Some of the most commonly known marine phyla are:
Phylum Chordata, which includes organisms with a rod supporting their "dorsal" or back side such as humans and other mammals, bony fish, reptiles, amphibians, and birds. The name "Chordata" derives from the Greek root chord-, meaning "string"!
- All chordates (the organisms in Phylum Chordata) have the following features at some point in their lives:
> A notochord, a rod of cells and connective tissue. For many organisms, including humans, this is quickly replaced with bony, segmented vertebrae.
> Pharyngeal slits or clefts, which develop in some organisms to filter food or oxygen from aquatic environments, or disappear in other organisms like humans.
> A hollow nerve tube in the dorsal or back side that sits above the notochord and from which nerves branch into muscles and other organs. It eventually thickens as it grows, and it almost loses the hollow space with time.
> A post-anal tail. Yes, humans start life with a tail! Our tail is very quickly reduced to a nub--the tailbone as we develop before birth, unlike other tail-sporting chordates we're familiar with such as most dogs, birds, and fish.
- Most species in this phylum, like ourselves, are part of subphylum Vertebrata: they're vertebrates, or animals with backbones.
- Subphylum Urochordata, the tunicates, and subphylum Cephalochordata, the lancelets, are the only invertebrates in Phylum Chordata, though they still have a notochord. Both groups are marine organisms!
Some examples of popular marine chordates: baleen whales, dolphins, orcas, sharks, rays, and seals
Licensed Use via Pixabay: Whales photo Elianne Dipp https://www.pexels.com/@eliannedipp; Dolphins photo (no author listed); Orca photo (no author listed); Rays photo by W W https://www.pexels.com/@w-w-299285; Seal photo Lachlan Ross https://www.pexels.com/@lachlan-ross
Licensed Use via Unsplash: Shark photo by Gerald Schombs https://unsplash.com/@geerald
Phylum Mollusca, which includes clams, snails, slugs, squids, and octopi, among others!
- All molluscs have
> A "poda" or muscular foot that is specialized for one or more purposes; this is usually for creeping along surfaces, swimming, grasping objects, or digging.
> A mantle, a layer of soft tissue that covers the body and its internal organs. The mantle of many species produces a shell unique to that species.
- Many molluscs also have a radula, a toothy organ that rasps or scrapes food from surfaces.
Below: giant clam, snail, sea slug, and cuttlefish
Licensed use via Unsplash: giant clam by NOAA https://unsplash.com/@noaa; snail by Gred Rosenke https://unsplash.com/@greg_rosenke; cuttlefish by Peter Boshra https://unsplash.com/@peterboshra80
Licensed use via Pixabay: sea slug by Arhnue Tan https://pixabay.com/users/arhnue-1896944/;
Three Phyla; Platyhelminthes, Nematoda, and Annelida, the worms
- All worms are bilaterally symmetrical; they have an anterior and posterior (or head and tail end, respectively). They display cephalization, meaning they have a nervous system that is more concentrated at the head for sensing nearby stimuli such as light, touch, and scent. They're a little more complex than most of us give them credit for--most have central nervous system, complete digestive system, and a circulatory system made of blood and blood vessels.
- Phylum Platyhelminthes includes the flatworms, and Phylum Nematoda includes the roundworms. Flatworms have the simplest physiology (physical characteristics) while roundworms are slightly more complex. Besides that, I don't want to spoil all the cool stuff they have to show us, so I'll save any more details on them for future Platyhelminthes and Nematoda posts!
- Phylum Annelida includes the worms most of us usually think of such as earthworms. All annelids are segmented, making their bodies the most complex of the three worm phyla.
From left to right: flatworm (platyhelminth), roundworm (nematode), and segmented worm (annelid)
Wikimedia Commons: Yellow Papillae Flatworm photo by Betty Wills, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0; Public Domain Nematode photo by Agricultural Research Service
Licensed Use via Pixabay: Annelid photo by Wolfgang Eckert at https://pixabay.com/users/anaterate-2348028/
Phylum Arthropoda, which includes crustaceans, insects, and other creepy-crawlies such as spiders, scorpions, centipedes, and millipedes.
- Arthropods are named for their jointed appendages using the Greek roots arthro-, meaning "joint", and pod-, meaning "foot".
- They're considered the most successful creatures of Kingdom Animalia: they make up about 85% of all known animal species!
Various aquatic arthropods; lobster, crab, and shrimp from left to right
Licensed Use via Unsplash: Mantis Shrimp by Dorothea Oldani https://unsplash.com/@dorographie
Licensed Use via Pixabay: Crab by Elijah Lovkoff https://pixabay.com/users/skylark-201564/
Wikimedia Commons: Lobster by Joe Kunkel, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0
Phylum Echinodermata, which includes sea stars, sea urchins, and sea cucumbers
- Echinoderms are named for their spiny or bumpy outer surfaces with the Greek root echino-, meaning "spiny," and the Latin root -derm, meaning "skin".
- Echinoderms, while they are animals, are unique for their water vascular system and pentaradial (five-sided) symmetry!
From left to right: a sea star, sea urchin, and sea cucumber
Licensed use via Unsplash: Sea star by Pedro Lasta https://unsplash.com/@peterlaster; Sea urchin by NOAA https://unsplash.com/@noaa
Licensed use via Pixabay: Sea Cucumber by Kevin Mc Loughlin https://pixabay.com/users/kevskoot-4296329/
Phylum Cnidaria, which includes jellyfish, corals, and anemones
- Yes, jellyfish, corals, and sea anemones are all in this same large group! They're called "cnidarians" for the "cnidocytes," or stinging cells, that they have, using the Greek root cnid-, which refers to stinging nettle plants. These cells function like miniature harpoons to inject venom, into prey or potential threats. Unlucky victims may experience a burning sensation, paralysis, a quick death, or no ill effect whatsoever, depending on the stinging creature and what species the recipient is. All cnidarians are carnivorous predators!
- Cnidarians lack organs and have no respiratory or circulatory systems! They do have sensory systems, however, and different species have various abilities of mechanoreception (response to touch or pressure), chemoreception (response to chemical stimuli such as taste and smell), and photoreception (response to changes in light) for aid in hunting or self-defense.
- Many cnidarians have two body forms during their life cycle: a smaller, polyp stage and a larger, medusa stage. You may have heard the term "polyp" in discussion of corals and "medusa" in discussion of jellyfish! In reality, some species such as corals only have a polyp stage while other groups such as jellyfish have both polyp and medusa stages.
On left: coral polyps. On right: medusa stage of a jellyfish
First photo: coral polyps (photo by zoosnow, Licensed Use via Pixabay) compared with second photo: the medusa stage of a jellyfish (photo by Icewall42, Licensed Use via Pixabay)
Phylum Ctenophora, which includes comb jellies and sea walnuts
- This group was once lumped in with Phylum Cnidaria, though they're now recognized as belonging to their own unique phylum.
- They are mostly planktonic, which means most are unable to swim against a current.
- Most are colorless, though most are bioluminescent too.
- They are highly valued in studies on evolution and nervous systems!
- They move around with cilia, or short finger-like structures--the cilia are grouped into "combs," giving comb jellies their name. When they wave these structures to push against surrounding water and move, their cilia diffract light, causing the colors of the rainbow to ripple along their combs.
- All ctenophores are carnivorous and feed on other tiny organisms, including the larvae (smallest stage) of clams and snails!
- Ctenophores, like many plankton, are a food source for many organisms including other ctenophores, cnidarians, fish, whales, and sea turtles.
Below: a comb jelly
Wikimedia Commons: Bruno C. Vellutini, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0
Phylum Porifera, the sponges
- We've probably all seen a sponge at some point in our life--at least synthetic ones! Did you know that sponges, before they were made in factories, were the real live thing taken straight from the ocean?
- "Porifera" means pore-bearing, and refers to the holes in sponges' bodies.
- Sponges are considered one of the simplest animals to exist, since they have no pores or tissues.
- Sponges gain nourishment by filtering particles from the water around them. They are the reason that some ocean environments have clear water!
Many sponges will look like:
Wikimedia: green encrusting sponge by Kirt L. Onthank, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0; red branching sponge by Alexander Vasenin, CC BY-SA 3.0; pink tubular sponge by Nick Hobgood, CC BY-SA 3.0
In the future, I plan to dive into these phyla and some of the narrower groups within them, such as their classes and orders, in greater detail. Keep an eye out for articles on these in the coming months!
Don't recognize some scientific terms such as phylum, class, order, and taxon? Check out my previous article, "The Main Classifications of Life: Taxonomy, Systematics, and Phylogeny," at https://theuwwc.wixsite.com/discover/post/the-main-classifications-of-life-taxonomy-systematics-phylogeny to learn what they mean and why they're important for biology!
Sources:
http://www.mesa.edu.au/phyla/ This link also had links to Marine Education Society of Australia webpages that explain these phyla!
The above link has subpages to all of the phyla I've discussed in this blog post and more!
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