MISSION  CREEK
MICROORGANISMS
Meroplankton

Arthropoda
 
      Order Coleoptera
          Family Gyrinidae  (Whirligig beetles)

     Order Diptera
          Family Chironomidae
          Family Dixidae
               Dixa sp.
          Family Culicidae

               Culicinae
               Anopheles larva (mosquito larva)
              
Chaoborinae  (Phantom midges)

  
     Order Ephemeroptera (mayflies)
      



     Order Hemiptera
          Family Corixidae (water boatman)
               Corixa sp.
          Family Gerridae (Water Strider)
               Gerris gibbiffer

     Order Megaloptera
          Family Sialidae (alderflies)

           
   Neochauliodes bowringi
 
    
Order Odonata
          Zygoptera (damselflies)
          Argia agrioides
   (California dancer)
  

Meroplankton refers to organisms that live only part of their life in the plankton.  Usually meroplankton has a complete or incomplete metamorphism.  The early stages are usually planktonic and then they emerge either as a land or flying critter.  Eggs of fish or other animals are included in this group.  Other organisms include their larval or nymph stages.  Some groups, like the dragonflies can spend up to 2 years as plankton and then emerge only to live on land for a few months. 

 Note:  Consult Quick Identification of Fresh Water Microorganisms for approximate sizes of organisms shown in this section.

ARTHROPODA

Order Coleoptera
Family Gyrinidae (Whirligig beetles)

Beetles are black, shiny, oval and ventrally depressed.  Adapted for rapid locomotion with its middle and back legs which are flattened and paddle-like.  Frequently fly but unable to take off from the surface, but can dive.  Larva and pupa stage tends to be in the mud and not in the water column.

 

Order Diptera 

This order includes many members that are in their larval and pupa stages and adapted to fresh water. The transition from larval and pupa may have very different forms.  The larval stages may last several weeks or up to two years depending on species, temperature, and food availability.  The skin usually molts 3 times.  Adults are never truly aquatic.  All aquatic representatives are legless although there may be pseudopods on the thorax or abdomen.  Diptera include the common mosquito, midges, gnats, crane fly, and the common fly.

Order Diptera
Family Chironomidae

This group is referred to as non-biting midges because the adult mandibles are poorly developed.  Larval chironomid species can help track ecological conditions.  This group can tolerate polluted water.  However, low numbers if found within a diverse population can indicate non-polluted conditions. 

Order Diptera
Family Dixidae
Dixa sp
.

Adult dixa midges are small insects that swarm around a pond or stream at dusk.  Females deposit eggs in shallow water.  The larvae have distinct thoracic segments and is U-shaped at rest.  The pupa stage  (photograph)  is not truly aquatic, as they attach themselves just above the water.

Order  Diptera
Family Culicidae  (Culicinae)
Mosquito (Anopheles larva)

Culicidae larvae are easily distinguished because their thoracic segments are fused and thicker than the rest of the body.  They mainly feed on algae, protozoa, and organic debris by using their bristles.  The larvae lie quietly on the surface and have a characteristic wiggling motion.

Order Diptera
Family Culicidae (Chaoborinae)
Phantom midges

Similar to mosquito but the adults do not bite.  The larva are called phantom because they are transparent.  They have jerky, lashing movements of the body.  The larva is predatory and catches small crustacean and other larvae with their antennae. 

Order Ephemeroptera
Mayflies

Small to medium terrestrial insect with incomplete metamorphism.  Its wings are delicate and held together at rest.  The have large compound eyes with a reduced mouth because the adult does not eat, as it lives for a few hours to a week.    The nymphs however are herbivores and browse on the  substrate.  The nymphs have three occasionally two distinct cerci (tails).  Cerci may be fuzzy or thread-like.  Nymphs are climbers, bottom crawlers, or burrowers. 

 

Order Hemiptera
Family Corixidae  (Water boatman)
Corixa  sp.

Water boatman* are totally aquatic.  Nymphs develop through 5 growth stages or instars.  Like all aquatic bugs they lack gills, so they need to breathe at the surface.  Most eat algae while some eat mosquito larva and other small aquatic organisms.

* Boatman are strong swimmers as adults.  So technically not planktonic.  We include them in the meroplankton section for that reason.

 

Order Hemiptera
Family Gerridae (Water Strider)
Gerris gibbiffer

 The adult lives around water.  Belly is covered with hair. Short front legs are used to catch prey while back legs are used to steer and move.  They are predators and scavengers.  They eat other small insects that fall in water or eat larvae.  Striders stay on top of water because of surface tension.

 

Order Megaloptera
Family Sialidae (alderflies)
Neochauliodes bowringi

Adults  are 10-70 mm with two pairs of wings held over their  body at rest.  Head has a long slender antennae and biting mouth parts.  The larva has a single tail filament with distinct hairs.  Segments of abdomen have 6 to 8 filaments on each side.  Not tolerant to pollution.

 

 

Order Odonata
Zygoptera (damselflies)
Argia agrioides (California dancer)

Nymphs are elongated with three paddle-like tails.  Two large eyes on top of head.  Nymphs are carnivorous, feeding on other aquatic invertebrates.

 

 

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