Animals you never knew about

kw: book reviews, nonfiction, animals

Bestiaries of the past combined natural history, legend, speculation and moral instruction. Based on better science, and including rich commentary instead of crude moralizing, Caspar Henderson has produced The Book of Barely Imagined Beings: A 21st Century Bestiary.

He goes through the alphabet, sometimes in a surprising way, including two "X" chapters. I am endlessly fascinated by natural history, but I'll keep this shorter by just touching on three special animals, and where his riffs upon them take us.

Barrel Sponges include the Giant Barrel Sponge, Xestospongia muta, which can live more than 2,000 years. Sponges were apparently the first animals to reach sizes larger than a few aggregated cells. They are most sophisticated than they look. There are apparently several (perhaps six) kinds of cells with semi-specialized functions, but no tissues as we would consider them. A small sponge can be forced through a sieve and thoroughly disaggregated to loose cells. It will re-form itself as it originally was.

Henderson discusses the concepts of multicellularity at some length, including some ways it goes wrong, as was seen with the Elephant Man, Joseph Merrick, who suffered the continuous growth of portions of his body. It is still quite mysterious how an animal body, whether sponge or starfish or surfer, keeps its parts proportional. From there the riff goes on to the development of life, once the Bacteria and Archaea split, and creatures that we call Eukaryotes, composed of large, nucleated cells were split off from the Archaea (or descended from one of them by engulfing some bacteria and keeping them as "pets" that are now termed mitochondria and chloroplasts). Every visible creature is a Eukaryote, but they (we) are outnumbered (trillions-to-one) and even greatly outweighed by non-Eukaryotes.

Nautilus, a genus of cephalopod (an order that includes octopus, squid, cuttlefish and others). They and their kind, the Ammonites, were the primary predators in the pre-Dinosaur-age oceans. Today, these are rare and getting more rare. Cephalopods have two kinds of appendages, arms and tentacles. A nautilus has 90 slender arms, without suckers on them. An octopus also has only arms, eight of them, but the arms are well equipped with suckers along their entire length. Squids, cuttlefish and some others have both arms and tentacles. The two tentacles are longer than the arms and have a pad at the end with suckers on it, and only there.

I show this image a little bigger than the others to make the eye more visible. Other cephalopods have eyes with lenses, but this eye has a small pupil with no lens. It is like a "pinhole camera", and it makes a very blurry image. That seems to be enough, along with the animal's tactile and chemical senses, to track down its prey and avoid predators.

Venus Girdle (see video below of Cestum veneris) is a surprisingly lovely type of salp. Salps and other "comb jellies" look kind of like jellyfish, but are in a different phylum, the Ctenophora (ten-o-fore-uh); jellyfish, corals and sea anemones are in the phylum Cnidaria. The "comb" of a comb jelly refers to the rows of cilia that it uses for locomotion. Ctenophores are the largest animals to move about primarily using cilia.

Taking off more from the name Venus (goddess of "love", that is, lust), than from the animal itself, Henderson spends a page or so on sex, and the indications that nearly all animals seem to enjoy it. (I would except those females of species in which the male's "member" actually pierces or spears the female's body to deposit its load somewhere inside!). Comb jellies reproduce very fast, so perhaps the Venus association is actually rather apropos. Where their predators are eliminated, they can rapidly take over an ecosystem and turn a large chunk of ocean into a teeming mass of gooey critters.

One other animal has a rather sideways association with sex in its name, Gonodactylus, the Mantis Shrimp. The scientific name arose when the naturalist who described it thought the paired forelimbs, when held at the ready, looked a lot like a pair of testicles, so the name means "gonad hand". However, those "hands" can move faster than any part of any other animal, when the mantis shrimp clobbers its prey, or even causes cavitation (a kind of shock wave) in the water to stun nearby prey. But I was much taken by the description of their eyes. Humans and most primates have three-color vision. The millions of colors we can see are a mix of the sensations caused by light received by three kinds of cells. Mantis shrimp have around ten different color sensitive cells. In the very brightly-colored and visually confusing environment of a coral reef, they can more clearly distinguish color differences that help them pick out what they need to see.

A book like this is great fun to read, and it is equally great fun to learn of the myriads (millions!) of different animals with which we share this planet.