PEET: Leptostraca: Morphology: SEM

Leptostracan Morphology

...a look with the scanning electron microscope

CONTENTS

Rostrum
Eye
Antennule
Antenna Carapace
Abdomen
Telson Thoracopods
Pleopods
Caudal furcae

The rostrum of leptostracans is essentially a flap of cuticle that articulates with the carapace at the anterior (front) end of the animal.

The eyestalks of leptostracans vary considerably from one genus to the next. In fact, the leptostracan eye is perhaps the most notably variable character. In the genus Nebalia, the eye is relatively simple, and it is usually as long or shorter than the rostrum. In

The leptostracan antennule includes a peduncle of four basal articles. From the fourth article an antennular scale and a multiarticulate flagellum arise. The latter feature typically exhibits marked sexual dimorphism, with articles of the antennular flagella of the males often fused and forming a callynophore-like structure (for examples, see Modlin, 1991; Walker-Smith & Poore, 2001; Haney and Martin, 2004).

The antenna of leptostracans are uniramous (unbranched). The antennal peducle consists of three articles. The antennal flagellum is highly variable in length; it may bear as few as seven or as many as 70 articles.

Unlike the carapace of a crab, the carapace of all leptostracans is folded around the body. Superficially, this gives the animal a bivalved appearance similar to that of other crustaceans such as clam shrimps and ostracodes. However, in these other taxa, the carapace actually consists of two valves (the two sides) that are connected by a hinge. In the Leptostraca, the carapace is continuous and unhinged...much like an upside-down taco.

The abdomen of leptostracans consists of seven segments, or somites. The abdominal segments of Crustacea are referred to also as pleonites. Although the limbs that arise from them are conspicuous, the first three pleonites are usually concealed by the carapace. The fourth pleonite, particularly its extended postero-lateral margin, is often visible without dissection of the specimen. The fifth, sixth, and seventh pleonites are quite similar to each other in form and extend posteriorly from the carapace.

The telson is the terminal segment of the leptostracan's body and bears the anus. In most Crustacea of the class Malacostraca, the telson articulates with the sixth pleonite; in Leptostraca, the telson follows the seventh pleonite.

The limbs that arise from the thorax in Crustacea are called pereopods or thoracopods. Leptostracans possess 8 thoracopods.

The pleopods are those limbs that arise from the abdomen. All leptostracans possess 6 pairs of pleopods. The first pleopod arises from the first abdominal segment (pleonite), the second pair from the second abdominal segment, and so on. The last two pairs of pleopods (the fifth and sixth pair) are considerably smaller than the first four, consisting only of two (and in several cases, one) segments.

The caudal furcae are the posteriormost appendages of the leptostracan. These single-segmented appendages arise from the telson. They are generally long and narrow and bear multiple rows of setae.