MBE 230-Chapter 16: Deuterostomes

Types of Deuterostomes:

- Chaetognaths

- Hemichordates

Acorn worms
Pterobranchs

- Tunicates

Thaliaceans
Ascidians
Larvaceans

- Cephalochordates -- Lancelets

Chaetognaths (120 species) (arrow worms):

- They have both protostome and deuterostome characteristics

- They are a pelagic rigid worm (some are benthic)

- They have lateral fins and tail, they are streamlined

- They have a flexible body for quick darting

- They have 4-14 large spines on their head that can grab zooplankton and then they will inject toxins

- They have 2 compound eyes and can detect vibrations

- They are hermaphroditic, have internal fertilization, and have direct development

- Some are bioluminescent

- They are cosmopolitan

Acorn worms (120 species) - Enteropneusts:

- They are worms that live in burrows

- They are mostly deposit feeders (ingest particles associated with sediments or, in many cases, they ingest the sediment particles themselves and strip off nutrition in the form of detritus associated with the sediment grains and also associated microbes)

- Some filter feed with their gills

- They get oxygen with their pharyngeal gills

- They have no eyes and have a few sense organs

- They have planktonic larvae that looks like starfish larvae

Pterobranchs (30 species):

- They are worms living in tubes

- They are mostly colonial

- They have large ciliated tentacles that are extended into water

- They are filter feeders

- They have planktonic larvae

- They can bud new individuals asexually

- Mostly in deep waters

Ascidians - Sea squirts (2,300 species):

- They are benthic filter feeders and have incurrent and excurrent holes

- They are gelatinous with tunic, single, clumped, or colonial

- There are colonies of up to several meters, and there is partial fusion of individuals

- They have a circulatory system with excurrent hole

- They have a ciliated network with mucus in their pharynx

- They have a weak sensory system

- They are hermaphrodites

- They have planktonic larvae that looks like tadpoles

- They can conduct asexual budding in colonies

- Mostly in shallow waters on hard substrates

Thaliaceans:

- They are pelagic gelatinous "barrels"

- They have cilia and mucus on pharyngeal net in the barrel

- They have open and close valves at each end of the barrel

- There are circular muscles around the barrel

- They pump water through for propulsion and filter feeding

- They are mostly in the open ocean

- They have a simple nerve net

- Many are bioluminescent

- They have a complex lifecycle with asexual and sexual forms

- Some have larvae that resemble tadpoles

Larvaceans - Appendicularia:

- They are tadpole shaped

- They have a large mucus house

- They are pelagic filter feeders

- Their tail generates a current for propulsion and feeding

- Their mucus house filters the food

- The house becomes discarded when clogged with particles (every 4 hours)

- They are found in coastal and oceanic waters

Cephalochordates (30 species) - Lancelet:

- They are a rigid "worm"

- They burrow in the sand

- They have cartilage and segmented muscles

- They have pharyngeal gills

- They are filter feeders

- Simple eyes

- At least half of their body is buried in the sand and only the top part of their body with the tentacles pokes out.

- Found in shallow temperate and tropical seas