List of species named simplex

• Amitostigma simplex, a species of plant in the family Orchidaceae
• Bulbophyllum simplex, a species of orchid in the genus Bulbophyllum
• Coelogyne simplex, a species of orchid
• Puccinellia simplex, a species of grass known by the common names western alkali grass and California alkali grass
• Oenocarpus simplex, a species of flowering plant in the family Arecaceae
• Vriesea simplex, a species of the genus Vriesea

• Acacia simplex, perennial climbing tree native to islands in the western part of the Pacific Ocean
• Buddleja simplex, a small shrub, probably extinct, as no record of it has been made for nearly 200 years
• Brassaiopsis simplex, a species of plant in the family Araliaceae
• 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
• Pseudopanax simplex, a species of evergreen plant
• Stirlingia simplex, plant endemic to Western Australia
• Utricularia simplex, commonly known as bluecoats, is a very small perennial carnivorous plant that belongs to the genus Utricularia

• 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

• Anomia simplex, or the common jingle shell, a species of bivalve mollusc in the family Anomiidae

• 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

• Argiope simplex or Argiope trifasciata, also called banded garden spider in the USA, a species of spider found around the world
• Digamasellus simplex, mite in the family Digamasellidae
• Gamasellus simplex, in the genus of mites in the family Ologamasidae
• Halolaelaps simplex, family of mites in the order Mesostigmata

• Acartia simplex, a species of marine copepod belonging to the family Acartiidae
• Asconiscus simplex, the only species in the genus Asconiscus, family of marine isopod crustaceans in the suborder Cymothoida
• Branchinella simplex, a species of crustacean in the family Thamnocephalidae
• Ovatis simplex, a species of crabs in the family Xanthidae, the only species in the genus Ovatis
• Paradiaptomus simplex, a species of copepod in the family Diaptomidae
• Tropodiaptomus simplex, copepod in the family Diaptomidae

Moths of the family Noctuidae:

• Achaea simplex, a species of moth of the family Noctuidae
• Avatha simplex, a species of moth of the family Noctuidae
• Cyligramma simplex, moth of the family Noctuidae
• Penicillaria simplex, moth of the family Noctuidae
• Plusia simplex or Anagrapha falcifera, a moth of the family Noctuidae
• Schinia simplex, moth of the family Noctuidae
• Schrankia simplex or Schrankia altivolans, moth of the family Noctuidae
• Speiredonia simplex, a species of moth of the family Noctuidae

Other lepidopterans:

• Aloeides simplex, a butterfly of the family Lycaenidae
• Anatrachyntis simplex, moth in the family Cosmopterigidae
• Azygophleps simplex, moth in the family Cossidae
• Chilo simplex or Chilo suppressalis, moth of the family Crambidae
• Coleophora simplex, moth of the family Coleophoridae
• Endotricha simplex, a species of snout moths in the genus Endotricha
• Eriogaster simplex or Panacela lewinae is a moth of the family Eupterotidae
• Eulophota simplex, a species of snout moths in the genus Eulophota
• Hemistola simplex, moth of the family Geometridae
• Oroplema simplex, a species of moth of the family Uraniidae
• Proutiella simplex, moth of the family Notodontidae

• Anabrus simplex or Mormon cricket, large insect that can grow to almost three inches in length
• Chlaenius simplex, a ground beetle in the large and diverse genus Chlaenius
• Holcobius simplex, beetle species in the family Anobiidae
• Mirosternus simplex, beetle species in the family Anobiidae
• Rhadinosticta simplex or Rhadinosticta, a species of damselfly in the family Isostictidae
• Rhamphomyia simplex, a species of dance fly, in the fly family Empididae
• Thesprotia simplex, common name grass mantis, is a species of praying mantis found in Brazil
• Urophora simplex, a species of tephritid or fruit flies in the genus Urophora of the family Tephritidae

• Anthreptes simplex or plain sunbird, a species of bird in the family Nectariniidae
• Calamonastes simplex or grey wren warbler, a species of bird in the family Cisticolidae
• Chlorocichla simplex or simple greenbul, a species of songbird in the family Pycnonotidae
• Columba simplex or lemon dove or cinnamon dove, a bird species in the pigeon family (Columbidae)
• Geoffroyus simplex, blue-collared parrot, simple parrot, lilac-collared song parrot, or lilac-collared Geoffroy's parrot, found in New Guinea
• Myrmothera simplex or tepui antpitta or brown-breasted antpitta, a species of bird in the family Formicariidae
• Pachycephala simplex or grey whistler, a species of bird in the family Pachycephalidae
• Passer simplex or desert sparrow, a bird of the sparrow family Passeridae
• Phaetusa simplex or large-billed tern, a species of tern in the family Sternidae
• Piculus simplex or Rufous-winged Woodpecker, a species of bird in the family Picidae
• Pogoniulus simplex or green tinkerbird, a species of bird in the family Lybiidae
• Pseudotriccus simplex or hazel-fronted pygmy tyrant, a species of bird in the family Tyrannidae
• Pycnonotus simplex or cream-vented bulbul, a species of songbird in the family Pycnonotidae
• Rhytipterna simplex or greyish mourner, a species of bird in the family Tyrannidae
• Sporophila simplex or drab seedeater, a species of bird in the family Thraupidae

• Betta simplex, a species of fish in the family Osphronemidae
• Hesperomys simplex, a species of rodent in the family Cricetidae from south-central South America
• Hyla simplex, a species of frog in the family Hylidae
• Melanophryniscus simplex, a species of toad in the family Bufonidae
• Sarcoglanis simplex, a species of catfish (order Siluriformes) of the family Trichomycteridae, and the only species of the genus Sarcoglanis