MALACOLOGIA, 1989, 31(1): 175-195
BIOLOGY AND COMPARATIVE ANATOMY OF DIVARISCINTILLA YOYO AND
D. TROGLODYTES, TWO NEW SPECIES OF GALEOMMATIDAE (BIVALVIA)
FROM STOMATOPOD BURROWS IN EASTERN FLORIDA
Paula M. Mikkelsen^ & Rüdiger Bieler^
ABSTRACT
Two new galeommatid bivalves, Divariscintilla yoyo and D. troglodytes, are described as
commensals in burrows of the stomatopod Lysiosquilla scabhcauda from central eastern Flor-
ida. They are remarkable in their snail-like appearance and behavior, due to elaborately orna-
mented palliai layers enclosing the shell, and their ability to actively crawl on a highly mobile foot.
Both are simultaneous hermaphrodites, brooding their larvae in the suprabranchial chamber
prior to release of straight-hinged veligers. The two new species differ from one another in shell
morphology, the number of secretory "flower-like organs," and the nature and ornamentation of
the mantle. They differ from the type and only other described species in this genus, D. maoria,
primarily in shell characters, namely in anterior (rather than posterior) prolongation, and in the
absence of a ventral cleft. The genus Divariscintilla, previously known only from New Zealand,
is redefined with the following diagnostic characters: incompletely internalized shell with anterior
or posterior prolongation, species-specific numbers of palliai tentacles and papillae, a two-part
foot used in active crawling and "hanging" utilizing both byssus-and byssus adhesive glands,
secretory "flower-like organs" on the anterior surface of the visceral mass, eulamellibranch
ctenidia with interlamellar and interfilamentary junctions, and simultaneous hermaphroditism
with larval brooding.
Keywords: Divariscintilla, Galeommatidae, Galeommatoidea, systematics, anatomy, Sto-
matopoda, commensalism, Florida.
INTRODUCTION
A wide variety of mollusks are known to
associate with other invertebrates in symbi-
otic relationships. Galeommatoidean [= ga-
leommatacean] bivalves are among the best
known symbionts (Boss, 1965, as Erycina-
cea), and are interesting in the anatomical
and behavioral modifications associated with
their specialized mode of life. These include
(1) internalization of the shell by the middle
palliai fold, (2) elaboration of this pallia! layer
by tentacles and papillae, (3) snail-like loco-
motion on a highly extensible foot, and (4) the
occurrence of hermaphrodites or dwarf
males. Anatomical data are available for spe-
cies in less than 30 of the approximately 110
Recent, presumably valid genera (Vokes,
1980; Chavan, 1969).
Within the family Galeommatidae Gray,
1840, the monospecific genus Divariscintilla
Powell, 1932, was originally based on empty
shells of the New Zealand species D. maoria
Powell, 1932. Distinguishing shell characters
include a deep ventral notch, a strongly ob-
lique posterior prolongation, and dentition lim-
ited to a small conical tooth in each valve. The
anatomy and biology of D. maoria were sub-
sequently described by Judd (1971) from
specimens found living in the burrows of the
stomatopod crustacean Heterosquilla tricari-
nata (Claus).
A study of organisms associated with the
sand-burrowing stomatopod Lysiosquilla sca-
bricauda (Lamarck) in shallow waters in
eastern Florida has yielded a number of
undescribed or poorly known molluscan
species. Data on the two species of vitrinellid
gastropods in the burrows have appeared
elsewhere (Bieler & Mikkelsen, 1988). Five
previously undescribed species of galeom-
matid bivalves were also encountered, and
two, assignable to Divariscintilla, are here
described. The data presented here identify
anatomical characters of value at the generic
level and represent a step toward clarification
of the taxonomic disorder in this super-
family.
'Indian River Coastal Zone Museum, Harbor Branch Océanographie Institution, 5600 Old Dixie Highway, Ft. Pierce, Florida
34946, and Dept. of Biological Sciences, Florida Institute of Technology, Melbourne, Florida 32901 U.S.A.
^Delaware Museum of Natural History, P.O. Box 3937, Wilmington, Delaware 19807 U.S.A.
175
Biology and comparative anatomy of Divariscintilla yoyo and D. troglodytes, two new species of Galeommatidae (Bivalvia) from stomatopod burrows in eastern Florida
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