THE PHYSIOLOGY OF ASCIDIANS
73
storage cells, i.e. orangc cells and nephrocytes. The proportion of diffcrent cell types in the hlood iLPPciLrR to differ widely between species
and may be a reflection of diflibrent types of activity either in different
species or in animals at tlifferwit scitsons of the year (Table X).
It is clear that much of the confusion in the literature must arise
from the existence of cells in transition from one cell type to another,
particularly in the formtttion of morula cells. The sequence of events
involves changcs through hyttlinc amoebocyte, vacuolated amoebocyte,
signet-ring cell, compartment cell and finally the mature morula cell.
This is a dynamic process involving considerable metabolic activity and
synthesis within the cell and the cliunges cannot be accommodated
adequately in simple morphological descriptionH. It is further discussed
below.
C. Heavy metals in ascidian b l d
Sea water contains betwecbn 0.3 mtl 3.0 pg of vanadium per litre
(Harvey, 1955) but valum as high as 3700 p.p.m. organic dry weight
have been found in ascidians (Ciereszko et al., 1963) so that the degree
of conccntration of the metal i n t h e body is very great. In the blood
cells of xome ascidians the conctentration of vanadium may be in excess
of one million times as high as that in sea water (Rummell et al., 1966).
Henzc (191 1) was the first to show that ascidians are capable of
accumulating vanadium in their bodies as a complex organic molecule
and this observation has been confirmed by many authors since that
time. Thc earlier literature htts been reviewed by Webb (1939, 1956)
and Table XI provides it summary of the occurrence of vanadium in the
Ascidiacea. It is appitrent that most species of ascidians are able to
conccntrute the rnctul in small amounts but only in a few families of
phlebobranchiate ascidiuns, notably Asridiidae and Perophoridae, does
the metal OUCIII' in large quantity. In the Pyuridae iron appeam to be
concentrated instead of vanadium (Endean, 1953, 1955a, Smith, 1970a)
and niobium, tctntalum arid titanium have all been reported in other
species (Table XII). It is generally agreed that the iron and vanadium
are coiicentratcd in the blood and particularly within the morula celln
(see especially Webb, 1939, 1 956 ; Balt~cheffsky and Baltscheffsky,
1963; Endean, k955a, 1960; Biclig et aE., 196la; Kalk, 1963b ; Koval'nkii
and hzueva, 1963; Smith, 1970a; Rummel et al., 1966), but there
does not seem to be any concrete evidence that niobium, tantalum or
titanium are concentrated in blood cells. Assuming that the mechanisms
of uptake are the same for all metals (see below) it is likely that they
will become concentrated in tho blood. It is of interest that in the
pelagic tunicate Salpa, where a iiumber of metals are also concentrated,
73
storage cells, i.e. orangc cells and nephrocytes. The proportion of diffcrent cell types in the hlood iLPPciLrR to differ widely between species
and may be a reflection of diflibrent types of activity either in different
species or in animals at tlifferwit scitsons of the year (Table X).
It is clear that much of the confusion in the literature must arise
from the existence of cells in transition from one cell type to another,
particularly in the formtttion of morula cells. The sequence of events
involves changcs through hyttlinc amoebocyte, vacuolated amoebocyte,
signet-ring cell, compartment cell and finally the mature morula cell.
This is a dynamic process involving considerable metabolic activity and
synthesis within the cell and the cliunges cannot be accommodated
adequately in simple morphological descriptionH. It is further discussed
below.
C. Heavy metals in ascidian b l d
Sea water contains betwecbn 0.3 mtl 3.0 pg of vanadium per litre
(Harvey, 1955) but valum as high as 3700 p.p.m. organic dry weight
have been found in ascidians (Ciereszko et al., 1963) so that the degree
of conccntration of the metal i n t h e body is very great. In the blood
cells of xome ascidians the conctentration of vanadium may be in excess
of one million times as high as that in sea water (Rummell et al., 1966).
Henzc (191 1) was the first to show that ascidians are capable of
accumulating vanadium in their bodies as a complex organic molecule
and this observation has been confirmed by many authors since that
time. Thc earlier literature htts been reviewed by Webb (1939, 1956)
and Table XI provides it summary of the occurrence of vanadium in the
Ascidiacea. It is appitrent that most species of ascidians are able to
conccntrute the rnctul in small amounts but only in a few families of
phlebobranchiate ascidiuns, notably Asridiidae and Perophoridae, does
the metal OUCIII' in large quantity. In the Pyuridae iron appeam to be
concentrated instead of vanadium (Endean, 1953, 1955a, Smith, 1970a)
and niobium, tctntalum arid titanium have all been reported in other
species (Table XII). It is generally agreed that the iron and vanadium
are coiicentratcd in the blood and particularly within the morula celln
(see especially Webb, 1939, 1 956 ; Balt~cheffsky and Baltscheffsky,
1963; Endean, k955a, 1960; Biclig et aE., 196la; Kalk, 1963b ; Koval'nkii
and hzueva, 1963; Smith, 1970a; Rummel et al., 1966), but there
does not seem to be any concrete evidence that niobium, tantalum or
titanium are concentrated in blood cells. Assuming that the mechanisms
of uptake are the same for all metals (see below) it is likely that they
will become concentrated in tho blood. It is of interest that in the
pelagic tunicate Salpa, where a iiumber of metals are also concentrated,