SEA ANEMONES: MARINE PREDATORS

Sea Anenome on Coral Reef

Sea anemones are a group of predatory marine animals in the order Actiniaria. They are named after the anemone, a terrestrial flowering plant because of the colourful appearance of so many of these lovelies.

Sea anemones are in the phylum Cnidaria, class Anthozoa, subclass Hexacorallia. As cnidarians, sea anemones are related to corals, jellyfish, tube-dwelling anemones, and Hydra.

Unlike jellyfish, sea anemones do not have a medusa stage in their life cycle. A typical sea anemone is a single polyp attached to a hard surface by its base, but some species live in soft sediment and a few float near the surface of the water. The polyp has a columnar trunk topped by an oral disc with a ring of tentacles and a central mouth.

The tentacles can be retracted inside the body cavity or expanded to catch passing prey. They are armed with cnidocytes (stinging cells). In many species, additional nourishment comes from a symbiotic relationship with single-celled dinoflagellates, zooxanthellae or with green algae, zoochlorellae, that live within the cells. Some species of sea anemone live in association with hermit crabs, small fish or other animals to their mutual benefit.

SEXUAL DIMORPHISM

Despite the differences between these two ammonites, both represent the same species, Macroscaphites yvani. The difference you see here is caused by sexual dimorphism. The larger of these is the female macroconch and the smaller specimen is the male of the species. These beauties are in the collection of the deeply awesome José Juárez Ruiz.

NOTOCHORDS AND SPINAL COLUMNS

Having a backbone or spinal column is what sets apart you, me and almost 70,000 species on this big blue planet.

So which lucky ducks evolved one? Well, ducks for one. Warm-blooded birds and mammals cheerfully claim those bragging rights. They're joined by our cold-blooded, ectothermic friends, the fish, amphibians and reptiles. All these diverse lovelies share this characteristic.

And whether they now live at sea or on land, all of these lineages evolved from a marine organism somewhere down the line, then went on to develop a notochord and spinal column. Notochords are flexible rods that run down the length of chordates and vertebrates. They are handy adaptations for muscle attachment, helping with signalling and coordinating the development of the embryonic stage. The cells from the notochord play a key role in the development of the central nervous system and the formation of motor neurons and sensory cells. Alas, we often take our evolution for granted.

Let's take a moment to appreciate just how marvellous this evolutionary gift is and what it allows us to do. Your backbone gives your body structure, holds up that heavy skull of yours and connects your tasty brain to your body and organs. Eating, walking, fishing, hunting, your morning yoga class, are all made possible because of this adaptation. Pick pretty near anything you love to do and it is only possible because of your blessed spine. And it sets us apart from our invertebrate friends.

Arturia nautiloid, Olympic Peninsula

While seventy thousand may seem like a large number, it represents less than three to five percent of all described animal species. The rest is made up of the whopping 97%'ers, our dear invertebrates who include the arthropods (insects, arachnids, crustaceans, and myriapods), mollusks (our dear chitons, snails, bivalves, squid, and octopus), annelids (the often misunderstood earthworms and leeches), and cnidarians (our beautiful hydras, jellyfish, sea anemones, and corals).

You'll notice that many of our invertebrate friends occur as tasty snacks. Having a backbone provides a supreme advantage to your placement in the food chain. Not always, as you may include fish and game on your menu. But generally, having a backbone means you're more likely to be holding the menu versus being listed as an appetizer. So, enjoy your Sunday 'downward dog' and thank your backbone for the magical gift it is.

AUSTRALOPITHECUS AFRICANUS

Two views of a natural endocranial cast articulated with a fragmentary skull of Australopithecus africanus, an early hominid living between 2-3 million years ago in the late Pliocene and into the early Pleistocene -- and the first pre-human to be discovered. They shared many characteristics with their older relatives the Australopithecus afarensis including a more gracile body. The casts you see here show the left maxilla, the orbital area and most of the skull base.

Australopithecus africanus had a larger brain and more humanoid facial features than their older ancestors with an average endocranial volume of 485 cm3 (29.6 cu in). This specimen is TM 1511 and lives in the Ditsong National Museum of Natural History, an amalgamation of eight museums, seven in Tshwane and one in Johannesburg. These museums have diverse collections covering the fields of fauna and flora, palaeontology, military history, cultural history, geology, anthropology and archaeology. The museum is enjoyed by children, youth, adults, students, tourists (foreign and local), researchers and the public in general. The museum is in Pretoria, South Africa which straddles the Apies River and has spread eastwards into the foothills of the Magaliesberg mountains.

Prior to a closer look by researchers, the skull was incorrectly believed to be a separate species, Plesianthropus transvaalensis. It was first discovered in South Africa by G. W. Barlow and described by Robert Broom in 1938. Photo credit: José Braga and Didier Descouens.