Tartaruga vs. cágado vs. jabuti
In Portuguese, the general English category of turtle is split into three specific words—tartaruga, cágado, and jabuti—based strictly on the animal's habitat (water vs. land) and anatomy (feet structure).
Tartaruga
A2This term generally refers to sea turtles or freshwater turtles that spend almost all their time in the water. Morphologically, a tartaruga has flippers (if marine) or webbed feet (if freshwater) and generally does not retract its head sideways.
A tartaruga nadou rapidamente para o fundo do oceano quando viu o barco.
(The sea turtle swam quickly to the bottom of the ocean when it saw the boat.)
Todos os anos, a tartaruga volta à mesma praia para depositar seus ovos.
(Every year, the sea turtle returns to the same beach to lay its eggs.)
Infelizmente, a tartaruga confundiu a sacola plástica com uma água-viva.
(Unfortunately, the sea turtle confused the plastic bag with a jellyfish.)
A tartaruga de água doce precisa de um aquário com bastante espaço para nadar.
(The freshwater turtle needs an aquarium with plenty of space to swim.)
Cágado
C1This refers to semi-aquatic freshwater turtles, often called terrapins in English. The most distinct feature of a cágado is that it bends its neck sideways to hide its head under the shell, and it lives in rivers or lakes but frequently comes onto rocks or logs to sunbathe.
O cágado estava imóvel sobre o tronco, tomando sol no meio do lago.
(The terrapin was motionless on the log, sunbathing in the middle of the lake.)
Diferente dos outros, o cágado dobra o pescoço lateralmente para se proteger.
(Unlike the others, the terrapin bends its neck laterally to protect itself.)
Encontrei um pequeno cágado atravessando a estrada perto do brejo.
(I found a small terrapin crossing the road near the swamp.)
Como ele vive em água doce e na terra, o cágado tem membranas entre os dedos.
(As it lives in fresh water and on land, the terrapin has membranes between its toes.)
Jabuti
B2This word refers exclusively to terrestrial tortoises. A jabuti has a high, heavy, dome-shaped shell and thick, cylindrical feet (resembling elephant feet); it cannot swim and will drown if placed in water.
O jabuti gosta de comer frutas vermelhas e vegetais escuros no jardim.
(The tortoise likes to eat red fruits and dark vegetables in the garden.)
Nunca coloque um jabuti na piscina, pois o casco dele é muito pesado.
(Never put a tortoise in the pool, because its shell is too heavy.)
A lenta caminhada do jabuti é lendária nas fábulas infantis.
(The slow walk of the tortoise is legendary in children's fables.)
As patas do jabuti parecem patas de elefante, feitas para aguentar peso na terra.
(The tortoise's legs look like elephant legs, made to support weight on land.)
Summary
To distinguish them, look at the feet and habitat: tartaruga lives in water (flippers/webbed feet), cágado lives in fresh water and on rocks (side-necked), and jabuti lives strictly on land (elephant-like feet).