9
Table I.
Ontogenetic patterns of major crustacean taxe (exemplified by particular taxa) compared to the larval series of Rehbachiella
kinnekullensis; number of top and lower rows refer to stages before and after appearance of trunk segments (= Rehbachiella stages LI-4;
TS 1-13; TS 13+ developed in Anostraca, Cephalocarida and Decapoda); moults (stages) indicated by black bars according to their development
of segments and/or limbs (thinner bars after achievement of definite number of trunk segments to reduce length of table); Cinipedia and
Bredocaris; larval stages cannot be directly sequenced due to missing external segmentation and suppression of limb development on hind
body; asterix in Copepoda, Mystacocarida, Cirripedia and Bredocaris refers to original (ground pattern) number of II trunk segments in front
of the telson ; ? = not documented by further development of Rehbachiella (simplified from Walossek 1993 ; Tab. 4).
L
T S
1234 1 2 3 4 5 6 7 8 9 10 11 12 13 ?
II 11111111111 111111 I 111111 141;16171810
Rehbachlella
Anostraca
Artemia
I I I I I I I I
,I I I I 11111111111 ~UII
Copepoda
Drescherfella
Mystacocarlda
Derocheilocarfs
1111 II cope~r ll I I ~ull *
I I I I I IIII:~'
Clrrlpedla
1_ 1_ 1_ 1_ 1_ 1 CY~~UII
*
Bredocaris
Cephalocarlda
Hutchinsoniella
lightiella
Decapoda
Macropetasma
II
I -I ~I -I - I
I I I
IIII
Adult
- I
I
I
*
141518 171810
1111 1111I11I1,:u"
I III 1111111 ':Ull
1111111111 ::.u n
1 2 3 4 1 2 3 4 5 6 7 8 9 10 11 12 1314
L
TS
these observations provide evidence that the reduced
state of the antennules in all extant Branchiopoda and
of the second antennae in Euanostraca and Calmanostraca has been achieved merely by convergence, Again,
Rehbachiella has well developed maxillulae and maxillae, while these are largely modified or reduced in
extant Branchiopoda. The hypothesized ingroup status of Rehbachiella implies, for this feature, also that
reduction had occurred independently among the different branchiopod lines.
Ontogenetic patterns among Crustacea
The larval sequence of Rehbachiella is not only strictly anameric, but the series is actually doubled because
each of the trunk segments is laid down in two steps.
I have used this gradual pattern as a reference base for
comparisons between the sequences of all major crustacean taxa. As examples, I took forms for which the
sequence has been fully documented. There are two
different methods for surveying the major characteristics of external development. The method presented by
Sanders (1963), refers to moult stages. It proved to give
a rapid overview of the entire process of development,
with the appearance of segments, appendages and their
development, 'jumps' in development, and the formation of tagmata. Its disavantages are that it refers to
a relative scale, because development can be largely
modified in any species, environmentally as well as
individually. Accordingly successive moults may not
indicate an identical state of development in different
species. Moreover, it is very much affected by incompleteness of data on taxa and differences in their life
strategies. The possiblity of misinterpretation becomes
apparent in Fig. 27 of Sanders (1963) which shows
only very fragmentary data for Branchiopoda (example Artemia), Copepoda and Cirripedia, and thus gives
the misleading impression that Cephalocarida have the
longest, most complete and plesiomorphic postembryonic series among the Crustacea.
Table I.
Ontogenetic patterns of major crustacean taxe (exemplified by particular taxa) compared to the larval series of Rehbachiella
kinnekullensis; number of top and lower rows refer to stages before and after appearance of trunk segments (= Rehbachiella stages LI-4;
TS 1-13; TS 13+ developed in Anostraca, Cephalocarida and Decapoda); moults (stages) indicated by black bars according to their development
of segments and/or limbs (thinner bars after achievement of definite number of trunk segments to reduce length of table); Cinipedia and
Bredocaris; larval stages cannot be directly sequenced due to missing external segmentation and suppression of limb development on hind
body; asterix in Copepoda, Mystacocarida, Cirripedia and Bredocaris refers to original (ground pattern) number of II trunk segments in front
of the telson ; ? = not documented by further development of Rehbachiella (simplified from Walossek 1993 ; Tab. 4).
L
T S
1234 1 2 3 4 5 6 7 8 9 10 11 12 13 ?
II 11111111111 111111 I 111111 141;16171810
Rehbachlella
Anostraca
Artemia
I I I I I I I I
,I I I I 11111111111 ~UII
Copepoda
Drescherfella
Mystacocarlda
Derocheilocarfs
1111 II cope~r ll I I ~ull *
I I I I I IIII:~'
Clrrlpedla
1_ 1_ 1_ 1_ 1_ 1 CY~~UII
*
Bredocaris
Cephalocarlda
Hutchinsoniella
lightiella
Decapoda
Macropetasma
II
I -I ~I -I - I
I I I
IIII
Adult
- I
I
I
*
141518 171810
1111 1111I11I1,:u"
I III 1111111 ':Ull
1111111111 ::.u n
1 2 3 4 1 2 3 4 5 6 7 8 9 10 11 12 1314
L
TS
these observations provide evidence that the reduced
state of the antennules in all extant Branchiopoda and
of the second antennae in Euanostraca and Calmanostraca has been achieved merely by convergence, Again,
Rehbachiella has well developed maxillulae and maxillae, while these are largely modified or reduced in
extant Branchiopoda. The hypothesized ingroup status of Rehbachiella implies, for this feature, also that
reduction had occurred independently among the different branchiopod lines.
Ontogenetic patterns among Crustacea
The larval sequence of Rehbachiella is not only strictly anameric, but the series is actually doubled because
each of the trunk segments is laid down in two steps.
I have used this gradual pattern as a reference base for
comparisons between the sequences of all major crustacean taxa. As examples, I took forms for which the
sequence has been fully documented. There are two
different methods for surveying the major characteristics of external development. The method presented by
Sanders (1963), refers to moult stages. It proved to give
a rapid overview of the entire process of development,
with the appearance of segments, appendages and their
development, 'jumps' in development, and the formation of tagmata. Its disavantages are that it refers to
a relative scale, because development can be largely
modified in any species, environmentally as well as
individually. Accordingly successive moults may not
indicate an identical state of development in different
species. Moreover, it is very much affected by incompleteness of data on taxa and differences in their life
strategies. The possiblity of misinterpretation becomes
apparent in Fig. 27 of Sanders (1963) which shows
only very fragmentary data for Branchiopoda (example Artemia), Copepoda and Cirripedia, and thus gives
the misleading impression that Cephalocarida have the
longest, most complete and plesiomorphic postembryonic series among the Crustacea.