height on the island of Tenerife mainly in Macizo de Anaga
Firmiana simplex, the Chinese parasol tree or wutong, an ornamental plant or tree of the cacao, or chocolate family Sterculiaceae of the order Malvales, native to Asia
Gentianopsis simplex, a species of flowering plant in the gentian family known by the common name oneflower fringed gentian
Gymnophragma simplex, a species of flowering plant belonging to the family Acanthaceae
Nemiana simplex, the only species in Nemiana, a genus of simple, sessile organisms
Protanthea simplex, a species of sea anemone found in deep water off the coasts of north west Europe
Tubularia simplex, or oaten pipes hydroid, a species of hydroid native to the northeast Atlantic Ocean, North Sea, Norwegian Sea, and English Channel
Molluscs
Bivalves
Anomia simplex, or the common jingle shell, a species of bivalve mollusc in the family Anomiidae
Gastropods (snails and slugs)
Arinia simplex, a species of small land snails with an operculum, terrestrial gastropod mollusks in the family Diplommatinidae
Bittium simplex, a species of sea snail, a marine gastropod mollusk in the family Cerithiidae
Blanfordia simplex, a species of land snail that has an operculum, a terrestrial gastropod mollusk in the family Pomatiopsidae
Boucardicus simplex, a species of land snail with an operculum, a terrestrial gastropod mollusk in the family Cyclophoridae
Calliostoma simplex, a species of sea snail, a marine gastropod mollusk in the family Calliostomatidae
Cirsonella simplex, minute sea snail, a marine gastropod mollusc in the family Turbinidae
Cristilabrum simplex, a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Camaenidae
Enatimene simplex, a species of sea snail, a marine gastropod mollusk in the family Muricidae, the murex snails or rock snails
Eulimella simplex, a species of sea snail, a marine gastropod mollusk in the family Pyramidellidae, the pyrams and their allies
Janoliva simplex, a species of sea snail, a marine gastropod mollusk in the family Olividae, the olives
Mohnia simplex, a species of sea snail, a marine gastropod mollusk in the family Buccinidae, the true whelks
Natica simplex, a species of predatory sea snail, a marine gastropod mollusk in the family Naticidae, the moon snails
Obesotoma simplex, a species of sea snail, a marine gastropod mollusk in the family Mangeliidae
Opisthostoma simplex, a species of minute land snail with an operculum, a terrestrial gastropod mollusk in the family Diplommatinidae
Pepta simplex, a species of sea snail, a marine gastropod mollusk in the family Cancellariidae, the nutmeg snails
Pyrgulopsis simplex or fossil springsnail, a species of minute freshwater spring snails, aquatic gastropod mollusks or micromollusks in the family Hydrobiidae
Serrata simplex, a species of sea snail, a marine gastropod mollusk in the family Marginellidae, the margin snails
Sukashitrochus simplex or Sukashitrochus morleti, a species of sea snail, a marine gastropod mollusk in the family Scissurellidae
Arthropods
Arachnids
Argiope simplex or Argiope trifasciata, also called banded garden spider in the USA, a species of spider found around the world