scalidophora – Nix Illustration

Cambrian Explosion #36: Phylum Loricifera

Even more obscure and poorly-understood than the mud dragons, loriciferans weren’t even discovered until the 1970s. Over 40 living species of these tiny meiofaunal animals are currently known, but much like the kinorhynchs there are probably many more still to be described.

Less than 1mm long (0.04″), their most distinctive feature is the “lorica”, a stiff corset-like casing surrounding their body. They’re also the first multicellular organisms discovered able to live completely without oxygen in a deep basin in the Mediterranean Sea.

Cambrian Explosion #35: Phylum Kinorhyncha

After the slightly unfortunately-shaped priapulids, let’s move on to something much safer-for-work: dragons!

More accurately, kinorhynchs, tiny spiky scalidophoran worms with the delightful common name of “mud dragons“. These animals weren’t even discovered until the mid-1800s and are so small – less than 1mm (0.04”) in size – that they’re considered to be “meiofauna“, wriggling around between grains of sediment using the spines on their heads to pull themselves along.

Cambrian Explosion #34: Phylum Priapulida

Named for their resemblance to human penises, priapulids (or “penis worms”) are marine scalidophoran worms that live on or in muddy seafloor sediment, with some species having a surprisingly high tolerance for oxygen-poor environments and toxic levels of hydrogen sulfide. Despite being a rather low-diversity phylum with only around 20 living species, they’re widespread and sometimes very numerous, with over 80 adult individuals per square meter (~10ft²) recorded in some locations.

The earliest definite modern-style priapulid in the fossil record comes from the late Carboniferous (~308 million years ago), but their ancestry was probably somewhere in the early Cambrian among the taxonomic mess of palaeoscoloecids and archaeopriapulids.

Cambrian Explosion #33: Early Scalidophora

The earliest branches of the ecdysozoan evolutionary tree are made up of the scalidophorans – animals with spiny retractable proboscises, represented today by the worm-like priapulids and kinorhynchs, and (sometimes*) the weird little loriciferans.