Phylums Nematoda, Nematomorpha, + Tardigrada

Phylum Nematoda form + function

• ecdysozoans (grow by shedding their cuticles)

• no circulatory or respiratory system

• pseudocoelomate

  • fluid-filled main body cavity that isn’t or is only partially lined w/mesodermal tissue

  • creates hydrostatic skeleton

Nematoda sensory systems

• have mouth + internal cephalization, but not much of a head

• underdeveloped sense organs

• sensory papillae around head + tail

• pair of amphids (sense organs) on each side of head

  • have pore-like openings that lead to a pit of sensory structures

  • sense chemical cues

Nematoda feeding

• complete digestive system

• mouth, pharynx, long intestine, short rectum, anus

• no esophagus

• plant-parasitic nematodes have a spearlike stylet to insert into plant cells for feeding

Nematoda excretion

• lack cilia

  • don’t use flame cells + nephridia for excretion

• excretory tubes move solid waste to anus

• ammonia excreted thru body wall

  • no special organ for this

Nematoda reproduction

• dioecious (separate male + female sexes)

• sexual reproduction only (NO asexual)

parasitic Nematodes

• capable of parasitizing nearly all vertebrates + invertebrates

• also important crop pests

• rely on behavior of hosts to be ingested by them

• have 2 - 4 hosts

  • eggs passed in host feces

  • larval stages happen outside the host

  • larvae ingested by host, migrate to GI tract + lay eggs

Phylum Nematomorpha

• used to be in same phylum as Nematoda

• has cuticle

• has muscular system + nervous system structure

• live in wet + moist surroundings

• parasitic in arthropods as juveniles

• free-living as adults

Nematomorpha form + function

• unlike Nematoda, absorb food from hosts thru body wall

• lack circulatory, respiratory, + excretory system

• dioecious

• sexual reproduction only (NO asexual)

• external fertilization

Nematomorpha life cycle

• adult + egg forms pretty much always in water

• hatched larvae are eaten by aquatic insect

• encysts in insect (not consumed by them)

• insect eaten by suitable host

• nematomorph worm matures in host

• may influence host behavior to cause it to seek out water

• once in water, leaves host, mates + lays eggs

Phylum Tardigrada

• aka water bears

• usually less than 1mm long

• ~900 species

• live in wet soils + water film around mosses + lichens

• can also be marine

• 4 pairs of stubby unjointed legs w/4-8 claws

Tardigrada form + function

• some prey on algae, nematodes, rotifers, + other small animals

• others are parasitic on sea cucumbers + barnacles

• no circulatory system

• no respiratory system

  • gas exchange by diffusion w/in body surface

  • rely on body being moist for this

• have brains + eyes

• separate sexes

Tardigrada feeding

• feed by sucking w/2 piecing stylets

• pharynx sucks in liquid contents

• will also cannibalize other live or dead tardigrades

Tardigrada cryptobiosis

• can withstand harsh conditions

  • -272 degrees C to 149 degrees C

  • ionizing radiation

  • being submerged in ether + alcohol

  • dehydrated from body water content of 85% → 3%

• do this by entering “tun” state

  • state of suspended animation

  • extremely low metabolism 

  • no development, no cellular repair, no reproduction