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Macroinvertebrates home

Streams project

 

Seymour Brook

These are the ten most common macroinvertebrates identified from samples from Seymour Brook.

Click on images to zoom in. 

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.  Chironomidae 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 members of the family Philopotamidae.

ORDER: Coleoptera
FAMILY: Elmidae
GENUS: Stenelmis

The larvae of Stenelmis, as in Ordobrevia, have a sternum on the ventral side of the pronotum. The main difference between the two genera is in the antennae- the second segment is less than twice as long as the first in Stenelmis.

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

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: Trichoptera
FAMILY: Hydropsychidae

This family of net-spinning caddisflies is very abundant at several sites.  They are important filtering collectors and are quite common at urban and agricultural sites where particles of organic material can be important food resources.  Genus-level identification is possible for mature specimens and we will include the genera we found at your site if possible. Commonly found genera include Cheumatopsyche, Ceratopsyche, and Hydropsyche. Less commonly, we have found Arctopsyche and Potamyia.

When using the key, some features that are challenging to see are the forked trochantin and the paired sclerites in the folds between segments.  Other, more easily seen key features include filamentous gills on the abdominal segments and the sclerotization of the dorsal surfaces of all three thoracic segments. Keep in mind that with smaller or more immature specimens, genus-level ID may not be possible.

ORDER: Coleoptera 
FAMILY: Elmidae
GENUS:
Optioservus

The larvae of Optioservus have open 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 scutellum observable in the dorsal view.
SMC

 

ORDER: Coleoptera
FAM
ILY: Psephenidae
GEN
US:
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

Another genus encountered in this family is Ectopria.

 

ORDER: Trichoptera
FAMILY: Philopotamidae

GENUS: Chimarra

Chimarra are distinguished from the other Philopotamidae by a prominent asymmetrical notch in the frontoclypeus as well as a prominent process on the femora which bears a single hair (seta). SMC


 

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: Baetidae
 

This mayfly has either two or three cerci ("tails") and a unique head shape. Its gills are oval shaped and insert dorsally.

Commonly encountered genera include Acerpenna, Baetis, and Pseudocloeon.

ORDER: Diptera
FAMILY: Tipulidae
 

Like other larvae from the order Diptera, members of the family Tipulidae (crane flies) lack legs. Tipulidae have retracted, difficult-to-see head capsules at one end, and a spiracular disk at the other end. Upon gently cutting the head open,  one can see that the mandibles are not parallel to each other, but rather move against each other.

The genera we've encountered include Antocha, Dicranota, Hexatoma, Limnophila, Molophilus, Pedecia and Tipula.

 

The images are not a substitute for keying, but should serve as an aid in identifying common macroinvertebrates in samples.

Feedback - Partner schools: send us specimens not included above.  Taxonomists: click to email: Declan McCabe
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