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Ostracod [Photo: Antonio Guillen, 2008, Tree of Life]
Ostracods are small (1-2 mm long) and characterized by a hinged, bivalve carapace (shell). Ostracods are generally free-living, from the nearshore habitats to the deep ocean. The bodies of most ostracods consists of a dominant head region with a single eye and two pairs of antenna used for locomotion. Podocopods have a much more calcified carapace that myodocopods, resulting in an extensive podocopod fossil record; thus, making the group useful for deciphering paleo-environments. Mydocopods and podocopods can be differentiated based on the morphology of their second antenna.
Phylum: Arthropoda (Crustaceans)
Arthropods are the largest phyla on Earth; species numbers are estimated in the tens of millions. They are ubiquitous in terrestrial and marine habitats, existing at all elevations and depths. Arthropods have segmented bodies and an exoskeleton made of chitin and proteins. The name arthropod means jointed feet, due to the joints located between the chitin body armor plates. Arthropods must shed (molt) to grow in size.
Red night shrimp
(Cinetorhynehus manningi)
[Photo: G.P. Schmahl, Flower Garden Banks National Marine Sanctuary]
The subphyla Crustacea comprise most of the marine arthropods in the Gulf of Mexico with the exception of Cheliceriformes (horseshoe crabs and sea spiders). Crustacea are mostly free-living with the exception of the sessile Cirripedians (barnacles). Crustaceans are similar to other Arthropods in that they possess a hardened exoskeleton, and in general have segment with one pair of appendages.
This discussion will focus on seven groups in the subphylum Crustacea: Cirripedia (barnacles) and Copepoda under the class Maxillopoda; Podocopa and Myodocopa under the class Ostracoda (seed shrimp); and Stomatopoda (mantis shrimp), Amphipoda, and Decapoda (crabs, lobster, shrimp, crayfish) under the class Malacostraca.
(Information from
Gulf of Mexico Origin, Waters, and Biota: Volume 1, Biodiversity,
Texas A&M University Press 2009).
Stomatopoda (mantis shrimp) is an order under the class Malacostraca. There are 45 species of Stomatopods identified in the Gulf of Mexico. Stomatopods are very agile predatory crustaceans which are shrimp-like in form. Stomatopods are aggressive carnivores that feed on mollusks, cnidarians and other crustaceans, including
other stomatopods. This group is advanced because they can learn, have individual recognition and complex communication via tactile, chemical, visual and sound stimuli. Stomatopods have extremely modified appendages that are shaped for smashing or spearing. They have very complex vision with two eyes on stalks.
Amphipoda
Amphipods are usually whitish in color and shrimp-like in form. They are small, less than 10 mm long, and notable in that they do not have a carapace. Amphipod means different footed and refers to the several different types of appendages on its body. Most amphipods are free-living but some are symbiotic or parasitic species. They are a planktonic species, grasping, burrowing, tube-dwelling or hopping.
Decapoda are mostly a marine group that includes species such as shrimp, hermit crabs, squat lobster, mud shrimp, lobsters, crayfish and true crabs. Of the almost 15,000 species of decapods worldwide, 1007 have been
identified from the Gulf of Mexico.
They can be pelagic, burrow in sediment, or live on the surface or substrates on the bottom of the ocean floor. Decapoda means ten legs; they have five pairs of thoracic appendages which may terminate in pinchers or may be otherwise modified for feeding, crushing, defense, clinging, walking, swimming or cleaning.
Maxillopoda
Lepas spp. (Cirripedia) [Image: After Pilsbry, 1907, from Gulf of Mexico Biodiversity, Origin, Waters, and Biota, Chapter 45. Page 827]
Cirripedians,
or barnacles, are the only group of sessile crustaceans. Most Cirripedians burrow and live within corals or shells, or on other animals. Barnacles are immobile and have adapted to this lifestyle by suspension feeding. Unlike most other crustaceans, barnacles do not molt their carapace but
rather, secrete more calcareous plates to cover their growing body.
There are 1270 Cirripedian species worldwide, with 89 species documented in the Gulf of Mexico.
Copepods
are micro crustaceans (0.5-15 mm in size) and show a wide variety of body forms. This group contains both free-living, parasitic, and associated species.
A copepod of the family Aetideidae [Photo: NOAA Ocean Explorer]
Copepods are the most abundant species on earth, occurring in marine, freshwater and terrestrial habitats. Because of their abundance as marine plankton, copepods serve as an important food source for fish, whales, and others.
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