Origins of Multicellular Animals and Sponges

3 hypotheses of multicellular animals

syncytial, colonial flagellate, symbiotic

Syncytial hypothesis is

ancestor is single celled multiple nuclei which eventually separate into individual cells and remain attached

colonial flagellate hypothesis is

ancestor is colonial flagellate like volvox

symbiotic hypothesis is

multiple species living in a colony eventually merged genomes into one organism

choanoflagellates are considered

the closest living relative to animals (metazoa)

metazoa are

multicellular animals

metazoa include

placozoa, porifera, and eumetazoa

placozoa are

marine, free living, few species

porifera are

sponges, no tissue (parazoa)

eumetazoa are

with tissues, all other multicellular animals

phylum porifera nickname

pore bearer

porifera were originally thought to be

plants

porifera live primarily

marine, mostly shallower waters

porifera are

sessile

porifera are the most

primitive metazoans, have neither true tissues or organs

porifera have cells but the cells

do not communicate

pinacocytes are

outer cells covering sponge, equivalent to epidermis

porocytes are

cells which line the pores of the sponge, water is drawn through

choanocyts are similar to

choanoflagellates

choanocytes are

collared cells with flagella which create water current and collect food matter or sticky contractile collar

amoebocytes are

amoeba like cells found through the sponge

what do amoebocytes do

store, digest, and transport food, excrete wastes, secrete skeleton and may give rise to buds in asexual reproduction, there are several different types

types of amoebocytes

large amoebocytes, archeocytes, scleroblasts

large amoebocytes do what

distribute food to other cells of sponge, move by way of pseudopods

archeocytes do what

undifferentiates sponge cells that can give rise to more differentiated cells such as pinococytes or porocytes

archeocytes can

transform itself into any other type of cell

scleroblasts do what

produce spicules, two types

scleroblasts two types are

calcoblasts and silicoblasts

calcoblasts make

calcium carbonate spicules

silicoblasts make

siliceous spicules

spongin give phylum its

common name

some species have no spicules but do have

spongin

spongin is

a type of hardened secreted protein

some species of porifera have both

spicules and spongin

mesohyl means

noncellular

beneath the pinococytes is a

gelatinous protein layer, mesohyl

mesohyl contains the

skeletal material (spongin and spicules) and amoebocytes

three basic structural sponges are (from smallest to largest)

asconoid, syconoid, leuconoid

The structural type is based on

how much water they can bring in, how efficiently they can move water

asconoid sponges are the most

primitive

asconoid sponges are shaped like

small tube shaped with radial symmetry

asconoid sponges forms

clusters of tubes

asconoid sponge has two basic openings the

ostia and osculum

ostia is the

incurrent channal

osculum is the opening of the

spongocoel

asconoid sponge design imposes definite

size limits to sponges due to the problem of water flow, limited number of choanocytes

asconoid sponge design, the spongocoel contains such a large

volume of water that it is hard to push it out rapidly

syconoid sponges have a higher degree of

invagination (body wall folds)

syconoid sponges are more

advanced but still retains radial symmetry

syconoid structure helps

to rectify some of the water movement problem

syconoid structure increases the

surface area there are more choanocytes to water volume

syconoid structure decreases the

spongocoel volume

leuconoid sponges have the highest degree of

invagination

leuconoid sponge has

flagellated chambers that replace radial canals

leuconoid sponge design further increases the

surface area

leuconoid sponge design the spongocoel is gone except for

canals that lead to the osculum, or there may be a seres of excurrent openings

leuconoid sponges are the most

hydrologically efficient

sexual reproduction in animals typically in parasites or in an environment that will disappear

hermaphroditic, monoecious

separate sexes, male and females

dioecious

unisexual reproduction, females produce eggs and young without fertilization by males, eggs and young are either diploid or haploid are

parthenogenesis

parthenogenesis found in

rotifers, cladocerans, and others

sponges reproduce

sexually and asexually

sexual reproduction in sponges are when

amoebocytes produce eggs and sperm

sexual reproduction in sponges includes

hermaphroditic and dioecious

process of reproduction in sponges

sperm is released into environment, brought in by another sponge via ostia, fertilization takes place, zygote is expelled

zygote in sponges is known as

amphiblastula larva

the amphiblastula larva is expelled and

drops to the bottom to begin to develop

asexual reproduction in sponges includes

budding and gemmules

budding is when fragmentation of body wall

buds appear as outgrowth on sides of sponge

for buds on a sponge, at a certain

size they drop off and settle to bottom to form a new sponge

gemmules occurs only in

freshwater sponges

gemmules are groups of

food laden amoebocytes that deposit a hard covering of spicules around them

gemmules formation is triggered by

environmental conditions

gemmules allow the sponge to

pass the winter or periods of drought after which they break open and a new sponge develops

osmoregulation and excretion in sponges requires

no special organs

osmoregulation and excretion in sponges main waste is

ammonia

how is ammonia removed through osmoregulation and excretion in sponges

removed by water currents within the sponge

class calcarea spicules are composed of

calcium carbonate

class hexactinellida spicules fused to form

a lattice like skeleton

class hexactinellida are found in

deep waters

class hexactinellida are

syconoid sponges and marine

class calcarea have what sponges exhibited

all three types

class calcarea are found in

shallow coastal waters and all marine

class demospongiae spicules are

siliceous if present otherwise skeleton is made of spongin or both

class demospongiae shape

variously shaped, some are huge, all are leuconoid

class demospongiae all but one family is

marine

what family in demospongiae is freshwater

spongillidae

phylum placozoa is

trichoplax adhaerens

trichoplax adhaerens is the

sole species of the phylum although DNA suggests 8 species

trichoplax adhaerens is

marine

trichoplax adhaerens shape

platelike, no symmetry, no organs

trichoplax adhaerens may be considered

diploblastic since bottom layer is involved in feeding