Animals which are marine, bilaterally symmetrical, have a coelom and a notochord, but never form a vertebral column are placed under which one of the following groups ?
- (a)Chordata
- (b)Protochordata
- (c)Vertebrata
- (d)Mammalia
Correct — B, Protochordata. The stem is a checklist of the standard description, item by item. Protochordates are bilaterally symmetrical, triploblastic and have a coelom; they show a new feature of body design, namely a notochord, at least at some stages during their lives; and they are marine animals. The last clause of the stem is what excludes the more inclusive answers — these animals never form a vertebral column, which is precisely the line between the protochordates and the vertebrates. Vertebrates are defined by having a true vertebral column and an internal skeleton, so an animal that never develops one cannot be placed there. Balanoglossus is the figured example, with Herdmania and Amphioxus the other two the syllabus names. The notochord itself is a long rod-like support structure running along the back, separating the nervous tissue from the gut and giving muscles a place to attach; in protochordates it may be present only for part of the animal's life or along only part of its length.
- (a)Chordata — The larger group that contains both the protochordates and the vertebrates. It is not wrong as a broad label, but the stem asks for the specific placement of animals that never form a vertebral column, and Chordata does not make that distinction.
- (c)Vertebrata — Ruled out by the stem itself. Vertebrates are the animals that do have a true vertebral column and an internal skeleton.
- (d)Mammalia — A class deep inside the vertebrates, characterised by mammary glands, hair and, in most cases, live birth. Every mammal has a vertebral column.
The chordates are set apart by a small set of features — a notochord, a dorsal nerve cord, paired gill pouches and a coelomate body. Within them the protochordates keep the notochord but never build a vertebral column around it, and are marine throughout; the vertebrates replace or surround the notochord with a true backbone and an internal skeleton, which allows a completely different arrangement of muscle attachments and, with it, a far wider range of body sizes and habitats.
Three of the four options sit inside one another — Chordata contains Vertebrata, which contains Mammalia — so the item is asking for the right level of precision, not merely the right family. The clause that fixes the level is 'never form a vertebral column'. Read it as an instruction to stop just short of the vertebrates, and Protochordata is the only place left. A candidate who reads the earlier clauses and stops at the notochord will pick Chordata and lose the mark. Two cautions are worth carrying. The presence of a notochord at some stage is what makes an animal a chordate, so a notochord alone does not mean a backbone will follow; and the older grouping Protochordata is a convenience of school classification rather than a single natural lineage, since modern schemes place tunicates and lancelets on separate branches at the base of the chordates.
- Protochordates are bilaterally symmetrical, triploblastic, coelomate marine animals that show a notochord at least at some stage of their lives.
- They may not have a proper notochord present at all stages of their lives or for the entire length of the animal.
- The notochord is a long rod-like support structure running along the back, separating the nervous tissue from the gut and providing attachment for muscles.
- Vertebrates are distinguished by a true vertebral column and an internal skeleton, which protochordates never develop.
- Balanoglossus is the textbook figured example of a protochordate; Herdmania and Amphioxus are the other two commonly named.
- Stopping at Chordata because the notochord has been spotted; the stem asks for a placement that excludes the vertebrates.
- Assuming a notochord always develops into a backbone.
- Reading 'marine' as decisive on its own — many invertebrate groups are marine too.
As a description-to-group placement item, as a match list of animals against their phylum, or as a compare question on what separates protochordates from vertebrates.
Which one of the following is the correct sequence of levels of hierarchy of classification of organisms from higher to lower ?
- (a) Phylum – Class – Order – Family – Genus
- (b) Phylum – Class – Family – Order – Genus
- (c) Family – Order – Class – Species – Genus
- (d) Class – Family – Order – Species – Genus
Answer(a) Phylum – Class – Order – Family – Genus
The reason three of the options here cannot all be right. Chordata, Vertebrata and Mammalia sit at successively lower levels of the same hierarchy, so the question is really asking which rung the described animals belong on.
- practice — not a real PYQ
Which one of the following is a protochordate?
- (a)Balanoglossus
- (b)Scoliodon
- (c)Rana
- (d)Hemidactylus
Answer(a) Balanoglossus — the other three are vertebrates, a fish, a frog and a lizard respectively.
- practice — not a real PYQ
The notochord in chordates is best described as
- (a)a hollow tube carrying blood
- (b)a rod-like support structure running along the back
- (c)the outer covering of the body
- (d)a chain of bones enclosing the spinal cord
Answer(b) a rod-like support structure running along the back — it separates the nervous tissue from the gut and gives muscles a place to attach.