Mill Brook

ORDER: Ephemeroptera
FAMILY: Baetidae 
GENUS: Baetis 

This mayfly has three "tails" and a unique head shape. Its gills are oval shaped and insert dorsally. The wing pad shape is an obvious characteristic. More mature nymphs have long, dark wing pads. SMC

ORDER: Coleoptera
FAMILY: Elmidae
GENUS: Stenelmis

Riffle beetles appear in the streams as adults and larvae. The larvae of Stenelmis have a sternum on the ventral side of the pronotum.

The adult Stenelmis has a clear separation between the thorax and abdomen as well as a more distinctly separate head as compared to other genera. SMC

ORDER: Diptera
FAMILY: Chironomidae

 Midge larvae tend to be the most common macroinvertebrate at our sites.  As with other Diptera, there are no true jointed legs.  Chironomids do have a pair of prolegs at each end and preserved individuals tend to curl into a 'C'.  Identification past family requires slide-mounted heads.  We have seen philopotamid caddisflies misidentified with the chironomids and we suspect that that happens when samples are being sorted from trays.  Under a microscope, six prominent legs can be seen on the philopotamids.

© Aquatic Bioassessment Laboratory, California Digital Reference Collection

ORDER: Coleoptera 
FAMILY: Elmidae
GENUS: Ordobrevia
 

This genus of riffle beetles is distinguished by the second segment of antenna, which is more than twice as long as the first segment. The prosternum has no anterior median suture.

PHYLUM: Annelida
CLASS: Oligochaeta

Aquatic earthworms lack legs and are characterized by having 20 or more segments. Unlike leeches, they lack a suction disk.

ORDER: Ephemeroptera
FAMILY: Baetidae 
GENUS: Baetis 

This mayfly has three "tails" and a unique head shape. Its gills are oval shaped and insert dorsally. The wing pad shape is an obvious characteristic. More mature nymphs have long, dark wing pads. SMC

ORDER: Coleoptera 
FAMILY: Elmidae
GENUS: Optioservus

The larvae of Optopservus have a closed coxae, as determined by the straight definition between segments on the ventral side of the pronotum.

The adult Optioservus have a compact appearance, especially the head and thorax. There are also dorsal ridges and a characteristic diamond-shaped feature observable in the dorsal view. SMC

ORDER: Coleoptera
FAMILY: Psephenidae
GENUS: Psephenus

The true "water penny" is commonly found in the waters sampled. Psephenus has a rounded shape with relatively smooth edge. The false water penny, whose edges are serrated, has a more oval appearance. The gills on the ventral surface are found only in the true water pennies. SMC

NABS
ORDER: Trichoptera
FAMILY: Hydropsychidae
GENUS: Hydropsyche

Hydropsyche share most characteristics with Ceratopsyche, including the sclerites in the intersegmental folds. Hydropsyche are distinguished from Ceratopsyche by the presence of scale hairs and minute spines on the three most posterior abdominal segments. SMC

ORDER: Ephemeroptera
FAMILY: Heptageniidae

This family of mayflies can be characterized by their distinctly flattened heads and striking resemblance of the character 'Jack Skellington' from the movie 'The Nightmare Before Christmas.' This family can either have two or three tails.