In “an ant rant,” I asked readers how you could tell a boy ant from a girl ant. One person responded (I’m crying inside, btw), and he answered correctly. In a haplodiploid reproductive system, the sex-determining factor is the number of chromosome sets an individual has. Females have two sets of chromosomes and are therefore diploid. Males have only one, and so are therefore haploid. So, Roger Birkhead, this one goes out to you.
Today, we’re going to do a quick tour of five phyla of animals that receive way too little attention. Most of them are microscopic critters that are unloved either because A. go unnoticed B. lack a bilateral body plan. Let’s push through these prejudices.
|a typical Rotiferan (ucmp.berkeley.org)|
Rotifera: means “wheel bearer” in latin. Usually only a fraction of a millimeter, you need a microscope or a dissecting scope to get a good look at them. They live in freshwater and can either be sessile or travel by inching along a substrate. These guys look like they are wearing little crowns, called coronas, which are rings of cilia around the top of the head that help to filter food into the mouth. The coronas can be quite elaborate. They are capable of sensing light with their little eyespots, though incapable of forming images. They play an important part in freshwater ecosystems and are part of the beds of lakes and rivers.
|Velvet worm (brittanica.net)|
Onychophora: meaning “claw bearer” in latin. More commonly known as velvet worms. These soft-bodied curiosities live in tropical areas and look a lot like caterpillars, coming in a variety of eye-catching colors. They have tiny eyes and antenna, squirt slime at their prey to catch it, and give live birth. Their stubby feet are particularly interesting structures. There can be up to 40 jointless, hollow lobopods (lobed appendages) that terminate in two hardened claws that help the animal to travel treacherous surfaces. Weirdly enough, they are becoming popular in the pet trade.
|Jaw worm (zmuc.dk)|
Gnathostomulida: meaning “jaw mouth." More commonly known as jaw worms. They glide along the submerged sand grains in coastal areas. They are a little less than a millimeter long and are pretty much little threads with jaws at the end. They are extremely basic little animals. In fact, their most complex parts are their mouths, which resemble those of rotifers and therefore suggest that they are related phyla. Their digestive system ends in a “blind terminus”- meaning, they have no butt. Food simply enters and absorbs.
|A sea cucumber (wikicommons)|
Echinodermata: meaning “spiny skin.” This phylum includes sea stars, sand dollars, sea cucumbers, and sea urchins. Most follow a pentaradial body plan, meaning that they are arranged around 72° segments. Although sea cucumbers are heavily derived, they do follow a pentaradial body plan that is more easily seen in early stages of development when they are just little cucumberlets.
Rhombozoa: Known as “lozenge animals.” These are parasites that live inside of cephalopods (squid, octopi, cuttlefish, and nautiluses). They may grow to be several millimeters long and are surrounded by ciliated cells. So, they look like tentacle-covered threads that attach to the kidney cells of cephalopods, from which they receive all nourishment. Very strange.
That completes the tour of our 5 phyla. Roger, I am a little saddened that your name doesn’t contain a “p.” After all, the funniest of all the phyla starts with a “p.” So we’re going to do it as a bonus.
Priapulida: means “little penis.” I mean, just look at them.
Have a nice day!