Question: A sponge has six-rayed silica spicules and an asconoid body plan. Which class best fits these traits?
1 Hexactinellidae
2 Calcarea
3 Demospongae
4 Cnidaria
1. The problem asks to identify the class of sponge based on two traits: six-rayed silica spicules and an asconoid body plan.
2. Important biological facts:
- Hexactinellidae (glass sponges) have six-rayed silica spicules.
- Calcarea have calcium carbonate spicules and can have asconoid body plans.
- Demospongiae have silica spicules but not six-rayed, and usually leuconoid body plans.
- Cnidaria is a different phylum, not sponges.
3. Since the sponge has six-rayed silica spicules, it matches Hexactinellidae.
4. The asconoid body plan is typical of simpler sponges like Calcarea, but they do not have six-rayed silica spicules.
5. Therefore, the class that best fits both traits (six-rayed silica spicules and asconoid body plan) is Hexactinellidae.
Final answer: 1 Hexactinellidae