Invertebrate Zoology - Exam 1

What percentage of animal species are invertebrates?

96%

How long have invertebrates been in the fossil record?

600 mya

Where do a majority of invertebrates live?

Marine

Why?

-Most of the earth’s surface is marine

-Very stable

Nekton

aquatic animals that are able to swim and move independently of water currents

Plankton

aquatic animals that are carried by tides and currents

Epifauna

animals living on the surface of the seabed or a riverbed, or attached to submerged objects or aquatic animals or plants.

Infauna

invertebrates living within the matrix of aquatic sediments

Meiofauna

minute animals living in soil and aquatic sediments.

Why are there less invertebrates in freshwater habitats?

-More unstable

What does lentic mean?

Lakes and ponds

What does lotic mean?

Rivers and streams

Why are estuaries and coastal marshlands not a top choice for invertebrates?

Unstable, mixing of fresh and marine waters

Why are terrestrial habitats a struggle for invertebrates?

-Harsh

-No hydrostatic pressure to maintain the skeletal system

-More water loss

-Need adaptations to excrete waste

-Internal fertilization to protect young

Commensalism

an association between two organisms in which one benefits and the other derives neither benefit nor harm.

Mutualism

association between organisms of two different species in which each benefits

Parasitism

the practice of living as a parasite in or on another organism.

Free-Living

an organism is not parasitic, symbiotic, or sessile, and is capable of movement and metabolic independence

Sessile

permanently attached and unable to move around

Deposit Feeder

an organism that eats organic matter from sediment, either by moving along the surface or burrowing into it

Monophyletic

Includes ancestral species and all descendants

Paraphyletic

All are descendants of a common ancestor but group does not contain all descendants

Polyphyletic

Group contains species from two or more different ancestors

What can cladistics be based on?

Anatomical, morphological, and embryological

Synapomorphy

a character or trait that is shared by two or more taxonomic groups and is derived through evolution from a common ancestral form

Apomorphy

a unique, specialized trait or character that has evolved from an ancestral form

Convergent evolution

the process where two or more unrelated species independently evolve similar traits or features, usually as a result of adapting to similar environmental pressures or ecological niches, even though they do not share a recent common ancestor

Homologous structures

similar anatomical features found in different organisms that share a common ancestor

Molecular phylogenies

DNA sequence data to determine relatedness

What is bauplan?

a set of structural features that characterize a group of organisms, such as a phylum

places constraint on an organism either structurally, genetic, developmental, cellular, or metabolic

What invertebrates have asymmetrical symmetry

Sponges

What invertebrates have spherical symmetry

Rare, protists

What symmetry do most invertebrates have?

Biradial

Bilateral symmetry allows what?

Cephalization

What are the pros and cons of cephalization?

-Can lead to more complex neural tissue and complex behavior

-Sensitive and vital organs are left vulnerable in a centralized region

Diploblastic

Contains two tissues: ectoderm and endoderm, with an unofficial layer called the gastroderm

Triploblastic

Three layers: endoderm, mesoderm, ectoderm

Acoelomate

No body cavity, no spaces

Blastocoelomate

Body cavity not fully lined with mesodermE

Eucoelomate

Body cavity is fully lined with mesoderm

Enterocoelous

the process by which some animal embryos develop and the origin of the cells involved

Schizocoelous

a process by which some animal embryos develop a secondary body cavity, or coelom

Spiral determinant cleavage

Yolk on one end of the egg, first two divisions are equal, the next division is unequal, this forms micromeres and macromeres, with a rotation to the right

Radial indeterminant cleavage

Yolk that is evenly distributed throughout the egg, all divisions are equal so there are no micromeres, cell fate is not determined until later in development

Gastrulation

ectoderm invaginate inside to form endo and mesoderm tissues

Protostomes

Mouth first development from the blastopore, schizocoelous in nature (split-cavity), spiral determinant cleavage.

Groups: Mollusca, Arthropoda, Annelida

Deuterostomes

Other first, blastopore develops into the anus, and the mouth develops later. Enterocoelous. Radial indeterminant cleavage.

Groups: Chordata, Echinodermata

Metazoa origins

colonial theory: single celled organisms grouped together for their mutual benefit, and certain organisms specialized until they became the planula larva (with flagella), and they had primitive radial symmetry

Syncytial Theory

A ciliated protist had multiple nuclei

Polyphyletic Origin

Multiple ancestors, different origins for different groups. Flagellates became sponges, ciliates became flatworms

Monophyletic Theory

Singular ancestor, evidence based on 18s rDNA, and the origins are from choanoflagellates

Porifera

“Pore bearers”

Sponges - simplest metazoans

Sessile - larvae are motile

Lack symmetry

Few mm to over 2m

8.3k species - 98% marine

Choanocytes

Defining characteristic

-Generate water currents

-Food capture

-Sperm capture

General Characteristics of sponges

-No true germ layers, cell acting independently of one another

-No musculature, neurons, or organs

-Filter feeders, intracellular digestion inside single cells, archeocytes deliver food to the individual cells

-No specialized gas exchange, works on diffusion

-Spongocoel lined with choanocytes

Pinacoderm

Outer layer of poriferan body with pinacocytes (contractile cells)

Mesohyl

Gelatinous material between the pinacoderm and choanoderm in poriferans, archeocytes inside this layer the move the food into cells

Choanoderm

Inner layer of the poriferan body with choanocytes

Aquiferous system

Reliant on water currents. The poriferan body has ostium/dermal pores to allow incurrent water flow. The internal system of the sponge, has three possibilities, (asconoid and syconoid types have spongocoel, and leuconoid types have incurrent canals and choanocyte chambers). Osculum allows outcurrent water flow

Asconoid body

Vase like body, one large osculum and several small ostia, large spongocoel, simplest and least efficient sponge. Leucosolenia is an example we saw in lab.

Why is the asconoid body inefficent?

As the body increases in size, the ostia do no grow larger, meaning that the sponge is not drawing in more water with the increased size

Syconoid

Slight large than asconoid

-More infoldings of body wall - more surface area that form flagellates canals

-More efficient

-Still small

-Scypha and Grantia specimens in lab

Leuconoid

Most sponges

-Reduction of the spongocoel

-More infoldings with choanocyte chambers

-Many oscula

-Most efficient body type

-More common, much larger

Choanocyte

Collar cell

-Long thin pseudopodia and flagellum

-Responsible for generating water currents

-Can form eggs and sperm

Archeocyte

-Amoeba-like, undifferentiated cells

-Responsible for food digestion (nutrient storage)

-Waste removal

-Can form eggs and sperm

Sponge cell types

• Pinacocyte

• Porocyte - Form the ostium

• Myocyte - Contractile elements

• Sclerocytes - make needle like structures (spicules makes of CaCO3 or SiO2)

  • Spongocyte - scattered within the mesohyl, secretes spongin that allow support and flexibility

Spicules

Support structure that is glass-like, the spicule types can help identify different species

Parazoa

• Filter feeder

• Phagocytosis and intracellular digestion - involving the choanocyte and archeocytes

  • Eats DOM (Dissolved Organic Matter)

Parazoan Reproduction

• Asexual

  • Budding

  • Gemmules like a little egg

  • Freshwater and some marine

  • Archeocytes covered with spicules

    • Micropyle - spicules go out of this opening

    • Will form a new sponge

Regeneration

When sponges are cut into small pieces, each growing into a new sponge. If cells are separated, they will reaggregate

Other methods of sponge reproduction

• Hermophroditic

• Gametes develop from archeocytes and choanocytes

• Fertilization can be external or internal, and the sperm is captured by choanocyte

• Developing embryos may be retained for a period, and brooded

  • Flagellated larvae

Parazoa: Blastula Larvae

• Hollow blastula

• One end develops the flagella

• Blastula opens and inverts -Amphiblastula

  • Groups: Calcarea and some Demospongiaia

Parazoa: Parenchyma larvae

Solid mass of cells that are flagellated, this includes most demospongia

Parazoa biotoxins

They can produce biotoxins and allelochemicals that reduce predation and help with space competition

Example: Tedania - fire sponge

Parazoan medical applications

Antimicrobial and antitumor compounds

-Arabinosides, manoalide, halichondrins: eribulin

Class: Calcarea

• Spicules of CaCO3, that are 1, 3, or 4 rayed

• All three body types are possible, but out of living species are asconoid types

  • All marine

Class Hexactinellida

• 6 rayed silicon spicules

• Glass sponges

• Live in soft sediment

• Sycanoid or leuconoid

• Layers are syncytical

• May have radial symmetry

  • All marine in deep water

Class Demospongia

• 80-90% of species - alSuppl freshwater sponges

• All leuconoid

• Many growth forms

  • Supported by spongin

Cladorhizid sponges

• From class demospongia

  • No ostia or oscula

  • Carnivorous on arthropods

Class Homoscleromorpha

• Spicules lacking or silicon based spicules

• Basal membrane under pinacoderm

• Pinacoderm cells are ciliated

• May be linked to other metozoans

Phylum Placozoa

-3 Described species (molecular data suggests more)

-Discovered in a marine aquarium in 1883 (Trichoplax adherens)

-2-3 mm

-Motile (ameboid movement and cells are flagellated)

Placozoa characteristics

• Several 1000 cells arranged in double layer plate.

• Ventral layer has columnar cells with single flagellum and glandular cells that perform extracellular digestiion

• Dorsal layer has flagellated cells and shiny spheres that are defensive

  • Layers are separated by fluid layer with fibrous cell network and the fibers may have contractile functions

Placozoan Reproduction

• Asexual - budding, fission, and fragmentation, they can regenerate lost parts

• Sexual - genetic evidence shows this occurs and embryos never develop past 64 cells

Phylum Cnidaria

• 12,000 species

• Radial symmetry

• All aquatic and mostly marine

• Two body forms: Polyp (sessile) and Medusa (free swimming)

  • Two life forms

Cnidaria: Characteristics

• Cnidae - stinging thread, organelle produced in cnidocyte/cnidoblast

3 Types of Cnidae

• Nematocysts - Most common, 30 different types, may contain toxins

• Spirocysts - Only in anthozoa

• Ptychocyst - Only in Ceriantharians

More about cnidae

• Protein capsule that is closed on the top by an operculum, with a hollow coiled tuber, trigger is cnidocil.

• Cnidocil is a modified cilium that detects mechanical and chemical stimuli, coiled tube is forcefully everted, potentially with barbs and toxins.

• Cnidae function in food collection, defense, locomotion

Common characteristics of Cnidarians

• Diploblastic with ectoderm and gastroderm, mesoglea

• Mouth and gastrovascular cavity, have digestive and circulatory function, and perform extracellular digestion

Cnidarian muscles

Have muscle and nervous tissue, they have myoepithelia, nerve net, and specialized sensory structures

Cnidarian nerve net

• Non centralized

• Composed of neurons and neurites that multipolar and bipolar

• 2 reticular arrays

  • Between the epidermis and mesoglea (fast conducting)

  • Between gastrodermis and mesoglea (slow conducting)

• Better development in the medusa form, forming nerve rings

Special sensory structures in cnidarians

• Ocelli - light

• Statocysts - balance

• Sensory lappets - touch

• Rhopalia - guage and control swimming and muscle contraction

Cnidarian lifestyle

• Mostly carnivores - some are parasitic, some have symbiotic relationship with zooxanthellae (corals, jellyfish, hydra)

• No specialized gas exchange or waste excretion structures, relies on diffusion

Cnidarian anatomy

Incomplete digestive system, no circulatory system, that all occurs in the gastrovascular cavity.

Cnidarian reproduction

Asexual budding or fission. Sexual reproduction also happens. Gametes develop in the gastrovascular cavity and are expelled through the mouth.

Class Hydrozoa

• Primarily marine (a few freshwater)roder

• 3000 species

• Hydroids and hydromedusae - polyp form is more dominant life phase

• Lack cnidocytes in gastrodermis

• Alternation of generations is common, but one may be reduced, medusae may be retained

• Colonial polyps, individuals are not large

  • Forms: Zooids, Stolon, and Hydranth

• Perisarc made of chitin - Thecate vs athecate

• Gastrovascular cavity is continuous

Thecate

Having a sheath or being contained within a sheath. Athecate is without a sheath

Hydrozoan polyp specialization

• Gastrozooid

• Gonozooid —> Gonophore

• Dactylozooid

Hydrozoan medusa

Small and have a velum

Velum

Muscular ring of tissue inside the opening of the hydrozoan

Hydrozoan reproduction

• Asexual budding

• Sexual

  • solitary polyps form a sporosac

  • colonial form produce gonophores

  • medusa may be retained or released

  • gametes are released (spawned), and there are separate sexes

  • Produce planula larvae

Hydra

• Only the polyp stage with no planula or medusae

• Polyps are not colonial

• Have both seual and asexual reproduction