lab/lecture 14b: hemichordate

Question 1

Describe (Phylum) Hemichordata.

Answer 1

Marine deuterostomes; includes acorn worms (Enteropneusta), pterobranchs (Pterobranchia), and extinct graptolites (Graptolithina); share traits with echinoderms and chordates.

Question 2

Describe (Class) Enteropneusta.

Answer 2

~100 species of acorn worms; burrowing, deposit-feeding marine worms; simple body with proboscis, collar, trunk; gill slits present.

Question 3

Describe (Class) Pterobranchia.

Answer 3

small class of sessile, colonial, filter-feeding marine animals in the phylum Hemichordata. They live in branched tube structures called coenecia (similar to rhabdosome but flexible), secrete their own housing, and use ciliated arms with tentacles to catch food particles. Pterobranchs are the closest living relatives of extinct graptolites

Question 4

Describe (Class) Graptolithina (graptolites).

Answer 4

Extinct colonial hemichordates (Ordovician–Carboniferous); sessile (anchored to seafloor) or planktonic (free floating); organic-walled stick-like colonies; excellent biostratigraphic fossils. all graptolites live in rhabdosomes

Question 5

Describe (Order) Dendroidea

Answer 5

Mid-Cambrian–Carboniferous; bush-like colonies, attached to seafloor; three thecal types (autothecae, bithecae, stolothecae); sometimes developed floats. (class graptolithina)

Autothecae are the main thecae in the colony and house the feeding zooids. They are larger and more numerous than the other types.

Bithecae are smaller, secondary thecae thought to serve a protective or reproductive function. Their exact role is debated, but they often occur beside autothecae.

Stolothecae are tubular structures that run along the stipes, functioning like a conduit or stolon that connects the individual zooids. They help with the distribution of nutrients or zooid attachment.

Question 6

Describe (Order) Graptoloidea

Answer 6

Early Ordovician–Early Devonian; evolved from dendroids; planktonic, diverse shapes; single theca type; used for global stratigraphic correlation.

Question 7

Describe a graptolite rhabdosome.

Answer 7

Graptolites were colonial animals that lived in an interconnected system of tubes. From an initial ‘embryonic’, cone-like tube (the sicula), subsequent tubes (thecae) are arranged in branches (stipes) to make up the whole colony (rhabdosome).

Question 8

Describe uniserial vs. biserial graptoloids.

Answer 8

Uniserial: one row of thecae per stipe (e.g., Monograptus); biserial: two rows, stipes back-to-back (e.g., Diplograptus).

Question 9

How do dendroid and graptoloid lifestyles differ?

Answer 9

Dendroids: benthic, attached
graptoloids: planktonic, drifting or possibly controlling depth in the water column.