BIOL 475 U1
Several features distinguish ctenophores from cnidarians
- Ctenophores swim using rows of cilia. - Many ctenophores possess a pair of retractile tentacle - Ctenophores are biradially symmetric (because of tentacles). - Two planes exist through which the animal can be divided into mirror-image halves. - Ctenophores lack nematocysts. - Instead, have adhesive cells called colloblasts on epidermis of tentacles - Colloblasts stick to prey on contact - voracious predators on small plankton, especially copepod (opepods: microscopic, planktonic crustaceans; extremely abundant in many oceanic areas; a favorite food of ctenophore) - Bioluminescence
Why does cubazoa have such toxic sting
- Cubozoans are small (most ~ 2-4 cm) and delicate - Their prey (fish, crustaceans) are often bigger, stronger, and potentially able to inflict damage - It may be advantageous for cubozoans to paralyze and kill prey almost instantly, so that thrashing of the prey doesn't damage the box jelly.
body wall of an asconoid sponge
- Outermost: pinacoderm (consists of flattened pinacocytes) - Middle layer: mesohyl (contains collagen, ameboid cells, and skeleton of sponges called spicules) - Innermost: flagellated layer (collar cells called choanocytes. Choanocytes move water through sponge & obtain food) - In addition to these three layers, cells called porocytes extendfrom the outer surface of the sponge to the atrium. - Porocytes are shaped like bagels and form the pores in manyasconoid sponges.
How do scyphozoan jellyfish swim
- Rhythmically contract band of circular muscle fibers in subumbrella - when muscles relax, mesoglea slowly "pops" back to normal state - water is expelled from under the bell; jellyfish is propelled inopposite direction
What is special about Stomphia
- a type of sea anemone that can swim
Three body plans of sponges(NOTE: these are NOT taxonomic categories)
- asconoid sponges (simplest) - leuconoid sponges (most complex AND most common) - syconoid sponges
Many sponges can control rate ofwater flow to some degree by:
- inhibiting flagellar beating - partly closing osculum - some can close ostia (pores) andstop water flow entirely
Characteristics of Phylum Porifera
- no head; nothing resembling a head - no gut - and gutless condition is primary condition irregular shape (no reliable symmetry) - barely motile - but many sponges can move -- slowly - no mouth (Note: opening at top is not a mouth) - no nervous system; no nerve cells - have some degree of cell differentiation (cells not all exactly alike-some are specialized for specific tasks) - no circulatory system
What is special about cnidarian sensory systems
- not polarized - one signal triggers nerve net - no spinal cord, no brain, no CNS
Cnidaria: two structural types
- polyp (sessile) - medusa
Polyp
- sessile • body usually a tube or cylinder • end bearing mouth and tentacles(oral end) usually directed up • opposite end (aboral end)usually attached to substrate
Three critical features ofPhylum Porifera
- sessile (immobile) - built around a system of water canals - inhabit hard bottoms
Phylum Cnidaria Class Anthozoa Subclass Alcyonaria (Octocorallia)
- soft corals and relatives - When alive, soft corals are flexible and can bend. Scleractinians (stony corals) are rigid. - nearly all are colonial - most have small polyps - diagnostic feature: feeding polyps have 8 tentacles - other than these features, a diverse group (hard to generalize)
What are hydras and why are they unique
- they are hydrozoans & are unique because they are solitary - most hydrozoans are colonial - colonies by budding & not separating (like plants)
Aggression in anemones
- they have clonal wars - Acrorhagi are inflatable structures containing numerous nematocysts.
Balanophyllia
-a solitary cup coral -only intertidal scleractinian along U.S. west coast
Sponge defense
1. chemical 2. spicules
Food particles are captured in two places:
1.) "Large" particles (5-50 microns) are phagocytized by cells that line theinhalant pathways. .2.) "Small" particles (1 micron or less) are removed and engulfed by choanocytes. Choanocytes can transfer engulfed particles to amebocytes (also known asarchaeocytes). Regardless of where particles are captured, digestion is intracellular
Symbiotic Associations of Anemones
1.) Anemones and zooxanthellae (photosynthesizing dinoflagellates) 2.) Anemones that live on the shells of hermit crabs (e.g., European anemone Calliactis) - Benefit to anemone: constantly around food; may get scraps of things that the crab eats - Benefit to crab: camouflage and protection (nematocysts repel octopuses that otherwise eat the crabs)
Reproduction of turbellarian flatworms
1.) Asexual reproduction - by fission (shown on picture) - by fragmentation Note: some reproduce asexually during some seasons and reproduce sexually during others. Asexual reproduction through fragmentation • animal splits into several (sometimes many) parts • each part grows into a full animal 2.) Sexual reproduction (most common) - many are simultaneous hermaphrodites - copulation; internal fertilization followed by egg deposition
Nutritive needs of scleractinian corals are met by:
1.) Feeding on plankton 2.) Internal symbionts •zooxanthellae (dinoflagellates) •zoochlorellae (algae) (Note: increasingly the two are lumped together under the term zooxanthellae) Corals use some photosynthetic products produced by internal symbionts. Many corals cannot live in deep water without light.
Important Features of Turbellarians
1.) Have a ciliated epidermis - either all over or just on ventral surface (NOTE: all other classes of flatworms lack this.) 2.) Numerous glands: some for adhesion and mucus secretion -some have duogland system for adhesion - consists of two glands - one provides adhesive material to make an anchor - other provides enzymes to digest anchor Flatworm essentially glues itself to a spot; to move, it creates enzyme and dissolves glue. Often done by small species (some interstitial) that are likely to be swept away by water currents. 3.) Most locomote using cilia or muscular waves or both. For cilia, mucus is required. • ciliary tips dig into layer of mucus laid down on substrate • flattened body surface gives large surface area in contact with the substratum
Class cubazoa
1.) bell is often tall, with 4 flat sides(cubical, like a box); often 4 tentacles 2.) complex eyes; can form images(other jellyfish like scyphozoans cannot) 3.) often have an extremely dangerous sting• bad sting can kill an adult in ~3 minutes
cubozoan toxin
1.) neurotoxin that interferes with passage ofcalcium through myocardial membrane(can stop heart) 2.) another neurotoxin can enter the brainand suppress breathing 3.) some toxins rupture red blood cells,disrupting circulatio
Are anemones carnivorous
Although anemones are carnivores, some have internal photosynthetic symbionts (little organisms living inside that can photosynthesize). • usually live within cells in the gastrodermis • some photosynthetic products are made available to host. • several types, but the main one is zooxanthellae (photosynthesizing dinoflagellates, same as in upside-down jellyfish)
Phylum Cnidaria Class Anthozoa Subclass: Zoantharia (Hexacorallia) Order: Actiniaria
Anemones • solitary polyps • usually ~ 1-10 cm in length; 1-5 cm in diameter • often brightly colored • vast majority live attached to hard substrates
Asconoid body plan can only work for tiny sponges. WHY?
Asconoid sponges are all small (1-3 mm)• small surface area of flagellated layer• relatively few choanocytes, so cannot pump much water through sponge• means that an asconoid sponge cannot filter a large volume of water per unittime so cannot get a large amount of food - only works if sponge diameter is very narrow
Features of Cnidarians (body wall)
Body wall consists of 3 basic layers 1.) outside layer: epidermis 2.) middle layer: mesoglea ("jelly" in middle)-may be thin or thick-may be cellular or acellular 3.) inner layer lining the gastrovascular cavity: gastrodermis
upside down jellyfish
Cassiopea rests upside down on bottom with tentacles directed upward (like an anemone) • catches zooplankton that crawl over it • also has symbiotic dinoflagellates (protists) in its tissue • dinoflagellates can photosynthesize; if light is sufficiently strong, Cassiopea can surviveon photosynthetic products
Not all animals have cephalization:
Cephalization is particularly beneficial to animals that: are mobile and active actively hunt food fast and agile enough to escape predators General evolutionary strategy: concentrate sensory receptors and nerve cells in the part of the body likely to encounter food or predators first Move → cephalization → bilateral symmetry Type of symmetry tells a lot about the type of animal & its lifestyle
Medusa
Characteristics of medusa • free swimming • body usually resembles a bell orumbrella; top surface is convex,undersurface is concave • end bearing mouth and tentacles(oral end) usually directed down • mesoglea (middle layer) is verythick and gelatinous, giving rise tocommon name "jellyfish"
Phylum Porifera
Class Calcarea Class Hexactinellida Class Demospongiae (90% of living sponges)
Class Demospongiae
Class Demospongiae (90% of living sponges) • a few (like bath sponges) lack spicules and havespongin (springy collagen) • most have siliceous spicules • most are marine; a few live in fresh water • all are leuconoidAn "encrusting sponge" is one that grows allover a rock or other hard substrate
Class Hexactinellida
Class Hexactinellida - "glass sponges" • have siliceous spicules - which is why called "glass sponges" • strictly marine, mostly in deep water (>50 meters) • entirely syconoid; often large, firm upright growths (up to 1 m high)
Phylum Cnidaria taxonomy
Class Hydrozoa Class Scyphozoa Class Cubozoa Class Anthozoa
Cnidarian organ & systems
Cnidarians have very limited organ development • no circulatory system • no excretory/osmoregulatory system • no respiratory structures (no gills or lungs) **Defining feature of cnidarians:capture prey with stinging structures called nematocysts.
Hydrozoa
Diverse body forms; difficult to identify on external appearance alone. • Unified by having acellular mesoglea and lacking gastrodermal nematocysts. • Body structure can be: (1) polypoid; (2) medusoid; (3) both at different points in the life cycle.~3,000 species - Most are small; most are marine BUT the only Freshwater cnidarians are hydrozoans.
Coral bleaching
Due to zooxanthellae expelling from tissues Could be a cyclical thing (normal for corals), but most believe its due to stress Lab studies have indicated that several factors can cause bleaching •excess shade •disease •pollutants •sedimentation •changes in salinity •high seawater temperatures increased UV radiation The fact that high temperature and increased UV cause bleaching is a particular concern because of climate change and reduction in the ozone layer.
Benefits of cephalization:
Example of animals without cephalization: anemones can't move & have the same chance for food (and predators) to approach from each side Example of animals with cephalization: can move. Head approaches things first, helpful to sense signals from predators and food Cephalization makes sense for moving animal
Feeding in scyphozoan
Feeding in Scyphozoan jellyfish • all are predators; feed opportunistically on whatever they can capture • capture prey with tentacles; subdue with nematocysts • plankton and small crustaceans are often eaten; some species eat fish
Three types of coral reefs:
Fringing reef (borders continents and islands) Close to shore Inner reef: shallow - Outer reef: acute dropoff → deep water Barrier reef - Near coast but 15 km to 150 km to shore - Separated from land by a channel/ lagoon Atolls - Shaped like a circle with lagoon in the center - Used to be fringing reef → island sinks → reef stays - The environment differs greatly among different locations within an atoll; the animals also differ greatly
What are jellyfish?
Hydromedusae are one of several types of animals that are oftencollectively called "jellyfish". (Note that "jellyfish" has no scientificdefinition; it is a catch-all for gelatinous animals.) Other jellyfish include: - cnidarians in the class Scyphozoa (includes all large jellyfish;sometimes called scyphomedusae to distinguish them fromhydromedusae) • members of the phylum Cubozoa (a.k.a. box jellies, seawasps) • members of the phylum Ctenophora (comb jellies)
How are synconoid sponges different from asconoid sponges (places where water enters sponges)
In asconoid sponges, water enters the sponge through tube-shapedstructures known as porocytes, which are usually single cells. Syconoid sponges are much larger than asconoid sponges. They stillhave many openings, but these openings are known as prosopyles.These are passageways, not single cells.
In colonial corals, new polyps are produced by ______________
In colonial corals, new polyps are produced by budding. • Structure of each polyp is the same • Adjacent polyps are connected by a sheet of tissue (coenosarc)
What are zooids?
Individual polyps are usually called zooids. A less common term for them is modules. In most hydroids, there has been a tendency toward polymorphism (i.e., there is more than one type of polyp (zooid) and different polyps are specialized for different functions) Some (but not all) colonies have a third type known as dactylozooids,which contain dense clusters of nematocysts and are used for defense. All colonies have at least two types of polyps: 1.) feeding polyps called gastrozooids(typically has tentacles for feeding) 2.) reproductive polyps called gonozooids(typically shaped like a small barrel or club)
Phylum: Cnidaria Class: Hydrozoa Order: Siphonophora
Local siphonophore: Physalia a.k.a. Portuguese Man-of-War• Siphonophores are pelagic, colonial hydrozoans Siphonophores are NOT considered to be hydromedusae (theydo not have the classical medusoid form).
What are marine colonial hydrozoans shaped like polypoids called?
Marine colonial hydrozoans of this type are called hydroids • term is short for "polypoid hydrozoan" • many different types • hard to tell where one individual ends and another begins • colonies grow by budding but not separating A colony typically has a common nervous system and often a common gut (i.e., gut cavities of most polyps in a colony are continuous)
Feeding in Anemones
Most anemones catch and eat various invertebrates • usually depend on waves/water currents to wash prey into tentacles (anemones often live in areas with good water currents) • capture prey with nematocysts on tentacles • will try to eat ANYTHING that tastes right (has amino acids) and that the anemone can drag into its mouth
Feeding in turbellarian flatworms
Most are carnivorous • Typical prey: insect larvae (mosquito larvae for some!), small crustaceans, snails, annelids • Prey can be swallowed whole (if small) or juices are sucked out (if too big to swallow). Either way, digestion occurs in the gut. • Some flatworms are scavengers (eat dead things) as well as carnivores.
Scyphozoan reproduction
Most species are dioecious (have two separate sexes) • gonads are located in gastrodermis • when time to mate, jellyfish basically spit up eggs and sperm • complex life cycles, involving asexual reproduction through strobilation
Sponge reproduction
No universal method of reproduction 1. asexual reproduction in some: - budding - gemmules: cast off by parents in autumn, survive winter, grow to adult next spring 2. sexual reproduction - sperm released into water, eggs fertilized inside sponges, develop into larvae before leaving - many are sequential hermaphrodites (produce only eggs or sperms at one time) - some species are dioecious (separate sexed)
Coral classification
Phylum Cnidaria Class Anthozoa Subclass Zoantharia (Hexacorallia) Order Scleractinia: stony corals (can be solitary or colonial)
Reproduction in Anemones
Reproduction in Anemones 1.) Asexual - often through pedal laceration - pieces of pedal disk become new anemone 2.) Sexual reproduction - most anemones are dioecious - typically release eggs and sperm directly into sea water - development is highly variable (we won't get into it)
Class Scyphozoa
Scyphozoans include nearly all of the "large" jellyfish-like animals - Key traits of Class Scyphozoa• - mesoglea is cellular(acellular in hydrozoans) • generally much larger than hydromedusae(sometimes called scyphomedusae) • approximately 200 species worldwide • medusoid form is dominant and conspicuous • asexual reproduction by strobilation• gastrodermal cnidocytes(hydrozoans have cnidocytes only inepidermis)
Why are worms so prevalent in the animal kingdom?
Speculation: • Maybe worm form is the simplest way to house a complete digestive system (mouth at one end, anus at other). • A complete digestive system provides huge benefits (can have food move one way; be at different stages of digestion; more complex diet; etc.) • Worm body has much surface area in contact with substrate, making crawling/swimming easy
Spicules
Spicules are typically composed of: • calcium carbonate • silica (technically silicon dioxide)A few sponges (like bath sponges) lack spicules but they are the exception.Note: instead of spicules, bath sponges have soft, rubbery fibers of a material called spongin
Two subclass of anthozoa
Subclass: Zoantharia (Hexacorallia)- anemones, stony corals, etc. Subclass: Alcynonaria (Octocorallia)- soft corals, etc.
Regenerative abilities of flatworm
Triclad turbellarians (such as planarians) have the most extreme cases of regeneration. Polyclad turbellarians have more modest regenerative abilities • cannot regenerate brain itself but can regenerate nerves and neural connections • capable of brain transplants! Brain transplant experiment: flatworm can flip back after you flip it upside down --> remove brain --> can't flip back --> implant brain --> can flip back again
What are the 2 common types of internal architecture for leuconoid sponges
Tubular vs solid: - Tubular: - hollow - one giant osculum at the top, all water exit from there - Solid: - mostly solid inside - multiple oscula scattered over body surface
Turbellarian nervous systems
Turbellarian nervous systems are variable. All have ganglia (clusters of nerve cells) near anterior end - a "brain", depending on definition. All have longitudinal nerves. First hint of a central nervous system (CNS)!
Turbellarians sensory structures
Turbellarians have numerous sensory structures • statocysts (for sensing gravity) • chemosensory pits (in epidermis) • touch receptors • photoreceptors associated with eye spots (many turbellarians are negatively phototactic - they avoid light) • planarians can detect Earth's magnetic field
Statocyst
a small organ of balance and orientation in some aquatic invertebrates, consisting of a sensory vesicle or cell containing statoliths ( a rock/ condensation that moves to gravity)
Phylum Cnidaria Class Anthozoa
anemones, corals, and relatives• contains ~ 70% of all cnidarians • approximately 6,000 species • can be solitary or colonial • can live 50+ years • entirely polypoid; no medusoid stage• although polypoid, differ greatly fromhydrozoan polyps (much larger; easilyvisible to naked eye)
Cnidarians are diploblastic (what does this mean)
body is constructed of two germlayers (endoderm and ectoderm) Note: Don't get confused - 3 layers of body wall are derived embryologicallyfrom 2 different germ layers start with ectoderm & endoderm development finish with epidermis, mesoglea, gastrodermis
Phylum Ctenophora:
comb jellies Size: usually marble to golf ball "Ctenophore" comes from the Greek word ktenes, meaning combs Originally thought to be an offshoot of medusoid cnidarians. Current view: not closely related to cnidarians; similarities between the two groups are likely due to convergent evolution. Growing evidence that ctenophores might have evolved before cnidarians; might be an early offshoot of the animal kingdom (like sponges)
Flagella of choanocytes
directed into the cavity of an aconoid sponge (movement of the flagella pumps water through the sponge)
Flatworm pharynx anatomy
ejects pharynx when eating
Pneumatophore
float filled primarily with nitrogen or carbonmonoxide (depending on species) keeps the organism at thesurface of the water.
Phylum Cnidaria Class Anthozoa Subclass Alcyonaria Order Gorgonacea
known as gorgonians or gorgonian corals Eg. sea fans, sea whips
What eats jellyfish
leatherback sea turtle
Phylum Cnidaria Class Anthozoa Subclass Alcyonaria Order Pennatulacea:
sea pens, sea pansies Sea slugs eat sea pens, but neither have eyes
Phylum Cnidaria Class Anthozoa Subclass Zoantharia (Hexacorallia) Order Scleractinia
stony corals (can be solitary or colonial) Basic structure of a scleractinian polyp resembles that of a sea anemone ... EXCEPT that scleractians have a calcareous skeleton Anemone: soft, corals: have hard skeletons
Hydromedusae
very small (typically ~0.5 - 6 cm in diameter) are often partly transparent usually have a delicate or fragile appearance distinguishing feature is the presence of a velum (alittle shelf that projects into the interior of the bell)
Features of Phylum Platyhelminthes (overview)
• All are acoelomate (solid with no body cavity). • Show some cephalization, including brain-like cluster of ganglia at one end. (Note: a ganglion is a cluster of neurons.) • dorsoventrally flattened (thus the name "flatworm") • IF a digestive system exists (doesn't always), mouth is the only opening lack respiratory and circulatory systems. - no digest system: usually live inside living organisms (eg. tapeworm) - no respiratory/ circulatory system: flat, large surface area to volume ratio, can just do gas exchange. • lack a skeleton (body entirely soft) • triploblastic (body is derived from three germ layers - ectoderm, mesoderm, and endoderm (Note: recall that cnidarians are diploblastic)
Class Turbellaria
• about 4,500 species described; maybe 10,000 additional species that have not yet been described • contains the only free-living species (overall, about 85% of flatworms are parasitic, including a few turbellarians) • vast majority are marine. Often live on plants or are interstitial (live between grains of sand). A few freshwater and land species also exist. • most are small (few cm or less); a few reach 60 cm
Class Calcarea
• all marine, mostly shallow coastal water KEY FEATURE: have CaCO3 spicules (feel crunchy to the touch) asconoid, syconoid, leuconoid types
Some threats to coral reefs
•climate change •delicate ecosystems (easily disrupted by pollutants, runoff) •coral collectors •accidental destruction by divers •trade in aquarium fish
Coral reefs
•reefs are based on hermatypic (reef-building) scleractinian corals •tropical and subtropical seas (temperature > 20 degrees C) •shallow water (most corals grow best at depths of 30 m or less) •sunlight is required for zooxanthellae to photosynthesize
Bilateral symmetry is largely the result of what?
- Cephalization - Cephalization involves concentrating most sensory receptors and neurons at one end of the body - once sensory receptors are concentrated in one area, having neurons concentrate nearby is helpful
Do cnidarians have sensory receptors?
- Cnidarians have neurons (unlike sponges). They also have sensory receptors. - cnidarians typically have a nerve net but no "brain" - synapses can be either polarized or unpolarized - receptors respond to touch, chemical cues, and light - receptor cells abundant near tentacles around mouth
