Phylum Cnidaria Part 2: Class Hydrozoa

Summary

This video delves into the diverse and fascinating world of the phylum Cnidaria, focusing on the Hydrozoa class. It covers a range of species, including hydras, which are known for their regenerative abilities and biological immortality, as well as the 'immortal jellyfish' Turritopsis dohrnii. The script also explores the complexity of colonial hydrozoans like Obelia and siphonophores, which consist of specialized zooids performing distinct functions. Additionally, the video touches on other hydrozoans such as hydrocorals and freshwater jellyfish, providing insight into the unique adaptations and behaviors that make this phylum so remarkable.

Takeaways

• 😀 The five best-known classes of Phylum Cnidaria are Hydrozoa, Scyphozoa, Staurozoa, Cubozoa, and Anthozoa.
• 😀 Hydrozoans are typically small, predatory polyps, some of which are colonial and others solitary.
• 😀 Hydra, a freshwater example of Hydrozoa, can grow up to 30mm and are found on the underside of leaves in shallow pools and streams.
• 😀 Hydras are capable of unique body morphing, such as contracting into spheres when frightened or stretching to over four times their length when feeding.
• 😀 Hydra reproduce both sexually and asexually. They can form new individuals by budding or splitting in two when conditions are favorable.
• 😀 Hydra possess the ability to regenerate tissues and even stem cells, making them biologically immortal by preventing aging.
• 😀 The “immortal jellyfish” (Turritopsis dohrnii) can reverse its life cycle and regenerate into a polyp colony, escaping death under extreme conditions.
• 😀 Obelia, another hydrozoan genus, forms colonial structures with specialized zooids for feeding and reproduction, including the release of medusa buds.
• 😀 Siphonophores, such as the Portuguese man o' war, are colonial hydrozoans made of multiple specialized zooids, and they can float and drift in the ocean.
• 😀 Hydrocorals, like fire corals, are colonial hydroids that form calcareous skeletons and resemble true corals from a distance but are actually hydrozoans.
• 😀 Other notable hydrozoans include chondrophores, air ferns, and freshwater jellyfish, with some species becoming invasive in new environments.

Q & A

What are the five best-known classes of Phylum Cnidaria?

The five best-known classes of Phylum Cnidaria are Hydrozoa, Scyphozoa, Staurozoa, Cubozoa, and Anthozoa.

What are the lesser-known classes of Phylum Cnidaria?

The lesser-known classes of Phylum Cnidaria are Myxozoa and Polypodiozoa, though their classification is more complicated.

What is the general size and habitat of Hydrozoa species?

Hydrozoa species are generally very small and predatory. They are found in marine waters worldwide, though some species like Hydra inhabit freshwater environments.

How does the Hydra use its body for feeding?

The Hydra extends its tentacles to capture prey from the water column, using its lasso-like, volvent type cnidocytes to ensnare passing animals.

What is the Hydra's unique ability when it comes to regeneration?

Hydras possess the ability to regenerate tissue indefinitely, allowing them to regrow body parts or even form new individuals if cut in half.

What does it mean that Hydra are biologically immortal?

Hydras are biologically immortal because they do not experience senescence (aging). They can regenerate stem cells indefinitely, meaning they do not age like most other organisms.

How does Turritopsis dohrnii (the immortal jellyfish) exhibit biological immortality?

The immortal jellyfish can undergo reverse metamorphosis and transdifferentiation, allowing it to revert to a polyp form under stressful conditions, essentially escaping death.

What is the unique process of reproduction in Turritopsis dohrnii?

Turritopsis dohrnii reproduces both sexually and asexually. It releases sperm and eggs into the water for sexual reproduction, while also forming polyps that reproduce asexually by budding.

How does the colonial hydroid genus Obelia function?

In the genus Obelia, a single hydroid colony consists of stalks called hydrocauli, which extend upward. The colony contains specialized zooids for feeding (gastrozooids) and reproduction (gonozooids).

What are siphonophores and how do they differ from other colonial hydroids?

Siphonophores are colonial hydrozoans made up of specialized zooids, including medusae and polyps. Unlike other colonial hydroids, siphonophores can float and drift in the ocean, and some species, like Apolemia, can grow up to 45 meters long.

What are hydrocorals, and how are they related to true corals?

Hydrocorals, such as fire and rose corals, resemble true corals but are not actual corals. They are hydrozoan colonies that form calcareous skeletons similar to corals.

What are some other notable species of colonial hydrozoans?

Other notable colonial hydrozoans include chondrophores, which have a central gas-filled disk, and freshwater jellyfish, which are now considered an invasive species in various water bodies.