Thamnocephalus platyurus

Irving P.
Mar 5, 2023
2 min read

Updated: Aug 31

Taxonomy and Classification

• Phylum: Arthropoda

• Class: Branchiopoda

• Order: Anostraca

• Family: Thamnocephalidae

• Genus: Thamnocephalus

• Species: T. platyurus

• Authority: Packard, 1877

Thamnocephalus platyurus, commonly known as the Beavertail Fairy Shrimp, belongs to the order Anostraca and the family Thamnocephalidae. First described by Packard in 1877, this species is named for its broad, paddle-shaped abdomen and distinctive swimming style—upside-down, like most fairy shrimp.

The distribution of T. platyurus spans west of the Mississippi River, including states from Missouri to California and Montana to Texas, with notable populations in New Mexico’s Rio Grande and Pecos River basins.

The characteristics outlined below may exhibit variations influenced by environmental conditions, population dynamics, and the organism's age.

IDENTIFIABLE TRAITS OF THIS SPECIES

Male Second Antenna:

In the genus Thamnocephalus (Anostraca: Thamnocephalidae), species-level differentiation is primarily based on the morphology of the male second antennae and cephalic frontal appendages, which are integral to reproductive behavior. The second antennae are sexually dimorphic and exhibit species-specific variation in segmentation, curvature, and distal ornamentation, including cone-like processes and digitiform lobes. Additionally, the frontal appendage, often arborescent and highly branched, provides further diagnostic value due to its complex structure and branching pattern.

Telson & Cercopods:

Additionally, the telson and cercopods provide key diagnostic features. The telson, located posterior to the last abdominal segment, varies in shape and armature across species—often bearing spines, setae, or lobes that assist in locomotion and reproductive positioning. The cercopods, paired appendages flanking the telson, are typically elongated and may be setose or smooth, with their length, tapering, and setation patterns offering further resolution in species-level taxonomy.