By Ryan Jonna and Monica Weinheimer
Diversity
Dactyloscopids derive their common name, sand stargazers, from their eyes, which protrude from the tops of their heads, sometimes on stalks. Sand stargazers usually remain burrowed into the sand with only the eyes, along with the snout and sometimes the top of the head, uncovered. Members of this family occupy shallow warm waters and are carnivorous. They are small, cryptic fishes and little is known about their behavior or reproductive habits. There are nine genera in the family and about 41 species. (Böhlke and Chaplin, 1993; Nelson, 1994; Springer, 1998; Wheeler, 1985)
Geographic Range
Dactyloscopids, or sand stargazers, are found in tropical and warm temperate waters of the western hemisphere. The Atlantic Ocean (from the United States to Brazil) contains 17 species, and the Pacific Ocean (from the Gulf of California to Chile) contains 24. (Allen and Robertson, 1994; Böhlke and Chaplin, 1993; Nelson, 1994; Springer, 1998; Wheeler, 1985)
Biogeographic Regions:
nearctic 
(native ); neotropical (native ); atlantic ocean (native ); pacific ocean (native ).
Habitat
Dactyloscopids live buried in the sand with only the eyes, along with the snout and sometimes the top of the head, uncovered. They usually occupy shallow warm water at depths between two and 15 m, but one species, Gillellus semicinctus, has been found between five and 137 m. Some groups inhabit bare, open beaches in or behind the surge zone, but others are found exclusively in patches of sand that are near rocks, coral structures, or marl bottoms. A few species can be found in estuaries, and at least one enters fresh water. (Allen and Robertson, 1994; Böhlke and Chaplin, 1993; Wheeler, 1985)
These animals are found in the following types of habitat:
temperate ; tropical ; saltwater or marine .
Other:
estuarine ; intertidal or littoral .
Systematic and Taxonomic History
The family Dactyloscopidae is divided into nine genera and 41 species. Four Pacific species contain 29 subspecies. Sand stargazers are virtually unique among teleosts in that a branchiostegal rather than an opercular pump moves water through the mouth and gills. It is likely that internal fingerlike projections keep the gills free of sand. (Helfman, Collete, and Facey, 1997; Nelson, 1994)
- branchiostegal pump
Physical Description
Sand stargazers (family Dactyloscopidae) are small fishes adapted to burrowing in the sand. Their eyes are situated on the top of the head, sometimes on stalks, and their nostrils are tubular. They have upturned mouths, and fingerlike projections (fimbriae) line the mouth and gill covers, keeping sand out of the gills and mouth. These fish maintain water flow through the gills with a branchiostegal pump. Sand stargazers are covered with cycloid scales. The dorsal fin, which contains 7-23 spines and 12-36 soft rays, may be divided or continuous. The pelvic fins have three thickened rays with tips that are free from the fin membrane. The largest dactyloscopids reach 17 cm, but most are less than six cm. They are colored to blend in with their sandy environment: most are whitish or drab brown, and many have red-tinged or dark mottling along the back and head. (Click here to see a fish diagram) (Allen and Robertson, 1994; Böhlke and Chaplin, 1993; Nelson, 1994; Springer, 1998; Wheeler, 1985)
Some key physical features:
ectothermic ; bilateral symmetry .
Sexual dimorphism: sexes alike.
Development
No information was found on development in Dactyloscopidae.
Reproduction
No information was found on mating systems in Dactyloscopidae.
While no information was found on reproduction in Dactyloscopidae, blennies (which are in the same suborder Blennioidei) in general tend to lay relatively large eggs that adhere to a surface. In the case of sand stargazers, eggs may adhere to each other, as males carry them in two clumps under the pectoral fins. (Thresher, 1984)
Key reproductive features:
sexual ; fertilization (external ); oviparous .
Sand stargazers display a unique trait among fishes in that males guard eggs by carrying them in two balls, one in the “armpit” (axilla) of each pectoral fin. (Allen and Robertson, 1994; Böhlke and Chaplin, 1993; Helfman, Collete, and Facey, 1997; Wheeler, 1985)
Parental investment:
male parental care .
Lifespan/Longevity
No information was found on lifespan of dactyloscopids.
Behavior
Sand stargazers burrow in the sand and remain there most of the time lying in wait for their prey. They delve into the sand using sinuous body and anal fin motions, and swimming movements of the pectoral fins. They may bury themselves completely or leave the eyes, snout or top of the head uncovered. One behavior engaged in by males is egg-guarding, accomplished by carrying a ball of eggs under each pectoral fin. (Allen and Robertson, 1994; Böhlke and Chaplin, 1993; Springer, 1998; Wheeler, 1985)
Key behaviors:
natatorial ; motile .
Communication and Perception
No information was found on communication in Dactyloscopidae. Because their eyes are placed on top of their heads, often on stalks, so as to remain uncovered by sand, it is logical to infer that they perceive their surroundings visually.
Food Habits
Sand stargazers are carnivorous, lying in wait under the sand to attack small fishes and invertebrates. (Allen and Robertson, 1994; Wheeler, 1985)
Predation
Sand stargazers conceal themselves from predators by hiding under the sand. They are cryptically colored, so any exposed parts blend in well with the sand. (Böhlke and Chaplin, 1993; Springer, 1998; Wheeler, 1985)
Anti-predator adaptations::
cryptic .
Ecosystem Roles
Sand stargazers occupy a specific habitat, that is, sandy bottoms of shallow warm waters, and in that setting impact the tiny fishes and invertebrates that serve as their prey. (Allen and Robertson, 1994; Wheeler, 1985)
Economic Importance for Humans: Negative
No specific information was found concerning any negative impacts to humans.
Economic Importance for Humans: Positive
No information was found on human importance of Dactyloscopidae.
Conservation
There is no known conservation threat to any members of Dactyloscopidae. (The World Conservation Union, 2002)
Contributors
Ryan Jonna (author), Animal Diversity Web. Monica Weinheimer (author), Animal Diversity Web.
