The group of animals to which Sycon belongs, can be best described as

The correct option is "Multicellular without any tissue organization".

Here is the step-by-step educational explanation of why this is the correct answer:

1. Understanding the Organism (Sycon):
Sycon is a genus of marine sponges belonging to the phylum Porifera. Sponges are among the simplest multicellular organisms found in aquatic environments.

2. Cellular Level of Organization:
Although Sycon is multicellular (composed of many cells working together), it exhibits a cellular level of organization. This means that its cells are loose aggregates and are not organized into distinct tissues or organs to perform specialized functions. Instead, individual cells or groups of cells carry out different physiological activities independently.

3. Why other options are incorrect:
- Unicellular or acellular: Sycon is multicellular, not unicellular or acellular.
- Multicellular with a gastrovascular cavity: A gastrovascular cavity is characteristic of Cnidarians (like Hydra or jellyfish), not Poriferans, which have a canal system.
- Multicellular having tissue organization, but not a body cavity: Sycon lacks true tissue organization entirely.

Therefore, Sycon is best described as multicellular without any tissue organization.