Phylum Hemichordata: A Small Phylum with a Big Taxonomic Lesson
Hemichordates are a small group of worm-like marine animals that once sat inside Phylum Chordata as a mere sub-phylum. The culprit was a rudimentary structure in the collar region called the stomochord, which superficially resembles a notochord. Modern classification now treats them as a separate phylum under non-chordata.
This quiz tests the essentials of Lesson 19:
- Their earlier and current taxonomic position
- The three body regions: proboscis, collar and trunk
- Bilateral symmetry, triploblastic and coelomate organisation
- Open circulation, gill respiration and the proboscis gland
- Standard examples: Balanoglossus and Saccoglossus
Work through all 15 questions carefully — each explanation links a structure to its functional or diagnostic significance.
Q1. Hemichordata was earlier considered as a sub-phylum under which phylum?
Historically, hemichordates were placed as a sub-phylum under Phylum Chordata, mainly because of the stomochord's resemblance to a notochord.
Q2. In the present classification, Phylum Hemichordata is placed as:
Modern classification places Hemichordata as a separate phylum under non-chordata, since a single resemblance does not justify chordate status.
Q3. The rudimentary structure present in the collar region of hemichordates is called the:
The stomochord is a rudimentary structure in the collar region, similar to a notochord — the very feature that once caused the phylum to be misplaced.
Q4. The stomochord of hemichordates is located in which body region?
The stomochord lies in the collar region, one of the three body regions (proboscis, collar and trunk).
Q5. The body of a hemichordate is cylindrical and composed of which three regions in order?
The body is composed of an anterior proboscis, a collar and a long trunk, in that order from front to back.
Q6. Hemichordates are best described as:
The phylum consists of a small group of worm-like marine animals showing organ-system level of organisation.
Q7. Which set of features correctly describes the symmetry and germ-layer condition of hemichordates?
Hemichordates are bilaterally symmetrical and triploblastic animals, unlike adult echinoderms which are radially symmetrical.
Q8. With respect to the coelom, hemichordates are:
Hemichordates are coelomate animals, and they also show the organ-system level of organisation.
Q9. The circulatory system of hemichordates is of which type?
The circulatory system of hemichordates is of the open type, as stated in the lesson.
Q10. In hemichordates, respiration takes place through:
Respiration in hemichordates takes place through gills.
Q11. The excretory organ of a hemichordate is the:
The excretory organ of hemichordates is the proboscis gland.
Q12. Which of the following is a standard example of Phylum Hemichordata?
Balanoglossus and Saccoglossus are the examples of hemichordates; Asterias and Ophiura are echinoderms, and Pila is a mollusc.
Q13. Regarding sexes and fertilisation in hemichordates:
Hemichordates have separate sexes, fertilisation is external, and development is indirect.
Q14. The type of development seen in hemichordates is:
Development in hemichordates is indirect, as stated in the lesson.
Q15. Which statement about the stomochord is correct?
The stomochord is a rudimentary structure in the collar region that is similar to a notochord; the excretory organ is the proboscis gland.