PROC. BIOL. SOC. WASH. 97(1). 1984, pp. 43^*8 DENDROGASTER ARGENTINENSIS, NEW SPECIES, A SOUTH AMERICAN SEA-STAR PARASITE (CRUSTACEA: ASCOTHORACIDA) Mark J. Grygier and Mariana B. Salvat Abstract.— Dendrogaster argentinensis is a coelomic parasite of the subantarctic sea-star Anasterias rninuta Perrier at Puerto Deseado, Argentina. Mature and juvenile females, and males, are described. This species resembles D. fisheri Gry-gier and D. arctica Korschelt from the northern Pacific Ocean, but is distinguished by the extreme reduction of the antennular claw guard in females. Presence of the parasite sometimes is obviously detrimental to the host. Dendrogaster argenti-nensis is the first ascothoracid described from the South American coast. Resumen.— Dendrogaster argentinensis es un parasito de la cavidad celomica de la estrella de mar subantartica Anasterias minuta Perrier en Puerto Deseado, Argentina. Se describen hembras juveniles y maduras, y tambien machos. Esta especie es semejante a D. fisheri Grygier y a D. arctica Korschelt, ambas del Pacifko Norte, pero se distingue de ellas por la extrema reduction del proceso guardian de la una antenular en las hembras. La presencia del parasito es a veces obviamente perjudicial para el huesped. Dendrogaster argentinensis es el primar ascotoracido citado para las costas de America del Sur. The Ascothoracida are crustacean parasites of echinoderms and coelenterates, the most recent review being Wagin's ( 1 976) monograph. The genus Dendrogaster Knipowitsch, the most specialized in the subclass, are endoparasites of sea-stars (Asteroidea). They have replaced most of the structure and function of their segmented body with a greatly enlarged and elaborated, branched carapace or mantle (Wagin 1954). About 20 species of Dendrogaster were described or re-viewed by Wagin (1950, 1976), and Grygier (1981, 1982) added three more species. Few ascothoracids are known from the South Atlantic. Waginella sandersi (Newman) was collected on the bottom (5200 m) at 43°33.0'S, 48°58.1'W (New-man 1974, Grygier 1983a). Ascothorax bulbosus Heegaard, which infests two species of the ophiuroid Amphiura at 1 10-175 m near South Georgia (Heegaard 1951), actually represents two species (Grygier 1983b). Ascothorax gigas Wagin parasitizes Ophionotus victoriae Bell along the Antarctic Peninsula and in the South Sandwich Islands (Wagin 1968, Grygier and Fratt 1984). An undescribed species of Ascothorax lives in Ophiurolepis inornata (Lyman) at 800 m off the Patagonian shelf (Bartsch 1982, Grygier 1983b). Dendrogaster has been recorded twice in the South Atlantic. Le Roi (1905, 1907) described D. arborescens from Dipsacaster sladeni Alcock off Cape Town, and Fisher ( 1 940) noted Diplasterias meridionalis (Perrier) from 27 m at South Georgia infested with as yet unstudied Dendrogaster specimens. This report is the description of the first ascothoracid from the shores of the South American continent, a new species of Dendrogaster parasitic in the asteroid Anasterias minuta Perrier. This is a middle-sized, brooding, asteriid sea-star that inhabits rocky shores (0-80 m) in subantarctic waters: southern Argentina in Santa
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