Arantulas are found only in the Pit of 100 Trials in Levels, 81-89. It will have the attack like the Pider, but it's more powerful. Mario can only hammer it when it goes down, but not when it's up, unless he's equipped with the Hammer Throw. He can jump on it to damage it, but the best Star Power is Art Attack to draw around it to kill it quickly.
Arantula has the word, "Tarantula" without the letter "T".
There's also a Spy Guy called, "Hairy Arantula", which is a reference to Arantula.