Sphenopidae Family of Zoanthids
One Zoanthid of the Sphenophidae Family can be found in this website:
Colonial Zoanthid, Palythoa ignota. A representative of the Sphenopidae Family of Colonial Anemones.
Phylogeny: Zoanthids of the Sphenopidae Family, like hydroids, jellyfish and sea anemones are in the phylum Cnidaria. They are in the subphylum Anthozoa, the class Hexacorallia, the order Zoantharia, and the suborder Brachycnemina. The Sphenopidae Family is one of two families within this suborder. The Sphenopidae Family contains two genera and ninety-six species. The name Sphenopidae comes from both Greek and Latin and means “wedge-shaped” or “stalked”, and refers to the stalked polyps of some species in this family.
Morphology: Sphenopid Zoanthid polyps have radial symmetry, a hollow digestive cavity, and specialized stinging structures in tentacles surrounding the mouth. As hexacorals, the tentacles are in multiples of six. The tentacles are retractable. Their polyps have a flower-like appearance. These corals do not form a calcareous base. Instead the polyps have a leathery integument (“skin”) encrusted with sand particles. The two genera in this family differ in their structure and behavior. Species from the genus Palythoa are colonial and form massive encrusting mats. Those from the genus Sphenopus are solitary and free-living. Palythoans form sheet-like colonies, on hard substrates, that can span several square meters. The individual polyps are interconnected by stolons or a continuous coenenchyme, which enables resource sharing. Individual Palythoa polyps measure 3 mm (0.1 inches) -10 mm (0.4 inches) in diameter. Sphenopus polyps grow in soft sediments. They have a cylindrical shape to facilitate movement though the substrate. They have a basal, pedal disk to anchor and facilitate burrowing. These polyps reach 20 mm (0.8 inches) – 30 mm (1.1 inches) in height, and lack any interconnection with other polyps. Palythoa polyps are zooxanthellate and usually are brown, green, or yellow in color due to the zooxanthellae. Sphenopus polyps are azooxanthellate and usually white or transparent.
Habitat and Distribution: Sphenopid Zoanthids from the genus Palythoa are found attached to hard surfaces such as rock, coral, wreckage, or concrete. Because they are firmly attached they can live in areas with significant water movement. They are found in shallow, sun-lit waters from the intertidal zone to depths of 12 m (39 feet). Sphenopid Zoanthids from the genus Sphenopus are found in sand, mud, and silt. They require fairly calm waters. They are usually found at depths between 10 m (33 feet) – 20 m (66 feet), though some are found as deep as 114 m (374 feet). Sphenopid Zoanthids are found worldwide in subtropical to tropical seas. At least five species from this family are found in Mexican waters.
Reproduction: Sphenopid Zoanthid polyps are gonochoric (male or female for life). They reproduce sexually, through broadcast spawning, with external fertilization. The fertilized eggs hatch into planktonic larvae. Sphenopid Zoanthids may also reproduce asexually through fission or budding.
Ecosystem Roles: Sphenopid Zoanthids from the genus Palythoa are zooxanthellate. They have a mutualistic relationship with zooxanthellae (single-cell dinoflagellates). Zooxanthellae live within certain coral polyps, sea anemones, jellyfish, and nudibranchs. They produce energy by means of photosynthesis and the energy is passed along to their hosts, sometimes providing the majority of the host’s total energy needs. In return, the host provides nutrients, carbon dioxide, and a secure, sunlit, platform for the zooxanthellae. During periods of chemical or thermal stress the corals can eject the zooxanthellae to reduce metabolic stress. This causes the coral to appear white. This process is known as coral bleaching. Coral bleaching can be an indicator of an unhealthy environment, or a natural response to a short-term condition such as El Niño. The coral will replace the zooxanthellae after the stress is resolved, or it will acquire a different species of zooxanthellae that is better accommodated to the new environment. In either case, the polyp risks starvation if it is unable to replace the zooxanthellae quickly. They supplement their diet by using their tentacles to capture amphipods, fish larvae, invertebrate larvae, other zooplankton, and organic matter from the surrounding water. Unlike many other Zoanthids, Sphenopid Zoanthids from the genus Sphenopus, are not zooxanthellate (azooxanthellate) and they obtain all their necessary nutrients by using their tentacles to capture prey. Sphenopid Zoanthids are prey for gastropods, fish, crabs and sea turtles. Zoanthids contain palytoxin, a substance that is toxic to some potential predators. Sphenopid Zoanthids host epibionts such as amphipods, shrimp, polychaetes, and gastropods. They also provide microhabitats for fish, crustaceans and other invertebrates.