Biology Class: Anthozoa Characteristics

Class Anthozoa

• Polypoid body form, with no medusa stage
• Gastrovascular cavity is septate, with septa called mesentery
• Mouth is slit-like, with a stomodeum (invagination or depression that forms the mouth opening during embryonic development)
• They have both colonial and solitary polyp forms
• Reproduction is both sexual (through planula) and asexual (through budding and fission)

Structure of a Sea Anemone

• Sea anemones are shorter and stouter than Hydras
• They have more tentacles than Hydras, but Hydras have longer tentacles
• They have a septate gastrovascular cavity
• Some are hermatypic, meaning they are reef-forming Anthozoans that actively build corals

Phylogeny of Anthozoa

• Reconstruction of key morphological characters in Cnidaria based on phylogenetic hypothesis
• Hexacoralia have biradial symmetry, except Ceriantharia, which make their own tube
• Gastrodermal muscles are not organized in bunches
• Symmetry is biradial, except for Ceriantharia

Defining Characteristics

• They are polypoid, with the polyp being the dominant form
• No medusa stage
• Gastrovascular cavity is septate
• Septa is called mesentery
• Mouth is slit-like with pharynx called stomodeum
• Stomodeum leads into gastrovascular cavity, serving both digestive and circulatory functions

Modes of Colony Formation

• Meandrina - brain coral
• Siphonoglyph - specialized ciliated groove or furrow found in the pharynx to direct water flow
• Zooxanthellae - brown algae that live symbiotically with Cnidarians

Orders of Anthozoa

• Order Actiniaria - true sea anemones, with column-shaped bodies topped by an oral disk
• Order Zoanthidea - partly chitinous with leathery tissues, mostly colonial, with zooxanthellae
• Order Scleractinia - hard corals, with skeletons made of aragonite, living in shallow to deep water
• Order Corallimorpharia - coral-like anemones, solitary or aggregated polyps, without stony skeleton
• Order Antipatharia - soft, deep water corals, with chitin skeleton, colonial
• Order Octocorallia - blue corals, soft corals, sea pens, and gorgonians, with polyps embedded in a matrix of mesogleal tissues

Subclass Octocorallia

• Sea pens, all colonial, some resemble antique quill pens, others are club-like or radiating
• Suborder Subselliflorae - sea pens, cosmopolitan, develops a single polyp that becomes the rachis from which other specialized polyps arise
• Suborder Sessiliflorae - sea pansies, colonial, fleshy and leaf-shaped, living on sandy or muddy sediment

Subclass Ceriantharia

• Tube dwellers, constructing or inhabiting tubes for protection, shelter, feeding, and reproduction
• Body is elongated, with two whorls of tentacles, where the outermost is longer
• Larvae are planktonic and free-swimming
• Tentacles are not retractable into the column due to the lack of sphincter muscles