The Lophotrochozoa 1

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 Development is characterized by: blastopore becomes the mouth Spiral / determinate cleavage Schizocoely

Mouth Formation Blastopore becomes the mouth and the anus forms secondarily Future anus blastopore archenteron (primitive gut) mouth

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 blastocoel Mesodermal cells Split in mesoderm Developing coelom ectoderm endoderm mesoderm

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 Bilateral Symmetry with anterior and posterior ends Cephalization concentration of sensory organs in the head of the animal

Lophotrochozoans Characteristics Digestive System complete (they have an anus!) some regional specialization Circulation System no system (or organs) performed by the pseudocoelom fluid

Gnathiferans and Smaller Lophotrochozoans

The Lophotrochozoa

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 Eutely each individual of a species has the same number of cells growth occurs by cells getting bigger rather than dividing

P: Gnathostomulida : gnatho, “jaw”; stoma, “mouth” Benthic, interstitial Monociliated epidermal cells Jaws and muscular pharynx Often vermiform Hermaphroditic About 80 species have been described jaws and basal plate Gnathostomulid 19

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P: Micrognathozoa Limnognathia maerski Three sets of paired jaws, interstitial, cellular epidermis. 21

Phylum Rotifera the rotifers 1st phyla we will talk about and what we will cover in the lab today is… the 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 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 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 modified jaws within the mastax a modified muscular pharynx

Looking down into the corona….

Mastax-trophi complex

Some of the trophi (jaws): Malleate mastax Ramate 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)

Reproduction 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 Amictic eggs – Asexual 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 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 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

Reproduction 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!