Comparison of macrofaunal invertebrates in sand dollar (Dendraster excentricus) beds and in adjacent areas free of sand dollars

1981 ◽  
Vol 65 (2) ◽  
pp. 191-198 ◽  
Author(s):  
A. L. Smith
Keyword(s):  
Sand Dollar ◽  
Sand Dollars ◽  
Dendraster Excentricus

Vertical posture of the clypeasteroid sand dollar Encope michelini

2004 ◽  
Vol 84 (2) ◽  
pp. 407-408 ◽  
Author(s):  
John M. Lawrence ◽  
Joan Herrera ◽  
Janessa Cobb
Keyword(s):  
Vertical Posture ◽  
Sand Dollar ◽  
Apical System ◽  
Sand Dollars ◽  
Dendraster Excentricus

Vertical posture has been studied only in the scutellid sand dollar Dendraster excentricus although it has been reported in another Dendraster species and two species of laganid sand-dollars. The vertical posture has been associated with the posterior eccentric position of the apical system and petals of the test. We have discovered the scutellid sand dollar Encope michelini, which shows no eccentricity of the apical system and petals, also has the vertical posture in the population studied. Absence of eccentricity of the apical system and petals in living and fossil sand-dollars does not indicate absence of the vertical posture.

The biogeography of origin and radiation: dendrasterid sand dollars in the northeastern Pacific

Paleobiology ◽  
1991 ◽  
Vol 17 (4) ◽  
pp. 325-339 ◽  
Author(s):  
Steven C. Beadle
Keyword(s):  
Coastal Waters ◽  
Pacific Coast ◽  
Sand Dollar ◽  
Central California ◽  
The Pacific ◽  
Northeastern Pacific ◽  
Place Of Origin ◽  
Transitional Forms ◽  
Sand Dollars ◽  
And Behavior

Under favorable circumstances, biogeographic and biostratigraphic data can be combined to identify accurately the time and place of origin of a given taxon, and to reconstruct the pattern of its subsequent radiation. This study considers the dendrasterid sand dollars, which are abundant today along the Pacific Coast of North America. The Neogene sand dollar record in this region is particularly good; in fact, sand dollars have traditionally been used as provincial index fossils.The dendrasterids originated in central California at the end of the Miocene; the oldest forms are dated at about 6.0–6.5 Ma. They spread south to Baja California during the Pliocene, and then north to Alaska during the Quaternary. This historical pattern is not an artifact of the record; it is consistent with independent paleogeographic evidence. The dendrasterids supplanted an older Mio-Pliocene sand dollar fauna; they are now completely dominant in the temperate coastal waters of the northeastern Pacific. They have reached this position in less than 7 m.y. since their first local appearance. The rapid rise of dendrasterids could be related to their aberrant morphology and behavior; these adaptations allow dendrasterids to suspension-feed, in a manner unique among living echinoids.Dendrasterids are characterized by “eccentric” test morphologies. Even the oldest species are highly eccentric; transitional forms are unknown. The first dendrasterids appear suddenly in the provincial “Jacalitos Stage,” above an unconformity which represents no more than about 1 m.y. They do not occur in the underlying units, although other fossil sand dollars are abundant. The dendrasterids may have arisen rapidly, through a heterochronic change in the development of older, noneccentric forms. Recent ontogenetic studies have documented the feasibility of this process.

Enhanced Acoustic Backscatter Due to High Abundance of Sand Dollars, Dendraster excentricus

2001 ◽  
Vol 19 (2) ◽  
pp. 135-145 ◽  
Author(s):  
Lori E. Fenstermacher ◽  
Gregory B. Crawford ◽  
Jeffry C. Borgeld ◽  
Tristan Britt ◽  
Douglas A. George ◽  
...  
Keyword(s):  
High Abundance ◽  
Acoustic Backscatter ◽  
Sand Dollars ◽  
Dendraster Excentricus

scholarly journals Rethinking competence in marine life cycles: ontogenetic changes in the settlement response of sand dollar larvae exposed to turbulence

2015 ◽  
Vol 2 (6) ◽  
pp. 150114 ◽  
Author(s):  
Jason Hodin ◽  
Matthew C. Ferner ◽  
Gabriel Ng ◽  
Christopher J. Lowe ◽  
Brian Gaylord
Keyword(s):  
Life Histories ◽  
Immature Stage ◽  
Life Cycles ◽  
Sand Dollar ◽  
Ontogenetic Changes ◽  
Marine Animals ◽  
Settlement And Metamorphosis ◽  
Two Phases ◽  
Pass Through ◽  
Dendraster Excentricus

Complex life cycles have evolved independently numerous times in marine animals as well as in disparate algae. Such life histories typically involve a dispersive immature stage followed by settlement and metamorphosis to an adult stage on the sea floor. One commonality among animals exhibiting transitions of this type is that their larvae pass through a ‘precompetent’ period in which they do not respond to localized settlement cues, before entering a ‘competent’ period, during which cues can induce settlement. Despite the widespread existence of these two phases, relatively little is known about how larvae transition between them. Moreover, recent studies have blurred the distinction between the phases by demonstrating that fluid turbulence can spark precocious activation of competence. Here, we further investigate this phenomenon by exploring how larval interactions with turbulence change across ontogeny, focusing on offspring of the sand dollar Dendraster excentricus (Eschscholtz). Our data indicate that larvae exhibit increased responsiveness to turbulence as they get older. We also demonstrate a likely cost to precocious competence: the resulting juveniles are smaller. Based upon these findings, we outline a new, testable conception of competence that has the potential to reshape our understanding of larval dispersal and connectivity among marine populations.

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