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DactyloscopidaeSand stargazers

By Monica Weinheimer and R. Jamil Jonna

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)

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)

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, et al., 1997; Nelson, 1994)

  • Synapomorphies
    • 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)

  • 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)

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, et al., 1997; Wheeler, 1985)

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)

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: Positive

No information was found on human importance of Dactyloscopidae.

Economic Importance for Humans: Negative

No specific information was found concerning any negative impacts to humans.

Conservation Status

There is no known conservation threat to any members of Dactyloscopidae. (The World Conservation Union, 2002)

  • IUCN Red List [Link]
    Not Evaluated

Contributors

Monica Weinheimer (author), Animal Diversity Web.

R. Jamil Jonna (author), Animal Diversity Web.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

male parental care

parental care is carried out by males

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

visual

uses sight to communicate

References

Allen, G., D. Robertson. 1994. Fishes of the Tropical Eastern Pacific. Honolulu, HI: University of Hawaii Press.

Böhlke, J., C. Chaplin. 1993. Fishes of the Bahamas and Adjacent Tropical Waters. Wynnewood, PA: Published for the Academy of Natural Sciences of Philadelphia by Livingston.

Helfman, G., B. Collete, D. Facey. 1997. The Diversity of Fishes. Malden, MA: Blackwell.

Nelson, J. 1994. Fishes of the World – third edition. New York, NY: John Wiley and Sons.

Springer, V. 1998. Blennies. Pp. 216 in W Eschmeyer, J Paxton, eds. Encyclopedia of Fishes – second edition. San Diego, CA: Academic Press.

The World Conservation Union, 2002. "IUCN 2002" (On-line). IUCN Red List of Threatened Species. Accessed August 18, 2003 at http://www.iucnredlist.org/.

Thresher, R. 1984. Reproduction in reef fishes. Neptune City, NJ: T.F.H. Publications.

Wheeler, A. 1985. The World Encyclopedia of Fishes. London: Macdonald.

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