Sub-phylum: Protochordata/Acraniata

[Proto- primitive/ first, chordata- chord/ notochord]

• Habitat: These organisms are aquatic, exclusively found in sea water.
• Habit: They are free living organisms, some lead a solitary while others live in colonies.
• Symmetry: bilaterally symmetric.
• Body cavity: True coelomic cavity present.
• Body organization: they are triploblastic organisms having less segmented or unsegmented body.  They lack head and body is divided into proboscis, collar and trunk.
• Skeleton: Exoskeleton is absent but a cover [test/tunic] made up of cellulose is present in some of them.
• Gill slits:  present in pharyngeal region.
• Notochord: a primitive notochord is present which may be present thoughout their life or during certain stage like embryonic or larval stage. It may also extend throughout the body or may be limited to some region of body like in the tail.
• Cranium: these organisms lack brain box or cranium so this group is also known as acraniata. They also lack jaws and paired appendages.
• Reproduction: They reproduce by asexual or sexual reproduction. Development is indirect that passes through free living larval stage.

Examples:

• Herdmania, Balanoglossus, amphioxus etc.