Topic
3—Chordate Taxonomy and Origin
Acorn
worm—common name for members of the Phylum Hemichordata, referring to their
acorn-shaped anterior region.
Amphioxus—informal common name for lancelets in the Subphylum Cephalochordata.
The name was formerly used for the genus to which these animals belong,
but was the genus was changed to
Branchiostoma based on the taxonomic Law of Priority; however the previous
name has stuck around as a common name.
Ascidacea—class
within the Subphylum Urochordata which includes the most common tunicates, also
called sea squirts.
Bilateral
symmetry—a type of symmetry in which a single plane (the sagittal plane) can be
used to divide an animal into mirror-image left and right sides.
Bilateral animals also have an anterior and posterior end, and a dorsal
and ventral surface.
Bilateria—clade of animals within Kingdom Animalia which includes all animals
with bilateral symmetry. This group
includes all animals except sponges, cnidarians, placozoans, and ctenophores.
Cephalochordata—subphylum of Phylum Chordata that includes lancelets.
Chordata—phylum
which includes animals with a notochord, pharyngeal slits, a post-anal tail,
dorsal hollow nerve cord, and an endostyle or thyroid.
The phylum is divided into three subphylums, Cephalochordata, Urochodata,
and Vertebrata.
Coelomate—any
animal which has a coelom, a body cavity which contains and allows movement of
internal organs, especially the digestive tract.
Deuterostome—any
of a clade of animals (Deuterostomia) within the Bilataria which have a pattern
of embryological development in which the first opening in the blastula becomes
the anus, and the second opening becomes the mouth.
This group includes chordates, echinoderms, and hemichordates.
Dipleurula—hypothetical
larva-like common ancestor of all deuterostomes.
Echinodermata—phylum
of bilateral animals which includes sea stars, brittle stars, sea cucumbers, and
their relatives. It is related to
chordates.
Endostyle—a
longitudinal ciliated groove on the ventral wall of the pharynx which produces
mucus to gather food particles. It
is found in urochordates, cephalochordates, and some vertebrate larvae, and is
homologous to the thyroid gland in more derived vertebrates.
Hemichordata—phylum
of animals which includes acorn worms.
They are considered close relatives of chordates because they have
pharyngeal slits and a dorsal nerve cord somewhat similar to chordates, but lack
a notochord and a post-anal tail.
They are filter feeders who live in the sediments of marine habitats.
Myomere—one
of the segmented muscle blocks found in the vertebrate body.
It is the adult version of the embryonic myotome.
Nerve cord—a
large nerve which runs the length of the dorsal side of the body of members of
Phylum Chordata. The cord is
hollow, and in vertebrates, the anterior end everts during embryological
development to become the brain.
Notochord—a
cartilaginous rod which runs the length of the dorsal side of the body of
members of Phylum Chordata. The
notochord is used for attachment of muscles which allow chordates to use their
post-anal tail for swimming.
Paedomorphosis—the retention of larval characteristics in sexually mature
animals.
Pharyngeal
slits—openings found in the pharynx of members of Phylum Chordata.
The openings allow filter-feeding in some members of the group, and are
used as gill slits in some more derived members.
Pikaia gracilens—extinct fossil
member of Subphylum Cephalochordata.
P. gracilens is one of the
earliest known chordates. It was
discovered in the Burgess Shale of Canada.
Post-anal
tail—a muscular tail that extends past the anal opening, found in members of
Phylum Chordata. This tail makes
chordates strong swimmers compared to most invertebrates.
Protochordate—an
informal, paraphyletic grouping which includes hemichordates, urochordates, and
cephalochordates.
Protostome—any
of a clade of animals (Protostomia) within the Bilateria which have a pattern of
embryological development in which the first opening in the blastula becomes the
mouth. This group includes the
arthropods, molluscs, nematodes, annelids, tardigrades, and many other
invertebrates.
Sea
squirt—common name for tunicates in the Class Ascidacea
Thyroid
gland—an endocrine gland found in most adult vertebrates which is a major
control gland for metabolism. It is
homologous to the endostyle.
Tunic—the
tough outer body covering of adult tunicates.
Tunicate—an
animal which is a member of Subphylum Urochordata.
Tunicates are bottom-dwelling, filter feeding organisms found in marine
habitats. They develop from tadpole
larvae which have all the characteristics of chordates, but undergo a
metamorphosis into adults which are sessile filter-feeders which pump water
through a mucus-covered basket to obtain organic material.
Urochordata—subphylum
of Phylum Chordata that includes tunicates.
Vertebrata—subphylum of Phylum Chordata that includes all animals with a bony or
cartilaginous endoskeleton.
Sometimes referred to as Craniata.