Gnathiferans and Smaller Lophotrochozoans Chapter 9 Protostomes Characteristics

Gnathiferans and Smaller Lophotrochozoans • Chapter 9

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 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 ectoderm endoderm Developing coelom mesoderm

Body Cavities in Triploblastic Animals

Acoelomate Characteristics No body cavity ectoderm mesoderm Gut endoderm

Pseudocoelomate Characteristics “false” body cavity ectoderm pseudocoelom mesoderm Gut endoderm the pseudocoelom is lined by mesoderm on ONE side only

Eucoelomate (Coelomate) Characteristics Have a “true” body cavity that is completely surrounded by mesoderm ectoderm coelom mesoderm Gut endoderm

Coelomate or Eucoelomate Characteristics the coelom • is a closed, fluid filled cavity that surrounds the gut • mesodermal membranes (mesenteries) suspend organs in the coelom

The Lophotrochozoa

Lophotrochozoans Characteristics Organ level of organization Tissues are organized to form organs which are used to accomplish physiological functions. Triploblastic 3 Germ Layers 3 Tissue Layers endoderm gastrodermis mesoderm ectoderm 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

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 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

P: Micrognathozoa Limnognathia maerski

Phylum Rotifera 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 don't 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 like 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): Ramate mastax These are crushing/grinding forms. Malleate mastax

Some of the trophi (jaws): Forcipate mastax These are grasping, predatory forms. Incudate mastax

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 • 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) Ø if unfertilized, develop into haploid males Ø if fertilized, secrete a thick, protective shell until the environment is favorable again, after which they develop into diploid, amictic females

Resting eggs of monogonot 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!