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Tunicate (Molgula spp.) [Image: Britton and Morton, Gulf of Mexico Origin, Waters, and Biota, Chapter 73, Page 1209]
Tunicata is a subphylum of the phylum Chordata. There are 78 documented species of tunicates in the Gulf of Mexico. Tunicates, or sea squirts, are a marine invertebrate species that display chordate characteristics such as a notochord, dorsal nerve cord, pharyngeal slits, and a post-anal tail during its larval stage. These features are reduced to a simple ganglion in adult tunicates.
Larval tunicates are highly mobile and resemble tadpoles. These larval tunicates eventually affix to a hard substrate on the sea bottom, undergo metamorphosis, and remain immobile as adults, living as simple filter feeders. Adult tunicates have a simple body structure, consisting of a sack-shaped body with two siphons at either end, through which water is
filtered.The hard covering on the outside of their bodies is called a tunic.
Neon gobies
(Gobiosoma oceanops)
cleaning parasites and dead skin from a tiger grouper
(Mycteroperca tigris)
[Photo: E. Hickerson, Flower Garden Banks National Marine Sanctuary]
All species of the phylum Chordata have the following characteristics in common (although not in all stages of life): pharyngeal slits, dorsal nerve cord, notochord (undeveloped backbone), and a post-anal tail.
The two major groups under Chordata are the two subphylums, Urochordata and Vertebrata.
Urochordata are the sea tunicates, which are considered part of Chordata because of chordate characteristics present in their larval stage. Vertebrata is comprised of species with a vertebral column, a more advanced form of the notochord. Important vertebrate groups in the Gulf of Mexico are Fishes (Pisces), Reptiles (Reptilia) and Mammals (Mammalia).
(Information from
Gulf of Mexico Origin, Waters, and Biota: Volume 1, Biodiversity,
Texas A&M University Press 2009).
The class Reptilia is comprised of four orders, three of which have representatives in the Gulf of Mexico. These are Crocodilia (alligators and crocodiles), Squamata (lizards and snakes), and Testudines (terrapins, tortoises, turtles).
Hawksbill Sea Turtle
(Eretmochelys imbricata)
[Photo: E. Hickerson, Flower Garden Banks National Marine Sanctuary]
Crococodilia is represented by the American crocodile
(Crocodylus acutus).
It is an estuarine species with one population in southern Florida. They are large lizard-like reptiles with heavily armored bodies and webbed feet. They are oviparous, laying their eggs in mounds which are aggressively guarded.
The lizards and snakes are represented by two species, the saltwater marsh snake,
(Nerodia clarki),
and cottonmouth
(Agkistrodon piscivorus),
a freshwater species which only occasionally occupy marine habitats.
The order Testudines is represented by three families, totaling six species within the Gulf of Mexico. These species are exclusively marine, with the exception of the terrapin
(Malaclemys terrapin),
which spends some of its time on land. Each of the five marine species in the Gulf of Mexico Testudines is a federally listed threatened or endangered species.
There are thirty species of marine mammals in eight families documented from the Gulf of Mexico. The Class Mammalia represents an important part of the marine ecosystem in the Gulf. Marine mammals are responsible for most of the consumption at the varying trophic levels. There are three major groups of mammals in the Gulf, the Cetaceans (whales, dolphins and porpoises), Sirenia (sea cows), and Carnivora, specifically the family Otariidae (sea lions or fur seals).
Sirenia and Carnivora are represented by one member each in the Gulf, the West Indian manatee
(Trichechus manatus)
and the California sea lion
(Zalophus californianaus)
.
Marine mammals are different from other marine life because of their unique mammalian characteristics, such as having hair, giving birth to live young, breathing air and displaying thermoregulation via blubber. In general, marine mammals are large; the Blue Whale
(Balaenoptera musculus)
is the largest mammal to ever have inhabited the Earth.
Fishes (Vertebrata: Pisces)
Rock beauty (Holacanthus tricolor) [Photo: G.P. Schmahl, Flower Garden Banks National Marine Sanctuary]
Fish, or Pisces, is a grouping under Chordata that is composed of four major classes: Chondrichthyes (cartilaginous fishes), Actinopterygii (bony fish), Myxini (hagfishes), and
Petromyzontida (lampreys). Pisces has 1541 documented species in the Gulf of Mexico.
The cartilaginous fishes are jawed fishes with skeletons made of cartilage. They have paired fins, scales, and a two-chambered heart. This group is comprised of sharks, rays and skates. Bony fish are the largest class of Vertebrate species, with over 20,000 species worldwide. These fish have a swim bladder and prominent bony structures over which thin tissue is stretched to create bony rays. Hagfish and lampreys have a tail and caudal fin, but no paired appendages; and their skeletons are cartilaginous. Their lack of jaw limits the type of food they intake and both hagfishes (decomposers) and lampreys (parasites) have a row of sharp teeth used for shredding.
Birds (Aves)**
Brown Pelican (Pelecanus occidentalis) [Photo: US Bureau of Land Management]
There are 395 bird species in Gulf of Mexico habitats, including sea birds, birds associated with coastal habitats, and birds that cross the Gulf of Mexico during migration, utilizing its waters and islands. Gulf of Mexico birds represent diverse orders from Procellarioformes, or large seabirds, to Passeriformes, small land-birds that cross the Gulf during migration.
**Note: Gulf of Mexico birds are not included in the associated mapping
application. Visit CSWGCIN Texas Coastal Waterbirds mapping application
to view some of the waterbird colonial nesting sites along the Texas
coast of the Gulf of Mexico.
The NBII Program is administered by the Biological Informatics Program of the U.S. Geological Survey
