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Overview: Life Without a Backbone

An Introduction to the Invertebrates, v Invertebrates are animals that lack a backbone Part One § 95% of known animal species Phyla Placozoa, Porifera, Cnidaria, Ctenophora § Morphologically very diverse

Reference: Chapter 33.1, 33.2

How are invertebrates related to protists? Colonial Choanoflagellate Protists – Is this our Great Grandpappy?

Metazoa vs. Eumetazoa The Basal Metazoans – Phyla Placozoa and Porifera v Kingdom Animalia = Metazoa (animals) v The basal animals lack true tissues and organs § Eukaryotic, multicellular, heterotrophs § Phylum Placozoa – one species (relation to other basal § No cell walls groups not clear) § Motile at some point in life history § Phylum Porifera (sponges) – 5500 species v Resemble choanoflagellate protists v Eumetazoa (“true” animals) § In addition to metazoan characteristics, this group has: § True tissues organized into germ layers § Neurons § An embryo that goes through a gastrula stage

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Phylum Placozoa Phylum Porifera (“sponges”) v Only one formally recognized species, Trichoplax adhaerens v Sessile animals with simple body plan, but diverse shapes § Most simply organized metazoan known and colors v Three-layered “sandwich” organization v Live in marine waters (most species) or fresh water § Upper (protective) and lower (nutritive) monociliated epithelia § Middle layer a meshwork of connected fiber cells v Global distribution- crawls along rocks, corals, etc. v Avoids predation by using chemical defenses

Sponges consist of three layers Sponges are suspension feeders

1. Outer epidermis v Capture food particles 2. Mesohyl is the middle, suspended in the water that gelatinous noncellular passes through their body layer § Water is drawn through § Mobile amoebocytes play roles pores into a cavity called in digestion and structure the spongocoel and out § Spicules are skeletal fiber structures of calcium through an opening called carbonate or silica the osculum 3. Choanocytes are flagellated § Choanocytes trap food in collar cells making up the “collar” and ingest it by inner lining phagocytosis 1. Generate a water current § Food particles may be through the sponge and ingest transferred to suspended food amoebocytes (named for their use of pseudopodia)

Most Sponges are hermaphrodites Sponges create current to aid feeding & reproduction v Each individual sponge functions as both male and female § Most are sequential hermaphrodites- function first as one sex, then the other § Gametes arise from either choanocytes or amoebocytes § Eggs stay within the mesohyl but sperm disperse on the water current § Zygotes disperse as flagellated larvae before settling v Sponges are harvested for their bodies, Sponge-dye experiment (~5-min video): composed of spicules https://www.youtube.com/watch?v=8ueKlShb9Ls

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The Eumetazoan Diploblasts: Phyla Cnidaria & Phylum Cnidaria Ctenophora

v Cnidarians have diversified into a wide range of both sessile v Eumetazoan = “true” tissues and motile forms including jellies, corals, and hydras v Diploblasts v The basic body plan of a cnidarian is a sac with a central § Two primary germ layers digestive compartment, the gastrovascular cavity § Endoderm and ectoderm v A single opening functions as mouth and anus § Radial symmetry

Cnidarian Body Plan Cnidarian are carnivores v Depending on species, there are two variations on the body v Use tentacles to capture prey plan: the sessile polyp and motile medusa v Tentacles are armed with cnidocytes § Polyp: adheres to the substrate by the aboral end of its body (the end opposite the mouth) § Specialized cells for defense and capture § Medusa: bell-shaped body with the mouth/anus on the of prey underside § Contain Nematocysts v Example of polymorphism – the presence of more than one morphological type in a taxon § Specialized organelles within cnidocytes that eject a stinging thread

Nematocysts in action Cnidarian Tissues

v No brain or nervous system – but do have a nerve net v No true muscles (diploblastic!) § Instead, epitheliomuscular cells control locomotion

Excerpt from video, https://www.youtube.com/watch?v=7WJCnC5ebf4 ~1:08-3:50

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Phylum Cnidaria is divided into four major classes Phylum Cnidaria: Class Hydrozoa

1. Hydrozoa- alternate between polyp and medusa v Most alternate between polyp and medusa forms 2. Scyphozoa- “true” jellies v Hydra, a freshwater cnidarian, exists only in polyp 3. Cubozoa- box jellies form and reproduces asexually by budding 4. Anthozoa- anemones and corals

Life cycle of Hydrozoan Obelia - MEMORIZE IT! Phylum Cnidaria: Unusual Hydrozoan

Reproductive v The Portuguese Man of War Feeding polyp polyp § Often mistaken for true jellyfish (scyphozoa)

Medusa MEIOSIS § Has no polyp form bud Gonad § Severe sting can cause major harm Medusa Egg Sperm SEXUAL § Preyed upon by Glaucus, a nudibranch (mollusc) ASEXUAL REPRODUCTION Portion REPRODUCTION § Incorporates the nematocysts into its own body for of a (BUDDING) defense colony FERTILIZATION of polyps Zygote Developing Planula polyp (larva)

Mature polyp Key Haploid (n) 1 mm Diploid (2n)

Phylum Cnidaria: Class Scyphozoa Phylum Cnidaria: Class Cubozoa

v In the class Scyphozoa, jellies (medusae) are the v In the class Cubozoa, which includes box jellies and sea dominant form of the life cycle wasps, the medusa is box-shaped and has complex eyes v Cubozoans often have highly toxic cnidocytes- painful and possibly lethal v Most common in tropical Indo-Pacific

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Phylum Cnidaria: Class Anthozoa Phylum Cnidaria: Class Anthozoa

v “Flower animals” v Many corals form obligate symbioses with algae v Include the corals and sea anemones § Polyp tissue (green) around mouth and base of the v Occur only as polyps tentacles v “Hard” corals secrete a calcareous exoskeleton; “soft” § Symbiotic zooxanthellae (red fluorescence from corals do not chlorophyll) in tissue between polyps

James Nicholson, Olympus BioScapes

Phylum Ctenophora Ctenophore gallery v “Comb jellies” § 8 comb-like rows of cilia used for locomotion § One group has tentacles; another does not § Swim “mouth first,” unlike cnidarian medusa § No polyp morph v Predators § No cnidocytes; instead have colloblasts arrayed along tentacles that produce sticky substance to trap prey v Many capable of bioluminescence

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