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Aplacophora is a class of small wormlike marine animals. For a long time they were a mystery to marine biologists: up until 1987 they were classified as sea cucumbers (which are echinoderms). However the shell-free Aplacophorans are not echinoderms at all, no more than penguins are insects. Aplacophorans are tubular and lack shells, but they are actually mollusks—like clams, belemnites, octoposes, and gastropods.
Aplacophorans are divided into two subclasses: (1) the Solenogasters, which are typically carnivores which feed on feeding on corals and worms; and (2) the caudofoveates which tend to be detritovores feeding on leftover bits rolling around the ocean floor (although some caudofoveates eat foraminiferans (which are large unicellular organisms).
All of this talk of small mollusks which look like little worms…or maybe like little echinoderms…or even possibly like little early chordates (which were basically little tubes) sounds unpromising, but some of the Aplacophorans have a subtle beauty. Additionally they throw a light upon a bygone time when the mollusks, cnidarians, sponges, worms, and proto-vertebrates really weren’t all that different. They help illustrate the common bonds of kinship which tie all of the animals together, no matter what airs some of us put on.
A large single tunicate (blue) with a colony of smaller tunicates (saffron)
It’s time to talk tunicates! Many people blithely dismiss tunicates as primitive sack-like marine invertebrates which derive sustenance from filter-feeding. Although that is technically true, it is a very reductive and dismissive way to think about this ancient, ancient subphylum of animals. Tunicates are chordates…barely, but they are also classified as invertebrates. Because they mostly consist of delicate tissue sacks filled with fluids, the fossil record of tunicates is understandably exiguous, but it is believed they existed in Ediacaran times (circa 550 million years ago) and were part of the mysterious soft Ediacaran biota which blossomed into the Cambrian era’s suffusion of life forms. Tunicates probably closely resemble the basal organisms from which Pikaia and all other vertebrates (lynxes, caecilians, hummingbirds, triggerfish, humans, ichthyosaurs, turkeys, moeritheriums, and suchlike animals) sprang. Of course tunicates also resemble hydrozoans, mollusks, worms, and even arthropods—so they may be very basal indeed!
A free-swimming larval tunicate (microphoto by Wim van Egmond of Rotterdam)
All–or very nearly all–tunicates are hermaphrodites with both male and female reproductive organs (a single ovary and a lone testis). Not only do tunicates keep their romantic options open, they also metamorphose into different forms throughout their lives. The majority of tunicates have a free-swimming larval stage when they are motile (and have a little sliver of nerve chord). As they reach sexual maturity, their nerve chords disintegrate and they settle down to become sessile—attaching to a permanent base. Some tunicates live their entire lives as solitary individuals whereas others form colonies (like corals or siphonophores).
Not only do they have multiple genders they have multiple methods of reproduction
Colonial tunicates integrate at different levels depending on the species. In some, the zooids (the individual living organisms) merely live next to each other like coral or Brooklynites, whereas other tunicate colonies grow entwined and share common organs and anatomical structures. There are many different tunicates going by many different lifestyles and they have all sorts of crazy names. Wikipedia poetically avers that “…various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips.”
Komodo National Park sea squirt (Polycarpa aurata) by nick Hobgood
As you could guess from these names, tunicates have an otherworldly beauty. Here is one which looks like a diseased zombie heart! Others look like transparent alien shrimp, fluorescent pens, or strangely hieroglyphed eyes. There are bioluminescent tunicates of the deep ocean, and pelagic tunicates that form long chains (with a single digestive tract running through the individual zooids). They live in coastal waters, pelagic waters, and in the depths.
Colonial tunicate with multiple openings in each zooid
Most of these zoology articles end with a sad coda about how the subject organism is threatened in the modern world–no so for tunicates! As humans overfish the oceans and drive countless teleosts to the edge of extinction, so-called primitive species like jellyfish and tunicates are flourishing! Acidification, climate change, and pollution seem to be resetting the great worldsea back to Neoproterzoic times. Additionally tunicates easily travel the world in ballast water and numerous species are becoming invasive pests (like the evocatively named carpet tunicate). In this troubled era, there is raw power in being a primitive protean organism with only a wisp of a nervous system (as we should have known just by looking at successful late-night comedians). Get used to the tunicate–not just an incredibly distant ancestor, but the once and future (and always) avatar of animal life in the oceans.
Chain of fluorescent tunicates. (photo by Francis Abbott/Nature Picture Library)
Grey Dun Icelandic Horse (Paula Jantunen)
Because of humankind’s long close association with horses, horse coloration has a very specific and complex vocabulary (as any fan of wild west literature could attest). One of the most interesting horse colors is grullo a dun color characterized by gray body hair. Grullo gray can be either tan gray or mouse colored.
A grullo horse
Grullo horses have bodies which are lighter in hue than their tails and manes. They also often have primitive markings such as stripes, spots, and stipples. Some grullo horses even have striped legs as though they were zebras or quaggas.
Cave painting of a grullo wild horse from Lascaux, France (ca 15,000-10,000 BC)
Grullo is of interest as an ancestral coloration of wild horses. The tarpan (Equus ferus ferus), an extinct subspecies of wild horse from Eurasia was believed to have grullo coloring. The last tarpan died in captivity in Russia in 1909, but mad attempts to recreate it through selective breeding have resulted in the primitive looking Heck horse (a breed of horse which tend to be grullo). Additionally many small harry northern horses like Norwegian Fjord horses and Welsh ponies tend to be grullo. Look at how cute they are!
A Heck Horse
Magnolias at the Brooklyn Botanic Garden
Spring has come early this year and the beautiful tulip-like petals of New York City’s magnolia trees are already beginning to fall into great drifts of white and pink. If you stop and pick up one of the pretty petals from such a pile you will be surprised by the leathery resilience of the delicate-looking petals. The durability of the petals of magnolia flowers is not coincidental—the flowers are different from other common flowering trees because Magnoliidae trees were among the first flowering trees to evolve. The earliest known fossils of such flowers date from the upper Cretaceous period around 130 million years ago. Magnoliidae petals are tough because they were originally meant to attract the attention of beetles rather than bees (which do not appear in the fossil record until 100 million years ago). Since there were no insects specially adapted to live as pollinators when magnolia-like trees first appeared, the petals and reproductive structures of these first flowering trees had to be robust to survive attention from the hungry clumsy beetles (toughness which has passed on to the modern ornamental trees).
Beetles on a Magnolia flower by Beatriz Moisset http://pollinators.blogspot.com/2011/06/magnolias-and-beetle-pollination.html
Paeleobotanists have not yet unraveled the entire history of the evolution of flowering plants (indeed, Charles Darwin called the abrupt appearance of flowers in the fossil record “the abominable mystery”) however magnolia-like trees appeared long before the great radiation of angiosperms which occurred approximately 100 million years ago. The first magnoliid trees must have seemed tremendously strange–explosions of color and shape surrounded by great uniformly green forests of gymnosperm trees (like the familiar conifers). Magnolia blossoms betray evidence of their ancient lineage through several “primitive” features: the petals are nearly indistinguishable from the sepals; each flower has many stamens which are arranged in spiral rows; there are multiple pistils; and all of the stamens and pistils are supported by a “fingerlike receptacle.”
By attracting the attention of animals (either through the colorful appearance and appealing scent of flowers, or by the edible nectar and fruit) flowering plants were better able to reproduce themselves. Magnolias spread around the temperate world and began the complicated interdependent relationship which all sorts of animals (including humans) have with flowering plants.
ferrebeekeeper 