Lecture 17: Protostomes 2

Question 1

What is the muscular foot and how is it used for movement? What is its difference in bivalves/cephalopods?

Answer 1

The muscular foot is a large muscle located at the base of an animal and is used in movement.
Snails and Chitons: have the muscular foot
- works as hydrostatic skeleton called muscular hydrostat
- waves of muscle contractions allow individuals to crawl around surface

In bivalves: the foot is modified as a diggind appendage
In cephalopods: the foot is modified to form tentacles for crawling and grasping

Question 2

What is visceral mass?

Answer 2

Visceral mass is a region containing main internal organs and external gill. It is also where all mollusks have organs and surrounding fluids.

(separate from muscular foot)
*separation from muscular food may have enabled greater diversification of both features across the phylum

Question 3

Visceral Mass separaters organs from hydrostatic skeleton

What is a coelom?

Answer 3

The coelom is the fluid-filled body cavity in an animal.
- highly reduced in most mollusks
- functioning mostly in reproduction and excretion of wastes

Question 4

What is the hemocoel?

Answer 4

The hemocoel is a body cavity that occupies the organs.
- Body fluids bathe organs directly in open circulatory system
- Different from coelom–not lined in mesoderm and has distinct developmental origin

Question 5

The Radula is Unique to Mollusks

What is the radula? How it it used to ingest food? When was it lost evolutionarily?

Answer 5

The radula is a feeding structure in the mouth that functions like a rasp or file. It is found at the anterior end of the visceral mass.

The radula is moved back and forth over food source causing many sharp plates to scrape material so it can be ingested.

It was probably lost in bivalves, which acquire food by suspension feeding.

Question 6

Mollusk anatomy: mantle

What is the mantle?

Answer 6

The mantle is an outgrowth of body wall that covers visceral mass, forming the mantle cavity.

• the mantle secretes a shell made of calcium carbonate
• some mollusk species have shells with various parts called valves

Many snails can retract into their shells when attacked or when tissues begin to dry out.
Also, in bivalves, protective shell is hinged and closes.

Question 7

What diverse functions does the mantle have other than secreting shells?

Answer 7

Terrestrial snails: mantle forms an internal lung
Bivalves: mantle is lined with muscle and forms tubes called siphons
Cephalopods: mantle forms siphon that functions in jet propulsion

Question 8

What makes arthropods the most important phylum within Ecdysozoa and when did it appear in the fossil record?

Answer 8

Arthropods are the most important phylum based on duration in fossil record, species diversity, and abundance of individuals.

They appear in the fossil record over 520 million years ago and are the most abundant animals observed in both aquatic and terrestrial environments.

Question 9

What are the four major lineages of arthropods?

Answer 9

1. Myriapoda (millipedes, centipedes)
2. Insects
3. Crustacea (shrimps, lobsters)
4. Chelicerata (spiders, scorpions)

• Insects and myriapods are considered sister groups due to shared morphological characteristics
• Recent studies also provide support for placement of insect clade within crustacean lineage

Question 10

What 3 key features define arthropods?

Answer 10

1. A segmented body - organized into tagma
2. An exoskeleton - made of chitin
3. Jointed appendages - joints between segments in the legs and other appendages enable rapid and precise movements

Question 11

What do studies of Hox genes and other tool-kit genes show?

Answer 11

Studies show that small changes in timing and location of gene expression can result in novel shapes and sizes.

Variation in gene expression combined with ecological opportunity through natural selection can result in the diversification of arthropod body segments and appendages.

Question 12

What were the first organisms to gain wings?

Answer 12

Insects were the first animals to achieve powered flight. This enabled them to escape predators and search for new food resources.

Evidence shows that wings evolved only once before adaptive radiation of insects on land.

Question 13

Did wings evolve from jointed limbs of arthropods?

Answer 13

Hell no they didnt!
-Wings occur as unjointed extensions of dorsal cuticle on second and third segments of insect thorax
Wings have been lost or modified many times

Question 14

What are the two distinct types of metamorphosis and what is it defined by?

Answer 14

1. Incomplete metamorphosis (hemimetabolous)
2. Complete metamorphosis (holometablolous)

defined by the presence or absence of larval stage

Question 15

What are the two distinct types of metamorphosis and what is it defined by?

Answer 15

1. Incomplete metamorphosis (hemimetabolous)
2. Complete metamorphosis (holometablolous) has larval stage

defined by the presence or absence of larval stage

Question 16

What is incomplete metamorphosis?
What is complete metamorphosis?

Answer 16

Incomplete metamorphosis:
-form of direct development
-juveniles called nymphs look like smaller versions of adult

Complete metamorphosis:
-form of indirect development –distinct larval stage
- when they have grown sufficiently, larvae stop feeding and secret a protective case, becoming a pupa
- during pupation, the pupa’s body is completely remodeled into a new, adult form

Mosquito larvae live in quiet bodies of fresh water and suspension feed on microbes. Adult mosquito flies and feeds.

Question 17

How much more common is complete metamorphosis than incomplete metamorphosis? Why?

Answer 17

Complete metamorphosis is 10 times more common than incomplete metamorphosis. Biologists hypothesize that this is because of feeding efficiency.
-if adults and juveniles feed on different materials, they do not compete with each other

Another hypothesis is the advantages of functional specialization:
-specializaion can lead to higher efficiency in feeding and reproduction and thus higher fitness

Question 18

What protostome group do flatworms belong to and what are they named for?

What is the hypothesis about the flattened body?

What do flatworms lack?

Answer 18

Flatworms are a lophotrochozoan named for their broad, flattned shape of their bodies.

The hypothesis is that the flattened body is an adaptation. The advantages of which include large surface area for gas exchange and that the flat body plan allows nutrients and gases to diffuse efficiently to cells with minimal expenditure in complex internal structures.

However, this requires flatworms to live in an aquatic or moist environment.

Flatworms lack a coelom and structures specialized for gas exchange and circulation of oxygen and nutrients.

All except Turbellaria are parasites
All except Cestodes (tapeworms) have blind digestive tracts

Question 19

What makes annelids different from flatworms?

Answer 19

Annelids are wormlike lophotrochozoans and are diverse.
Unlike flatworms, most annelids have a coelom: fully developed digestive tract with mouth, anus, and segmented body

Before molecular data, biologists grouped annelids and arthropods together due to their segmentation

Question 20

What are specius in phylum Nematoda called and what are they?

Answer 20

They are commonly called roundworms or nematodes.
They are unsegmented worms with a pseudocoelom:
- Tube-within-a-tube body plan
- No appendages
- Have elastic cuticle that is molted during growth