Which of the following combinations of phyla and characteristics is incorrect?

Options

A. Nematoda-round worms, pseudocoelomate
B. Cnidaria—radial symmetry, polyp and medusa body forms
C. Platyhelminthes—flatworms, gastrovascular cavity, acoelomate
D. Porifera-gastrovascular cavity, mouth from blastopore

Explanation

To determine which combination of phyla and characteristics is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Option 1: Nematoda - Pseudocoelomate**
- Nematodes, also known as roundworms, belong to the phylum Nematoda. They are characterized by having a pseudocoelom, which is a body cavity that is not completely lined by mesoderm. This option is correct.

2. **Option 2: Cnidaria - Radial symmetry, Polyp and Medusa body forms**
- Cnidarians, which include organisms like jellyfish and corals, exhibit radial symmetry. They have two main body forms: the polyp (e.g., Hydra) and the medusa (e.g., jellyfish). This option is also correct.

3. **Option 3: Platyhelminthes - Flatworms, Gastrovascular cavity**
- The phylum Platyhelminthes includes flatworms, which are indeed characterized by their flattened bodies. They possess a gastrovascular cavity, which serves both digestive and circulatory functions. This option is correct as well.

4. **Option 4: Porifera - Gastrovascular cavity, Mouth from blastopore**
- The phylum Porifera, which includes sponges, does not have a gastrovascular cavity. Instead, sponges have a simple body structure with pores and canals for water flow, and they lack a true digestive system. Additionally, their mouth does not develop from a blastopore. This combination is incorrect.

### Conclusion:
The incorrect combination of phyla and characteristics is:
**Porifera - Gastrovascular cavity, Mouth from blastopore.**