Chapter 7Chapter 7

Phylum HemichordataPhylum Hemichordata

Phylum ChordataPhylum Chordata

Phylum HemichordataPhylum Hemichordata• Characteristics:Characteristics:

– Rare group, but these worms seem to span a Rare group, but these worms seem to span a gap between invertebrates and more gap between invertebrates and more advanced chordate animalsadvanced chordate animals

– Acorn worms share some features with Acorn worms share some features with chordates including pharnyngeal gill slits chordates including pharnyngeal gill slits and a nerve cord that is similar to the and a nerve cord that is similar to the chordate notochordchordate notochord

– Acorn worms are deposit or suspension Acorn worms are deposit or suspension feeders and use proboscis for feedingfeeders and use proboscis for feeding

– Acorn worms have larvae that resemble Acorn worms have larvae that resemble those seen in echinodermsthose seen in echinoderms

– 90 known species90 known species

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Phylum CordataPhylum Cordata(the inverts)(the inverts)

• Subphylum Urochordata - tunicates Subphylum Urochordata - tunicates

• Subphylum Cephalochordata – lanceletsSubphylum Cephalochordata – lancelets

• Chordates have several common features Chordates have several common features that are seen at least during some portion that are seen at least during some portion of the life.of the life.

• Lancelets are the only chordates that Lancelets are the only chordates that possess all the common features as possess all the common features as adults.adults.

Phylum ChordataPhylum Chordata• Characteristics:Characteristics:

– Notochord – flexible support rod between nerve Notochord – flexible support rod between nerve cord and gutcord and gut

– Tubular nerve cordTubular nerve cord– Muscular pharynx (gut)Muscular pharynx (gut)– Gill slitsGill slits– Post-Anal Tail Post-Anal Tail – Ventral heartVentral heart– Note: no backbone. In vertebrates, notochord is Note: no backbone. In vertebrates, notochord is

surrounded or replaced by the vertebral column.surrounded or replaced by the vertebral column.

Invertebrate ChordatesInvertebrate ChordatesTunicates – Subphylum Urochordata, Tunicates – Subphylum Urochordata,

Class AscidiaceaClass Ascidiacea• Characteristics:Characteristics:

– Commonly called Commonly called ““sea squirtssea squirts”” because most filter feed because most filter feed via an incurrent siphon and via an incurrent siphon and ““squirtsquirt”” water out an water out an excurrent siphon after the water has been filtered excurrent siphon after the water has been filtered (Exception: (Exception: Predatory tunicate))

– Larvae has chordate characteristics that are not seen in Larvae has chordate characteristics that are not seen in adults- only pharynx remains adults- only pharynx remains

– Called tunicates because of thick outer covering called a Called tunicates because of thick outer covering called a tunictunic

– Larvae are free swimming after fertilization occurs in Larvae are free swimming after fertilization occurs in open water- mass reproduction - see Fig. 7.51open water- mass reproduction - see Fig. 7.51

– Adults normally live attached to boats, docks, reefs, or Adults normally live attached to boats, docks, reefs, or other hard substrate other hard substrate

– All 3000 known species are marineAll 3000 known species are marine

TunicatesTunicates

• AA

Figure 7.51 A. Clavelina picta, colonial ascidian. B. tadpole larva of ascidians exhibits all the distinguishing characteristics

of chordates.

A B

Figure 7.52 A. Cliona intestinalis, shallow water sea squirt. B. Adult tunicate

A B

Phylum ChordataPhylum ChordataSubphylum Cephalochordata, the Subphylum Cephalochordata, the

LanceletsLancelets• Characteristics:Characteristics:

– 23 species23 species– Very small, only up to 3 inches longVery small, only up to 3 inches long– Live in shallow marine waters as filter Live in shallow marine waters as filter

feedersfeeders– Body shows segmented muscle tissueBody shows segmented muscle tissue– Notochord attached to the musclesNotochord attached to the muscles– Gills are used to filter food, not in Gills are used to filter food, not in

respirationrespiration– Only invert chordate to possess all Only invert chordate to possess all

chordate features as an adultchordate features as an adult

Phylum ChordataPhylum ChordataSubphylum Cephalochordata, the Subphylum Cephalochordata, the

LanceletsLancelets

Phylogenetic relationships of animal Phylogenetic relationships of animal phylaphyla

Characteristics of Major Characteristics of Major Animal PhylaAnimal Phyla