order
                        
                      
                                    Coleoptera
                                       “Adult Beetles”
                                  
                                    Coleoptera
                                       “Larval Beetles”
                                  
                                    Diptera
                                       “True Flies”
                                  
                                    Ephemeroptera
                                       “Mayflies”
                                  
                                    Hemiptera
                                       “True Bugs”
                                  
                                    Lepidoptera
                                       “Aquatic Caterpillars, Snout Moths”
                                  
                                    Megaloptera
                                       “Alderflies, Dobsonflies, and Fishflies”
                                  
                                    Odonata
                                       “Dragonflies and Damselflies”
                                  
                                    Plecoptera
                                       “Stoneflies”
                                  
                                    Trichoptera
                                       “Caddisflies”
                                 family
                        
                     Elmidae
               
            Optioservus
            
                  “Riffle Beetle Larvae”
               
      Genus Overview
                  
               
                        This is a widespread genus with 13 North American species. Larvae and adults live in fast and slow portions of streams, clinging to substrate. Larvae are scrapers of periphyton on rock surfaces.
                  
               Characteristics
                  
               POLLUTION TOLERANCE
                        Southeast: 2.7 and higher
                                 Upper Midwest: 4 and higher
                                 Midwest: 2.75 and higher
                                 Mid-Atlantic: 4 and higher
                              0 = least tolerant, 10 = most tolerant
                        FEEDING HABITS
                        
                                 Collector / Gatherer
Scraper / Grazer
                        
                     Scraper / Grazer
MOVEMENT
                        
                                 Clinger
                        
                     DISTRIBUTION
                        
                                 Widespread (east of the Rocky Mtns.)
                        
                     HABITAT
                        
                                 Lotic-depositional
Lotic-erosional
                        
                     Lotic-erosional
Diagnostic Characters
               order
                         
                                       
                                       
                                    Eye Spots
                                  
                                       
                                       
                                    Lateral Gills USUALLY Absent
                                  
                                       
                                       
                                    USUALLY 4-5-Segmented Legs
                                 family
                         
                                       
                                       
                                    Brown, Sclerotized, Spindle-Shaped Body
                                  
                                       
                                       
                                    Operculum
                                 
                  + Expanded Character List
                  
                     
               
            
                        Order:
                           Larvae: Usually without lateral abdominal gills. If gills present, then 4 hooks clustered on segment 10. Thoracic legs each usually with 4 or 5 segments and with 1 or 2 claws; if without legs, head distinctly sclerotized and posterior body (thorax and abdomen) simple, without gills, hair brushes, suckers, or breathing tube. Eye spots usually present, but compound eyes absent.
                     
                     
                        Family:
                           Labrum and clypeus separated by distinct suture. Antennae 2–3 segmented. Head with ocelli in groups of 5. Legs adapted for walking, sometimes small, each 3–4 segmented and with single claw. Thoracic tergites clearly defined. Abdomen 9-segmented, ventral gills absent from segments 1–8. Segment 9 (posterior-most segment) with ventral lid-like flap (operculum) concealing thread-like gills and pair of hooks. Body strongly sclerotized (hardened), dark brown or red-brown, roughly cylindrical or spindle-shaped, with head and legs visible in dorsal view.
                     
                     
                        Genus:
                           Prothorax with lateral postpleurites each composed of two parts, without posterior sternum. Mesopleuron composted of one part. Abdominal terga without median and sublateral humps or small median humps present, pleura present on segments I-VII.
                     
                   
                   
                   
            Dorsal
               Lateral
               Ventral
               


