The non-cellular layer present between pinacoderm and choanoderm in body wall of poriferans is known as
A. Mesoderm
B. Middle lamellae
C. Mesenchyme
D. None of these

Hint: Poriferans are a phylum of primitive invertebrate animals which is composed of sponges and has a cellular grade of construction without any true tissue or formation of organs. The body of Poriferans has canals and chambers through which water flows. And it passes through one or more cavities lined with choanocytes.

Complete answer:
Option A Mesoderm: A germ layer that is present in animal embryos which give rise to specialized tissue types is known as mesoderm. One of the three germ layers found in triploblastic organisms is the mesoderm. Between the germ layers ectoderm and endoderm, the layer of mesoderm can be seen. Mesoderm is not the non-cellular layer present in body walls of Poriferans.
Hence option A is not correct.
Option B Middle lamellae: The middle layer which cements the primary cell walls of two adjoining plant cells together is known as the middle lamellae. Middle lamellae are the first formed layer that is deposited at the time of cytokinesis. Since middle lamellae is not the layer present in body walls of Poriferans.
So, option B is also not correct.
Option C Mesenchyme: The mesenchyme refers to more-or-less solid but loosely organized tissue which consists of a gel matrix known as the mesoglea with various cellular and fibrous inclusions, that is located between the epidermis and the gastrodermis. The mesoglea is noncellular in some cases. Mesenchyme is the non-cellular layer that is present between pinacoderm and choanoderm in the body walls of Poriferans.
Hence option C is the correct answer.
Option D None of the above: Since option C is the correct answer.
So, option D is wrong.

Hence,Option C. Mesenchyme is the correct answer.

Note:
As in cnidarians, when the cellular material is sparse or densely packed, the mesenchyme may sometimes be called as collenchyma, or parenchyma in flatworms. As in hydrozoa, when no cellular material is present, the layer is properly called mesoglea. The mesenchyme is perforated by gastrovascular channels that are continuous among colony members in some colonial cnidarians.