No description available.

Interest in the endemic Pisaster was first aroused by the great variation of external color in Pisaster ochraceus. This in turn led to observations of the diversity of the spinous patterns of this sea star. Following the suggestion of Dr. Jool D. hedgepeth it was decided to make an extensive comparison of the common species of Pisaster. Detailed comparison between Pisaster brevispinus and Pisaster ochraceus have been made only by Fisher (1930) and Verrill (1914). Both of these investigators restricted their observations largely to the endoskeleton and its calcareous protuberances. In addition to analyzing the work of Fisher, an attempt to differentiate between the two species regarding behaviour, tolerances, gross anatomy and natural history has been made. In addition some mention of the relationships with other members of the family Asteriidae is recorded in this study.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1985. / Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1985. / Document électronique également accessible en format PDF. CaQCU

Thesis (Ph.D.)--Oregon, Dept. of Biology Vita Bibliography: l. 177-184

Little is known of the biology of the parasite Dendrogaster (Crustacea: Ascothoracida), an obligate endoparasite of sea stars. There are some 25 species of Dendrogaster reported worldwide. The highly modified females live within the coelomic cavity of the host, and heterochronous males are parasitic within the mantle cavity of the female. Two sea star species from the Otago Coast were found to be infected with two species of Dendrogaster. These parasite populations were studied from July 1993 to December 1994 to investigate specific aspects of their biology and the interactions between these parasites and their hosts. The parasite found in Allostichaster insignis (Asteridae) was identified as Dendrogaster argentinensis Grygier and Salvat 1984, and Asterodon miliaris (Odontasteridae) was found to contain a previously unknown species, herein described and named Dendrogaster otagoensis n. sp. The structure and function of the mantle of female Dendrogaster sp were determined using light, scanning and transmission electron microscopy. The ultrastructure of the mantle is modified, sharing characteristics found in Rhizocephala (Crustacea: Cirripedia), copepods, and Ulophysema oeresundense (Ascothoracida: Dendrogasteridae), which enable these crustaceans to absorb nutrients. Such modifications include a very thin, crenulated epicuticle, a soft, unscleratinised procuticle, and infoldings of the apical plasma membrane. In Dendrogaster the gut is likely to retain the capacity to absorb nutrients. In general, aspects of infestation of Dendrogaster argentinensis and D. otagoensis are the same. Prevalence of Dendrogaster sp. in Otago sea stars is high and parasitism occurs throughout the year. Seventy-seven point five percent of Asterodon miliaris are infected with D. otagoensis and 97.4% of Allostichaster insignis are infected with D. argentinensis. Up to 144 females are found in a single host, and as many as 34 males in a single female. Mean number of parasites per host changes little over time, but began to decrease in D. argentinensis towards the end of the sample period. The female population is dominated by small individuals, with maximum size likely to depend on space available within the host. Males achieve a large size quickly, but their growth is also restricted by the size of the female they are within. The size and number of females per host are not related to size of the host. Females acquire new males and males grow larger with an increase in female size. Males occur in females of all reproductive stages, but occur with the greatest frequency in brooding females. Reproduction is spread evenly through females in less heavily infected hosts, and there is a reduction in mean size of females as the number of females per host increases, indicative of the crowding effect. Three indices of aggregation show that both sexes of Dendrogaster are highly aggregated in their hosts, with few hosts harbouring most of the parasites. Dendrogaster is a parasitic castrator. Infected hosts have parasite loads ranging from 0.1% - 112% total sea star wet weight. Infected sea stars have smaller pyloric caecae and gonads, however, no gonads were present in uninfected Allostichaster insignis. Effect on the gonads and pyloric caecae increases as parasite load increases. Rather than directly affecting the germinal tissue of the host, Dendrogaster castrates its host indirectly through crowding and/or competitive castration. This castration is variable among hosts in Asterodon miliaris, but is important in Allostichaster insignis. The presence of D. argentinensis in A. insignis is associated with an increase in the incidence of asexual reproduction among larger (R>25mm) individuals. Specific growth rates of intact and regenerating arms in fed and starved A. insignis are lower in infected individuals. Larvae are brooded in the mantle cavity of the female until reaching the infective, swimming ascothoracid II stage. The larval development of Dendrogaster argentinensis and D. otagoensis is abbreviated. Larvae moult directly from the egg into the metanauplius. Metanauplii moult into ascothoracid I stage, which moult into the ascothoracid II stage immediately upon release from the female. Ultrastructure confirms the putative sensory function of the lattice organs. Other larval cuticular structures are also sensory. Histological examination revealed that Dendrogaster has unique system of ovulation among Crustacea. The ovarian membrane contains primary oocytes, early vitellogenic and vitellogenic oocytes, but not maturing oocytes, which are found outside the ovarian membrane. The ovarian membrane forms follicles from which vitellogenic oocytes burst into the surrounding mesodermal tissue. These oocytes mature within the mantle wall tissue until entering the mantle cavity, where they are fertilised. Ovaries are absent in most brooding females. Spermatogenesis takes place within the males posterior protrusions and is continuous. Dendrogaster are likely to be labile hermaphrodites, as sperm are found in 20% of ovaries. Female Dendrogaster display asynchronous reproduction, with females of all sizes at different stages throughout the year. Females within one host are also at different stages. Spermatogenesis is present in males of all sizes. The presence of spent males in some females is indicative of a females outliving the males.

Oreaster reticulatus was studied in eight populations inhabiting shallow-water grassbeds and/or sand bottoms off Carriacou and Union Island in the Grenadines, and off St. Croix in the U.S. Virgin Islands (Caribbean). The sea star is fundamentally an omnivorous, microphagous substratum grazer: grassblades and/or surface sediments are accumulated beneath the disc by tube feet, and associated micro-organisms and detritus are ingested and digested by extraoral eversion of the cardiac stomach. Substratum grazing involves minimal foraging effort; however, the low concentration of particulate food resources necessitates frequent feeding. O. reticulatus also has a limited capacity for herbivory and can hydrolyze soluble algal cell contents. Opportunistic predation and scavenging of macrofauna may provide an important nutritional supplement, although capturable prey or carrion are generally unavailable or inaccessible to the sea star. Marked differences in individual size, storage and reproductive capacity among neighboring populations of O. reticulatus are attributed to differences in the quality and/or quantity of food resources. Intraspecific competition may limit productivity, particularly in isolated sand patches containing dense and extremely aggregated populations.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2009. / Additional advisors: Bill J. Baker, James B. McClintock, Donald D. Muccio, Robert W. Thacker. Description based on contents viewed June 3, 2009; title from PDF t.p. Includes bibliographical references.

Pteraster tesselatus is noted for its external secretion of massive amounts of mucus. The mucus repels most animals, and fouls their respiratory physiology, if contact is maintained for any length of time. It provides protection essentially 100% of the time from Solaster dawsoni and Pycnopodia helianthoides, the only local stars that attempt to feed on Pteraster. The mucus, which is a simple mucopolysaccride, is produced in three different types of unicellular glands located in the epidermal tissues along the supradorsal membrane. Pores along the lateral walls of the ambulacral grooves provide fresh sea water for the dermal branchiae contained in the nidamental cavity located between the supradorsal membrane and the body wall. P. tesselatus has a very strong chemoreceptive ability to locate prey. It prefers sponges, but feeds on a great variety of sessile organisms, as well as detritus. It also feeds on Chlamys hastata and C. rubida, which have their valves epizoically overgrown with either Myxilla incrustans or Mycalft adhaerens.

No description available.