To solve this problem, we need to identify the type of cells that line the spongocoel in Poriferans. Let's analyze the options:$\newline \bullet$Oscula:$\newline$ - Oscula are the large openings in sponges through which water exits. They are not cells that line the spongocoel.$\newline \bullet$Choanocytes:$\newline$ - Choanocytes, also known as collar cells, are flagellated cells that line the spongocoel.$\newline$ - They are responsible for creating water currents and capturing food particles.$\newline$ - Therefore, choanocytes are the correct answer.$\newline \bullet$Mesenchymal cells:$\newline$ - Mesenchymal cells are involved in forming the mesohyl, the gelatinous matrix within a sponge.$\newline$ - They do not line the spongocoel.$\newline \bullet$Ostia:$\newline$ - Ostia are small pores on the sponge's body through which water enters.$\newline$ - They are not cells lining the spongocoel.$\newline$Based on the analysis, the correct option is 2: Choanocytes.