The Streptocephalus mattoxi, commonly known as the Mattox or Crenate Thumb Fairy Shrimp, is a unique species of branchiopod that is endemic to Kenedy County, Texas. Streptocephalus mattoxi is deemed to be in a critical state of endangerment, with its global status last evaluated in 2008. The species is reported to exist solely in two playas within its native region (“NatureServe Explorer”).
Based on the paper ‘Anostracan (Crustacea: Branchiopoda) Zoogeography II: Relating Distribution to Geochemical Substrate Properties in the USA’ by D. C. Rogers, it is noted that Streptocephalus mattoxi inhabits saline playas in coastal regions. The substrate in these localities contains a low percentage of both calcium carbonate and calcium sulfate (2014). The substrate of these saline playas habitats was mainly sand to sandy loam soils.
Anatomy: The characteristics outlined below may exhibit variations influenced by environmental conditions, population dynamics, and the organism's age.
Head:
Second Antenna:
Male: The shrimp has a long extension (peduncle) that doesn’t have a swelling (pulvinus), but instead, it has about 14 cone-shaped bumps on the inner side of its far end. The inner upper side of the base of the shrimp’s ‘hand’ has a forward-pointing spine-like structure. It has a triangular projection (spur) with a tip that has a prolonged digit-like structure. There is a thin layer or plate on the side (lateral lamella) that forms a sharp angle with the far end of the ‘thumb’ and the inner thin layer of the spur. This arrangement creates a cavity in the middle-lower part. The far end of the ‘thumb’ is bent like an elbow on the lower side. The upper edge is slightly scalloped or notched, with a pointed tip on the ‘finger’. The shrimp has a double-bend (digeniculate) structure. On the inner upper side of the near part, it has two ‘teeth’. The one closer to the body is a small sharp tooth, while the one further away is an oblique digit-like tooth that points forwards and upwards. The first bend of the ‘finger’ has a wide upper layer (dorsal lamella) which becomes narrow at the second bend. The tip of the ‘finger’ is pointed, with a slightly split lower lobe near the tip. The frontal appendage is simple, short, and has two lobes at the tip. The mouthparts (georalia) don’t have tongue-like outgrowths (Maeda-Martinez et al., 1995).
Female: The second antennae are smaller, broad, oval, flattened, and smooth, with no protrusions (Maeda-Martinez et al., 1995, Rogers, 2014).
Thorax:
Dorsolateral Process (Lobes):
The thoracic segments are smooth and without lobes, which is characteristic of the genus
Thoracopods:
The structure is comparable across sexes, characterized by delicate setae along the limb's edges.
Reproductive Segments:
Male: A pair of penises.
Female: The fairy shrimp possess biramous ovaries, which are branched in two parts. These ovaries typically stretch from the sixth and seventh segments of the thorax—the area between the head and the abdomen—to the first and second segments of the abdomen, as noted by Maeda-Martinez et al. in 1995.
Abdomen:
Uniform across sexes without distinctive characteristics.
Telson & Cercopods:
The cercopods, or tail appendages, feature bristles along their inner and lateral margins, exhibiting pigmentation that ranges from red to orange.
Egg:
The egg, or the closed sac-like structure, has a surface that is decorated with dips (indentations) and raised lines (ridges). It is round in shape and has rib-like structures that form many-sided (polygonal) areas.
Morphology:
Size: 2.0cm to 2.5cm in length, contingent on prevailing environmental conditions.
Coloration: body is transparent but may have hues of blue, pink, green.
Captivity and Growth:
Growth is influenced by multiple factors such as temperature, salinity, and care. These temperature ranges are based on our experience but do not represent the maximum or minimum.
Hatching Temperature Range: 68 to 78°F.
Temperature Range for Adults: 68 to 78°F.
Hatching: At temperatures of 72 to 78 Fahrenheit, nauplii appear after 24 to 48 hours.
Growth Rate: This species has a moderate growth rate reaching sexual maturity at around 10 to 14 days with an average life span of 8 to 10 weeks.
Behavior: This species prefers to swim in open water, feeding on microorganisms in the water column, and is constantly swimming.
Reproduction: males use their second antenna to latch onto the females only taking but a few seconds to mate.
References:
NatureServe Explorer.” NatureServe, Arlington, Virginia. Available at NatureServe Explorer website. Accessed: April 22, 2024
Maeda-Martinez, A. M., Belk, D., Obregón-Barboza, H., & Dumont, H. J. (1995). Diagnosis and phylogeny of the New World Streptocephalidae (Branchiopoda: Anostraca). In D. Belk, H. J. Dumont, & G. Maier (Eds.), Studies on Large Branchiopod Biology and Aquaculture I(pp. 15-44). Kluwer Academic Publishers.
Rogers, D. C. (2014). Anostracan (Crustacea: Branchiopoda) zoogeography II. Relating distribution to geochemical substrate properties in the USA. Zootaxa, 3856(1), 1-49. Magnolia Press. https://doi.org/10.11646/zootaxa.3856.1.1
D. Christopher Rogers, Two New Cryptic Anostracan (Branchiopoda: Streptocephalidae, Chirocephalidae) Species, Journal of Crustacean Biology, Volume 34, Issue 6, 1 November 2014, Pages 862–874, https://doi.org/10.1163/1937240X-00002272
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