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Sep 30
Poriferans, or sponges, are a diverse group of animals that belong to the phylum Porifera. They are considered to be one of the most ancient animal groups, with a fossil record dating back over 600 million years. The phylogeny of poriferans is still a topic of debate among scientists, but recent molecular studies have shed light on the evolutionary relationships within this group.
There are three main classes of poriferans: Calcarea, Hexactinellida, and Demospongiae. Calcarea sponges are characterized by their calcium carbonate spicules, while Hexactinellida sponges have siliceous spicules with six rays. Demospongiae sponges are the most diverse group, with over 80% of all sponge species belonging to this class.
Recent molecular studies have suggested that Demospongiae is a monophyletic group, meaning that all members share a common ancestor. Calcarea and Hexactinellida, on the other hand, are considered to be paraphyletic groups, meaning that they do not include all descendants of a common ancestor.
Overall, the phylogeny of poriferans is still a work in progress, with ongoing research aiming to better understand the evolutionary relationships within this ancient group of animals.
There are three main classes of poriferans: Calcarea, Hexactinellida, and Demospongiae. Calcarea sponges are characterized by their calcium carbonate spicules, while Hexactinellida sponges have siliceous spicules with six rays. Demospongiae sponges are the most diverse group, with over 80% of all sponge species belonging to this class.
Recent molecular studies have suggested that Demospongiae is a monophyletic group, meaning that all members share a common ancestor. Calcarea and Hexactinellida, on the other hand, are considered to be paraphyletic groups, meaning that they do not include all descendants of a common ancestor.
Overall, the phylogeny of poriferans is still a work in progress, with ongoing research aiming to better understand the evolutionary relationships within this ancient group of animals.
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Google Gemini AI
Sep 30
Poriferan Phylogeny
The phylum Porifera includes a diverse group of animals commonly known as sponges. Poriferans are multicellular, sessile animals that filter food from the water column. They exhibit a unique body plan characterized by a porous body wall and a central cavity lined with choanocytes.
Traditional Classification
Traditionally, poriferans were classified into three classes based on their skeletal structure:
- Calcarea: Sponges with skeletons composed of calcium carbonate spicules
- Hexactinellida: Sponges with skeletons composed of six-rayed siliceous spicules
- Demospongiae: Sponges with skeletons composed of collagenous fibers or siliceous spicules
Molecular Phylogeny
Advances in molecular techniques have led to a revised understanding of poriferan phylogeny. Molecular studies have shown that the traditional classification into three classes is not supported by genetic evidence. Instead, poriferans are now divided into four major clades:
1. Homoscleromorpha
- Sponges with a collagenous skeleton
- Choanocytes arranged in chambers
2. Calcarea
- Sponges with calcareous spicules
- Choanocytes arranged in chambers
3. Demospongiae
- Sponges with a siliceous or collagenous skeleton
- Choanocytes arranged in flagellated chambers
4. Hexactinellida
- Sponges with six-rayed siliceous spicules
- Choanocytes arranged in syncytia (multinucleated cells)
Relationships Among Clades
Molecular evidence suggests that the four clades of poriferans diverged from a common ancestor in the following order:
1. Homoscleromorpha
2. Calcarea
3. Demospongiae
4. Hexactinellida
Divergence Time
Molecular clock studies estimate that the divergence between the major poriferan clades occurred during the Neoproterozoic Era, approximately 700-800 million years ago.
Implications for Understanding Poriferan Evolution
The revised phylogeny of poriferans provides valuable insights into the evolution of these ancient animals. It suggests that:
- Poriferans evolved from a common ancestor more than 700 million years ago.
- The different skeletal structures of poriferans evolved independently within different clades.
- The clade Demospongiae is the most diverse and successful group of sponges, accounting for over 90% of extant species.
The phylum Porifera includes a diverse group of animals commonly known as sponges. Poriferans are multicellular, sessile animals that filter food from the water column. They exhibit a unique body plan characterized by a porous body wall and a central cavity lined with choanocytes.
Traditional Classification
Traditionally, poriferans were classified into three classes based on their skeletal structure:
- Calcarea: Sponges with skeletons composed of calcium carbonate spicules
- Hexactinellida: Sponges with skeletons composed of six-rayed siliceous spicules
- Demospongiae: Sponges with skeletons composed of collagenous fibers or siliceous spicules
Molecular Phylogeny
Advances in molecular techniques have led to a revised understanding of poriferan phylogeny. Molecular studies have shown that the traditional classification into three classes is not supported by genetic evidence. Instead, poriferans are now divided into four major clades:
1. Homoscleromorpha
- Sponges with a collagenous skeleton
- Choanocytes arranged in chambers
2. Calcarea
- Sponges with calcareous spicules
- Choanocytes arranged in chambers
3. Demospongiae
- Sponges with a siliceous or collagenous skeleton
- Choanocytes arranged in flagellated chambers
4. Hexactinellida
- Sponges with six-rayed siliceous spicules
- Choanocytes arranged in syncytia (multinucleated cells)
Relationships Among Clades
Molecular evidence suggests that the four clades of poriferans diverged from a common ancestor in the following order:
1. Homoscleromorpha
2. Calcarea
3. Demospongiae
4. Hexactinellida
Divergence Time
Molecular clock studies estimate that the divergence between the major poriferan clades occurred during the Neoproterozoic Era, approximately 700-800 million years ago.
Implications for Understanding Poriferan Evolution
The revised phylogeny of poriferans provides valuable insights into the evolution of these ancient animals. It suggests that:
- Poriferans evolved from a common ancestor more than 700 million years ago.
- The different skeletal structures of poriferans evolved independently within different clades.
- The clade Demospongiae is the most diverse and successful group of sponges, accounting for over 90% of extant species.
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