BIOL 2003: Lesson 4 (Ctenophores)

Ctenophores AND Xenacoelomorpha

Ctenophores

• comb jellies

  • 8 comb rows with paddle like ctenes for swimming

• biradial symmetry 

• colloblast cells 

  • ‘lasso’ cells

• exclusively marine 

• 150 species 

Ctenes

• cillary comb/like groups of cilia used for swimming

• swim mouth forwards

  • by waves of beating cillia acting as propulsion

Where does colour come from

• most are colourless and transparent 

  • some deep-water species are pigmented 

• light refraction off of ctenes acts as a rainbow 

  • not true colour, but light refracting off 

• bioluminescence

  • can emit light (usually at night) 

  • phylum with the greatest % of bioluminescence 

  • usually blue and green, via proteins in the photocyte cells 

Predation 

• most have 2 retractable tentacles with adhesive colloblasts 

  • tentacles wiped across the mouth so they can eat 

• some use muscular mouth lobes to engulf prey

• some use cilia on lobes to draw water/prey to mouth

• they do not have nematocysts (unlike cnidaria)

Body forms

• tentaculate

• lobate

• thimble-shaped

• ribbon shaped

  • largest animal to swim using cilia

• creeping sole

  • found only at the bottom of the ocean

Nervous system 

• nerve net similar to cnidarians

  • nerve plexus concentrated under each comb plate

• all have a statocyst

statocyst 

• sense organ on the aboral pole

• has a statolith (calcareous particle) which is used to maintain equilibrium 

Reproduction 

• may be either asexual or sexual

• asexual

  • regeneration of virtually any lost part

• sexual

  • most monoecious (one single animal can produce both sperm and egg)

  • gametes shed into water via mouth, and free swimming larva

  • some undergo internal fertilization and brood their eggs 

Ctenophores organization

• tissue level 

Ctenophores symmetry

• biradial symmetry 

Ctenophores body cavity

• no true body cavities 

Ctenophores development

• diploblastic 

Ctenophores segmentation

• no true segmentation 

Bilateria

• bilateral symmetry 

  • mirrored left and right halves when cut on saggital plane, meaning they have an anterior, posterior, dorsal and ventral view 

• cephalization 

• triploblasts

Cephalization

• development of sense organs at the anterior end to sense environment head-first

• moving in one direction 

• forward movement gives an anterior and posterior 

• mouth in head region 

  • anus/wastes in rear 

Triploblasts

• three embryonic germ layers

  • ectoderm, endoderm, mesoderm

• this gives way for the creation of body cavities…

  • acoelomate: cavity space filled with tissue

  • pseudocoelomate: cavity filled with fluid, and only partially lined with mesodermal tissue

  • coelomate: cavity filled with fluid, and fully lined with mesodermal tissue

Xenacoelomorpha

• xenoturbella + aceoelomorpha 

  • phylum of the bilateria 

• bilateral, triploblasts, and acoelomates 

• lack an anus, nephridia, and circulatory system 

• pink sock marine worms 

Xenacoelomorpha organization

• organs 

Xenacoelomorpha symmetry

• bilateral symmetry 

Xenacoelomorpha body cavity

• acoelomate 

Xenacoelomorpha development

• triploblasts 

Xenacoelomorpha segmentation

• no segmentation