Whaleships are a biological means of transportation used by the inhabitants of the Chaskan underwater cities. These ships are essentially a “basket” lashed around a large sea creature that provides a fully or partially enclosed compartment that can be used to carry passengers and cargo. Whales of various species are most often used for this purpose; other creatures, such as giant squids, giant turtles, liopleurodons, and tylosaurs are not unknown in this role, but are far less common.
The animals trained to carry these ships are generally treated quite well - among the underwater communities that utilize them, abusing the creatures is seen as an anathema likely to anger the sea. Those that train and care for the whales are referred to as mysticetes. Each mysticete usually only has a single animal under their watch at any given time. Whales are usually adopted at a young age, prioritizing orphans if possible, and only used to carry the ships for a relatively short period of their lives.
The ships themselves are made of lightweight materials like bone or metal alloys. The sides and top of the basket are generally constructed of translucent materials, to allow anyone inside at least some vision of the surrounding seas. Both the ships and the whales are often decorated with bright pigments, usually in distinctive patterns specific to their mysticete.
Whaleships are not the fastest means of transportation below the waves, but they are one of the most reliable for carrying large loads at a time. Many of the underwater cities within the Chaska Sea have "harbors" for the whaleships, providing a space to both berth the ship and allow the whale to roam or rest.