Cnidarian ecstacy

I am still working on understanding Evolution, but once you start delving even into the shallows of the science, there is necessarily a fundamental shift in the way in which you see the world around you. Evolutionary theory shows us the wiring under the board so to speak, and elucidates the connectedness of seemingly unrelated parts of the natural world.

For example, these two do not look the same but they are family:

Coral
Coral

Jellyfish

Jellyfish

In order to make sense out of the complexity of the natural world scientists have developed a science called Cladistics (also known as Systematics or Phylogenetics) which besides just linking physically similar features, relies heavily on genetic analysis and computational methods to determine the linkages between creatures, plants and bacteria back to their common ancestors.

Cladistics goes further than just grouping creatures (or plants, bacteria) in terms of their gross morphological (physical shape, size) characteristics and includes an analysis of the  ancestral linkages between a particular individual specimen and its predecessors. In their lingo they are looking for monophyletic groups – groupings which include 1) all the descendants of an ancestral organism and 2) the ancestor itself – this they call a clade, or one part of one branch in the tree of life.

Anything not part of the clade is called paraphyletic, even if it may seem to be morphologically similar – if they dont have a common ancestor, they are not part of the same clade.

This is useful because it is helpful in building a picture (a Cladogram is a graphical representation of a clade of organisms, and most importantly for a scientific persepctive,  is a testable proposal of relatedness) of how all the living things we see in the world today came to be, and it describes the history of the process of development from ancient forms of creatures (like Dinosaurs) to modern forms of creatures (like Birds).

Once you see that it can be shown that birds evolved from long extinct Dinosaurs –

The fossil record indicates that birds evolved from theropod dinosaurs during the Jurassic period, around 150–200 Ma (million years ago), and the earliest known bird is the Late Jurassic Archaeopteryx, c 150–145 Ma. Most paleontologists regard birds as the only clade of dinosaurs to have survived the Cretaceous–Tertiary extinction event approximately 65.5 Ma.

Archaeopteryx has clearly reptilian characteristics: teeth, clawed fingers, and a long, lizard-like tail, but it has finely preserved wings with flight feathers identical to those of modern birds. It is not considered a direct ancestor of modern birds, but is the oldest and most primitive known member of Aves or Avialae, and it is probably closely related to the real ancestor.

…you may have some idea of the benefits of an Evolutionary understanding brought to bear on your perception of the world around you – I for one will never look at a Mynah bird the same again…

But enough about birds (for now!).

Jellyfish keep cropping up in my reading on Evolution

 Prehistoric Life: The Definitive Visual History of Life on Earth (Hardcover) by David Burnie (Author)

Prehistoric Life: The Definitive Visual History of Life on Earth (Hardcover) by David Burnie (Author)

and I was super curious to find out more about these cool fauna… I thought I would share some of the wonder with you.

Chondrophores, Jellyfish, Portugese Man Of War (Blue Bottle), Corals, Sea Anemones and a few other minor relatives, all belong to a clade of creatures called Cnidarians

Phylum Cnidaria – corals, sea anemones, hydroids, jellyfish

  • ~10,000 species worldwide.
  • Mostly marine with a few freshwater species.

Cnidarians are radially symmetrical, with gelatinous bodies, and a mouth surrounded by a ring of tentacles.

All cnidarians possess cnidae also called nematocysts. These are the stinging cells which are used in food capture and defence. Cnidarians have a very diverse range of life histories including being sessile, pelagic, solitary, and colonial or combinations of each over alternating generations. The pelagic form (From Latin pelagicus (and possibly pelagus); from Greek πελαγικός (pelagikos), from πέλαγος (pelagos) ‘sea’. – Meaning : Living in the open sea rather than in coastal or inlandwaters ) is typically called the medusa, while the sessile form (From New Latinsessilis (“‘sitting’”) – Meaning: permanently attached to a substrate; not free to move about ) is typically called a polyp.

These are truly fascinating creatures, including what we commonly run into at our South African beaches, the Jellyfish and the Blue bottle – affectionately (or not) referred to by surfers and beach-goers here as Jellies and Blue’es. I can tell you from personal experience that a Jelly will sting you far more vigorously than a Blue’e – I once had portion of Jellyfish go down the back of the wetsuit – most entertaining for my mates on the shoreline, not so much fun for me – but both creatures will introduce you to the sensation of considerable pain.

Besides looking at the evolutionary transition from earlier forms of these creatures to more modern forms, some Cnidarians go through a process of metamorphosis over their life cycle.

The above illustration is of Obelia, a Hydroid that passes through both the medusa and the polyp phase.  This organism goes through stages where it is in effect a different organism, a true  metamorphosis .

The above illustration is of Obelia, a Hydroid that passes through both the medusa and the polyp phase. This organism goes through stages where it is in effect a different organism, a true metamorphosis .

Porpita porpita has a small disc like body and floats freely in the water column. Related to the jellyfish, this species measures just one inch in diameter. Image courtesy of Islands in the Sea 2002, NOAA/OER.

Hydrophores are stunningly beautiful. Porpita porpita has a small disc like body and floats freely in the water column. Related to the jellyfish, this species measures just one inch in diameter. Image courtesy of Islands in the Sea 2002, NOAA/OER.

Physalia physalis

Physalia physalis - Portugese Man Of War / Blue Bottle

The Blue Bottle is a difficult creature to classify because it is actually a siphonophore, a colony of specialized sub-creatures in various stages of form, which need each other to survive and would not survive on their own. They are difficult to classify because they inhabit a boundary between individual organisms and collective symbiosis – I want to say that they are like the Borg of the sea, but it may be a tenuous simile. The parts of the siphonophore all share the same genetic material.

The innovation that evolution has produced also inspires the Homo Sapiens of the world to design structures in their likeness:

Physalia-Amphibious-Garden-Boat

Physalia-Amphibious-Garden-Boat

Jellyfish

Jellyfish

Nothing makes for more tantalising science than creatures shrouded in mystery – for example we know that Jellyfish have no brain and yet they are able to sense prey items, navigate oceans and are somehow able to process informational input from the environment and respond in adaptive ways. They seem to have a distributed nervous system and process information in a non centralised way. They “sleep“, and have eyes to actively, visually seek out prey items but it is unclear how they make sense of visual stimuli because they have no brain to centrally process visual information.

Jellyfish eyes

In this close-up of a rhopalium (right), you can see six reddish spots, all of which are sensitive to light. The four smallest spots are relatively simple. However, the two larger regions actually contain lenses, corneas, and retinas, not so unlike those in your eyes.

Some species are at the mercy of tidal forces and cannot swim in a purposeful and directional manner, whilst other species can motor along rather quickly and actually move contra flow to the direction of the tide.

Cnidaria can reproduce asexually, and regenerate after fragmentation.

Cnidarian evolutionary history

“All organisms do not have an equal chance (of being fossilised). The soft parts of animals and plants, and whole organisms composed completely of soft organic matter, cannot be preserved unless some set of very unusual conditions prevent destruction and inhibit decay. There are large groups of animals and plants that did not produce hard parts and are unrepresented, or scarcely represented, in the fossil record. Jellyfish, for example, a group of marine organisms that are abundant in the ocean at present, have an extremely poor fossil record. However, we know from impressions made in the soft mud by these floating organisms, when they became stranded, that they existed about 570 million years ago.”  – McRae, C. (1999). Life Etched in Stone, Fossils of South Africa. South Africa: The Geological Society of South Africa pgs. 31-32.

It is amazing that we have any record of Cnidaria at all because their physical morphology does not lend itself to easy fossilization.

Cnidaria are some of the earliest known forms of life.

Cnidaria cladogram

Cnidaria cladogram

Recently,  scientists have discovered that ctenophores

Bathocyroe fosteri a common but fragile deep-sea lobate, oriented mouth down

Bathocyroe fosteri a common but fragile deep-sea lobate, oriented mouth down

(also known as Comb Jellies) are likely to have a common ancestor with cnidaria, and that humans and other vertebrates did not have an ancestral connection to sponges as earlier thought, sponges developed from their own unique ancestral line – despite what some of us might think at our family gatherings.

Ancient Jellyfish have been discovered in rocks more than 500 million years old, and in great detail – the benefit of a quick fossilization in mud so that they can be definitively identified…

500 million year old Jellyfish

500 million year old Jellyfish

Fossils of Essexella, a progenitor of more modern Jellyfish are commonly found in the United States in Mazon Creek, Illinois. You can clearly see the rim of tentacles around a disc like body.

Essexella fossil

Essexella fossil - 8 to 12cm

Although they sting and can have other deleterious environmental effects, I just love the little buggers in all their varied forms – they are so prehistoric, so seemingly alien and out of place amongst the other usual creature body forms, but a beautiful example of how diverse the products of evolution can be.

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~ by Fluxosaurus on June 19, 2010.

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