Some observations on pigments of the pacific sand dollars,Dendraster excentricus andDentraster laevis

1955 ◽  
Vol 11 (7) ◽  
pp. 270-271 ◽  
Author(s):  
T. W. Goodwin ◽  
D. L. Fox
Keyword(s):  
The Pacific ◽  
Sand Dollars ◽  
Dendraster Excentricus

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

Morphological variation in the Pacific sand dollar Dendraster excentricus

1995 ◽  
Vol 73 (3) ◽  
pp. 576-583
Author(s):  
Raymond K. Nakamura
Keyword(s):  
Principal Component Analysis ◽  
Principal Components ◽  
Morphological Variation ◽  
Correlation Matrix ◽  
Principal Component ◽  
Sand Dollar ◽  
Coastal Habitats ◽  
Point Conception ◽  
The Pacific ◽  
Dendraster Excentricus

Correlations between latitude, habitat, and morphology in the Pacific sand dollar Dendraster excentricus were identified with principal component analysis. Twenty-two lengths were measured on the oral and aboral surfaces of 615 specimens from 31 sites. Samples were divided at latitude 34°30′N (Point Conception) and into bay and coastal habitats by relative wave exposure. Principal components (PC) were estimated from a correlation matrix of sample means of log-transformed measurements. PC1 accounted for 90% of the variance and was a measure of overall size. All 22 PC1 coefficients were positive and differed significantly from 0, according to a jackknifing test. PC1 differed significantly with latitude (ANOVA, p < 0.01) but not habitat. Southern populations tended to be smaller. PC2 accounted for 5% of the variance and described overall shape. Of the 22 variables, 13 had significant coefficients that varied in sign. PC2 varied significantly with habitat (ANOVA, p < 0.05) but not latitude. In coastal populations, the peristome and petaloids tended to be more posteriorly positioned and the food grooves were branched more peripherally. These features correspond to the greater tendency for coastal specimens to use their posterior end to suspension feed.

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

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.

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