Lecture 9: The Deuterostomes Flashcards

Comprehensive practice questions covering the evolution, development, and classification of Deuterostomes, including Chaetognatha, Echinodermata, Hemichordata, and Chordata.

What are the four primary developmental features that unite the Deuterostomia?

Radial cleavage, regulative (indeterminate) embryo, blastopore becomes anus, and coelom forms by outpocketing (enterocoelous).

What type of embryo is characterized by the ability of an excised blastomere to develop into a normal larva?

Regulative embryo.

In deuterostome development, what does the blastopore eventually form?

The anus.

How is the coelom produced in deuterostomes?

By enterocoely (outpocketing of the gut).

Which major feature is shared by Hemichordates, Urochordates, and other deuterostomes for feeding or respiration?

Pharyngeal gill slits.

What are the four major deuterostome groups mentioned in the lecture?

Chaetognatha, Ambulacraria (Echinodermata and Hemichordata), and Chordata.

What is the common name for members of the Phylum Chaetognatha?

Arrow worms.

What does the name 'Chaetognatha' translate to?

Bristle mouth.

Despite being enterocoelous, what atypical feature do Chaetognaths show in their development?

Spiral cleavage.

What specialized feeding structures are found on the heads of Chaetognaths?

Grasping spines.

Describe the reproductive strategy of Chaetognaths.

They are hermaphroditic and will self-fertilize.

What systems are notably absent in Phylum Chaetognatha?

Respiratory and excretory systems.

According to molecular dating, approximately when did protostomes and deuterostomes diverge?

In the Ediacaran approx. $600\,Mya$.

When did stem ambulacrarians and chordates first appear in the fossil record?

In the Cambrian period.

What does the name 'Echinodermata' translate to in Greek?

ekhinos (hedgehog) + derma (skin).

What is the endoskeleton of an echinoderm composed of?

Hardened ossicles (stereom).

What system do echinoderms use for locomotion, feeding, and respiration?

Water-vascular system.

What are the specialized structures used by echinoderms for gripping and locomotion?

Tube feet.

What type of symmetry is characteristic of adult echinoderms?

Pentaradial symmetry.

Why is it stated that echinoderms 'secondarily lost' gill slits?

Because only primitive forms retain them, while they are absent in modern adults.

Which group of echinoderms is characterized by attachment to a substratum by the aboral surface?

Pelmatozoa (e.g., Crinoidea).

Which echinoderm group includes members that move with their oral surface against the substratum?

Eleutherozoa.

What are the five major classes of Echinodermata?

Crinoidea, Asteroidea, Ophiuroidea, Echinoidea, and Holothuroidea.

What is the common name for members of Class Crinoidea?

Sea lilies and feather stars.

In Crinoidea, what structures on the arms are used for filter-feeding?

Pinnules.

What are 'encrinites'?

Limestone made of >50\% crinoid remains.

Where is the ambulacral groove located in Crinoids, and what is its function?

On the arms; it transports food to the mouth.

What does the class name 'Asteroidea' mean?

aster (star) + eidos (form or likeness).

Approximately how many species belong to Class Asteroidea?

$1,500$ species.

What is the minimum number of arms found in Asteroidea?

$5$ arms.

On which surface of a sea star is the madreporite located?

The aboral surface.

What is the specific function of the madreporite?

It serves as a sieve/opening for the water-vascular system.

Trace the flow of water through a sea star's water-vascular system starting from the madreporite.

Madreporite -> stone canal -> ring canal -> lateral canals -> tube feet.

What are 'pedicellariae' in sea stars?

Tiny muscular clamps on the surface.

How do sea stars consume prey like bivalves?

They use tube feet to pry open the prey and evert their cardiac stomach to digest it.

Who identified Pisaster ochraceus as a keystone species?

Robert Paine.

Define a 'keystone species'.

A species with a large effect on its environment relative to its abundance.

What does the class name 'Ophiuroidea' mean?

ophis (snake) + oura (tail).

What are the common names for members of Class Ophiuroidea?

Brittlestars and basketstars.

How does respiration occur in Ophiuroidea?

Via gills.

What is unique about the tube feet of Ophiuroids compared to Asteroids?

They lack suckers.

Where is the site of digestion in Ophiuroids?

The central disk (the cecum does not enter the arms).

Which echinoderm class is characterized by having a strongly reduced coelom?

Ophiuroidea.

What are the common names for members of Class Echinoidea?

Sea urchins and sand dollars.

What is the rigid structure formed by fused dermal ossicles in echinoids called?

A test.

What features do echinoids use for locomotion and defense instead of arms?

Moveable spines.

What is the complex mouth structure of a sea urchin called?

Aristotle's lantern.

In which country are the gonads of echinoids considered a major delicacy?

Japan.

What is the scientific name for the purple urchin?

Arbacia punctulata.

What is the scientific name for the sand dollar mentioned in the notes?

Clypeaster reticulatus.

What are the common names for Class Holothuroidea?

Sea cucumbers.

How do the dermal ossicles of Holothuroidea differ from those of Echinoidea?

They are reduced in holothuroids.

Where do the oral tentacles of a sea cucumber originate?

They surround the mouth.

What structure fans out from the cloaca in sea cucumbers for respiration?

The respiratory tree.

What is 'evisceration' in sea cucumbers?

The expelling of innards as a defense mechanism.

Which sea cucumber species can reach lengths of over $2$ feet?

Thelenota ananas.

Where does the pearlfish live in relation to sea cucumbers?

Inside the anus of the sea cucumber.

What is the common name for Scotoplanes?

Sea pig.

Which deep-sea holothuroid lives at depths of almost $5,000\,ft$?

Pelagothuria natatrix.

What is the common name for Phylum Hemichordata?

Acorn worms.

What are the three main body regions of a hemichordate?

Proboscis, collar, and trunk.

What chordate-like feature do hemichordates possess that was lost in adult echinoderms?

Gill slits.

What is the function of the glomerulus in hemichordates?

It is part of the axial complex located near the heart and proboscis coelom.

What phylum includes 'everything with backbones (and a few without)'?

Chordata.

Name the five primary synapomorphies of Phylum Chordata.

Notochord, dorsal hollow nerve cord, pharyngeal slits, endostyle (or thyroid), and postanal tail.

What is the notochord?

A rigid structure containing fluids in a fibrous sheet, located below the central nervous system (CNS).

How is the dorsal hollow nerve cord formed during development?

It forms from the ectoderm by folding inwards and is separated from the epidermis by neural crest cells.

What is the function of the endostyle in lower chordates?

It secretes mucus.

What structure does the endostyle become in more derived chordates?

The thyroid gland.

In humans, at what developmental stage is a postanal tail visible?

In the embryo at $5$ weeks.

What is Pikia gracilens?

The earliest undisputed fossil chordate (dating to approx. $500\,Mya$).

What unusual feature did Pikia gracilens possess alongside a notochord?

A cuticle.

Why are fossils of early chordates from the Precambrian scarce?

Because early chordates were soft-bodied.

Which two subphyla are considered 'basal' or invertebrate chordates?

Cephalochordata and Urochordata.

Which subphylum retains all five chordate synapomorphies throughout its life?

Cephalochordata.

In Cephalochordates, how far does the notochord extend?

To the tip of the head.

What structure in cephalochordates creates a ciliary current for filter feeding?

The wheel organ.

What are the segmented muscles found in cephalochordates called?

Myomeres.

What major organ is missing from the cephalochordate circulatory system despite being vertebrate-like?

A heart.

What does the subphylum name 'Urochordata' mean?

uro (tail) + chord (notochord).

What are the common names for Subphylum Urochordata?

Sea squirts or salps.

What happens to the chordate features in most Urochordates as they transition to adulthood?

Adults lose almost all chordate features that are present in the larvae.

What are the three major groups within Subphylum Urochordata?

Ascideacea, Thaliacea, and Appendicularia.

How do Ascideaceans (sea squirts) typically live?

They are marine and mostly sessile; they can be solitary or colonial.

Describe the movement and structure of Thaliaceans (salps).

They are colonial, form long chains of clones, and move by jet propulsion (pumping water through their bodies).

What is unique about the adult form of Appendicularia (larvaceans)?

They remain tadpole-like as adults.

What do larvaceans build to assist in feeding?

Houses made of cellulose.

What is the 'test' or 'tunic' in Urochordates?

The external covering of the body.

Which echinoderm class includes sand dollars?

Echinoidea.

What is the common name for the long-spined urchin?

Diadema setosum.

In which echinoderm class are there arms broadly connected to a central disc?

Asteroidea.

What is the buccal diverticulum in hemichordates?

A structure in the collar region, formerly thought to be a notochord.

What are the two major divisions of Hemichordata shown in the phylogeny?

Enteropneusta and Pterobranchia.

Which group of organisms is described as a 'pilgrimage through the major branches of the metazoan family tree'?

The Deuterostomes.

What is the function of the 'stolon' in Ascideacean morphology?

It is a base structure used for attachment or colonial growth.

What is the function of the 'atrium' in a sea squirt?

It is the chamber that collects water from the pharyngeal slits before it exits the excurrent siphon.

Which group of chordates lacks gills, kidneys, liver, AND a brain?

Cephalochordata.

What is the term for the endoskeletal plates with a porous, sponge-like structure in echinoderms?

Stereom structure.

Which echinoderm class has an elongated oral-aboral axis and oral tentacles?

Holothuroidea.

According to the transcript, which clade is the sister group to Chordata?

Ambulacraria (containing Echinodermata and Hemichordata).