Class Malacostraca in the Christopher B. Smith Preserve

Class Malacostraca Characteristics: Class Malacostraca is the largest class of the six classes of crustaceans. There are more than 25,000 species of malacostracans. Species include crabs, lobsters, shrimp, woodlice, amphipods, and mantis shrimp. Some are marine, while others live in freshwater or are terrestrial. Most are scavengers; some are filter feeders and some are carnivores. Most have a 5-segmented head, an 8-segmented thorax and an 6-segmented abdomen. The thoracic segments may be fused with the head to form a cephalothorax. Each body segment has a pair of jointed appendages. The class name, "Malacostraca" is derived from the Greek words "malakos" meaning "soft" and "ostrakon" meaning "shell." Malacostracans have soft shells immediately after they moult.

The head has two pairs of antenna and a pair of stalked compound eyes. Most species have distinct sexes. Each thoracic appendage has a gill. There is usually a metamorphosis between the larval and adult form.

Interactions in the Smith Preserve: Two malocostracans have been photographed in the Preserve, Caridea shrimp and sow bugs. Shrimp are omnivores, eating both plants and animals. They are preyed upon by fish and wading birds. Sow bugs are detritivores, eating dead plant matter. Sow bugs help produce compost, mix soil, and provide food for insectivores.

Species Name
Common Name
Palaemonetes paludosus
Atlantoscia floridana


Palaemonetes paludosus

Grass Shrimp / Ghost Shrimp / Caridean Shrimp

Palaemonetes paludosus live in fresh water and brackish water. They are nocturnal and remain hidden in vegetation during the day, becoming active foragers at night. The specimens shown in the first 3 photographs were living in the freshwater pond at the Christopher B. Smith Preserve. They were captured in dipnet samples on November 19, 2013.

When alive, these shrimp have transparent bodies. Upon dying, the carapace (outside shell) becomes orange and translucent.

As the first two photographs show, the abdomen shows a pronounced bend that is typical of caridean shrimp.

As shown in photograph three, this particular species of grass shrimp has six teeth on the dorsal surface of the rostrum and three on the ventral surface.

Female grass shrimp almost always have a green saddle or eggs underneath their bellies. They also have a high ridge along the top of the tail and they are generally larger than males. Males lack the saddle and ridge. The individuals in these photographs appear to be males.

Reproduction is sexual. During copulation, the male extrudes a spermatophore (sperm capsule) and transfers it to the female. Within seven hours, the female releases her ova (eggs). At that time, the spermatophore dissolves and sperm are released. As the ova are extruded, they are fertilized and adhere to the ventral portion of the female's abdomen.

In Florida, grass shrimp breed year round. Individuals live 6 to 13 months.

Grass shrimp are filter feeders. Food includes algae (diatoms and green algae), vascular plants, detritus and aquatic insects (mayfly nymphs and fly larvae). In the previous sentence, food items are listed in decreasing importance.

These shrimp are important for energy flow and turnover of detritus in the Preserve pond. They provide an important link between the organisms living in the benthic (bottom) and water column habitats; they are important prey for many different species of birds and fish.

Below are images of a living grass shrimp captured in a net in mid February 2018. Note the transparent body and pronounced bend (arch) of the back.

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Atlantoscia floridana

Sow Bugs

There are several different types of wood lice. Sow bugs are one. All wood lice have two pairs of antennae, 7 pairs of jointed limbs on the thorax, and 5 pairs of paddle-shaped, branching appendages on the abdomen that they use for respiration. The dorsal surface is covered by overlapping, articulated plates that provide protection and flexibility. Unlike pill bugs, another type of woodlouse, sow bugs have a uropod. A uropod is a tail that extends beyond the last abdominal segment.

Females brood their young in a pouch under their thorax.

Woodlice live in terrestrial environments. In order to survive, they must replace water lost through excretion and through the cuticle. For that reason, woodlice are usually found in damp, dark places and are usually nocturnal.

The individual shown in the first three photographs was captured in a pit trap placed under a laurel oak tree just north of Smith Preserve Way on November 17, 2015. The sow bug was 4 mm long. Other individuals were also collected in the sample, but they were smaller. These photographs were submitted for identification on November 24, 2015 to <>, sponsored by Iowa State University Department of Entomology.

Sow bugs feed on fungi and bacteria that infest dead and rotting vegetation. They are eaten by insectivores, some of which are known to prey exclusively on woodlice. Examples include spiders of the genus Dysdera and land planarians. Predators also include frogs, toads, lizards, small mammals, and even other woodlice. Woodlice are generally considered beneficial because they produce compost and help mix soil.

On November 5, 2016, this sow bug was identified as Atlantoscia floridana by Hisserdude, a Contributing Editor to <>. Atlantoscia floridana is a species found from the United States (Florida) to Brazil and Argentina.

On February 10, 2016, the 6 mm long specimen below was living in leaf litter beneath an oak hammock in the northwest quadrant of the Christopher B. Smith Preserve, north of Smith Preserve Way. It and several like it were removed from the litter by using a Berlese Funnel.

These three photographs were created using photomicroscopy and sent for identification to <> On March 20, the individual was identified as belonging to Suborder Oniscidea by "Blocky", a Contributing Editor to <>. On November 5, 2016, it was identified by Hisserdude as another example of Atlantoscia floridana.

Note, this specimen has a distinctive set of lines along its lateral surface.



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© Photographs and text by Susan Leach Snyder (Conservancy of Southwest Florida Volunteer), unless otherwise credited above.


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