bio 4

Arthropods:

Arthropod structure - division of tissues(endoderm,mesoderm,ectoderm),bilateral symmetry, a coelom, and segmentation

Metamerism: repetition of body segments.

Tagmata: individual segments often exist only during embryological development of the animal. These fuse into functional groups, called tagmata (in a process called tagmatization).


  • The typical body plan of an arthropod includes a head, thorax, and abdomen

  • In some, the head is fused with the thorax to form a cephalothorax

  • Arthropods are the first group to have an exoskeleton and jointed appendages. 


Exoskeleton - Has to two layers (outer layer the epicuticle-waterproofing + chemical resistance) (inner layer - made of chitin allowing exoskeleton to move) 

Coelom - is a open circulatory system

Ocellus - simple eye that detects light intensity and motion 

Compound eye - detects movement can form primitive images 


Horseshoe crab:

  • Telson (tail)

  • Shield-like carapace (covers the cephalothorax)

Crayfish:

  • The body is divided into two main regions, the cephalothorax and the abdomen, with appendages on both.

  • An extension of the cephalothorax is the pointed rostrum, covering a pair of compound eyes on eyestalks.

  • There are also two pairs of antennae: the longer true antennae and the shorter, branched antennules.

  • Chelipeds with its chela, both for defense and for capturing and killing prey

  • Chelipeds: one of the 5 pairs of walking legs. (BUT NOT USED FOR WALKIN)

  • Swimmerets: found ventrally on the abdomen

  • The swimmerets move to circulate water for respiration.

  • In females fertilized eggs are attached to the swimmerets where they are brooded as they develop

  • The tail fan also helps protect eggs and young on the female’s swimmerets.

  • Males have gonopods, females do not. (large first swimmerets)



Echinoderms:

Asteroidea - 

usually pentamerous (five-armed)  

spiny skin with pedicellariae 

aboral madreporite and anus within a central disc 

tube feet confined to ambulacral grooves on the oral surface


Ophiuroidea

  • thin, mobile arms, usually pentamerous in brittle stars

  • many branching arms in basket stars 

Echinoidea

  • arms lacking

  • urchins globular in shape, sand dollars and sea biscuits more flattened

  • in sand dollars the aboral tube feet penetrate the skeleton via petaloid slits for respiration; mouth and anus both on the oral surface 

  • spines short and numerous in sand dollars, longer, often very long, in urchins 

  • sand dollar endoskeletons penetrated by openings (lunules) for stability in rushing water

  • all forms have a feeding device called an Aristotle’s lantern


Sea cucumbers


  • no arms 

  • bilateral symmetry; anterior-posterior body axis 

  • anterior tube forming a whorl of tentacles around the mouth 

  • remaining tube feet limited to ventral surface for locomotion 

  • no spines or pedicellariae; skin warty 

  • endoskeleton reduced to microscopic ossicles embedded in skin 


Sand dollar: 


Oral side:

Mouth: food

Food grooves: Where small food particles are captured.

Anus: gas exchange.


Aboral:

Gonopores; where gametes are released. (reproduction)

Petaloids: respiratory surfaces (very small)

Lunes: Allow water to pass through the dollar without flipping it over.

Madreporite; Where water comes in.