Reproduction

Freshwater Bryozoa are hermaphroditic

So are most marine species.

Some brood their eggs in "Ovicells"

Some bryozoa exhibit polyembryony—divisions of an embryo into multiple embryos that each become clones—a way to establish a new colony quicky (and exponentially).

Polyembryony is also found in hymenopteran wasps.

Some bryozoa produce larvae called CYPHONAUTES

This larva gives rise to an Ancestrula zooid—the first to form a colony.

Colonies may live from 1 to at least 12 years.

Some freshwater forms overwinter as stolons and the colony regenerates the following year.

Others produce statoblasts that are produced asexually in a gelatinous mass and recolonize the following year—Cristatella mucedo is a good example of a species that does this. You can find these in Faylor Lake not far from here.

They are similar to gemmules of freshwater sponges and have a similar function.

A chitinous covering is used-two valves. Up to 1 million statoblasts from 1 colony

SHOW OVERHEAD FROM 1004 RUPPERT AND BARNES

Explain diagram

Another lophophorate are the phoronids. They comprise a meager 12-14 species or so all marine. The good thing about this-is it is easy to discuss their basic features since they aren’t nearly as variable as other groups.

1) Coelomate protostome but with radial cleavage, enterocoely, and indeterminate cell fate

2) Vermiform lophophorate

3) Sessile, marine filter-feeder

4) Epistome covers mouth

5) U-shaped gut with anus just outside lophophore

6) One pair of metanephridia

7) Secretes chitinous tube

8) Closed circulatory system

9) Dioecious or hermaphroditic

Phoronids look like long cylindrical sacs that are about 12 centimeters long. They burrow in mud or even burrow into coral before secreting their tubes.

They could easily be mistaken for a tube-dwelling polychaete except that the lophophore is distinctive.

1) They are coelomate protostomes which suggest that they are allied with the other protostomes-not the deuterostome lophophorates. But they have radial cleavage and enterocoely as well as indeterminate cell fate-three distinct deuterostome traits.

2) They have a wormlike shape with no real appendages other than the lophophore poking out of the top. The feeding structure can be retracted very quickly due to an associated giant nerve fiber. Sometimes they drop it from the rest of the body and regenerate a new one.

The lophophore is variable in shape. Usually it is small and standardly U-shaped-but the larger the phoronid, the more convoluted and coiled the lophophore becomes-this is because it serves a respiratory function as well as a feeding function.

3) The lophophore works like any other lophophorate-a feeding current is created to suck in small organic particles. They stay in their burrows permanently once they are made.

4) A flaplike structure covers the mouth-called an epistome. This is hollow because their is a vestige of a portion of the coelom within it.

5) The mouth leads into a U-shaped digestive system like other lophophorates and the anus terminates just outside of the lophophore.

6) Phoronids have one pair of metanephridia. They are ureotelic-so excrete urine instead of ammonia. Some evidence shows that crystalized waste matter is also secreted. Strangely, the larval forms have protonephridia that resemble larval excretory structures in protostomes like annelids.

7) All phoronids have chitinous tubes they live in. They do not ventilate the tube like many tubicolous polychaete worms do-but they have some adaptations to get around the low oxygen levels involved.

8) They have a closed circulatory system for efficient movement of blood and afferent and efferent vessels that move into and out of the lophophore as they do in the ctenidia of a mollusc. They have a thickened muscular artery that serves as a pumping heart. Many blood vessels are associated with the stomach suggesting that nutrients are picked up here and transported through the circulatory system.

The blood contains cell-bound hemoglobin. So they can carry oxygen as efficiently as we can or better since it has proportionately as much blood volume as we do

9) Phoronids are either diocious or hermaphroditic but asexual reproduction by budding was documented in at least one species. This may be more common given the regenerative abilities of these animals.

The hermaphroditic forms may be protandric or simultaneous.

Fertilization methods are diverse. Some fertilize internally, others broadcast spawn.

In either case, larvae or eggs are shed via the metanephridia-as is the case in Brachiopods too.

1) Coelomate, deuterostomes

2) Dorsal and ventral valves (shell) present

3) Attached to substratum by a stalk (pedicel)

4) Valves produced by mantle lobes, water filled mantle cavity

5) Lophophore circular to coiled

6) Gut U-shaped, may or may not be complete

7) One (sometimes 2) pair of metanephridia

8) Circulatory system open

9) Mostly dioecious sexually reproducing

10) Marine benthic solitary

Brachipods represent another group of lophophorates that are very well represented in the fossil record-particularly around Cincinnati.

There are only about 335 living species but there are at least 12,000 of them that have been identified from the fossil record-testifying to their past evolutionary success.

Brachiopods represent yet another case of remarkable convergence in evolution with the bivalve molluscs to which they are only distantly related. Thayer proposed with some evidence, that bivalves outcompeted and displaced brachiopods and at least were partly responsible for their decline.

1) Brachiopods are coelomate deuterostomes.

2) They have two valves like in bivalves except the orientation is different. Bivalves have to lateral shell halves, but brachiopods have a dorsal and ventral valve instead.

3) Unlike bivalves, brachiopods are usually attached to the substratum by a stalk. This is the pedicel and arises from between the shell halves.

It actually arises from the posterior of the ventral shell which is usually a bit larger than the dorsal one. For this reason, the ventral valve is sometimes called the pedicel valve, and the dorsal valve, the brachial valve.

There are two types of brachiopods, Articulate and Inarticulate. The inarticulate use poor grammar and syntax....

Actually these two groups that represent the two classes of brachiopods, are categorized based on how the two valves attach.

In the inarticulates, the valves are held together only by muscle.

In the articulates, the valves are held together through a pair of hinge teeth that fit into sockets on the dorsal valve.

These brachiopods have adductor muscles (close) and diductors to open the shell.

Most brachiopods are of the class Articulata.

The articulate and inarticulate brachiopods differ in other ways too.

The pedicel of inarticulate brachiopods has a portion of the coelom within it and some muscle layers.

The articulate brachiopod pedicel lacks a portion of the coelomic cavity and musculature.

4) The valves are produced by the mantle lobes-much like in molluscs.

The material of the shell differs between the articulates and inarticulates however.

inarticulates have a Chitinophosphate shell (Calcium phosphate and chitin)

Articulates have a calcite based shell

Like bivalves, brachiopods have an outer periostracum.

Brachiopods have chitinous setae lining the edges of the valves and when the lophophore cilia generate a current-the valves are held slightly open and the setae act as a coarse sieve to screen out large particles.

5) The lophophore is modified in brachiopods from the general U-shaped plan. It is coiled into a circle or has two coiled arms that project forward. These are called brachia-thus the name brachiopoda.

6) Through ciliary action and a water current, food-usually phytoplankton is swept into the mouth. The digestive tract is U-shaped.

Here too there is a difference between the articulate and inarticulate brachiopods. The inarticulates the intestine extends to the rectum and exits to the outside.

In the articulates, the intestines terminates as a blind sac-most digestion occurs in the digestive cecae.

7) There are one or two pairs of metanephridia. These also serve to discharge gametes into the water since gametes are stored in the coelomic cavity

8) The circulatory system is open but is usually reduced.

There is a blood vascular system with a pumping heart and coelomocytes present. The respiratory pigment is hemoerthryin.

9) The are four gonads that produce gametes that are usually stored in the coelom before being broadcast spawned. The larval are usually planktonic for a short period of time.-although direct development is known in some such as Lingula. In planktonic forms usually the lophophore can be used as a swimming organ until the animal grows to large and settles.

It is fairly clear that lophophorates are closely related to each other except for the entoprocts that are believed to exhibit convergent evolution of this feeding organ.

Lophophorates have clear affinities with the deuterostomes-the echinoderms and chordates. The phoronids, composed of only a few species, may provide a link between the protostomes and deuterostomes since they have embryological features of both.

Further studies of lophophorates may clear up where deuterostomes and protostomes branched off the metazoan tree.

There are other odd phyla with possible deuterostome affinities.

The chaetognaths are one of these phyla.

There are only about 100 species of these little animals.

Entoprocta

The other lophophorate the entoprocta, is very different from the other three. It shares few if any true synapomorphies with the rest.

The entoprocta and ectoprocta phyla are named based on the location of the anus. In the endoprocta, it lies inside the lophophore, but in the ectoprocta or bryozoa, it lies outside this feeding structure. It also lies exterior in the phoronids.-it is usually absent in many brachiopods.

The entoprocta have only about 150 species. They lack a coelom, have spiral cleavage, The anus position is different than in the other lophophorates and their gonads have ducts associated with them.

The direction of the current created by the lophophore is the opposite direction suggesting that the two groups bear no characteristics other than convergent body plans from both living in a box. The current starts at the bottom and moves up rather than the other way around.

1) Triploblastic, bilateral, unsegmented

2) Sessile and solitary or colonial with zooids borne on stalks

3) Visceral mass housed within a cup-shaped calyx, the ventral surface of which is directed away from the substratum

4) Zooid bears a ring of tentacles that encloses a mouth and anus

5) Gut complete and U-shaped

6) Area between gut and body wall filled with gelatinous mesenchyme-functionally acoelomate

7) One pair of protonephridia

8) No specialized circulatory or gas exchange structures

9) Mostly hermaphroditic

10) All are marine except Urnatella (freshwater)

1) Bilaterally symmetrical

2) Head, trunk, post-anal tail.

3) Deuterostome , enterocoelous

3) Fluid filled cavity-not lined with mesoderm

4) Straight simple through-gut

4) Four longitudinal muscle bands (no circular muscles)

5) No respiratory, circulatory, or excretory system

6) Pelagic marine predators

7) lateral and caudal fins present

8) Vibration sensors and chemoreceptors cover body. Eyes are five pairs of pigment-cup ocelli

9) Grasping spines, toxic venom

10) Hermaphroditic-no planktonic stage

Chaetognaths, or "setae jaws" represent only about 70 species of pelagic predators. "Arrow worms"

They are ubiquitous in the world's plankton however.

Between 4-14 large recurved spines

Eyes are located posterior-pigment-type eyes.

Have a hood that can be pulled down over the head.-

Reduce water resistance.

Small animals-2mm to 12 cm long.

I state the body cavity is not lined with mesoderm. It is embryonically enterocoelous, but the outer mesoderm becomes heavily muscularized, and the inner mesoderm becomes lost-leaving only myoeithelium from the endoderm. Thus it is embryonically a coelomate-but the adult body cavity is not quite one.

They also have a peritoneal lining (sac)

Alternately swim and float.

Fins aid in floating and directing motion forward.

Posterior adhesive papillae present to attach to surfaces among the few benthic forms.

Only longitudinal muscle

Carnivorous-feeding mostly on copepods which they detect through vibrations.

Sagitta, a common genus, feeds on other chaetognaths as well as small fish.

They eat 37% of their weight in prey daily.

Inject bacteria-derived tetrodotoxin (sodium ion channle blocker) that immobilizes prey.

(also found in the blue-ringed octopus)

Exact site of toxin production are not known--except that they are in the head region somewhere.

Digestive tract-

Pharynx joins a straight intestine and a pair of diverticuli.

Food is swished forward and back during digestion.

The nervous system is made up of six ganglia. One makes a ring around the gut--the cerebral ganglion.

Simultaneous hermaphrodites with spermatophore transfer.

They are deuterostomes-with a tripartite coelom--as is the case in echinoderms and lophophorates--suggesting some evolutionary affinity.

Coelom formation is different-to lobes of the coelom formed different.

Radial and indeterminant cells fate.

Why is their deterostome relations questioned?

1. no ciliated larval stage
2. no fossil record
3. only longitudinal muscles in bundles
4. molecular evidence allies them with nematodes
5. but no sinusoidal muscle contractions
6. no eutely
7. no cuticle like they have
8. no cryptobiotic tendencies
9. coelom is completely different

1) Bilaterally symmetrical deuterostome coelomates

2) Ciliated pharyngeal gill slits

3) Open circulatory system

4) Glomerulus excretory structures

5) Complete gut

6) Sometimes hollow nerve cord

7) Dioecious, but asexual reproduction common

8) Marine benthic

Hemichordates are a group of benthic dwelling deposit feeding or filter-feeding animals that are unremarkable in most regards. They are interesting to us primarily for one reason-they tell us something about the evolution of ourselves since most phylogenetic trees show this phyla as our closest relatives.

1) They are coelomate deuterostomes-although the coelom may form by enterocoely or schizocoely depending on the class. Cleavage is radial-at least initially.

2) They have pharyngeal gill slits that function in breathing. The gill slits have stiffening supports that are found between them. They may function in removing excess water from the food-and then took on an additional respiratory function second. The supports around the gills also bear blood vessels and are likely involved in gas exchange

3) The circulatory system is an open one but it has a contractile heart for pushing blood through it. The heart is located in the proboscis and has evaginations that increases surface area as blood passes through. There are podocytes along these evaginations that ultrafilter the blood to the protocoelom-the portion of the coelom lying in the probocis. Urine is formed and drained out of a pore.

This structure is called a glomerus and is a bizarrely unique means of excretion.

Thus the hemichordate heart is also a urine-forming kidney. Now if poets that write love poems could get a hold of that metaphor-wouldn’t that be interesting.

Most of the other facts that make up this phylum are uninteresting-but they have pharyngeal gill slits and a dorsal nerve cord that is sometimes hollow. These are two traits that are shared with the phylum to which we belong.

Hemichordates have a stiff structure in the collar called a proboscis skeleton that they use to anchor the heart and muscles in the proboscis. This was thought to be a notochord at one time and hemichordates were considered chordates for this reason. Since they have only half the characteristics of chordates-they are called hemichordates.

PHYLUM CHORDATA

Another, perhaps more familiar phylum-the chordates.

We represent members of , by far, the largest sub-phylum among the chordates.

But there are two other sub-phyla among the chordates-

The urochordates and cephalochordates

The urochordates are the sea squirts, salps and some other groups comprising about 3,000 species

The cephalochordates are the lancelets (20 species) that you are probably well familiar with from freshman biology.

1) Coelomate deuterostomes

2) Usually bilaterally symmetrical

3) Notochord

4) Dorsal hollow nerve cord

5) Pharyngeal gill slits

6) Post-anal tail

8) Through-gut

9) Closed or open circulatory system, heart surrounded by pericardial sac

10) Dioecious, hermaphroditic, or asexual reproduction

11) Terrestrial, freshwater, or marine

I’d like to show a few cladograms of all the phyla we have covered-and some that we haven’t- as a sort of summary for the course.

I have shown cladograms for various groups. The business of figuring out who is related to whom is no easy task.

The one good thing about evolution-is there is an evolutionary tree-and only one true tree.

Figuring out which one is the right tree is another problem altogether.

An entire discipline of phylogenetic systematics is charged with this goal-of discovering the one true tree.

Those who make trees-are almost religious in their furvor for methods for generating trees-or as they like to say-reconstructing phyletic relationships

The methods used to determine trees can be complex and usually involve heuristic tools or algorithms.

Regardless of the method used, all tree-building has one thing in common-

The first step is to generate characters for a tree.

Characters may be behaviors, morphology-from living or fossilized animals, they may be biochemical-the conformation of hemoglobin subunits, enzymes, or genetic- the sequence of particular nucleotide sequences within ribosomal RNA, mitochondrial DNA or other genetic material. Even ecological characters have been used -albeit not very successfully.

These characters are then compared across different taxonomic groups.

I am under the opinion that no single type of data is better than any other. In fact the different sources from which these characters are generated allow for a test of one hypothetical tree against another.

Of course, the characters are supposed to be independent from each other- criteria that is seldom fulfilled-no matter what characters you choose to use. With an exoskeleton comes a loss of oxygen through diffusion across the body wall-they are different.

Nucleotide sequences are not independent of each other. Recombination is non-random. Transitions and translations do not occur with equal freqency etc.

Thus there are many arguments made at the level of choosing appropriate characters-but at the same time you don’t want to pick characters that will a priori favor one tree over another and bias your data.

These characters are then subjected to different rules for generating a tree.

One of these rules that we’ve talked about and has been the method used for all the trees I’ve shown-is parsimony.

That is assign characters that allows for the least number of cases of convergence or independent evolutionary events of a character.

There are many other rules that may be used instead-particularly with molecular data.

The important point is that no matter what rule is used- it is a hypothesis about how evolution is occurring.

Molecular data is used for many trees recently.

For phylum level analyses, this is usually 18S ribosomal RNA because there are regions of this nucleotide sequence that are highly conserved through evolutionary time. Many molecular data sets look for differences in nucleotide sequences between taxa (often based on a single individual) and treat each nucleotide as a character.

Some rules for example are differential weighting of transversions and transititions of nucleotides along a sequence.

This is a hypothesis about how evolution is occurring along that gene sequence.

Therefore, the tree is only as good as the hypothesis. Falsifying the method, necessarily falsifies the tree-which is why cladists are at each other’s throats so often.

Lets look at some examples-

Here is a basic tree based on morphological characters and using parsimony as a rule.

Lets compare it to others-

Well, we are about out of time for this course.

It is my hope that one of the things you’ve gotten out of this class is a shifted perspective on the diversity of life on this planet.

Our bias for vertebrates is abundant in what we see. I hope I’ve provided an escape from that tunnel vision.

You hear of the diversity of animals around us-but I think you’ve all peeled back a couple layers of this diversity and seen just how bizarrely fascinating animals can be.

I hope that when you hear locomotion-you no longer think only about moving on two or four legs.

I hope that when you hear respiratory system-you don’t just think of lungs

Excretion-think of a hemichordate heart or an urn of a sipunculan.

Or when you think of feeding-you don’t assume a mouth is necessary-or even a digestive system.

And for reproduction-don’t think that animals necessarily require a mate to reproduce.

Out of all the major classes and phyla that we have covered in class,

28 out of 66 classes reproduce by sexual means exclusively.

1 is exclusively asexual

Out of those that reproduce sexually (38), 17 are exclusively dioecious. 9 are exclusively hermaphroditic.

Translation: what is normal for vertebrates, isn’t the norm for all animals.

I know after I took invertebrate zoology-I found alien creatures from science fiction movies to be decidedly uncreative and homogenous compared to what lies between the pages of an invert. textbook.

I hope you liked the class as much as I did

good luck on your exams