Q.Describe the general features of class Anthozoa (Actinozoa).

Anthozoans (sea anemones, corals) are marine cnidarians that exist only as polyps (no medusa), have a stomodaeum and septa (mesenteries) dividing the coelenteron, and many form calcareous coral skeletons.

Salient features of the anthozoans (Class Anthozoa, Phylum Cnidaria):

• They are EXCLUSIVELY MARINE animals, found solitary or in colonies.

• They exist ONLY in the POLYP form; the MEDUSA stage is entirely ABSENT (this is a chief distinguishing feature from other cnidarians).

• The body is cylindrical, with an oral end bearing a mouth surrounded by tentacles (usually numerous, in multiples).

• The mouth leads into a tubular, ectoderm-lined pharynx called the STOMODAEUM (gullet), which may bear one or two ciliated grooves (siphonoglyphs) for water circulation.

• The gastrovascular cavity (coelenteron / enteron) is divided by numerous vertical, radiating partitions called MESENTERIES or SEPTA, which increase the digestive surface and bear stinging cells (nematocysts) and gonads on their free edges.

• Many anthozoans (the corals) secrete a hard, CALCAREOUS (calcium carbonate) exoskeleton, which forms coral reefs.

• Reproduction is both asexual (budding) and sexual; there is no alternation of generations (as there is no medusa).

• Examples: sea anemones (Metridium, Adamsia) and corals (Madrepora, Astraea, Fungia).

Anthozoa is a class of Cnidaria containing sea anemones and corals, existing only as polyps and never as free-swimming medusae.

Salient features of class Anthozoa ("flower animals"):

1. Entirely marine, found from shallow coastal waters to deep sea.
2. Exist only in the polyp form — there is no medusa stage in their life cycle (unlike Hydrozoa/Scyphozoa).
3. May be solitary (e.g., sea anemones) or colonial (e.g., corals).
4. The body is cylindrical, with a central mouth surrounded by tentacles, leading into a gastrovascular cavity that is partitioned by radiating septa (mesenteries), increasing the internal surface area for digestion.
5. Many members (the stony/reef-building corals) secrete a hard calcium carbonate (calcareous) exoskeleton, which accumulates over generations to form coral reefs.
6. Tentacles bear cnidoblasts/nematocysts (stinging cells) used for capturing prey and defence, a feature shared with other cnidarians.
7. Reproduction occurs both asexually (budding, in colonial forms) and sexually.

Examples: Adamsia (sea anemone), Gorgonia (sea fan), Meandrina (brain coral), Fungia (mushroom coral), Pennatula (sea pen).

Anthozoa ('flower animals') is a class of exclusively marine, polyp-only cnidarians that includes sea anemones and reef-building corals.

Salient features of the class Anthozoa:

1. Habitat: Exclusively marine; found from shallow tropical waters to the deep sea.

2. Body form: Exist only in the polyp form throughout the life cycle; the medusa stage is completely absent (unlike Hydrozoa and Scyphozoa).

3. Colonial/solitary habit: May be solitary (e.g. sea anemones such as Adamsia, Metridium) or colonial (e.g. corals such as Gorgonia, Meandrina, Pennatula, Fungia).

4. Gastrovascular cavity: The coelenteron is divided by radiating partitions called septa or mesenteries, increasing the surface area for digestion.

5. Tentacles: The mouth is surrounded by tentacles arranged in multiples of six (Hexacorallia, e.g. sea anemones, stony corals) or eight (Octocorallia, e.g. soft corals, sea fans, sea pens), correlating with the number of septa.

6. Skeleton: Many anthozoans, especially corals, secrete a calcareous (limestone) or horny exoskeleton; accumulation of these skeletons over generations builds coral reefs.

7. Polymorphism: Colonial forms often show polyps connected by a common coenosarc, sharing the gastrovascular cavity.