Q.86 Acorn worms (Saccoglassus sp.) belong to which ONE of the following Phyla?
(A) Platyhelminthes
(B) Achelminthes
(C) Hemichordata (Chordata)
(D) Annelida
Acorn worms, including species like Saccoglossus, belong to the phylum Hemichordata. This classification reflects their unique marine biology bridging invertebrates and chordates. Understanding this helps in exams like NEET or CSIR NET.
Correct Answer
The correct option is (C) Hemichordata (Chordata). Acorn worms (Saccoglossus sp.) are enteropneusts in the class Enteropneusta of phylum Hemichordata, known for a tripartite body: proboscis, collar, and trunk.
They exhibit pharyngeal slits and a stomochord, traits linking them to early chordates, and live as burrowing marine deposit feeders.
Option Breakdowns
| Option | Phylum | Key Traits | Why Not Acorn Worms? |
|---|---|---|---|
| (A) Platyhelminthes | Flatworms | Acoelomate, bilateral symmetry, no anus, parasitic/free-living forms like planaria. | Acorn worms have a coelom, tripartite body, and gill slits unlike flatworms’ simple sac-like gut. |
| (B) Achelminthes | Pseudocoelomate worms (e.g., nematodes, rotifers) | False body cavity, no true coelom, often microscopic. | Hemichordates possess a true coelom and chordate-like features absent in pseudocoelomates. |
| (C) Hemichordata (Chordata) | Acorn worms, pterobranchs | Proboscis/collar/trunk, pharyngeal gill slits, marine burrowers. | Matches perfectly: Saccoglossus is a classic example with iodine-like odor and helical trunk. |
| (D) Annelida | Segmented worms | Metamerism, setae, closed circulation (e.g., earthworms, leeches). | No segmentation or setae in acorn worms; their body is unsegmented with distinct regions. |
Biological Relevance
Hemichordata provides evolutionary insights into deuterostome origins, with Saccoglossus kowalevskii used in genetic studies for its larval development and bromine compounds. This phylum underscores transitions from invertebrates to vertebrates, aiding research in developmental biology.
