Metazoan without tissue grade organization are called :

Question

Accepted Answer

Metazoan without tissue grade organization are called Parazoa. Let's explore why Option 2 is the correct answer and why the other options are incorrect.

1. **Explanation for Option 2 (Parazoa):**
   - Parazoa is a subkingdom of animals that lack true tissues and organs. The most well-known example of Parazoa is the phylum Porifera, commonly known as sponges. Sponges are simple multicellular organisms that do not have a tissue-level organization. Instead, they have a loose aggregation of cells that perform various functions. This lack of tissue differentiation is a defining characteristic of Parazoa, making them distinct from other metazoans that possess organized tissues.

2. **Explanation for why other options are incorrect:**

- **Option 1 (Protozoa):**
     - Protozoa are not metazoans; they are single-celled eukaryotic organisms. While they are often studied in the context of zoology, they do not fit the definition of metazoans, which are multicellular animals. Therefore, Protozoa cannot be considered metazoans without tissue grade organization.

- **Option 3 (Deuterostomia):**
     - Deuterostomia is a superphylum of animals that includes groups such as echinoderms and chordates. These organisms have a complex tissue and organ system, with a distinct embryonic development pattern. Deuterostomes are characterized by their tissue-grade organization, which is the opposite of what is described in the question.

- **Option 4 (Eumetazoa):**
     - Eumetazoa is a clade that includes all major animal groups except for sponges and a few other simple organisms. Eumetazoans have true tissues and exhibit a higher level of organization compared to Parazoa. They possess differentiated tissues and organs, which disqualifies them from being categorized as metazoans without tissue grade organization.

In conclusion, Parazoa is the correct answer because it accurately describes metazoans that lack tissue grade organization, unlike the other options which either do not fit the definition of metazoans or possess organized tissues.