Animal Diversity - Hickman - 7th Edition - Chapter 7

Hydroid Reproduction

* Can reproduce sexually in some spp., but also reproduce by budding * New polyps formed via budding can separate from parent polyp or remain attached and share a gastrovascular cavity with their colony of connected polyps * Individuals in colonies of polyps are specialized for different functions (defense, reproduction, feeding, etc.)

Phylum Ctenophora (comb jellies)

* Commonly called comb jellies or sea walnuts * All known spp. are marine * Have 8 rows of ciliated comb plates, used for locomotion - most swim, some creep along the ocean floor * Typically have biradial symmetry * Diploblastic * Typically have a jelly-like substance called collenchyme (like mesoglea), which contains cells derived from both the ectoderm and the endoderm * One-way digestive tract * Oral-aboral axis (mouth and anus at opposite ends) * Specialized cells called colloblasts secrete a glue-like substance that is used to trap prey, which is then transferred to the mouth (ctenophorans do not produce cnidocytes/nematocysts) * No respiratory/excretory structures * Some spp. feed upon cnidarians and incorporate their prey's undischarged cnidocytes into their own tissues (defense mechanism) * Most spp. possess statocysts, cells that detect pressure changes, and chemosensitive cells * When a noxious chemical is detected, the cilia on the comb plates reverse their beating, and the animal swims in the opposite direction * Most species are bioluminescent, (defense mechanism?) REPRODUCTION * Most spp. are monoecious and hermaphroditic * Larvae are free-swimming (called cydippids) and gradually develop into adults, with no metamorphosis (larva look like small adults)

Class Cubozoa (Cube/Box Jellies)

* Dominant Life Stage = Medusa * Most cubozoan spp.'s polyps are tiny - some spp. do not appear to have a polyp stage at all * Medusa bell is square in shape, with ≥1 tentacles extending from each corner * Medusae are typically smaller than those of a scyphozoan. However, the venom of many spp. is extremely toxic - some can kill humans * Sensory organs of cubozoans are well-developed, Many spp. have both ocelli and functioning eyes, complete with lenses that can form crude images

Class Anthozoa (Flower Animals)

* Dominant life stage = Hydroid/Polyp * In most species, there is apparently no medusa stage at all * Called "flower animals," because of their flower-like body structures * Includes soft corals, hard corals, sea fans, sea pens, and sea anemones * Anthozoans often grow to much larger sizes than most hydrozoans * Many spp. secrete hard, calcareous exoskeletons * Colonial hard coral species form coral reefs * Distinguished from all other cnidarians as their body walls are folded inward to form septae (mesenteries) that subdivide the gastrovascular cavity and increase its digestive surface area * Muscles in the body wall allow some anthozoans to move and even swim (to an extent) TYPES OF ANTHOZOA * Sea Anemones * Hard Corals * Soft Corals * Sea Fans * Sea Pens

Class Hydrozoa (Hydra)

* Dominant life stage = Hydroid/Polyp * Marine hydrozoans are typically colonial, and different zooids are specialized for different tasks: - Gastrozooids - specialized for digestion of prey - Dactylozooids - specialized to capture prey and then deliver it to gastrozooids - Gonophores - specialized reproductive sacs containing ovaries or testes * Some marine hydrozoans form colonies that, instead of being rooted to a surface, swim or float (such as Portuguese Man-o-War) HYDROID * Most spp. are marine and colonial, though free-living and freshwater species occur * Polyps reproduce asexually, and eventually produce medusae * Most spp. secrete chitinous sheaths in which they live - in colonial spp., the sheaths are joined - Some sedentary, colonial marine hydrozoans secrete calcareous exoskeletons and form reefs similar to those of the true corals (hydrocorals/fire corals) * In colonial species, the individuals animals (a.k.a. zooids/hydroids) often perform specialized tasks (feeding, defense, reproduction, etc.) * Captured food is digested in a shared gastrovascular cavity & distributed throughout the colony MEDUSA * Reproduce sexually * Typically very small * The margin of the bell folds inward into a shelf-like velum that surrounds the mouth and increases the speed of ejected water * Typically have sensory cells, such as statocysts and ocelli

Class Scyphozoa (True Jellyfish)

* Dominant life stage = Medusa/Jellyfish * Medusa is relatively large * Medusa of a scyphozoan does not have a velum * Body wall folds outward to form 4 oral arms, which help capture and manipulate prey in addition to the tentacles * Gastrovascular cavity extends to form 4 gastric pouches connected by radial canals & may contain reproductive tissues REPRODUCTION * Most spp. are dioecious, and the gonads are located in the gastric pouches * Fertilization is internal - sperm is drawn into the female's gastric pouches by the beating of cilia lining the gastrovascular cavity * A free-swimming planula larva eventually settles onto a surface to develop into a hydra-like form that eventually buds off ephyrae, which develop into new medusae

Cnidarian Body Structure

* Mouth leads to gastrovascular cavity. * Two-way digestive tract. * Have nervous tissue (typically nerve ring) and muscle tissue, which allows them to swim - or in the case of some polyps, to crawl * Diploblastic; 2 tissue layers - Outer epidermis forms from ectoderm - Inner gastrodermis forms from endoderm * Jelly-like mesoglea fills space between epidermis and gastrodermis * Cnidocytes possess cnidae (special organelle for stinging), specifically nematocysts * Nematocysts "harpoon" prey and inject paralyzing toxins when triggered, some capable of severely injuring or killing large animals (such as humans) * Most are carnivorous * No true nervous system * Nerve net (plexus of nerve cells) stimulate muscle cells to allow for swimming and food capture * Absorb oxygen and expel wastes through diffusion

Class Staurozoa

* ONLY EXIST AS POLYPS - No medusa life stage known * The top of the polyp resembles a medusa with 8 arms, but does not detach * Reproduce sexually, but the planula larvae do not swim * When the planula settles onto a surface, it develops directly into a new polyp

Anthozoa - Soft Corals, Gorgonians, and Sea Pens

* These colonial anthozoans do not form reefs - they often grow on reefs made by true coral *

Anthozoa - True (Stony) Corals

* True corals look like small sea anemones, with each animal living in a calcareous shell that it secretes * Over thousands of generations of building atop previous generations may create coral reefs * Many spp. form mutualistic relationships with zooxanthellae * Spp. with zooxanthellae are so dependent upon them that if the zooxanthellae die, so does the coral * Coral can form islands called atolls (reef is built around a volcano, and is left behind/continues growth after the island crumbles away) * *

Medusa/Jellyfish

* Typically have gravity-sensing statocysts and light-sensing ocelli (some spp. have functioning eyes w/ lenses) * Method of Swimming - typically swim by drawing water into the gastrovascular cavity, then contract their muscular tissue to forcefully expel it from the mouth (some spp. have a velum that surrounds the mouth and increases water velocity)

Medusa/Jellyfish Reproduction

* Typically, zygote develops into a ciliated, free-swimming planula larva * Planula settles onto a hard surface and develops into a polyp * Polyp form often reproduces asexually, producing many more polyps * Polyps eventually produce free-swimming medusae, which typically reproduce sexually * Medusae are usually dioecious (an individual is either male [produces sperm] or female [produces ova])

Class Hydrozoa, Genus Hydra

* Unlike most hydrozoans, members of the genus Hydra typically do not produce medusae at all * During warmer months, hydras typically reproduce asexually via budding (these hydrozoans are not colonial) * In the autumn, they often switch to sexual reproduction * Most spp. are dioecious, and shed sperm and ova into the water * A protective cyst forms around the embryo and allows it to survive cold temperatures/dehydration until conditions improve - new hydras hatch out when the weather warms

Anthozoa - Sea Anemones

* Usually solitary, and typically have much larger polyps than hydrozoans * The aboral surface attaches to substrate by a pedal disc, but can be detached if necessary * Many tentacles surround the mouth * When threatened, a sea anemone can contract its body musculature forcing the water out of its gastrovascular cavity and reducing the animal's size. This allows it to squeeze into its protective tube * Most sea anemones host zooxanthellae, and acquire some of their food from their dinoflagellate mutualists * Some spp. form mutualistic relationships with crabs, damselfishes, anemone fishes, or clown fishes * Typically dioecious, though some spp. are monoecious (spend part of their life as one sex and later become the other) - but not hermaphroditic * Sexual Reproduction - (External Fertilization) Sperm and ova are shed into the water * Asexual Reproduction - Budding, fission *

Phylum Cnidaria

- Possess cnidocytes - Some build reefs - Underwater spp. (marine or freshwater) * Form mutualistic/commensalistic relationships w/ other organisms (zooxanthellae and coral = mutualistic)(sea anemone and crab = commensalistic)

Characteristics of Radiata

- Radially symmetrical - Diploblastic - True tissues - Swimmer or sessile - Many are predators - Tentacles with cells for capturing prey - Mouths and gastrovascular cavities

Classes of Cnidaria

Class Hydrozoa - hydroids, fire corals, Man-of-War Class Scyphozoa - true jellyfishes Class Cubozoa - cube (box) jellyfishes Class Anthozoa - stony corals, soft corals, sea anemones Class Staurozoa - no true medusa stage is present (PROPOSED, NOT OFFICIAL)

Radiata

Cnidaria and Ctenophora

Cnidaria Body Plan

Dimorphic, nearly all cnidarians exhibit both body plans at different life stages, with one being the dominant form * Hydroid/Polyp - Sessile, tubular body, top/oral surface surrounded by tentacles. In some spp. the bottom/aboral surface attaches to substrate via pedal disc. * Medusa/Jellyfish - Free-swimming, body is typically bell/umbrella shaped, mouth/aboral surface and tentacles face downward, aboral surface faces upward.

Cnidocyte function

The nematocyst (cnida organelle of cnidocytes) discharges a venomous, harpoon-like thread when brushed against, which paralyzes or kills prey/whatever brushed against it