The Lophotrochozoa

Protostomes Characteristics

• Protostome groups consisting of two large clades the Lophotrochozoans and the Ecdysozoans.

• Lophotrochozoans include 10 smaller protostome phyla.

• Acoelomate, Pseudocoelomate or Eucoelomate bodies.

Protostome Characteristics

Protostome

Development is characterized by:

• blastopore becomes the mouth

• Spiral / determinate cleavage• Schizocoely

Mouth Formation

blastopore archenteron(primitive gut)

Future anus

mouth

Blastopore becomes the mouth and the anus forms secondarily

Cleavage

• Cleavage is the initial process of development after fertilization of the egg.

Radial Cleavage planes are symmetrical to the polar axis

Produces regulative development

Spiral Cleavage: cleavage planes are oblique to the polar axis

Produces mosaic development

Schizocoely

ectoderm mesodermendoderm

Split in mesoderm Developing coelom

Mesodermal cells

blastocoel

Lophotrochozoans Characteristics

The name Lophotorochozoa comes from the names of the larval type of the two major animal groups including the Lophophorata and the Torchozoa.

Trochophore Larva

Lophotrochozoans Characteristics

Organ level of organization

Tissues are organized to form organs which are used to accomplish physiological functions.

Triploblastic

3 Germ Layers

endoderm

mesoderm

ectoderm

3 Tissue Layers

gastrodermis

mesoderm

epidermis

Lophotrochozoans Characteristics

• with anterior and posterior ends

Bilateral Symmetry

Cephalization

• concentration of sensory organs in the head of the animal

Lophotrochozoans Characteristics

• complete (they have an anus!)• some regional specialization

Digestive System

Circulation System

• no system (or organs)• performed by the pseudocoelom fluid

Gnathiferans and Smaller Lophotrochozoans

The Lophotrochozoa

Gnathifera

There are 4 different phyla that are classified as Gnathifera.

Rotifera

Acanthocephala

Gnathostomulid

Micrognathozoa

Gnathifera Characteristics

• Other than the Acanthocephalans all phyla posses small, cuticular jaws with a homologous microstructure.

Gnathifera Characteristics

• each individual of a species has the same number of cells

• growth occurs by cells getting bigger rather than dividing

Eutely

P: Gnathostomulida : gnatho, “jaw”; stoma, “mouth”

Gnathostomulid

jaws andbasal plate

• Benthic, interstitial

• Monociliated epidermal cells

• Jaws and muscular pharynx

• Often vermiform

• Hermaphroditic

• About 80 species have been described

P: MicrognathozoaLimnognathia maerski

Phylum Rotiferathe rotifers

Phylum Rotifera: rota, “wheel”; fera, “to bear”

• Includes about 1,800 described species.

• Tiny metazoans (up to 3 mm), that are predominantly freshwater although some are marine and terrestrial (live in mosses).

The “wheel” animals

{{

Head{Trunk

Foot

Corona– have a “crown” of cilia called a corona – the corona creates a

current to bring food into the mouth

Corona of Foscularia species

Body Wall and Support

• Most rotifers possess a gelatinous cuticle outside the syncytial epidermis.

• They possess a skeletal lamina which produces the lorica and other surface structures.

Rotifers of the genus Keratella donot possess a foot. They are fast swimmers. Their lorica (shell) looks like a jigsaw puzzle and is covered with small spikes. There are long spines on each corner. The photograph shows how the cilia are grouped in tufts.

Kellicottia is a rotifer that lives in open waters of lakes. The long spines might prevent them from being eaten by predators.

Well developed and complex muscle bands

Body appears to be composed of segments, they are superficial segments.

Feeding– have a specialized feeding structure called

the:

mastax-trophi complex

a modified muscular pharynx

modified jaws

within the mastax

Looking down into the corona….

Mastax-trophi complex

Some of the trophi (jaws):

Ramate mastax Malleate mastax

These are crushing/grinding forms.

Some of the trophi (jaws):

Forcipate mastax Incudate mastax

These are grasping, predatory forms.

Nervous and sensory system- cephalization, cerebral ganglia- dorsal and ventral nerve cords- eyes

Circulatory system– no system (no organs)– performed by fluid in pseudocoelom

Excretion – protonephridia and flame cells– cloacal bladder (collects wastes)

Sexual- complex life cycle with different types of eggs- usually dioecious but in some groups, males

are absent (parthenogenesis)- Parthenogenesis:

unisexual reproduction where females produce offspring from unfertilized eggs (virgin birth)

Reproduction

Reproduction

• 2 types of eggs: amictic & mictic

Amictic eggs – Asexual Reproduction

• diploid (mitotically produced)• can’t be fertilized• develop into diploid, amictic females

Reproduction

Mictic eggs- Sexual and Asexual Reproduction

• haploid (meiotically produced)• produced after some sort of environmental stimulus

(eg. high density, change in temperature)

if unfertilized, develop into haploid males

if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females

Brachionus is a very common genus. They carry their eggs on their foot. The various species can be identified by the spines on their lorica (shell).

Asplanchna is a large bag-shaped rotifer. This individual carries an almost fully developed embryo inside.

Eggs maintained in maternal tube

Resting eggs of monogonont rotifers

• Because of the reduced role of males in reproduction, most males are incapable of feeding and do not even have a digestive tract (they are just there for sperm delivery!).

• Males have never been recorded in Bdelloid rotifers. This means they haven’t had sex in millions of years!

Reproduction