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Bauplan: Body Construction

I. UNICELLULAR – MOST PROTISTA:

II. MULTICELLULAR (METAZOA)

A. Without true tissues -

1.) Mesozoa: Phyla Orthonectida, Rhombozoa, Placozoa, Monoblastozoa

2.) Parazoa: Phylum Porifera

B. With true tissues Eumetazoa;

1.) Diploblastic eumetazoa (no true mesoderm): the „radiata‟,

2.) Triploblastic eumetazoa (has true mesoderm): the „bilateria‟

a) Acoelomates: no body cavity other than digestive tract; mesenchyme and muscle fill

region between gut and epidermis;

b) Blastocoelomates: have persistent blastocoel between gut and body wall;

c) Coelomates: have true coelom (mesodermal cavity);

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Body Construction

Each grade of body complexity is associated with inherent constraints and capabilities, &

within each grade there are limits to size.

WHY?

Must have exchange with environment (food, air, waste)

Small animals – exchange by diffusion, but only across small distances

More cells are needed in order to attain a larger size,

surface area : volume - surface area increases with the square of the radius, while volume

increases with the cube of the linear dimension

Imposes constraints on transport of materials into and out of cells.

HOW TO DEAL WITH THIS?

Non-living material such as „jelly‟ may be used to increase size – only a thin layer of cells in

contact with the environment.

Other adaptations include invaginations (sponges), geometrically constraining their volume

to two dimensions, growth in one dimension or

developing internal transport systems and organs (i.e. effectively bringing the environment

inside the organism)

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Body Construction

Eumetazoa: change in the process of embryonic development to allow more complex body

types to develop

The simplest system: two germ layers, the endo- and ectoderm, that ultimately result in adult

structures - called diploblastic. Include the Cnidaria and Ctenophora

The majority of animals are more complex:

adult structures develop from three germ layers, the endo-, ecto- and mesoderm – called

triploblastic.

Animals developing from triploblastic embryos have more building materials to start with: a

greater range of body constructions is therefore possible

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Body Construction of Triploblastic Animals

• Acoelomate: mesoderm forms a more or less solid mass of tissue, sometimes with lacunae,

between gut (endoderm) and body wall (ectoderm)

• Blastocoelomate: animals with small or large primary cavities formed during blastula stage

and persists as blood and/or tissue in adult

• Not lined by a peritonium

• Not formed from mesodermal tissue; organs lie free within body and are bathed in fluid;

originate from remnants of the embryonic blastocoel

• Coelomate: animals with a main (secondary) body cavity (coelom)

• Develops between the ecto- and endoderm;

• Enclosed within the peritonium (a thin layer of cells derived from the mesoderm); the gut is

suspended within the coelom

• Essentially a „tube-within-tube‟ construction. The inner tube is the gut and associated organs;

the outer tube is the body wall.

• Gut is attached to body wall only at mouth and anus, otherwise completely independent .

• Coelomic fluids act as mechanical buffer, storage chamber of various body products, medium

for circulation, and hydrostatic skeleton

protostomes and deutrostomes ....

pseudocoelomate

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Bauplan: Locomotion

• Ameboid movement: propelled by pseudopodia: governed by more liquid endoplasm

and a more viscous ectoplasm;

• ciliary and flagellar movement

• Cilia and flagella: beating of cilia/flagella: causes the animal to move with respect to the

surrounding water or water to move past attached animal.

• They also create feeding and gas exchange currents, line digestive tracts for food

movement, propel gametes and larvae;

• Also form sensory structures:

• Cilia: simple oar-like action,

• Flagella: back-and forth, rotary or undulating actions - effectively push or pull the cells or

animals along

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Locomotion

•Hydrostatic propulsion, locomotor limb movement need interaction between muscles and a

support structure - hydrostatic skeletons, structural endo or exoskeleton.

• Skeletons also function as attachment sites for muscles, and transmit the force of

muscles to perform work

• e.g. joint which acts as a lever; fluid-filled cavities - pressure extends relaxed muscles

• Disadvantages of the hydrostatic skeleton:

• lack well-developed defense mechanisms;

• risk of water loss: need watery or moist environments;

• restrictions on maximum size that can be reached on land (less water)

• Limited range of locomotion; gross changes in body shape may accompany locomotion

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Locomotion

• Internal skeleton derived from the mesoderm; external skeleton from the ectoderm

• Both have organic and inorganic constituents

• Exoskeletons: chitinous, calcareous (carbonates), may include phosphates, halides,

sulphates and iron oxides;

• Simple shell (gastropods, echinoderms), or more complex articulating types such as in

arthropods

• Endoskeletons: from simple microscopic spicules in porifera to very complex e.g.

vertebrates,

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BAUPLAN: Digestion

All heterotrophic animals, must locate, select, capture, ingest and digest food

Site of digestion: extracorporeal, extracellularly (in a gut chamber inside the animal), or

intracellularly (within a cell)

Cellular capture of nutritional products, digested or not, takes place via endocytosis:

phagocytosis and/or pinocytosis

Phagocytosis: “eating by cells”; extensions of a cell‟s plasma membrame engulf a food

particle - a small pocket forms on the cell surface within which the particle is captured,

the pocket is then pinched off and forms the food vacuole. Digestion takes place

within the cell, in the vacuole. Waste products are released via exocytosis

Pinocytosis: “drinking by cells”; soluble nutrients (the products of extracellular or

extracorporeal digestion such as sugars or amino acids, or DOM in the environment)

in water. Channels form as in phagocytosis, forming pinocytotic vesicles once pinched

of

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The Gut

• Metazoa generally have a gut (internal digestive tract; alimentary canal), but some do

not

• Some, such as some platyhelminths and cnidarians, have only one opening (i.e. they

have a incomplete or blind gut)

• Most others have a through gut, allowing for the one-way flow of food/excreta; implies

the presence of mouth and anus; Libbie Hyman: “The advantages of an anus are

obvious”;

• Some have specialised regions for grinding, storage, digestion, and absorption

(pinocytosis)

Brusca

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BAUPLAN: Nervous System and Sense Organs

Brusca & Brusca, pp. 77-82

Detect their environment (respond to stimuli) and react to it (response)

Functional unit is a nerve (sensory and motor nerves)

tactile receptors (touch)

georeceptors (orientation, respond to gravity)

proprioceptors (internal position and movement)

phonoreceptors (sound) – general sensitivity common, but not specific structures

baroreceptors (pressure) – mechanism poorly understood

chemoreceptors (chemical signals) – general sensitivity + specific receptors

photoreceptors (light)

thermoreceptors (temperature) – ectoparasites?

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Nervous System and Body Plans

Brusca & Brusca, pp. 82-83; Fig. 3.32

• Symmetry, sense organ distribution, nervous system organisation and lifestyle are

related

• Radially symmetrical animals: stimuli from any direction. Sense organs are distributed

around a non-centralised nerve net

• Bilateral symmetry – cephalisation, unidirectinal movement:

• Animal can sense and locate prey and move towards it, but also escape predators,

and interact with the environment in other ways

• Necessitated more centralised nervous system consisting of an anterior cerebral

ganglion or brain that receive impulses from the sense organs (usually also anteriorly

positioned)

• Relays signals to muscles via longitudinal nerve chords.

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BAUPLAN: Excretion,Osmoregulation;

Circulation and Gas Exchange

Brusca & Brusca, pp. 68-77

Excretion – getting rid of wastes, usually closely associated with osmoregulation.

Structures and associated processes are linked to the level of body complexity - this is why

it is important to look at the whole animal in unison

Also linked to habitat – aquatic (salt / freshwater) vs terrestrial

Circulation - based on finding ways to minimise diffusion distance by transport using

moving fluids

Gas exchange and transport - linked to circulatory system, includes exchange of gases

with the environment. Basic strategy similar throughout, but structures change with body

complexity

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Ecological Classification

Environment imposes physical and chemical constraints.

Evolution results in morphological, anatomical, physiological and

genetic traits to overcome these constraints

For example, in order to move from land into the air, it was

necessary for the development of wings (insects, birds, bats).

Shared „functional‟ attributes may not originate from the same

evolutionary lineage (i.e. polyphyletic)

Other functional classifications exist based on their mode of living

(e.g. parasitic, free-living, epiphytic, etc.); mode of feeding (e.g.

suspension feeders, deposit feeders, grazers, predators, etc.);

habitat (pelagic, benthic, etc.), and so on.

Useful in ecological studies where one looks at „functions‟ that

invertebrate groups fulfill in the environment but not „natural‟

classification (use the word ‘function’ with caution if used in an

evolutionary context!)

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Feeding Strategies

Brusca & Brusca, pp. 57-58

Autotrophs: organic carbon through photosynthesis (photoautotrophs) or chemosynthesis

(chemoautotrophs) using inorganic minerals and an energy source;

- Independent of external sources of organic carbon.

- Examples: plants, plant-like protists (algae).

- Called primary producers

Heterotrophs: ingest organic material in the form of other organisms, or parts thereof (such

as dead, detrital material);

Animals and animal-like protists.

Some symbiotic relationships with algae, especially dinoflagellates (zooxanthellae);

here photosynthates produced by the algae are used as secondary or even primary

sources of nutrition.

Called consumer organisms

Mixotrophs: photoautotrophic organisms that may also acquire organic material (DOM or

POM) from the environment. Some dinoflagellates, for example

Saprotrophs (saprobe): obtain organic material in solution from dead or decaying

sources

- extracellular enzymes secreted followed by absorption, through pinocytosis,

- Fungi and bacteria are good examples. Enable process of decay

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The Heterotrophs

Brusca & Brusca, p. 58

Further classification of heterotrophs based on whether they ingest plant matter, animal

matter, or a mixture of both:

herbivores (generally grazers)

carnivores (generally predators)

omnivores (generally scavengers)

Classes by comparative size of their food or prey:

microphages

macrophages

Classes according to the environmental source of their food:

suspension (filter) feeders

deposit feeders

detritivores

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Suspension Feeders

Brusca & Brusca, p. 58

Suspension feeding is the removal of food particles suspended in the surrounding medium

(usually water).

Small particles (microphagy); animal and plant particles captured (omnivores)

Three steps: water moves past the feeding structures,

food and other particles are removed from the medium,

food particles are moved to the mouth.

Food particles are usually selected by size - this is determined by the nature of the particle

capturing apparatus.

Widespread - poriferans, ascidians, brachiopods, ectoprocts, phoronids, most bivalves,

and many crustaceans, polychaetes, and gastropods;

Also found among the largest animals such as the whale and basking sharks, and some

whales

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Suspension Feeders

Brusca & Brusca, pp. 58-59

Motile animals water move through the feeding structures because of the animal‟s

movement relative to the water

Water may be moved towards (and sometimes through) sessile or planktonic animals:

by ciliary action alone (true filter feeders), example in sponges, ascidians, bivalves,

and some crustaceans; but is energetically costly;

by the movement of water past the sessile animal (turbulent water motion, currents,

tides, etc.);

a filtering apparatus may be swept through the water thus generating a current; e.g.

the setal brushes (feeding appendages) of barnacles and planktonic crustaceans;

Alternative - wait for „marine snow‟ i.e. gravity; e.g. in many deep sea benthic

invertebrates;

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Suspension Feeders

Brusca & Brusca, p. 60

many animals expose a sticky mucous to the water; POM adhere to the mucous which

is then moved to the mouth by ciliary tracts (e.g. crinoids), setal brushes (e.g. some

crustaceans), or some other mechanism;

tentacle or tube feet suspension feeding: used to capture particles (larger than in other

types of suspension feeding);, e.g. some echinoderms (brittle stars and crinoids) and

cnidarians (anemones and corals)

Ecological role in benthic-pelagic coupling

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Deposit Feeders

Brusca & Brusca, pp. 61-62

Also microphagous omnivores

Obtain POM from the sediments or soil:

direct deposit feeders: ingest sediment;

useable material is digested,

rest excreted;

e.g. many Annelids molluscs, some echinoderms;

tentaculate deposit feeder: tentacles select deposits on the sediment surface;

contains more organic matter than average

Sometimes they are called selective deposit feeders; Some actively select their own

fecal matter – coprophagy

Deposit feeders play a significant ecological role through bioturbation

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Herbivory / Carnivory

Brusca & Brusca, pp. 62-63

Macroherbivory requires the ability to bite or chew; eversible proboscises, mandibles and

jaws, radula, and teeth

e.g. in members of the molluscs, These animals may also be referred to as grazers,

browsers and scrapers (the latter term is frequently used by ecologist studying

freshwater systems)

Carnivory - Animals that actively capture other animals are termed predators

Structures needed to locate, pursue, capture and handle prey and ingest them.

As with macroherbivory, generally requires some cephalisation (except in the pentaradially

symmetrical sea urchin)

Carnivores may be further classified according the whether they are motile stalkers, lurking

predators (ambushers), sessile opportunists, or grazers:

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How inappropriate to call this planet earth, when

it is quite clearly ocean!

Arthur C Clarke

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Marine Habitats

Prefix (Greek) Definition (English)

Realm

(‘bottom’/water)

Depth

Pelag(os) Of the sea Pelagic: water

No specific depth;

the water volume

Epi- Outer, exterior

Epipelagic: water;

(epibenthic!)

See illustration

Meso- Middle Mesopelagic: water See illustration

Littoral; littoralis

(L.)

Of, or pertaining to

the edge of the water

Water/land boundary See illustration

Batho-; bathy- Depth

Bathyal: bottom;

bathypelagic: water

See illustration

Abyssos

Deep sea area or

space; chasm

Abyssal: bottom;

abyssopelagic: water

See illustration

Benthos

Depth of the sea;

bottom

Bottom See illustration

Hadal

Deepest part of the

sea; trenches

Hadalpelagic: water;

hadal: bottom

See illustration

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Classification by Marine Habitat

Plankton are the organisms which float in the water and have no ability to propel

themselves against a current. Plankton can be further divided into phytoplankton

(algae) and zooplankton (animals).

Holoplankton spend their entire life in the water column, while meroplankton spend part of

their life in the water column

Nekton are active swimmers and include marine fish, reptiles, mammals, birds and others

Benthos are the organisms which live on the bottom (epifauna) or within the bottom

sediments (infauna); others: epilithic, epipelic, epipsammic, epiflora, epifauna,

endolithic, epiphyte, epizoan, endophytic, biofilm

Some organisms cross from one lifestyle to another during their life, being pelagic early in

life and benthic later

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Other Habitats

Estuaries, coastal marshland (wetlands), freshwater (streams, rivers, lakes, etc.), terrestrial

Symbiotic:

Parasitic (endo- and ectoparasites)

Mutualism

Commensalism

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Classification by Size

megaplankton: between 20 and 200 cm

macroplankton: between 2 and 20 cm

mesoplankton: between 200 μm and 2 cm

microplankton: between 20 and 200 μm

nanoplankton: between 2 and 20 μm

picoplankton: between 0.2 and 2 μm (mostly bacteria, i.e. bacterioplankton)

femtoplankton: smaller than 0.2 μm (marine viruses)

microalgae (microphytobenthos, benthic microalgae etc.)

macrophytes (macroalgae, seagrasses)

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In each of the images below; the red circles are the species (or genera)

included in the taxon, while the white ones are not included in the taxon. The

pink bars serve to highlight the lineages present in the taxon.

Monophyletic taxon : A group composed of a collection of organisms, including

the most recent common ancestor of all those organisms and all the

descendants of that most recent common ancestor. A monophyletic taxon is

also called a clade. Examples : Mammalia, Aves (birds), angiosperms, insects,

etc.

Paraphyletic taxon : A group composed of a collection of organisms, including themost recent common ancestor of all those organisms. Unlike a monophyletic group,

a paraphyletic taxon does not include all the descendants of the most recent

common ancestor. Examples : Traditionally defined Dinosauria, fish, gymnosperms,

invertebrates, protists, etc

Polyphyletic taxon : A group composed of a collection of organisms in which the most

recent common ancestor of all the included organisms is not included, usually because

the common ancestor lacks the characteristics of the group. Polyphyletic taxa are

considered "unnatural", and usually are reclassified once they are discovered to be

polyphyletic.

Examples : marine mammals, bipedal mammals, flying vertebrates, trees, algae, etc