9.1 Porifera and Cnidaria
10 min read•august 20, 2024
and are ancient animal groups crucial to marine ecosystems. , the oldest known metazoans, have simple body plans and filter-feed. Cnidarians, including corals and , have more complex structures and unique stinging cells.
Both groups play vital roles in ocean habitats. Sponges filter water and provide homes for other organisms. Corals build massive reef structures, supporting incredible biodiversity. Their fossils offer insights into Earth's past environments and evolutionary history.
Porifera overview
- Porifera, commonly known as sponges, are multicellular organisms that belong to the kingdom Animalia
- Sponges are among the oldest known metazoan animals, with a fossil record dating back to the Precambrian
- Poriferans play important ecological roles in marine ecosystems, acting as filter feeders and providing habitat for various organisms
Sponge body structure
Top images from around the web for Sponge body structure
Sponges and Cnidarians | OpenStax: Concepts of Biology View original
Is this image relevant?
Morphology of Sponges | Biology for Non-Majors II View original
Is this image relevant?
Hydrodynamics of sponge pumps and evolution of the sponge body plan | eLife View original
Is this image relevant?
Sponges and Cnidarians | OpenStax: Concepts of Biology View original
Is this image relevant?
Morphology of Sponges | Biology for Non-Majors II View original
Is this image relevant?
1 of 3
Top images from around the web for Sponge body structure
Sponges and Cnidarians | OpenStax: Concepts of Biology View original
Is this image relevant?
Morphology of Sponges | Biology for Non-Majors II View original
Is this image relevant?
Hydrodynamics of sponge pumps and evolution of the sponge body plan | eLife View original
Is this image relevant?
Sponges and Cnidarians | OpenStax: Concepts of Biology View original
Is this image relevant?
Morphology of Sponges | Biology for Non-Majors II View original
Is this image relevant?
1 of 3
- Sponges have a simple body plan consisting of two cell layers: the outer pinacoderm and the inner choanoderm
- The body is permeated by a complex system of canals and chambers through which water flows for feeding and gas exchange
- Specialized cells called line the choanoderm and create water currents using their flagella
- , a gelatinous matrix, fills the space between the cell layers and contains various cell types (amoebocytes, archaeocytes)
Sponge skeletal elements
- Most sponges possess a skeleton composed of either organic fibers () or mineral elements ()
- Spicules are made of silica (in demosponges and hexactinellids) or calcium carbonate (in calcareous sponges)
- Spicule morphology varies greatly among sponge taxa and is used for classification and identification
- Spongin fibers provide flexibility and support to the sponge body
Sponge reproduction strategies
- Sponges can reproduce both sexually and asexually
- Sexual reproduction involves the production of (eggs and sperm) and subsequent fertilization
- occurs through , fragmentation, or the formation of (resistant structures containing totipotent cells)
- Gemmules allow sponges to survive unfavorable conditions and disperse to new habitats
Sponge fossil preservation
- Sponge fossils are commonly preserved as spicules or entire body fossils
- Siliceous spicules have a higher preservation potential than calcareous spicules due to their resistance to dissolution
- Sponge body fossils can be preserved through permineralization, carbonization, or as molds and casts
- Exceptional preservation of sponge soft tissues has been reported from deposits (Burgess Shale, Chengjiang)
Porifera classification
- Porifera is divided into four main classes: , , , and
- Classification is based on skeletal composition, spicule morphology, and other morphological characters
- Molecular phylogenetic studies have led to revisions in sponge classification and revealed new relationships among taxa
Demosponges vs hexactinellids
- Demospongiae is the most diverse class of sponges, characterized by the presence of siliceous spicules and/or spongin fibers
- Hexactinellida, also known as glass sponges, possess a skeleton composed of six-rayed siliceous spicules (hexactines)
- Demosponges are found in various marine habitats, while hexactinellids are primarily deep-sea dwellers
- Hexactinellids often have a more symmetrical body plan compared to demosponges
Calcarea sponges
- Calcarea, or calcareous sponges, have a skeleton made of calcium carbonate spicules
- Calcareous spicules are typically smaller and less diverse in morphology compared to siliceous spicules
- Calcarea sponges are generally smaller in size than demosponges and hexactinellids
- Most calcareous sponges inhabit shallow marine environments
Homoscleromorpha sponges
- Homoscleromorpha is a recently recognized class of sponges, previously classified as a subclass of Demospongiae
- Homoscleromorphs possess a unique combination of morphological and molecular characters, setting them apart from other sponge classes
- They have a simple body plan with a thin pinacoderm and a well-developed mesohyl
- Homoscleromorphs have siliceous spicules with a distinct morphology (tetraxons, calthrops)
Porifera evolutionary history
- Sponges are considered to be among the earliest diverging metazoan lineages
- Molecular clock estimates suggest that sponges originated in the Precambrian, possibly as early as 600-800 million years ago
- The sponge fossil record provides insights into the evolutionary history and diversification of the phylum
Earliest known sponge fossils
- The oldest unequivocal sponge fossils date back to the Ediacaran Period (635-541 million years ago)
- Ediacaran sponge fossils include body fossils and isolated spicules (, )
- Putative sponge biomarkers (24-isopropylcholestane) have been reported from even older Cryogenian strata (~650 million years ago)
Sponge diversification patterns
- Sponges underwent significant diversification during the (~541 million years ago)
- The Cambrian sponge fossil record is diverse, with representatives of all main sponge classes present
- Sponge diversity continued to increase throughout the Paleozoic Era, with notable radiations in the Ordovician and Silurian periods
- Post-Paleozoic sponge evolution is characterized by the rise of modern lineages and adaptations to new ecological niches
Mass extinctions and sponges
- Sponges have been affected by major mass extinction events throughout Earth's history
- The End-Permian mass extinction (~252 million years ago) had a significant impact on sponge diversity, with many lineages going extinct
- Sponges showed resilience and recovery after mass extinctions, with some lineages diversifying in the aftermath
- The Cretaceous-Paleogene mass extinction (~66 million years ago) had a less severe impact on sponges compared to other marine invertebrates
Cnidaria overview
- Cnidaria is a diverse phylum of aquatic animals, including corals, sea anemones, jellyfish, and hydroids
- Cnidarians are characterized by the presence of specialized stinging cells called , which contain
- Cnidarians play important ecological roles in marine ecosystems, particularly in coral reef habitats
Cnidarian body plans
- Cnidarians exhibit two main body forms: and
- Polyps are sessile and typically cylindrical in shape, with a mouth surrounded by tentacles (corals, sea anemones)
- Medusae are free-swimming and have a bell-shaped body with tentacles hanging from the margin (jellyfish)
- Some cnidarians alternate between polyp and medusa stages in their life cycle (), while others exhibit only one form
Cnidarian life cycles
- Cnidarian life cycles vary among different classes and orders
- Many cnidarians have a complex life cycle involving alternation of generations between polyp and medusa stages
- In the polyp stage, cnidarians reproduce asexually through budding or fission, forming colonies
- Medusae are the sexually reproductive stage, producing gametes that fertilize to form planula larvae
- Planula larvae settle on a substrate and metamorphose into polyps, completing the life cycle
Cnidarian nematocysts
- Nematocysts are specialized organelles found in cnidocytes, the stinging cells of cnidarians
- Nematocysts contain a coiled, thread-like tubule that can be discharged for prey capture, defense, or locomotion
- Different types of nematocysts exist, each with a specific function (penetrants, volvents, glutinants)
- The morphology and arrangement of nematocysts are used as taxonomic characters in cnidarian classification
Cnidaria classification
- Cnidaria is divided into two main subphyla: and Medusozoa
- Classification is based on morphological characters, life cycle patterns, and molecular phylogenetic data
- Recent molecular studies have led to revisions in cnidarian taxonomy, particularly at the class and order levels
Anthozoans vs medusozoans
- Anthozoa includes corals and sea anemones, which are characterized by the presence of only the polyp stage in their life cycle
- Medusozoa encompasses cnidarians that have both polyp and medusa stages (hydrozoans) or only the medusa stage (, )
- Anthozoans have bilateral symmetry and mesenteries, while medusozoans exhibit
- Medusozoans possess a velum or velarium, a shelf of tissue that partially closes the bell cavity, which is absent in anthozoans
Hydrozoans and siphonophores
- Hydrozoa is a diverse class of cnidarians that includes hydroids, fire corals, and siphonophores
- Hydrozoans typically have a complex life cycle with alternating polyp and medusa stages
- Siphonophores are colonial hydrozoans that consist of specialized polyps and medusae (Portuguese man-o-war)
- Some hydrozoans have reduced or absent medusa stages and reproduce primarily through asexual budding
Scyphozoans and cubozoans
- Scyphozoa, commonly known as true jellyfish, are characterized by a dominant medusa stage and a reduced or absent polyp stage
- Scyphozoans have a complex life cycle involving a planula larva, a sessile polyp (scyphistoma), and a free-swimming medusa (ephyra)
- Cubozoa, or box jellyfish, are a small class of cnidarians known for their complex eyes and potent venoms
- Cubozoans have a life cycle similar to scyphozoans, with a cubopolyp stage giving rise to medusae
Cnidarian skeletons
- Many cnidarians, particularly anthozoans, possess skeletons that provide support and protection
- Cnidarian skeletons can be composed of organic compounds (proteinaceous, chitinous) or minerals (calcium carbonate)
- Skeletal composition and microstructure vary among different cnidarian taxa and are used as diagnostic features
Coral skeleton formation
- Scleractinian corals secrete calcium carbonate skeletons in the form of aragonite
- Coral polyps deposit aragonite crystals extracellularly, forming a basal plate and vertical walls (septa, thecae)
- The process of skeleton formation is controlled by specialized cells () and organic matrix proteins
- Environmental factors, such as temperature and pH, can influence coral calcification rates
Coral skeleton types
- Coral skeletons exhibit a wide range of morphologies, reflecting adaptations to different environmental conditions
- Massive corals have solid, boulder-like skeletons that are resistant to wave action (Porites, Favia)
- Branching corals have tree-like or bushlike growth forms that are adapted to calm, well-lit waters (Acropora, Pocillopora)
- Encrusting corals have flat, plate-like skeletons that grow horizontally over the substrate (Montipora, Agaricia)
- Solitary corals, such as mushroom corals (Fungiidae), have a single, free-living polyp with a large, disc-shaped skeleton
Cnidarian biomineralization processes
- Biomineralization in cnidarians involves the controlled deposition of calcium carbonate by specialized cells
- The process is mediated by organic matrix proteins, which provide a template for crystal nucleation and growth
- Biomineralization is influenced by genetic factors, as well as environmental conditions (temperature, pH, salinity)
- Cnidarian biomineralization has evolved independently in different lineages, resulting in diverse skeletal structures and compositions
Cnidaria evolutionary history
- Cnidarians have a long evolutionary history, with fossils dating back to the Precambrian
- The cnidarian fossil record provides insights into the diversification and extinction patterns of the phylum
- Molecular phylogenetic studies have shed light on the relationships among cnidarian classes and the timing of major evolutionary events
Precambrian cnidarian fossils
- The oldest putative cnidarian fossils are from the Ediacaran Period (635-541 million years ago)
- Ediacaran fossils, such as Haootia quadriformis and Auroralumina attenboroughii, show possible cnidarian affinities
- These early fossils suggest that cnidarians were among the first animals to evolve complex body plans and tissue organization
Paleozoic coral diversity
- Corals underwent significant diversification during the Paleozoic Era (541-252 million years ago)
- Rugose corals (Rugosa) and tabulate corals (Tabulata) were dominant reef-builders in the Silurian and Devonian periods
- The End-Permian mass extinction had a major impact on coral diversity, with the extinction of rugose and tabulate corals
- Modern scleractinian corals (Scleractinia) originated in the Triassic Period and became the primary reef-builders in the Mesozoic and Cenozoic eras
Post-Paleozoic cnidarian evolution
- Cnidarians continued to diversify and adapt to new ecological niches in the Mesozoic and Cenozoic eras
- Scleractinian corals underwent a major radiation in the Jurassic Period, coinciding with the evolution of symbiotic relationships with photosynthetic algae ()
- The Cretaceous-Paleogene mass extinction had a less severe impact on cnidarians compared to other marine invertebrates
- Cnidarian diversity rebounded in the Cenozoic Era, with the rise of modern coral reef ecosystems
Cnidaria and reefs
- Cnidarians, particularly scleractinian corals, are the primary builders of coral reef ecosystems
- Coral reefs are among the most diverse and productive ecosystems on Earth, providing habitat for a wide range of marine organisms
- The evolution and distribution of coral reefs have been influenced by various biotic and abiotic factors throughout Earth's history
Coral reef formation
- Coral reefs form through the accumulation of calcium carbonate skeletons secreted by coral polyps
- Reef formation requires specific environmental conditions, including warm, clear, shallow waters with low nutrient levels
- Coral growth rates and reef accretion are influenced by factors such as temperature, light availability, and water chemistry
- Over time, coral skeletons and other calcifying organisms (coralline algae, mollusks) contribute to the buildup of reef structures
Coral reef types
- Coral reefs can be classified into different types based on their geomorphology and relationship to the surrounding environment
- Fringing reefs grow directly along the shoreline of islands or continents, with little or no lagoon separating them from the shore (Red Sea, Caribbean)
- Barrier reefs are separated from the shore by a deep lagoon and often form extensive linear structures (Great Barrier Reef, Belize Barrier Reef)
- Atolls are ring-shaped reefs that encircle a central lagoon, typically forming over subsided volcanic islands (Maldives, Tuamotu Archipelago)
- Patch reefs are small, isolated reef structures that grow within lagoons or on the continental shelf (Florida Keys, Great Barrier Reef)
Coral reefs through time
- The distribution and composition of coral reefs have varied throughout Earth's history, influenced by changes in sea level, ocean chemistry, and climate
- Ancient reef systems, such as the Permian Capitan Reef and the Devonian Great Barrier Reef, provide insights into past reef ecology and environmental conditions
- The Triassic-Jurassic transition saw the rise of scleractinian corals as the dominant reef-builders, a role they have maintained to the present day
- Quaternary coral reefs have experienced fluctuations in growth and distribution due to glacial-interglacial cycles and associated changes in sea level and climate
- Modern coral reefs face numerous threats, including climate change, ocean acidification, and human activities (overfishing, pollution)
Porifera and Cnidaria ecology
- Poriferans and cnidarians play crucial roles in marine ecosystems, contributing to nutrient cycling, habitat provision, and trophic interactions
- Both phyla have evolved diverse ecological strategies and adaptations, allowing them to thrive in a wide range of marine environments
Sponge ecological roles
- Sponges are important filter feeders, removing dissolved organic matter and particulate material from the water column
- Sponge filtration can significantly impact water clarity and nutrient dynamics in marine ecosystems
- Sponges provide habitat and shelter for various organisms, including crustaceans, polychaetes, and microbial symbionts
- Some sponge species are important bioeroders, contributing to the breakdown and recycling of calcium carbonate substrates (coral reefs, mollusk shells)
Coral ecological importance
- Corals, particularly reef-building , are ecosystem engineers that create complex, three-dimensional habitats
- Coral reefs support high levels of biodiversity, providing food, shelter, and nursery grounds for a wide range of marine species
- Corals are primary producers, with their symbiotic algae (zooxanthellae) contributing to the overall productivity
Key Terms to Review (36)
Anthozoa: Anthozoa is a class of marine invertebrates within the phylum Cnidaria, which includes organisms such as sea anemones and corals. These creatures are characterized by their polyp form, which is typically sessile, meaning they remain attached to a substrate. Anthozoans are significant for their role in marine ecosystems, particularly in building coral reefs, which provide habitat and protection for numerous marine species.
Asexual reproduction: Asexual reproduction is a mode of reproduction that involves a single organism producing offspring without the involvement of gametes or fertilization. This type of reproduction allows for rapid population increase and does not require a mate, making it advantageous in stable environments. Organisms that reproduce asexually can produce clones, which are genetically identical to the parent, leading to minimal genetic variation among offspring.
Budding: Budding is a form of asexual reproduction where a new individual develops from a small outgrowth or bud on the parent organism. This process is significant in the context of certain animal groups, allowing them to reproduce quickly and efficiently while remaining genetically identical to the parent. Budding is a notable feature in organisms such as sponges and cnidarians, showcasing their unique reproductive strategies.
Calcarea: Calcarea refers to a class of marine sponges characterized by the presence of calcium carbonate spicules, which give them a rigid structure. These sponges play a vital role in marine ecosystems and exhibit a range of body forms, often including asconoid, syconoid, and leuconoid structures. They are primarily found in shallow waters and can vary greatly in shape and size.
Calicoblasts: Calicoblasts are specialized cells found in certain marine organisms, particularly within the phylum Cnidaria, that are responsible for secreting calcium carbonate to form the structural components of their skeletons or corallites. These cells play a crucial role in building the hard parts of corals, which are vital for reef formation and maintaining biodiversity in marine ecosystems.
Cambrian Explosion: The Cambrian Explosion refers to a rapid diversification of life that occurred approximately 541 million years ago, marking the beginning of the Cambrian period. This event saw the emergence of most major animal phyla, making it a critical point in the history of life on Earth, as fossil records from this time reveal an abundance of complex organisms with various body plans.
Choanocytes: Choanocytes are specialized flagellated cells found in sponges (phylum Porifera) that play a crucial role in the feeding process. These cells create water currents through the sponge's body by beating their flagella, allowing for the intake of food particles and oxygen while also aiding in the removal of waste products. The structure and function of choanocytes are essential for understanding the basic biology and ecology of sponges.
Cnidaria: Cnidaria is a phylum of animals known for their unique stinging cells called cnidocytes, which are used for capturing prey and defense. This group includes diverse organisms such as jellyfish, corals, and sea anemones, showcasing a range of body forms and life cycles that highlight their ecological roles in marine environments.
Cnidocytes: Cnidocytes are specialized cells found in members of the phylum Cnidaria, responsible for the unique stinging mechanism used for capturing prey and defense. These cells contain organelles called nematocysts, which can inject toxins into other organisms upon contact, making them effective for both hunting and protection against predators.
Coronacollina: Coronacollina is an extinct genus of marine organisms that existed during the Ediacaran period, recognized for its distinct body plan which resembles a bell or crown shape. This organism is significant as it showcases early multicellular life and is thought to represent an early evolutionary experiment in the development of complex body forms that would later characterize more advanced organisms, connecting to the study of both Porifera and Cnidaria due to similarities in morphology and ecological roles.
Cubozoans: Cubozoans are a class of jellyfish characterized by their cube-shaped medusa stage, complex eye structures, and potent venom. This group includes some of the most well-known and dangerous jellyfish, such as the box jellyfish. Their unique body plan and advanced sensory systems set them apart from other members of the phylum Cnidaria.
Demospongiae: Demospongiae is a class of sponges characterized by a skeleton made of spongin fibers and/or silica spicules, representing the largest and most diverse group within the phylum Porifera. These sponges play crucial roles in marine and freshwater ecosystems, serving as important filter feeders and habitat providers for various organisms.
Ediacaran biota: Ediacaran biota refers to a group of ancient, mostly soft-bodied organisms that existed during the late Precambrian period, around 635 to 541 million years ago. These organisms are significant because they represent some of the earliest complex multicellular life on Earth, showcasing a variety of body plans that laid the groundwork for later evolutionary developments in animals. Their fossils provide valuable insight into early ecosystems and the transition to more recognizable life forms in the Cambrian period.
Filter feeding: Filter feeding is a feeding mechanism used by various aquatic organisms to obtain nutrients by straining suspended particles, including plankton and organic matter, from the water. This process involves drawing water through specialized structures that trap food particles while allowing excess water to flow out, playing a critical role in the nutrient cycling within aquatic ecosystems.
Gametes: Gametes are specialized reproductive cells that are involved in sexual reproduction, typically characterized by their haploid chromosome number. In the context of various organisms, these cells combine during fertilization to form a diploid zygote, which eventually develops into a new organism. Gametes play a crucial role in genetic diversity and evolution, as they carry different alleles from each parent that contribute to the genetic makeup of the offspring.
Gemmules: Gemmules are specialized asexual reproductive structures found in certain sponges, serving as a means for survival and dispersal. These structures can remain dormant in unfavorable conditions and can eventually develop into new sponge individuals when environmental conditions improve. Gemmules are significant for understanding the life cycles and reproductive strategies of sponges.
Hexactinellida: Hexactinellida, commonly known as glass sponges, are a class of sponges characterized by their unique siliceous skeletons composed of six-rayed spicules. These deep-sea organisms exhibit a fascinating structure, often forming intricate and beautiful forms that can resemble glass due to their silica composition. Their body plan is significantly different from other sponges, making them an essential group in the study of Porifera.
Homoscleromorpha: Homoscleromorpha is a class of sponges that are characterized by their unique cellular structure and the presence of a siliceous skeleton. This class is distinct from other sponge classes due to the presence of a true tissue layer, which sets them apart in the evolutionary lineage of Porifera. Their structural and genetic features provide insight into the evolutionary relationships between sponges and other metazoans.
Hydrozoans: Hydrozoans are a class of small, primarily marine animals within the phylum Cnidaria, characterized by their polyp and medusa life stages. They are often colonial organisms, forming intricate structures, and exhibit a variety of forms and reproductive strategies. These creatures play significant roles in marine ecosystems and display fascinating behaviors like predation and symbiosis.
Hyrtlia: Hyrtlia is a genus of extinct marine organisms that belonged to the phylum Cnidaria, characterized by their soft-bodied, jelly-like structure and their radial symmetry. These organisms are known primarily from fossil records, indicating their existence during the Cambrian period, and they provide insights into the early evolution of complex multicellular life forms in marine environments.
Jellyfish: Jellyfish are free-swimming marine animals belonging to the phylum Cnidaria, characterized by their gelatinous, umbrella-shaped bell and trailing tentacles. These fascinating creatures are known for their unique anatomy and simple body structure, which includes a radial symmetry that allows them to move through the water gracefully. Jellyfish possess specialized cells called cnidocytes, which contain stinging structures used for capturing prey and defense.
Lagerstätten: Lagerstätten are exceptional fossil deposits that provide a remarkable record of past life, often preserving organisms in extraordinary detail. These sites are crucial for understanding ancient ecosystems and the evolutionary history of life, as they can contain a wide variety of organisms, including soft-bodied species that are rarely preserved. Their unique conditions, such as rapid burial and low oxygen levels, contribute to the remarkable preservation of both hard and soft tissues.
Medusa: Medusa refers to a life stage of certain cnidarians, characterized by a free-swimming, umbrella-shaped body and tentacles that hang down. This stage is crucial for reproduction, as medusae often release eggs and sperm into the water, leading to the formation of new polyps. Medusae are typically associated with jellyfish, but they also appear in other cnidarian groups, highlighting their significance in the life cycles of these organisms.
Mesohyl: Mesohyl is a gelatinous substance found within the bodies of sponges, acting as a supportive matrix that separates the outer pinacoderm layer from the inner choanoderm layer. It contains various cells, including amoebocytes and skeletal elements, which contribute to the sponge's structure and function. This unique feature allows for nutrient transport and cellular communication, playing a crucial role in the sponge's overall physiology.
Multicellularity: Multicellularity refers to the condition of being composed of multiple cells that work together to form a complex organism. This organization allows for specialized functions and cooperation among cells, enabling organisms to grow larger and perform tasks that single-celled organisms cannot. Multicellularity has evolved independently in various lineages, giving rise to diverse forms of life, including those found in specific groups like sponges and jellyfish.
Nematocysts: Nematocysts are specialized stinging cells found in cnidarians, such as jellyfish, sea anemones, and corals. These cells contain a coiled, harpoon-like structure that can rapidly eject to capture prey or deter predators, playing a vital role in the feeding and defense mechanisms of these organisms.
Paleophragmodictya: Paleophragmodictya refers to a genus of extinct marine sponges that lived during the Paleozoic era, characterized by a unique skeletal structure. This genus showcases an intricate arrangement of spicules and demonstrates the evolutionary transition within the Porifera phylum. The structure of Paleophragmodictya provides insights into early sponge evolution and their role in marine ecosystems.
Polyp: A polyp is a cylindrical, sessile body form found in certain animals, particularly within the phylum Cnidaria, such as corals and sea anemones. This structure is characterized by a mouth surrounded by tentacles and is often attached to a substrate, playing a key role in the life cycle of these organisms, especially during their asexual reproduction phase.
Porifera: Porifera, commonly known as sponges, is a phylum of simple, multicellular animals that are characterized by their porous bodies and lack of true tissues and organs. They are primarily aquatic organisms found in marine and freshwater environments, playing vital roles in aquatic ecosystems as filter feeders and providing habitat for various marine life.
Radial symmetry: Radial symmetry is a body plan in which the body can be divided into similar halves by multiple planes that pass through a central axis. This type of symmetry allows organisms to interact with their environment from all directions, making it particularly advantageous for stationary or slow-moving creatures. Radial symmetry is commonly seen in certain groups of animals, facilitating their feeding, movement, and overall organization.
Scleractinians: Scleractinians, commonly known as stony corals, are a group of marine animals belonging to the class Anthozoa within the phylum Cnidaria. These corals are characterized by their hard calcium carbonate skeletons, which contribute significantly to coral reef structures. They play a crucial role in marine ecosystems by providing habitat and shelter for diverse marine life while also being vital contributors to the ocean's biodiversity.
Scyphozoans: Scyphozoans are a class of marine invertebrates within the phylum Cnidaria, commonly known as true jellyfish. They are characterized by their gelatinous, umbrella-shaped bell and long, trailing tentacles equipped with stinging cells called cnidocytes. These fascinating creatures play important ecological roles in marine ecosystems and exhibit a complex life cycle that includes both a medusa and a polyp stage.
Spicules: Spicules are small, needle-like structures that provide structural support and protection in certain organisms, particularly sponges. These skeletal elements can be made of silica or calcium carbonate and play a vital role in the organization and function of the body plan, contributing to the overall rigidity and shape of the organism.
Sponges: Sponges are simple, multicellular organisms belonging to the phylum Porifera, characterized by their porous bodies and the ability to filter feed. These animals are primarily aquatic and play a crucial role in marine ecosystems as they help to filter water and provide habitat for other organisms. Sponges lack true tissues and organs, making them unique in the animal kingdom.
Spongin: Spongin is a fibrous protein that forms the structural framework of certain types of sponges, particularly those classified under the phylum Porifera. This substance provides strength and flexibility to the sponge's body, allowing it to maintain its shape while also being able to expand and contract as water flows through it. Spongin is different from the mineralized structures found in some other sponge groups, highlighting the diversity in sponge anatomy and adaptations.
Zooxanthellae: Zooxanthellae are microscopic, photosynthetic algae that live in a symbiotic relationship with various marine invertebrates, particularly corals and certain species of mollusks. These algae provide essential nutrients to their hosts through photosynthesis, while benefiting from the protection and access to light offered by the host's tissues. This mutualistic relationship is crucial for the health of coral reefs and contributes significantly to the productivity of marine ecosystems.