Ectoprocts, common known as bryozoans or “moss animals”, are aquatic lophotrochozoans that usually live in colonies made up of many tiny cloned zooids. The exoskeletons they build for their colonies have a range of forms, including gelatinous blobs, chitinous branches, and calcified sheets and coral-like fronds.
They’re part of a sub-group of lophotrochozoans called lophophorates, closely related to brachiopods and horseshoe worms, and are characterized by having a ring or U-shaped “crown” of filter-feeding tentacles around their mouths.
Mineralized bryozoans have an extensive fossil record going back to the early Ordovician, about 481 million years ago, but they’re surprisingly absent from the Cambrian – with one possible exception.
Continue reading “Cambrian Explosion Month #27: Phylum Ectoprocta & Phylum Entoprocta”
Vetulicolians were a group of odd Cambrian animals known from between about 520 and 505 million years ago. The front half of their bodies were large and streamlined, with a prominent mouth, no eyes, and five pairs of openings that seem to have been gills, with some species having a rigid exoskeleton-like carapace. Their back half was slender, segmented, and flexible, and functioned as a tail for swimming, giving them an overall appearance like alien tadpoles.
Their evolutionary affinities have been problematic for a long time, but evidence of a notochord in some specimens suggest they were probably related to the chordates in some way. Sometimes they’re considered to represent their own phylum, but they might also be stem-chordates or stem-tunicates.
Continue reading “Cambrian Explosion Month #17: Phylum(?) Vetulicolia & Other Early Deuterostome Weirdos”
Vetulicolians were a group of small marine animals best described as “problematic”, known from the Early Cambrian (~518-507 mya) of China, Greenland, Canada, and Australia. They had bulbous but streamlined bodies with a mouth opening at the front, no eyes, a thick exoskeleton-like cuticle, and a segmented swimming tail. Most also had five pairs of openings which may have been gill slits.
The image above depicts Vetulicola rectangulata, a 7cm long (2.75″) vetulicolian with a fairly “typical” body plan for the group, and the more unusual 14cm long (5.5″) Skeemella clavula.
Their evolutionary affinities have been uncertain for a long time, and at different points they’ve been classified as arthropods, chordates, kinorhynchs, basal deuterostomes, or even given their own unique phylum. A genus named in 2014, Nesonektris, has been interpreted as having a possible notochord – making vetulicolians chordates, and potentially placing them close to the tunicates – but their exact relationships are still unresolved.
(Skeemella also complicates matters, having some features considered more arthropod-like than other vetulicolians. But since it’s only known from a single specimen, more fossil material is needed to figure out what’s going on with it.)