Chapter 12

_______ are the elementary units of life

Cells

Nature’s experiments with larger organisms without cellular differentiation are __________

limited

Large, single celled marine algae are _________

rare

What problems does increasing the size of a cell cause?

Exchanging molecules with the environment.

What does multicellularity prevent?

Surface-to-mass problems as smaller units greatly increase surface area for metabolic activities and makes them highly adaptive toward larger body size

What does it mean for a cell to be “multicellular”?

It is to specialize cell function and limit sexual reproduction among cells

Sponges are the simplest multicellular animals but their cell assemblages are distinct from other metazoans. How?

Sponges have cells embedded in an extracellular matrix supported by a skeleton with needle-like spicules and protein

Sponges neither look like nor behave as animals, so what demonstrates that they are phylogenetically groups with animals?

Molecular evidence demonstrates that they are phylogenetically grouped with animals

Eukaryotic cells evolved and diversified into many lineages that led to modern day descendants that includes who?

All unicellular eukaryotes, colonial and multicellular plants, animals, and fungi

Multicellular organisms were collectively called metazoans. What are they called now?

Animals

Where are metazoans placed? (What clade?)

The Opisthokont clade which include fungi, choanoflagellates, and other groups

What are choanoflagellates?

Solitary or colonial aquatic eukaryotes

Each choanoflagellate cell has a flagellum surrounded by a collar of what?

Microvilli. The flagellum beats and draws water into collar where the microvilli collects particles like bacteria

Most Choanoflagellates are _______ but one species attaches to floating diatom colonies and feed midwater

sessile

Choanoflagellates strongly resemble sponge feeding cells called _________

Choanocytes

Choanoflagellates and _________ may share a common ancestor

Choanocytes

What is the evidence of common ancestry between choanoflagellates and Metazoans?

The proteins used by colonial choanoflagellates for cell communication and adhesion are homologous to those that metazoans use in cell-to-cell signaling

What is the evidence against the claim that choanocytes and metazoans share a common ancestry?

Choanocytes are not part of the developmental pathway of sponges; they appear only in adult sponges and the collar cells appear in a few other animal taxa; if this trait is ancestral then it has been lost in most taxa

What is an approach that has been taken to the problem of animal origins, especially in sponges?

Comparing sponge genomes to those of other animals. Shared features would have been inherited from an ancestor of animals

Sponges today have simple bodies, and there would be expected to have simple genetic structure. Why is this not true?

Because sponge genome contains elements that code for regulatory pathways of more complex metazoans, they have proteins that code for spatial patterning that specify anterior and posterior pole of larvae, and therefore modern sponges may be less morphologically complex than their ancestors

What other phylum also exhibits puzzling features in terms of their animal origins?

Phylum Placozoa

Phylum Porifera are ________

sponges

Is Phylum Porifera (Sponges) sessile or mobile?

Sessile

What are sponges bodies designed for? (Phylum Porifera)

Efficient aquatic filter-feeding

What does Porifera mean? How does that relate to what Porifera is?

“pore-bearing”; sponges are sac-like bodies that are perforated by many pores

What do sponges use flagellated “collar cells”, or choanocytes, for? (Phylum Porifera)

To move water to bring food and oxygen while removing wastes

Where are sponges found? (Phylum Porifera)

Most of 8600 sponges are marine, found in all seas and all depths, while few live in brackish water and 150 live in fresh water

Growth Habits and Forms of Sponges

How big can sponges be? (Phylum Porifera)

They vary in size from a few millimeters to over 2 meters in diamete

Why are many species in Phylum Porifera brightly colors?

Because of pigments in dermal cells

Embryos are __________ while adults are always ____________. (Phylum Porifera)

Free-swimming, attached

What are some growth forms that sponges can have? (Phylum Porifera)

Some appear radially symmetrical but many are irregular in shape, some stand erect, some are branched, and others are encrusting.

What do growth patterns of sponges depend on? (Phylum Porifera)

The shape of the substratum, the direction of water, speed of flow, and availability of space

How do animals benefit from sponges? (Phylum Porifera)

Many animals such as crabs, nudibranchs, fish, and other species live as commensals or parasites in or on sponges. Sponges can grow on a variety of other living organisms with some crabs using sponges for camouflage and protections.

How does certain sponge extracts have manifested medical and pharmaceutical effectiveness? (Phylum Porifera)

Sponges and microorganisms living on animals often have a noxious odor and produce a variety of bioactive compound

What is the skeletal structure of a sponge like? (Phylum Porifera)

It can fibrous and/or rigid consisting of calcareous or siliceous spicules

Where does the fibrous portion come from in the skeletal structure of sponges? (Phylum Porifera)

Comes from collagen protein fibrils in intercellular matrix. There are several types of collagen, which vary in chemical composition; sponges contain spongin

What is the basis of the skeletal structure of sponges? (Phylum Porifera)

The composition and shape of spicules. Modern materials science view spicules for possible nanoparticle products

The ________ exterior of sponges often mask their chemical and function ___________. (Phylum Porifera)

Simplistic, sophistication

Spicule Forms

Sponges date to early ___________, maybe even Pre-__________. (Phylum Porifera)

Cambrian

How are sponges traditionally grouped? What are the three classes that they are grouped in? (Phylum Porifera)

Based on spicules and chemical composition. The three groups are Calcispongiae, Hexactinellida, Demospongiae.

Calcispongiae

Sponge with calcium carbonate spicules with one, three, or four rays

Hexactinellida

Glass sponges with six-rayed siliceous spicules

Demospongiae

Sponges with siliceous spicules around an axial filament, spongin fibers, or both

Class _____________ are identified as sponges without a skeleton, or with siliceous spicules without an axial filament (Phylum Porifera)

Homoscleromorpha

Cladogram of Poriferans

How do sponges feed? (Phylum Porifera)

By collecting suspended particles from the water pumped through internal canal systems.

Sponges has many small incurrent pores called what? Where are they located? (Phylum Porifera)

Dermal ostia, pinacoderm (outer layer of cells)

Explain the canal system in which sponges feed from (Phylum Porifera)

Water is directed past the choanocytes, which are flagellated collar cells that keep the current flowing via the beating of flagella. Microvilli in the collar trap and phagocytize food particles that pass by.

What is the efficiency of food capture of sponges dependent on? (Phylum Porifera)

Water movement through out the sponge body

Sponges non-selectively consume food particles such as what? (Phylum Porifera)

Detritus, plankton, and bacteria

What kind of particles are taken into the choanocytes by phagocytosis when sponges eat them? (Phylum Porifera)

The smallest particles (80%)

What kind of particles are taken into the choanocytes by pinocytosis when sponges eat them? (Phylum Porifera)

Protein molecules

What other cell types facilitate feeding in sponges? (Phylum Porifera)

Pinacocytes and archaeocytes

What else can be absorbed by sponges to feed on? (Phylum Porifera)

Dissolved nutrients

Spongy Body Structures

What is the simplest body organization for sponges? (Phylum Porifera)

Asconoid Sponge Body

Asconoid Sponge Body

Small and tube-shaped to allow water to flow directly across cells so no “dead space”

Where are choanocytes located in the Asconoid Sponge Body? What do they do?

In a large internal chamber called the spongocoel. Choanocyte flagella pull water through the pores and extract food particles and the used water is expelled through a large single osculum

What class are all asconoids in?

Calcispongiae. For example, Leucosolenia sp. and Clathrina sp.

Asconoid Sponge Example - Clathrina canariensis (class Calcarea) a common Asconoid on Caribbean reefs

What sponge body resembles asconoids, but larger with a thicker, more complex body wall?

Syconoid Sponge Body. The body wall is folded outwards with choanocyte-lined radial canals that empty into spongocoel

How do sponges with the Syconoid Sponge Body feed?

Water enters through dermal ostia and move through tiny openings (prosopyles) into the radial canals and the food is ingested by choanocytes and used water is pumped through internal pores called apopyles than outwards via osculum

What kind of cell is the spongocoel lined with in the Syconoid Sponge Body rather than choanocytes as in asconoids?

Epithelial cells

There is developmental evidence of syconoids being derived from ________ ancestors. What is this evidence?

Asconoid; Syconoids pass through an asconoid stage in development but do not form highly branched colonies and then flagellated canals form by evagination of the body

Which classes in Phylum Porifera have syconoid species?

Classes Calcispongiae and Hexactinellida

Syconoid Body Wall

What is the most complex and largest sponge body, with more food-collecting regions?

Leuconoid Sponge Body

How do sponges with the leuconoid sponge body feed?

These regions have choanocytes lining in small chambers that effectively filter all water present. Clusters of flagellated chambers are filled from incurrent canals and discharge to excurrent canals, leading to osculum. After the food is removed, used water is pooled to form an exit stream that leaves through an exit pore at very high velocity (the high rate of exit flow prevents the sponge from re-filtering used water and wastes)

What body type does most sponges have?

The Leuconoid Sponge Bodyzde

Why does the leuconoid sponge body have a highly adaptive value?

To efficiently meet high food demands of larger body size

What are some qualities that leuconoids have to meet high food demands of larger body size?

• Highest proportion of flagellated surface per volume of cell tissue

• More collar cells can filter more particles

• Water flow slows inside due to greater surface area in the chambers

  • Large sponges filter 1500 liters of water per day for maximum food collection

The leuconoid system has ______________ many times in sponges

evolved independently

Leuconoid Sponge Example - Orange demosponge, Mycale leavis, that often grows beneath plate-like colonies of the stony coral Montastrea annularis

What is the gelatinous extracellular matrix in which sponge cells are arranged in called?

The mesohyl or mesenchyme

Where is the connective “tissue” of sponges found?

In fibrils, skeletal elements, and amoeboid cells

What does the absence of organs require in sponges?

That all fundamental processes occur at the individual cell level. Such as respiration and excretion happening via diffusion and water regulation happening via contractile vacuoles in the archaeocytes and choanocytes.

What are some visible activities seen in sponges?

• Slight alterations in shape, local contraction, and propagating contractions

  Closing and opening of incurrent and excurrent pores

Sponges can close their osculum due to heavy sediment load in the water. Why is this puzzling and how do the sponges do it?

The movements occur very slowly but they suggest a whole-body response in organisms lacking complex organization above the cellular level (sponges). Apparently, the excitation spreads from cell to cell by mechanical stimuli and signaling molecules such as hormones or via electrical impulses which causes the closing of the osculum

Type of Sponge Cells

Choanocytes are ovoid cells. What does that mean?

They are egg shaped

One end of a choanocyte of a sponge is embedded in _________ and the exposed end has __________ surrounded by a collar

Mesohyl, flagellum

What does the collar of a choanocyte of a sponge consist of?

Microvilli connected to each other by fine microfibrils which forms a fine filtering device to strain food

What happens to particles that are too large to enter the collar of the choanocytes in sponges?

They are trapped in mucous and slide down to base to be phagocytized

In choanocytes, the food is passed to archaeocytes for ____________ digestion with no need for _____________

intracellular, gut cavity

Food trapping by sponge cells. (A) Cutaway section of canals showing direction of water flow. (B) Two choanocytes, and (C) Structure of the collar

What are archaeocytes?

Amoeboid cells with many functions that move about in the mesohyl

What are some functions of Archaeocytes?

They phagocytize particles in the pinaderm and receive particles for digestion from choanocytes. They can differentiate into many other mores specialized cell types

What are some more specialized cell types that archaeocytes differentiate into?

Sclerocytes, Spongocytes, Collencytes, and Lophocytes

Sclerocytes (Archeaocytes)

Secrete spicules

Spongocytes (Archaeocytes)

Secrete sponging

Collencytes (Archaeocytes)

Secrete fibrillar collagen

Lophocytes (Archaeocytes)

Secrete large amounts of collagen

What are pinacocytes and what are their functions?

They are thin, flat, and epithelial-like cells that:

• Cover the exterior and interior surfaces of sponges almost like real tissue

• Form pinacoderm with a variety of intercellular junctions but no basal membrane in most sponges

• Ingest food by phagocytosis and are contractile to regulate surface area of sponge

• Form myocytes, circular bands around oscula, that help regulate flow of water

Do sponges have a great ability to regenerate lost parts of repair injuries?

Yes, they do.

Complete reorganization of the structure and function of participating cells or bits of tissue, such as when a sponge is cut up into fragments and it creates a new sponges from the fragments, occurs in _______

somatic embryogensis

The process of reorganization _________ in sponges of different complexity

differs

Regeneration following fragmentation is one means of ___________

asexual reproduction

Asexual reproduction: Fragmentation

Sponge breaks into parts that are capable of forming a completely new sponge