According to Living National Treasures, agaves and a cactus are plants unique to Aruba, and two species of lizards are unique to Aruba.

Specifically, Melocactus stramineus, with striking red flowers, is unique to Aruba.

Agave rutteniae and Agave arubensis are two agaves which uniquely inhabit

Aruba. The Aruba leaf-toed gecko (Phyllodactylus julieni) and the Aruba whiptail

(Cnemidophorus arubensis) are two lizards which only are found on Aruba.

• X-Ray fish
• X-Ray tetra
• Xanclomys - a small mammal from the Paleocene of North America.
• Xanthareel - yellow eel
• Xantis - yak
• Xantus - a bird
• Xantusiidae (family of night lizards)
• Xantus murrelet - a small seabird found in the California Current system in the Pacific Ocean.
• Xeme - an artic fork-tailed gull.
• Xenarthra - mammal in South America
• Xenicidae (family of New Zealand wrens)
• Xenopeltidae (family of reptiles including sunbeam snake- Xenopeltis)
• Xenipirostris (genus of birds from Madagascar)
• Xenops - a rain forest bird from the Americas
• Xenopterygii (order of fishes including clingfishes)
• Xenopus - a frog; toad
• Xenurine - a species of armadillo; a cabassou.
• Xenurus unicinctus - an armadillo native of the tropical parts of South America.
• Xerus - a type of ground squirrel from Africa
• Xiphias - a swordfish.
• Xiphias gladius
• Xiphosuran - a horseshoe crab.
• Xoloitzcuintli - a dog
• Xoni - mystical creature.
• Xylophone Cat- A cat that is only by legend but some claim to have seen it.

Dinosaurs

• Xenoposeidon
• Xenotarsosaurus
• Xiaosaurus
• Xinjiangovenator
• Xuanhanosaurus
• Xuanhuaceratops
• Xuanhuasaurus

• Xenops(a type of bird)
  

• X: Parailia pellucida
• X-L Spring Tui Chub: Gila bicolor oregonensis
• X-Ray Fish: Pristella maxillaris
• X-Ray Tetra: Pristella maxillaris
• Xami Hairstreak: Callophrys xami, Callophrys xami texami
• Xanthippe's Shrew: Crocidura xantippe
• Xantic Sargo: Anisotremus davidsonii
• Xantus Leaf-Toed Gecko: Phyllodactylus xanti
• Xantus Swimming Crab: Portunus xantusii
• Xantus' Murrelet: Synthliboramphus hypoleucus
• Xantus's Hummingbird: Basilinna xantusii
• Xantus's Murrelet: Synthliboramphus hypoleucus
• Xeniades Swallowtail: Mimoides xeniades
• Xenoclea Longwing: Heliconius melpomenexenoclea
• Xenocrates Leafwing: Polygrapha xenocrates
• Xerces Blue: Glaucopsyche lygdamus xerces, Glaucopsyche xerces
• Xeric Ambersnail: Succinea indiana
• Xestia Badicollis: Xestia badicollis
• Xestia Elimata: Xestia elimata
• Xestus Fangblenny: Petroscirtes xestus
• Xestus Sabretooth Blenny: Petroscirtes xestus
• Xingu Corydoras: Corydoras xinguensis
• Xingu River Ray: Potamotrygon leopoldi
• Xinjiang Ground-Jay: Podoces biddulphi
• Xuthus Swallowtail: Papilio xuthus

Animals beginning with the letter X:

• Xanclomys: a small mammal from the Paleocene of North America.
• Xanthareel: yellow eel.
• Xantis: a yak.
• Xantus: a bird.
• Xantus murrelet: a small seabird found in the California Current system in the Pacific Ocean.
• Xantusiidae: family of night lizards.
• Xeme: an artic fork-tailed gull.
• Xenarthra: a mammal in South America.
• Xenicidae: a family of New Zealand wrens.
• Xenipirostris: genus of birds from Madagascar.
• Xenopeltidae: family of reptiles including sunbeam snake- Xenopeltis.
• Xenops: a rain forest bird from the Americas.
• Xenopterygii: order of fishes including clingfishes.
• Xenopus: a South African clawed frog (name means "strange foot").
• Xenurine: a species of armadillo; a cabassou.
• Xenurus unicinctus: an armadillo native of the tropical parts of South America.
• Xerarthra: mammel related to sloth
• Xerus: a type of ground squirrel from Africa.
• Xiphias: a swordfish.
• Xiphias Gladius
• Xiphosuran: a horseshoe crab.
• Xoloitzcuintli: a dog.
• Xoni: mystical creature.
• X-Ray fish: Pristella maxillaris
• X-Ray tetra: Pristella maxillaris
• Xylophone Cat: A cat that is only by legend but some claim to have seen it.
• X: Parailia pellucida
• Xami Hairstreak:Callophrys xami, Callophrys xami texami
• Xanthippe's Shrew:Crocidura xantippe
• Xantic Sargo:Anisotremus davidsonii
• Xantus Leaf-Toed Gecko: Phyllodactylus xanti
• Xantus Swimming Crab:Portunus xantusii
• Xantus's Hummingbird:Basilinna xantusii
• Xantus's Murrelet:Synthliboramphus hypoleucus
• Xeniades Swallowtail:Mimoides xeniades
• Xenarthrans: The superorder Xenarthra isa group of placental mammals
• Xenoclea Longwing:Heliconius melpomene xenoclea
• Xenocrates Leafwing:Polygrapha xenocrates
• Xenoposeidon
• Xenotarsosaurus
• Xerces Blue:Glaucopsyche lygdamus xerces, Glaucopsyche xerces
• Xeric Ambersnail:Succinea indiana
• Xestia Badicollis
• Xestia Elimata
• Xestus Fangblenny:Petroscirtes xestus
• Xestus Sabretooth Blenny: Petroscirtes xestus
• Xiaosaurus: plant eating dinasour from jurassaic period
• Xingu Corydoras:Corydoras xinguensis
• Xingu River Ray:Potamotrygon leopoldi
• Xinjiangovenator
• Xinjiani Ground-Jay:Podoces biddulphi
• X-L Spring Tui Chub:Gila bicolor oregonensis
• Xuanhanosaurus
• Xuanhuaceratops
• Xuanhuasaurus
• Xuthus Swallowtail:Papilio xuthus
• Xanthostigma - Longfin Sanddab fish
• Xantusia henshawi - Granite Night Lizard

Animals beginning with the letter X:

For the source and more detailed information concerning your request, click on the related links section (Answers.com) indicated at the bottom of this answer box.

• X-L Spring Tui Chub: Gila bicolor oregonensis
• X-ray Tetra (fish): Pristella maxillaris
• X: Parailia pellucida
• Xami Hairstreak: Callophrys xami, Callophrys xami texami
• Xanclomys: a small mammal from the Paleocene of North America.
• Xanthareel (yellow eel)
• Xanthidae - crab
• Xanthippe's Shrew: Crocidura xantippe
• Xanthostigma - Longfin Sanddab fish
• Xantic Sargo: Anisotremus davidsonii
• Xantis: a yak.
• Xantus (murrelet - small seabird)
• Xantus Leaf-Toed Gecko: Phyllodactylus xanti
• Xantus murrelet: a small seabird found in the California Current system in the Pacific Ocean.
• Xantus Swimming Crab: Portunus xantusii
• Xantus's Hummingbird: Basilinna xantusii
• Xantus's Murrelet: Synthliboramphus hypoleucus
• Xantusia henshawi - Granite Night Lizard
• Xantusiidae: family of night lizards.
• Xeme (Arctic fork-tailed gull)
• Xenarthra - mammal in South America
• Xenarthra: a mammal in South America.
• Xenarthrans: The superorder Xenarthra is a group of placental mammals
• Xeniades Swallowtail: Mimoides xeniades
• Xenicidae: a family of New Zealand wrens.
• Xenipirostirs - bird from Madagascar
• Xenipirostris: genus of birds from Madagascar.
• Xenoclea Longwing: Heliconius melpomene xenoclea
• Xenocrates Leafwing: Polygrapha xenocrates
• Xenopeltidae - snakes
• Xenopeltidae: family of reptiles including sunbeam snake- Xenopeltis.
• Xenoposeidon
• Xenops: a rain forest bird from the Americas.
• Xenopterygii: order of fishes including clingfishes.
• Xenopus: a South African clawed frog (name means "strange foot").
• Xenotarsosaurus
• Xenurine: a species of armadillo; a cabassou.
• Xenurus unicinctus: an armadillo native of the tropical parts of South America.
• Xerarthra: mammal related to sloth
• Xerces blu - extinct butterfly, Glaucopsyche lygdamus xerces, Glaucopsyche xerces
• Xeric Ambersnail: Succinea Indiana
• Xerus (a species of squirrel found only in Africa)
• Xestia Badicollis
• Xestia Elimata
• Xestus Fangblenny: Petroscirtes xestus
• Xestus Sabretooth Blenny: Petroscirtes xestus
• Xiaosaurus: plant eating dinasour from jurassaic period
• Xingu Corydoras: Corydoras xinguensis
• Xingu River Ray: Potamotrygon leopoldi
• Xinjiangovenator
• Xinjiani Ground-Jay: Podoces biddulphi
• Xiphias (swordfish)
• Xiphias Gladius
• Xiphosuran (horseshoe crab)
• xlot
• Xoloitzcuintli: a dog.
• Xoni: mystical creature.
• Xuanhanosaurus
• Xuanhuaceratops
• Xuanhuasaurus
• Xuthus Swallowtail: Papilio xuthus
• Xylophone Cat: A cat that is only by legend but some claim to have seen it.