| 11. | The spicules form blade-like structures, ornamented with concentric rings.
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| 12. | Sigma-C spicules have the shape of a C.
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| 13. | The skeleton is composed of many calcareous ossicles and spicules.
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| 14. | Spicule density is high with little to no spongin present.
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| 15. | Males have specialised tails for mating that include spicules.
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| 16. | Unroofing the early vesicles or pustules may permit manual extraction of the spicules.
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| 17. | The three groups are differentiated by the extent of fusion of adjacent spicules.
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| 18. | This may be calcified to form structures like spicules.
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| 19. | Spicules open a short distance from the tail tip.
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| 20. | The tendrils of new sponges wrap around spicules of older, deceased sponges.
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