Entry Category: Zoology - Starting with S

Salmonids include chars, graylings, salmon, trout, and freshwater whitefishes, all of which belong to the superorder Protacanthopterygii, order Salmoniformes, family Salmonidae, three lineages or subfamilies (Coregoninae, Thymallinae, and Salmoninae), eleven extant genera, and about 120 species. There are thirty-nine species known in North America. The family is widely distributed, with various species found north of the equator in Asia, Europe, and North America. Some important North American genera include Coregonus, Oncorhynchus, Prosopium, Salmo, Salvelinus, and Thymallus. Although no members are native to Arkansas, salmonids have been introduced, primarily for purposes of sports fishing. The family initially appears in the fossil record in the middle Eocene (48 to 38 million years ago) from fossils found in central British Columbia, Canada. A …

Scorpionflies belong to the Phylum Arthropoda, Class Insecta, Superorder Endopterygota, and Order Mecoptera. There are about 605 species within thirty-four genera and nine families worldwide. There are also 400 known fossil species in about eighty-seven genera, which are more diverse than even the extant members of the order. Sixteen species representing three families of scorpionflies occur in Arkansas. Most mecopterans live in moist environments, although adults of a few species are found in hotter semi-desert habitats and may be active and noticeable only for short intervals of the year. Those in the family Panorpidae generally inhabit broad-leaf woodlands with abundant damp leaf litter. Snow scorpionflies (family Boreidae) appear in winter and are often seen on snowfields and on moss; the …

Sculpins belong to the order Scorpaeniformes and superfamily Cottoidea. There are about 11 families, 149 genera, and 756 species. They reach their maximum diversity in the northern Pacific Ocean. The family Cottidae is the largest family, with approximately 258 species; the second-largest family is the Agonidae (marine poachers), with 47 species. The most speciose genus, Cottus (freshwater sculpins), is confined to North America and Eurasia. It includes about 68 taxa that are native to the Northern Hemisphere (Palearctic and Nearctic realms). There is fossil material similar to Cottus that dates to at least the Miocene Epoch (23 to 5.3 million years ago). Most sculpins are generally less than 15 centimeters (6 inches) in length, although a few species can reach …

Shrews are very small, secretive, mouse-like mammals that inhabit moist, shady woodland areas. Generally, they have long, flexible, pointed snouts and very small eyes and ears. Their fur is soft and dense, and most species have prominent scent glands. All shrews belong to the Family Soricidae (subfamilies Soricinae, Crocidurinae, Myosoricinae) and Order Eulipotyphia, which also includes moles, shrew-like moles, desmans, gymnures, hedgehogs, and solenodons. True shrews, talpids, and solenodons were formerly grouped in the clade Soricomorpha; however, Soricomorpha has been found to be paraphyletic (descended from a common evolutionary ancestor or ancestral group, but not including all descendant groups). Members of this order are nearly cosmopolitan in distribution, with the exception of Australia, New Zealand, Antarctica, extreme southern South America, …

Arkansas shrimps belong in the cosmopolitan Family Palaemonidae (subfamily Palaemoninae) and Order Decapoda, which also contains the crayfishes. Taxonomically, shrimps are differentiated from crayfishes by their first pair of legs with chelae and the abdomen laterally compressed, while crayfishes have the first three pairs of legs with chelae and their abdomens dorsoventrally flattened. The Palaemonidae is a large family (950 species within 137 genera) and is distributed on all the continents except in the deep oceans, in temperate and tropical regions, and having representatives in marine, brackish, and fresh water. Representatives of this family are mainly carnivores that feed on small invertebrates. The most prominent genus in the family is Macrobrachium, with over 240 species that include commercially fished species; …

Silverfish are small, wingless insects in the order Zygentoma (formerly Thysanura). There are four families: Lepidotrichidae (single species), Lepismatidae (about 200 species), Maindroniidae (three species), and Nicoletiidae (about twenty species). In the late twentieth century, it was recognized that the two suborders were not sister taxa; therefore Thysanura was paraphyletic, and the two suborders were each elevated to the status of an independent monophyletic order, with Archaeognatha the sister taxon to the Dicondylia, including the Zygentoma (fishmoths, firebrats, and silverfish). A nicoletiid, Speleonycta ozarkensis, occurs in eight different cave systems in Arkansas in Benton and Newton counties and in Oklahoma in Adair, Cherokee, and Delaware counties. In concert with jumping bristletails (Order Microcoryphia), the predecessors of silverfish are considered the …

Smelts belong to the family Osmeridae and order Salmoniformes. There are seven genera and about eleven species. Fishes of the genus Osmerus, to which the rainbow smelt (O. mordax) belongs, include the following: a North Pacific and Arctic species, O. dentex; the European smelt (O. eperlanus) of the Eastern North Atlantic; and the landlocked pygmy smelt (O. spectrum) of eastern Canada and New England, which some authorities suggest is not a valid species. In general, smelts are north circumpolar in geographic distribution, and they occur in marine and freshwater habitats in Asia, Europe, and North America. They date to the Paleocene Epoch (over 55 million years ago). The closest relatives are galaxioid (Protacanthopterygiid) fishes, and the marine argentinoid fishes are …

The southern cavefish (Typhlichthys subterraneus) is one of the two species of blind cave fishes found in Arkansas. The other is the Ozark cavefish. The southern cavefish is found in the subterranean waters of two major non-overlapping ranges separated by the Mississippi River: in the Ozark Plateau of central and southeastern Missouri and northeastern Arkansas and in the Cumberland and Interior Low plateaus of northwest Alabama, northwest Georgia, central Tennessee, and Kentucky. They are usually found at considerable depths (mostly between 175 and 240 meters below the land surface). This species, which can grow as long as ninety millimeters, has a large, broad head. The caudal fin has from zero to two rows of sensory papillae (one on the upper …

The speckled pocketbook is a bivalve mollusk belonging to the family Unionidae, commonly referred to as freshwater mussels, naiads, or clams. Each freshwater mussel is composed to two halves (valves) of a hard outer shell with the living animal (soft tissues) residing securely inside. The speckled pocketbook, scientific name Lampsilis streckeri, was described as a species new to science in 1927 by Lorraine Screven Frierson, a naturalist and landowner/merchant/planter residing south of Shreveport in the company town of Frierson, Louisiana. Frierson named the species in honor of his friend, colleague, and fellow naturalist John K. Strecker of Waco, Texas. Adults may reach a length of slightly more than 3.5 inches (or more than 90 millimeters), with a maximum life expectancy …

The phylum Porifera, which contains the sponges, is a highly successful group of metazoan animals that includes about 8,600 living species of marine and freshwater forms as well as some that inhabit brackish waters. The majority are marine, but there are about 150 species of freshwater sponges, including twenty-seven to thirty species found in North America north of Mexico. The family Spongillidae is the most speciose and widespread group of freshwater sponges and includes twenty-two genera and more than 130 species from a wide variety of habitats. Seven species of freshwater sponges have been documented in Arkansas. Sponges are an ancient group of asymmetrical invertebrates with a fossil record preceding the early Cambrian period (541 million years ago), and even …

Stoneflies (Phylum Arthropoda, Class Insecta, Order Plecoptera) are a group of aquatic insects well known to fishermen and biologists worldwide. The name Plecoptera means “braided-wings” from the Ancient Greek plekein and pteryx, which refers to “wing.” The name refers to the complex venation of their two pairs of wings, which are membranous and fold flat over their body. Generally, stoneflies are not strong fliers, and several species are entirely wingless. Stoneflies are called “indicator species” because finding them in freshwater environments generally indicates relatively good water quality, as they are quite intolerant of aquatic pollution. They are also prized and imitated by anglers as artificial tied-flies in trout fishing, particularly on Arkansas rivers such as the Eleven Point, Spring, and …

The order Strepsiptera, or twisted wing parasites, belongs to the class Insecta, phylum Arthropoda. It is a very small, cosmopolitan order of bizarre parasitoids containing about 624 named species of minute endopterygote insects with nine extant families. They parasitize thirty-four families and several orders of Insecta, including Blattodea (cockroaches), Diptera (flies), Homoptera (leafhoppers), Mantodea (mantises), Hemiptera (true bugs), Orthoptera (grasshoppers and crickets), Zygentoma (silverfish and firebrats), and Hymenoptera (ants, bees, and wasps). Three species of strepsiptera (halictophagids) have been reported from Arkansas hosts (all leafhoppers, Cicadellidae). Strepsiptera have two major groups: the Stylopidia and Mengenillidia. The former, which has endoparasitic females with multiple genital openings, includes seven families: the Bohartillidae (one extant and two fossil species), Corioxenidae (forty-six extant and …

The striped bark scorpion, Centruroides vittatus, is the only scorpion species recorded from Arkansas, where it is most abundant in the western part of the state. It is the most widely distributed scorpion species in the United States, having been recorded from Missouri, Arkansas, and Louisiana west to eastern Colorado and New Mexico and south to northeastern Mexico. The front body region, which bears the yellowish-brown pedipalps (pincers) and legs below, has a somewhat triangular median dark spot on top pointing backward and extending beyond the eyes. The wide body region that follows has a distinctive pair of broad, dark, longitudinal bands on top. The slender tail-like postabdomen is uniformly yellowish brown, except for the tip of the stinger, which …

Sturgeons (primitive Acipenseriform) are an ancient group of fishes dating back to the Triassic Period some 245 to 208 million years ago. True sturgeons appear in the fossil record during the Upper Cretaceous (101 to 66 million years ago). There are about twenty-five species of sturgeons, and all belong to the Family Acipenseridae, Order Acipenseriformes. Sturgeons can be found in subtropical, temperate, and sub-Arctic rivers, lakes, and coastlines of North America, with the greatest diversity in Eurasia. In North America, there are eight species that range along the Atlantic Coast from the Gulf of Mexico to Newfoundland, as well as along the West Coast in major rivers from California and Idaho to British Columbia, Canada. The family contains four genera …

Suckers belong to the Family Catostomidae, Order Cypriniformes, and Class Actinopterygii. There are about seventy-two species and thirteen extant genera of these benthic (bottom-dwelling) freshwater fishes. In Arkansas, there are eighteen species in eight genera. Suckers are Holarctic in distribution and primarily native to North America north of Mexico, but the longnose sucker (Catostomus catostomus) occurs in both North America and northeastern Siberia from Alaska, and the Asiatic Sucker (Myxocyprinus asiaticus) is found in the Yangtze River basin in China. Sucker-like fossils are known from Eocene epoch (56 to 33.9 million years ago) deposits from central Asia, and the fossil genus Amyzon, with Ictiobus and Myxocyprinus affinities, occurs in middle Eocene and Oligocene Epoch (33.9 to 23 million years ago) …

Symphylans belong to the Phylum Arthropoda, Subphylum Labiata, Superclass Myriapoda, and Class Symphyla. About 200 species of symphylans are known worldwide, predominantly in the tropics. There are two families: Scutigerellidae with five genera and about 128 species, and Scolopendrellidae containing nine genera and approximately seventy-three species. There are few reports of symphylans in Arkansas, aside from a new endemic scutigerellid species described in 1992 in Polk County. Many taxa are yet to be discovered and described in the state. The fossil record of symphylans is poorly known; only five species have been recorded, all placed within living genera. They are ancestral arthropods dating back to the early Silurian approximately 430 million years ago, although the only fossil symphylans are known …