Ch. 7 Hemichordata

Chapter 7
Phylum Hemichordata
Phylum Chordata
Phylum Hemichordata
• Characteristics:
– Rare group, but these worms seem to span a gap
between invertebrates and more advanced
chordate animals
– Acorn worms share some features with chordates
including pharnyngeal gill slits and a nerve cord
that is similar to the chordate notochord
– Acorn worms are deposit or suspension feeders
and use proboscis for feeding
– Acorn worms have larvae that resemble those seen
in echinoderms
– 90 known species
Phylum Cordata
(the inverts)
• Subphylum Urochordata - tunicates
• Subphylum Cephalochordata – lancelets
• Chordates have several common features that
are seen at least during some portion of the life.
Lancelets are the only chordates that possess all
the common features as adults.
Phylum Chordata
• Characteristics:
– Notochord – flexible support rod between
nerve cord and gut
– Tubular nerve cord
– Muscular pharynx (gut)
– Gill slits
– Post-Anal Tail
– Ventral heart
– Note: no backbone. In vertebrates, notochord
is surrounded or replaced by the vertebral
Invertebrate Chordates
Tunicates – Subphylum Urochordata,
Class Ascidiacea
• Characteristics:
– Commonly called “sea squirts” because most filter feed via an
incurrent siphon and “squirt” water out an excurrent siphon
after the water has been filtered (Exception: Predatory tunicate)
– Larvae has chordate characteristics that are not seen in adultsonly pharynx remains
– Called tunicates because of thick outer covering called a tunic
– Larvae are free swimming after fertilization occurs in open
water- mass reproduction - see Fig. 7.51
– Adults normally live attached to boats, docks, reefs, or other
hard substrate
– All 3000 known species are marine
Figure 7.51 A. Clavelina picta, colonial ascidian. B. tadpole larva of
ascidians exhibits all the distinguishing characteristics of chordates.
Figure 7.52 A. Cliona intestinalis, shallow water sea squirt. B. Adult tunicate
Phylum Chordata
Subphylum Cephalochordata, the Lancelets
• Characteristics:
– 23 species
– Very small, only up to 3 inches long
– Live in shallow marine waters as filter feeders
– Body shows segmented muscle tissue
– Notochord attached to the muscles
– Gills are used to filter food, not in respiration
– Only invert chordate to possess all chordate
features as an adult
Phylum Chordata
Subphylum Cephalochordata, the Lancelets
Phylogenetic relationships of animal phyla
Characteristics of Major Animal