N Mostly Aquatic, Esp. Freshwater. Some Terr. E.G Roundworms in Moist Soils

Pseudocoelomates

 9 phyla. – 5 ecdysozoan, 4 lophotrochozoan  mostly aquatic, esp. freshwater. some terr. e.g roundworms in moist soils  many microscopic  pseudocoelom –

 internal organs float on fluid that aids in circulation, digestion, & hydrostatic skeleton

Other distinguishing characteristics  eutely -  nuclear divisions are completed at hatching & subsequent growth involves increase in cell size  complete gut - mouth & anus w/tubular digestive tract.  cuticle –

 protonephridia present, esp. in freshwater sp.  some cephalization w/primitive brain  most dioecious & usu. direct development in free-living sp.

Pseudocoelomate phyla Ecdysozoan  Nematoda - 25,000 sp  Nematomorpha – 320 sp.  Kinorhyncha – 150 sp  Loricifera - 21 sp.  Priapulida – 17 sp.

Lophotrochozoan phyla  Rotifera – 2000 sp.  Acanthocephala – 1150 sp.  Gastrotricha – 450 sp.  Entoprocta – 150 sp

Phylum Nematoda  roundworms

1  microscopic (free-living)  several meters long (parasitic)  some free-living in aquatic habs (sea & fw). & soils (polar to tropics), many parasitic

General characteristics 1) triploblastic, bilateral, unsegmented 2) body 3) 4) complete gut. mouth usu. surrounded w/sensory organs 5) excretory system - 6) only

External features  cuticle –

 Functions 

  cuticle may have spines, bristles, papillae, warts, or ridges  outer cellular layer called

Excretory System  performs both osmoregulation & excretion of nitrogenous wastes  glandular system - aquatic sp. - renettes,

 tubular system - parasitic sp. - renettes form large canal which eliminates material thru excretory pore

Reproductive System  dioecious & dimorphic (males smaller)

 paired, tubular ovaries   

 single testis     bursa, posterior flap of tissue, aids in copulation

2  internal fertilization. sperm lack flagellum  female may then lay eggs or may retain eggs during development  larva hatch w/most adult features. four molts

Ecological, economic & medical significance  Ascaris lumbricoides - perhaps 1.26 billion people infected by roundworm  parasitic roundworms include: pinworms, hookworms, Trichinella w/trichinosis, Wucheria w/elephantiasis, dog heartworm  very abundant in soils. up to 5 bil./acre. 4.5 mil/m2 in ocean bottom mud

Coelomates  body cavity lined by:  allows the organs to be held in place better. prevents twisting  more room & flexibility is allowed for organ development  coelom provides hydrostatic skeleton  more organs are derived from mesoderm  smooth muscles found in many more structures, e.g. digestive tract

Phylum Mollusca  90,000 sp. diverse group (70,000 fossil sp.)  aquatic from tropic to polar waters, some terr. up to 7000 m in altitude

General characteristics 1) triploblastic, bilateral, unsegmented protostome 2) body of two parts: a) head-foot –

b) visceral mass - 3) coelom reduced to area around heart – pericardial cavity 4) mantle secretes calcareous shell 5) open circulatory system except in cephalopods 6) scraping usu. present 7) metanephridia remove excretory wastes

3 major classes, 4 minor

3  Gastropoda -  Bivalvia - – 30,000 sp - 2-lobes mantle producing 2 hinged shells  Cephalopoda - – 786 sp.- shell often reduce or absent

Gastropod distinguishing features  torsion -

 Poss. advantages: 1) allows foot to recede last & thus protecting head, some sp. have operculum on foot 2) allows clean water to enter mantle cavity, rather than water from behind snail that may be silted 3) more sensory receptors in anterior  disadvantage - anus & excretory openings are above head & poss. pollute water near mouth  some adaptations to avoid this (water in left side, waste out on right)

Class Cephalopoda  highly developed in many ways  anterior part of foot has been modified into:

 head & visceral mass are dorsoventrally lengthened & body is reoriented so that tentacles are ventral & visceral mass in dorsal  mantle encloses body except head & tentacles in muscular sheath

Shell  only Nautilus has shell but feature is found in ancestral forms  Nautilus shell is separated by:   cuttlefish have internal shell called  squid have chitinous , cartilaginous plates  octopus have no shells

4 Locomotion 

 muscles in mantle contract & water is forced out of posterior funnel in mantle  octopus usu. use tentacles for crawling, jet-propulsion in emergencies  Flying Squids shoot out of water & glide for short distances have been clocked at 20 mph

Other systems  Digestive carnivores w/ beak-like jaws, radula works like tongue  Circulatory – closed system  Nervous – highly-developed brains, single-lens eye, statocyst and many chemoreceptors  Integument – - pigment cells w/muscles for quickly changing colors  Ink glands –

Reproduction & development  dioecious, gonads in dorsal part of visceral mass  male releases sperm in encased packets -  eggs are large & yolky  copulation - male grabs female w/arms & uses specialized tentacle to transfer spermatophores to mantle cavity near oviduct  sperm are released & fertilize eggs as they leave oviduct  octopods tend eggs laid in substrate

 development. miniadults emerge

Ecological, economic & medical importance  many molluscs used for food by humans  shells and pearls also used as jewelry, currency, decorations, musical instruments  pests –  intermediate hosts for many human parasites  ecological – filter feeders, algae eaters, predators, some parasites