File Images: Caprella & Palaemonetes

Caprella mutica & Palaemonetes pugio

After the new year, I looked through my collection of stereomicroscopic images to see if any of them might be candidates for posting.  My microscope is an Olympus-like clone with a 0.7-4.5 zoom lens paired with a 10x objective.  As with most dissecting microscopes, it comes equipped with a clear glass stage insert for backlighting as well as an opaque two-sided black/white stage insert.  Many subjects such as algae and branching bryozoa photograph best with white backgrounds for contrast and reflective back lighting, but other species such as colonial ascidians and anemones photograph well with a black background.  Crustaceans also look good on a black background and there were two images in my collection that had an aesthetic appeal.  For seawater specimens, the stage insert was placed at the bottom of the collection tray.  For preserved material, formaldehyde-fixed samples were transferred through alcohols to water and then placed in a container with the black stage on the bottom. Micrographs were taken with a QImaging Micropublisher Digital Camera using QCapture Pro Software.

 

MIS Species Caprella mutica

Specimen of Caprella mutica collected in August 2011 observed against a black background.  In Provincetown, I have not seen Caprella mutica since Tropical Storm Irene, August 28-29, 2011. Stereozoom 0.8 x 10x objective.

 

Marsh Grass Shrimp Palaemonetes pugio

Preserved specimen of Palaemonetes pugio from Wellfleet Marina collected in summer of 2011.  Palaemonetes marsh grass shrimp live among algae and invertebrates attached to the floats and sometimes swim in small schools next to the docks.  Stereozoom 0.7 x 10x objective. 

 

Palaemonetes marsh grass shrimp are common in the western Atlantic Ocean from the Gulf of Mexico to the Gulf of Maine.   Adults are semi-transparent and grow to less than 5 cm (2.0 in) long, with most individuals on the docks 1-4 cm long (including antennae).  They are found clinging to algae and invertebrates on the dock and also can be seen swimming close to the dock.  Several species are found along the North American coast: P. pugio, P. vulgaris, and P. intermedius. Palaemonetes pugio and Palaemonetes vulgaris live north of Nantucket Sound and are common in the Gulf of Maine.  Morphologically, they are very similar, but can be distinguished by the pattern of spines on the rostrum (Anderson, 1985).  The shrimp collected in Wellfleet were identified as P. pugio by examining a group of preserved specimens collected in 2011.  The rostrum of all the specimens had a single, long, dagger-like tip characteristic of P. pugio.

 

Small numbers of the larger MIS shrimp Palaemon elegans can sometimes be found cohabitating with Palaemonetes in marinas (first sighted in Gulf of Maine in Salem Sound in 2010, and sighted in 2012 in Provincetown).  They are difficult to distinguish when they are about the same size as the smaller Palaemonetes, but larger individuals can clearly be distinguished, especially by the presence of blue and orange bands on Palaemon's front legs (see below).   Palaemon also grows several cm larger and is more colorful than Palaemonetes. So when looking for invasive marine species, populations of Palaemonetes are a good place to start by examining Palaemonid shrimp for blue banded legs.

 

Rostrum of Palaemonetes pugio

 Palaemonetes pugio has a dagger-like, pointed rostrum.  Black eye pigment had faded to a light gray in these preserved specimens. Two different individuals are shown. Top, rostrum is visible above the antennae and legs.  Bottom, clear view of the rostrum was obtained by removing the antennae which usually obscure a clear lateral view of the rostrum.  Original images captured using stereozoom 2.0 x 10x objectives.

 

LINKS:

Ashton GV.  Distribution and dispersal of the non-native caprellid amphipod, Caprella mutica Schurin 1935. Ph.D. Thesis, University of Aberdeen, 2006. (See numerous publications about Caprella mutica by Ashton et al since 2006)

Wiki Webpage on Caprella mutica:  Japanese skeleton shrimp.

Native Range of the Japanese Skeleton Shrimp Caprella mutica.

Native range in the Western Pacific along the coasts of Russia, Japan, and Korea.  Circles represent locations where Caprella mutica was found. 1) Peter the Great Bay, 2) Possjet Bay, 3) Olarovsky Cape, 4) Signalny Cape, 5) Sea of Okhotsk, 6) Kunashir Island, 7) Shikotan Island, and 8) Akkeshi Bay.

Rowe, CL. Differences in maintenance energy expenditure by two estuarine shrimp (Palaemonetes pugio and P. vulgaris) that may permit partition of habitats by salinity. Comp Biochem Physiol Mol Integr Physiol. 132: 341-351, 2002. 
Anderson, G. Species profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Gulf of Mexico) - Grass Shrimp.  US Fish Wildl Serv Biol Rep  82:  19 pp, 1985.

Comparative morphology of different grass shrimp species showing the rostrum of 

Palaemonetes pugio (a) and P. vulgaris (g).   P. pugio has a dagger-like, pointed rostrum, whereas the rostrum of P. vulgaris has a multi-spined, serrated tip.  

Gosner, KL. A Field Guide to the Atlantic Seashore from the Bay of Fundy to Cape Hatteras. Palaemonetes Species. 234-236, 1978.  The Peterson Field Guides.
Descriptions of P. pugio, P. vulgaris, and P. intermedius.   Web Preview of the Guide.

Comparative rostrum morphology of the three grass shrimp species found in New England.

EOL, Encyclopedia of Life: Palaemonetes pugio
     "The daggerblade grass shrimp, Palaemonetes pugio, is a small transparent to shrimp with a well-developed rostrum bearing several dorsal as well as three distinct ventral teeth, a smooth carapace and abdomen, and two pairs of chelate (claw-bearing) walking legs, the second pair more robust than the first. It has well-developed eyes with globular pigmented corneas and some slight yellow pigmentation in the eyestalks".
WoRMS, World Register of Marine Species: Palaemonetes pugio Hothuis 1949
EOL, Encyclopedia of Life: Palaemonetes vulgaris
WoRMS, World Register of Marine Species:  Palaemonetes vulgaris (Say, 1818)

Typical view of semi-transparent Palaemonetes vulgaris as seen from above. The pairs of black eyes are one of the most distinctive features.

EOL, Encyclopedia of Life: Palaemon elegans 

Blue and orange bands on legs of the European rock shrimp Palaemon elegans

Pedersen, J.  Invasive Species Survey Discovers First European Marine Shrimp to Invade North America.  Invasive Species of Eastern USA Blog, August 2010.