Final answer:
Urochordates, or tunicates, have four things within their lifetime: notochord and nerve cord during the larval stage, pharyngeal slits and endostyle, pharyngeal gill slits, and atrial cavity and gonad.
Step-by-step explanation:
Urochordates, also known as tunicates or sea squirts, have four things within their lifetime:
- Notochord and nerve cord during the larval stage: The larval stage of tunicates possesses all the characteristic features of chordates, including a notochord and a dorsal hollow nerve cord.
- Pharyngeal slits and endostyle: As adults, tunicates lose the notochord and nerve cord, but still have pharyngeal slits and an endostyle as remnants of their chordate morphology.
- Pharyngeal gill slits: Tunicate larvae have pharyngeal gill slits, which are used for respiration and filter feeding.
- Atrial cavity and gonad: Adult tunicates have an atrial cavity and gonads, which are involved in reproduction.