Which animal phylum is characterized by a lack of symmetry (asymmetrical), and a "skeleton" composed of spicules and sometimes a protein called spongin?
a) cnidaria.
b) annelida.
c) chordata
d) porifera.
e) mollusca

The correct answer is D. Porifera

Explanation

Porifera or sponges is a phylum that includes all simple primitive aquatic animals, distinguished by having a body full of channels and pores through which water flows. Sponges are formed by sets of cells that arrange in spicules which provide sponges a structure and spongin which is a protein. Additionally, sponges lack organs and are asymmetrical which means they have an irregular shape. Moreover, they stand out for having a great diversity of color and their sizes are varied from a few millimeters to more than 2 m high. So, the correct answer is D. Porifera.

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