Arthropoda: Decapoda

Decopod crustaceans are classified as an order of crustaceans in the phylum Arthropoda, class Malacostraca. Because decapod crustaceans are grossly, this chapter uses the lobster as the model in most discussions, and describes important anatomic differences that occur in other decapods. The lobster\u27s body is elongated and divided into a cephalothorax and an abdomen. The hard carapace that makes up most of the cephalothorax is further divided into head and thoracic regions by various indentations on the carapace. Underlying the carapace epithelium is the “spongy” hypodermis composed of large vacuolated cells (the glycogen contents are removed during histologic processing). The gastrointestinal tract of decapods is divided into the esophagus, foregut, midgut, hindgut, anterior and posterior ceca, and digestive gland. The excretory system of a decapod crustacean is the primary means of eliminating nitrogenous wastes and is composed of several parts: a coelomosac, a labyrinth, a bladder and bladder duct, a nephridiopore, and the surrounding hemosinus

Crustacea decapoda da praia rochosa da Ilha do Farol, Matinhos, Paraná: II. Distribuição espacial de densidade das populações

<abstract language="eng">Decapod crustaceans from rocky shore at Farol Isle, Matinhos, Paraná, Brazil. II. Spatial distribution of population densities. A study of the spatial distribution of the decapod populations from a rocky shore at Farol Isle, Matinhos, State of Paraná, Brazil (25º51'S, 48º32'W) was canied out. In the supralittoral the rocky surface is covered partially by a layer of litter coming from the terrestrial habitats; in the midlittoral boulders and pebbles cover the rocky basin and in the infralittoral, there is a belt of seaweeds. A total of 8 samples were taken by hand, two from each of the following levels: supralittoral (emersion time 8-12 hours), upper midlittoral (4-8), lower midlittoral (0-4) and limit between midlittoral and infralittoral, monthly, from May/1990 to April/1991. The number of species increased from supralittoral (5) to infralittoral (22) and a clear vertical zonation on density was observed according to the emersion time gradient. The supralittoral is characterized by grapsids Armases angustipes (Dana, (1852), Cyclograpsus integer H. Milne Edwards, 1837 and Metasesarma rubripes (Rathbun, 1897) which have terrestrial habits and aerial respiration as a main way in obtaining the oxygen. In the midlittoral, the decapods show three basic types of adaptation against emersion desiccation and thermal stresses: (1) by digging into wet mud among the stones such as Panopeus americanus Saussure, 1857, Panopeus occidentalis Saussure, 1857 and Eurypanopeus abbreviatus Stimpson, 1860, (2) by resting in shady and wet space between the boulders and pebbles or underside of them, like Pachygrapsus transversus (Gibbes, 1850), Petrolisthes armatus (Gibbes, 1850) and adults of Menippe nodifrons Stimpson, 1859 and (3) by clinging over the soaked filamentous algae layer on the pebbles or bouders surfaces, a strategy observed in small species such as Pilumnus dasypodus Kingsley, 1879, Podochela sp., Petrolisthes galathinus (Bosc, 1801 ), Alpheus bouvieri A. Milne Edwards, 1878 and juveniles of Menippe nodifrons. In the infralittoral, small species which are vulnerable to desiccation stresses share space by diversification of their diet and adaptation strategies such as camouflage, body color change according to the substratum, flattened body for tight adhesion on hard surface and rapid movements. The main species of this zone are Petrolisthes armatus, Petrolisthes galathinus, juveniles of Menippe nodifrons, Epialtus brasiliensis Dana, 1852, P. dasypodus, Synalpheus fritzmuelleri Coutière, 1909, Megalobrachium roseum (Rathbun, 1900) and species of Palaemonidae. The rocky shore at Farol Isle is a complex architectural environment due to the conjunction of diversified habitats such as litter over a hard surface, spaces and crevices among boulders and pebbles, muddy substratum and phytal