ECHINODERMATA - KU ScholarWorks - University of Kansas

16 THE UNIVERSITY OF KANSAS PALEONTOLOGICAL CONTRIBUTIONS
toids these plates are absent and any descriptions of
them would be a contribution to knowledge. The
plates appear to have flexible sutures between them
and one would hardly expect them to be found in
place. From this evidence it is probable that the anal
region was tightly covered by plates, and that the living
blastoid probably did not have a large gap on the
anal side. In the genus Polydeltoideus, two small plates
are present on the aboral side of the anal opening, abutting
against the hypodeltoid and resting upon the
cryptodeltoids. These are termed paradeltoi d plates.
The paradeltoids probably became fused with the
hypodeltoid to form an elongate hypodeltoid in later
blastoids.
TAXONOMY AND PHYLOGENY OF BLASTOIDS
INTRODUCTION
In the past, little uniformity has existed in classification
and interpretation of relationships between
the several kinds of known blastoids, and this lack
of consistency persists. Not only do authors disagree
as to placement of genera in families but there is even
wide variance of opinion as to delimitation of the
echinoderm group called blastoids. At different times
specimens regarded by authors as belonging to cystoids,
crinoids, and edrioasteroids have been described
as true blastoids and the blastoids have been classed
by some specialists as a subdivision of the cystoids.
It is even true that genera have been shifted back and
forth from classification with blastoids to placement
with cystoids or crinoids. Therefore, a systematic survey
of the Blastoidea is needed in order to evaluate
accumulated knowledge of their morphological features
and relationships objectively. In this connection
effort has been made to understand the significance of
every morphologically distinct structure. Because
many new structures have been recognized and new
genera are yet to be described, a comprehensive classification
of Blastoidea is not here attempted. Only two
orders are recognized—Fissiculata (hydrospire slits
exposed to the surface or bearing spiracular slits) and
Spiraculata (hydrospire slits hidden, pores formed
with spiracles), as distinguished by JAEKEL (1918).
The genera are not now grouped in families but arranged
alphabetically under each order.
PREVIOUS WORK
Since 1825, when THOMAS SAY introduced the name
Blastoidea for a "family" of echinoderms intermediate
between echinoids and crinoids, there has been
controversy over classificatory placement and phylogenetic
relations of these fossils. As early as 1808, S. L.
MITCHILL called one specimen "an Echinus of the
family galerite," thus expressing belief that a blastoid
is some type of echinoid. In 1819, J. L. M. DEFRANCE
used the name Encrina for the same blastoid, thus
indicating presumed affinity of the blastoids with
crinoids. In order to reconcile these divergent opinions,
SAY coined a noncommittal new name, "Blastoidea,"
referring to the predominant budlike form of
the calyx.
In 1851, C. F. ROEMER divided the blastoids into
four groups, named Floreales, Elliptici, Truncati, and
Clavati, based on form of the calyx and ambulacra.
He stated that the blastoids stand close to the cystoids
because of their lack of arms and presence of a stem.
The Floreales group was defined to include conical
forms with petaloid ambulacra, the Elliptici contained
elliptical forms, the Truncati comprised blastoids
with flat or truncated summits, and the Clavati
were defined as conical forms with linear ambulacra.
In 1886, R. ETHERIDGE & P. H. CARPENTER recognized
the blastoids as a separate class, distinct from
other pelmatozoan echinoderms, and they divided
them into two orders called Regulares and Irregulares.
The first comprise all blastoids with five normally
developed ambulacra, and the second include all
forms having four normal ambulacra associated with
a distinctly shortened fifth ambulacrum. The Regulares
were divided into five families called Pentremitidae
(pyriform, with five spiracles); Troostoblastidae
(pyriform, with ten spiracles); Nucleoblastidae (elliptical,
with ten spiracles); Granatoblastidae (elliptical,
with five spiracles); and Codasteridae (without hydrospire
pores). The Irregulares comprised a single family
named Astrocrinidae (three genera).
In 1900, CHARLES WACHSMUTH, who wrote the
chapter on blastoids in ZirrEL- EASTMAN'S Textbook of
Palaeontology, followed ETHERIDGE & CARPENTER in
almost every detail. However, in the same year F. A.
BATHER published a new classification of the blastoids
in which he recognized two "grades," named Protoblastoidea
and Eublastoidea. The protoblastoids included
two families: Asteroblastidae (with an indefinite
number of thecal plates and possessing diplopores)
and Blastoidocrinidae (with an indefinite number
of thecal plates and having "incipient" hydrospires).
The eublastoids (characterized by a constant