- inaba, Graptopsaltria
- inaequalis, Massilina
- inaequalis, Quinqueloculina
- incisa, Cyclammina
- incisa, Stephanandra
- incisa, Trapa
- incisolobata, Saxifraga fortunei
- inclytum, Buccinum
- incompta, Globigerina
- incompta, Neogloboquadrina
- incongrua, Macoma
- inconstans, Paradrillia
- Indian elephant
- indica var. maximowiczii, Artemisia
- indicum, Waagenophyllum
- Indocrassatella oblongata
- Indo-pacific spiny lima
- ineptum, Sinum
- inequivalve, Entolium
- inermis, Hyotissa
- inermis, Malletia
- inexpectata, Cooperina
- inflata, Achnanthes
- inflata, Globigerina
- inflata, Globorotalia
- inflatus, Tosapecten suzukii
- infralirata, Turritella
- infrequens, Stegodon
- ingens, Actinocyclus
- Inoceramus, genus
- Inoceramus amakusensis
- Inoceramus balticus
- Inoceramus eozensis
- Inoceramus higoensis
- Inoceramus "hobetsuensis"
- Inoceramus iburiensis
- Inoceramus japonicus
- Inoceramus orientalis
- Inoceramus (Platyceramus) eozensis
- Inoceramus (Platyceramus) higoensis
- Inoceramus regularis
- Inoceramus schmidti
- Inoceramus uwajimensis
- inornata, Barnea manilensis
- inornata, Ocenebra
- inornatum, Ceratostoma
- inornatus, Baculites
- inouei, Chlamys
- inouei, Cyclobalanopsis
- inouei, Quercus
- inouyei, Yabeina
- Inquisitor, genus
- Inquisitor jeffreysii
- Inquisitor pseudoprincipalis
- Insect
- Insecta, class
- insignis, Acila
- insolitus, Gryphus
- insueta, Globigerinatella
- integer, Astriclypeus
- integra, Salix
- interplicata, Arcopsis
- interplicata, Striarca
- interplicata, Verilarca
- intersculpta, Neptunea
- intricatum, Gomphonema
- intuscostatum, Parvamussium
- Inversidens, genus
- Inversiunio reinianus
- Isastrea, genus
- Isastrea kosodeensis
- isensis, Neilonella
- ishidae, Adiantopteris
- ishidae, Chlamys
- ishidae, Pedinoblatta
- ishiiana, Potamides
- ishiiana, Vicaryella
- ishikawae, Oncorhynchus masou
- ishikiensis, Gaudryina
- isimotoi, Crepidula
- islandica, Chlamys
- islandica f. helvetica, Melosira
- Islandiella japonica
- Islandiella norcrossi
- Isocrinus, genus
- Isodomella, genus
- Isodomella shiroiensis
- Isognomon, genus
- Isognomon hatai
- Isomonia umbonata
- Isorthis fukujiensis
- Isorthis (Isorthis) fukujiensis
- Isurus, genus
- Isurus desori
- Isurus hastalis
- Isurus planus
- itadoriensis, Fusulina
- itoigawae, Chlamys
- itoigawae, Glycydonta
- itoigawae, Leukoma
- itoigawae, Timoclea
- itoigawai, Argonauta
- itoigawai, Cypraea
- itoigawai, Ringiculopsis
- itoigawai, Zoila
- itoi, Pitar
- izuensis, Chlamys
- izuensis, Decatopecten
- izumidaensis, Sinanodelphis
- izumoensis, Cultellus
- izumoensis, Metacarcinus
- izumoensis, Mizuhobaris
- izumoensis, Phaxas
- izurensis, Gloripallium
- izurensis, Macoma
- izurensis, Macoma calcarea
- Izuus nakamurai