Zoosyst. Evol. 100 (2) 2024, 543-553 | DOI 10.3897/zse.100.121238

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BERLIN

A new species of Cyrenoida (Bivalvia, Cyrenoididae) from the
Western Atlantic, with remarks on Cyrenoididae anatomy

Barbara L. Valentas-Romera’, Luiz Ricardo L. Simone’, Rodrigo Cesar Marques*

1 Museu de Zoologia da Universidade de Sdo Paulo, Laboratorio de Malacologia, Avenida Nazaré, 481, CEP:04263—000, Sdo Paulo, Brazil
2 Universidade Federal dos Vales do Jequitinhonha e Mucuri - Campus JK, Departamento de Ciéncias Biologicas (DCBio-FCBS), Rodovia MGT,

367, CEP 39100-000, Diamantina, Brazil

https://zoobank. org/552E BECE-2FAB-4C54-8171-047763535D67

Corresponding author: Barbara L. V. Valentas-Romera (barbarella.lou@gmail.com)

Academic editor: Thomas von Rintelen # Received 20 February 2024 Accepted 3 April 2024 Published 14 May 2024

Abstract

Cyrenoida implexa sp. nov. is the first species of Cyrenoididae in the Southern West Atlantic. This new species exhibits external
similarities to C. floridana but is distinguished by distinct right hinge dentition, larger siphons and a more extensive siphonal area at
the mantle border, an incurrent siphon with three rows of papillae, a lack of papillae at the middle mantle fold, and smaller adductor
muscle volume. In the environment, it possesses a higher saline tolerance than C. floridana.

Key Words

Anatomy, Bivalvia, Cyrenoida, Cyrenoididae, estuary, mangrove, taxonomy, Western Atlantic

Introduction

Mangroves and estuaries globally face numerous chal-
lenges (Lugo et al. 2014; Romafiach et al. 2018). These
environments have increasingly garnered attention,
prompting extensive study and protection efforts. Conse-
quently, public and political awareness of their econom-
ic, cultural, and social significance has heightened (Ro-
mafiach et al. 2018; Moore et al. 2022). This increased
attention has facilitated advancements in understanding
the inhabitants of these unique environments.

In Brazil, studies on mangroves and estuaries have
shed light on various topics, including litter (e.g. Duarte
et al. 2023; Cavalcante et al. 2024), carbon storage (e.g.
Mariano Neto et al. 2024), impacts of urbanization (e.g.
Saad et al. 2019), and faunal distribution (e.g. Barroso
and Matthews-Cascon 2009; Rodrigues et al. 2016). As
anticipated, the advancement of these studies has resulted
in the discovery of new species.

Cyrenoida Joannis, 1835, is a poorly known genus
comprising six living species with infaunal filter-feeding
habits that inhabit nutrient-rich sediments in the brackish
waters of estuaries and mangroves across Western Africa,

the Western Atlantic, the Eastern Pacific of North and
Central America, and the Caribbean islands (Coan and
Valentich-Scott 2012; Huber 2015; Valentas-Romera et al.
2019; Wu et al. 2023). Historically, this genus has been
associated with lucinids, but recent phylogenetic studies
have placed it within the Cyrenoididae, primarily consist-
ing of species found in brackish, estuarine, or freshwater
environments (Taylor et al. 2009; Lemer et al. 2019; Wu
et al. 2023). Presently, the bulk of data on this taxon stems
from a single species, Cyrenoida floridana Dall, 1896.
However, C. floridana is restricted in distribution to North
and Central America, the Caribbean, and Suriname, and is
rare in scientific collections (Valentas-Romera et al. 2019).

With the goal of enhancing mollusk records along the
Brazilian coast and advancing the understanding of tax-
onomy, morphology, and anatomy within Cyrenoida, a
new species, Cyrenoida implexa sp. nov., is described
based on shell and soft tissue data. Additionally, a brief
comparison between the new species and C. floridana
is conducted, expanding the morphological, anatomi-
cal, and physiological characterization of the genus and
shedding light on new avenues for future research con-
cerning this genus.

Copyright Valentas-Romera, B.L. et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unre-
stricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

544

Methods

The specimens were initially identified as Cyrenoida sp.
in Barroso and Matthews-Cascon (2009), Rodrigues et al.
(2016), and Saad et al. (2019). Morphology of dry shells
and anatomy of soft parts were studied using standard
techniques (Valentas-Romera et al. 2019). All depictions
of soft parts in this study are based on specimens from
lots MZSP 99988 and MZSP 109105. Scanning electron
microscopy (SEM) was provided by the Laboratorio de
Microscopia Eletr6nica from the Museu de Zoologia of
the Universidade de Sao Paulo.

The following abbreviations are used in the anatomi-
cal descriptions and figures: aa: anterior adductor muscle;
an: anus; ar: anterior pedal retractor muscle; au: auricle;
cc: cerebral connective; cg: cerebral ganglia; eg: cerebral
ganglia; dd: digestive diverticula; dg: digestive gland;
dh: dorsal hood; dm: dorsal siphonal retractor muscles;
eo: excurrent opening; er: esophageal rim; es: esopha-
gus; ex: excurrent siphon; fg: food groove; fo: esophageal
folds; fs: F-shaped tooth ft: foot; gf: gill fusion; gi: gill;
go: gonad; gp: genital pore; gs: gastric shield; id: inner
demibranch; if: mantle border inner fold; in: intestine; io:
incurrent opening; ip: inner palp; ir: inner row of siphonal
papillae; is: incurrent siphon; ki: kidney; le: left caecum;
li: ligament; Ip: left pouch; Iv: inverted-V-shaped tooth;
mf: mantle border middle fold; mo: mouth; mr: middle
row of siphonal papillae; mt: major typhlosole; np: ne-
phropore; nt: minor typhlosole; od: outer demibranch; of:
mantle border outer fold; op: outer palp; or: outer row
of siphonal papillae; pa: posterior adductor muscle; pg:
pedal ganglia; pl: pallial line; pm: pallial muscle; pp:
papillae; pr: posterior pedal retractor muscle; re: right
caecum; sal: sorting area 1; sa2: sorting area 2; sa3: sort-
ing area 3; ss: style sac; st: stomach; t1: large lateral tooth
of right valve; t2: cardinal tooth of right valve; t3: small
lateral tooth of right valve; t4: lateral tooth of left valve;
t5: posterior cardinal tooth of left valve; t6: anterior car-
dinal tooth of left valve; ub: umbones; ve: ventricle; vg:
visceral ganglia; vm: ventral siphonal retractor muscles.

Institutional abbreviations: MZSP: Museu de Zoolo-
gia da Universidade de Sao Paulo.

Results

Superfamily Cyrenoidea J. E. Gray, 1840

Family Cyrenoididae H. Adams & A. Adams, 1857
(1853)

Genus Cyrenoida Joannis, 1835

Cyrenoida implexa sp. nov.
https://zoobank.org/B12440D9-A BCB-4A 6B-8E8A-528C8C697ED3
Figs 1-23

Diplodonta punctata: Barroso and Matthews-Cascon 2009: 82—83 (non
Say, 1822).

Cyrenoida sp.: Rodrigues et al. 2006: 395, 397; Huber 2015: 812; Saad
et al. 2019: 5-6.

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Valentas-Romera, B.L. et al.: A new species of Cyreno/da from Brazil

Types. Holotype: BRAZIL * specimen; MZSP 54637.
Paratypes: 40 specimens; same locality as holotype; Bar-
roso C.X. leg.;17 Oct.2005; MZSP 99988.

Type locality. BRAZIL. Ceara; Fortaleza, Ceara River
estuary, Parque Soledade, 3°42'07.94"S, 38°36'36.22"W,
IX Martins leg., 17.x.2005.

Extra material examined. BRAZIL « 1 specimen;
Maranhao, Sao Luis, Sao Marcos Bay, Carangueljos
Island, Igarapé mangrove; 2011; MZPS 100525. 2 spec-
imens: SAo Paulo, SAo0 Vicente, Branco River mangrove;
23°56'17"S, 46°25'12"W; 2 Jul. 2011; Saad, L.O. leg.;
MZSP 109103. 06 specimens; 08 Feb. 2012; Saad, L.O.
leg; MZSP 109105. 2 specimens: Peruibe, Una River
mangrove, Ecological Station Juréia Itatins; 24°25'33"S,
47°05'05"W; 03 Apr.2012; Saad, L.O. leg; MZSP 109104.

Measurements (length, height, and maximum width
in mm). MZUSP 54637: 7.2 by 7.3 by 4.3; MZSP 99988
#1: 7.1 by 6.9 by 4; #2: 8.2 by 8.3 by 4.5; #3: 6.7 by 6.6
by 3.6; #4: 6.7 by 6.2 by 3.4; #5: 4.9 by 4.6 by 2.9; #6: 5.4
by 5 by 3.1; #7: 6.8 by 6.3 by 3.4; #8: 6.1 by 5.5 by 3.3;
#9: 5.5 by 5.3 by 3.3; MZSP 100525: 7.7 by 7.2 by 4.1.

Diagnosis. Shell rounded to subquadrate, posteriorly
pointed; umbones high, thin; valves fragile; periostracum
thin, light brown. Internal surface opaque; no nacreous
aspect; no distinguishable muscular impression or pal-
lial line. Hinge with laminar cardinal and lateral teeth;
right hinge with inverse V-shaped tooth, formed by fu-
sion between cardinal and lateral tooth; laminar, lateral
tooth; left valve with recumbent F-shaped teeth, formed
by fusion of two cardinal teeth and lateral tooth. Nymph
is long and thin.

Description. Shell (Figs 1—7): Outline rounded to sub-
quadrate, with ventral margin slightly posteriorly point-
ed. Width ~55% of shell length. External surface cov-
ered with well-marked growth lines. Equivalve, almost
equilateral, ~5% longer than high, reaching maximum
length of ~8 mm. Laterally inflated, width ~55% of total
Shell length. Externally white, adorned only by growth
lines. Periostracum thin, light brown; slightly wrinkled at
ventral shell margin (Figs 1, 2). Walls thin, fragile. Um-
bones central, prosogyre, low, ~6% of total shell height
and ~27% of shell length, located almost at midpoint of
shell length (Fig. 5). Internal surface opaque (Figs 3, 4).
Muscle scars and pallial line almost imperceptible. Ante-
rior adductor muscle scar reniform, occupying ~1.32% of
total internal surface; twice higher than wide, located at
mid third of shell height; Posterior adductor muscle scar
oval, occupying ~1.49% of total internal surface; locat-
ed at mid-third of shell height. Pallial line entire, away
from shell margins ~8% of shell height. Hinge hetero-
dont (Figs 6, 7): right valve with inverse V-shaped tooth
(Fig. 7: lv), looking fusion between short cardinal tooth
and long lateral tooth, with ~1% of total shell length and
single laminar lateral tooth (Fig. 7: t3) located under in-
versed V-shaped tooth, ~38% longer than superior later-
al tooth, forming groove between superior and inferior
lateral teeth. Left valve with recumbent F-shaped tooth
(Fig. 6: fs), forming ~90° angle, with bifid appearance,
looking fusion of two cardinal tooth (t5, t6) at one lateral

Zoosyst. Evol. 100 (2) 2024, 543-553

545

Figures 1—7. Holotype of Cyrenoida implexa sp. nov. (MZSP 54637, 7.2 mm, H 7.3 mm, W 4.3 mm). 1. Left valve, outer view;
2. Right valve, outer view; 3. Left valve, inner view; 4. Right valve, inner view; 5. Whole dorsal view; 6. Right hinge under SEM;
7. Left hinge under SEM. Scale bar: 200 um (6, 7).

tooth (t4). Dorsal margin concave. Ligament parvincular,
opisthodetic, length ~40% of total shell length. Nymph
~9 times longer than wide, shape rhomboid. Lunule and
escutcheon absent.

Main muscle system (Figs 8, 9, 13): Anterior adduc-
tor (aa) muscle reniform in transverse section, twice heigh
than wide; ventral portion ~2.5 times wider than dorsal

portion; occupying ~5% of total internal shell volume;
located at median third of valve, clearly divided into
quick and slow components, quick component occupying
~30% of anterior portion of muscle, dark grey in color,
slow component occupying ~70% of posterior portion of
muscle, light cream in color. Posterior adductor muscle
(pa) elliptical in cross section, ~1.5 times wider than tall,

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546

~30% shorter and ~1.3 times wider than anterior adductor
muscle, located at opposite extremity of anterior adduc-
tor muscle, clearly divided into quick and slow compo-
nents, the former occupying ~45% of posterior portion of
muscle, dark gray in color, the latter occupying ~55% of
anterior portion of muscle, light cream in color. Pair of
foot anterior retractor muscles (ar) oval in section, thin,
elongated; originated dorsally at anterior adductor mus-
cle; running posteriorly and ventrally at ~20% of total
shell length; both branches fusing at anterior edge of foot
base. Pair of foot posterior retractor muscled (pr) oval
in section, thin; originated dorsally at posterior adductor
muscle; ~50% longer than pair of anterior retractors; both
fusing posterior edge of foot base (Fig. 11). Two pairs of
siphonal retractor muscles; dorsal siphonal retractors (dm)
~6 times longer than wide; insertion almost at central por-
tion of mantle lobe, 2 times as long as excurrent open-
ing, originating laterally at half of stphonal base height;
ventral siphonal retractors (vm) thin, ~5 times longer than
wide, length ~65% of total length of dorsal siphonal mus-
cle, originating at ventral end of inhalant opening.

Foot and byssus (Figs 8, 11): Foot (ft) short; relaxed
length ~50% of total shell height. Laterally flattened; end
blunt, swollen. Foot base at median portion visceral sac.
Byssus or byssal groove.

Mantle (Figs 8, 9, 11): Mantle lobes symmetrical,
thin, translucent, colorless. Pallial muscles (pm) reunited
in long muscles, distributed sparsely along ventral side
of mantle lobe; height ~12% of total shell length, sepa-
rated from each other by ~15 times pallial muscle basal
width. Mantle edge trifolded (Fig. 9), unpigmented; outer
fold (of) thick, ~7 times taller than wide; middle fold (mf)
short, half of total outer fold height, same width; inner
fold (if) short, length ~20% of outer fold height, ~30% of
its width. Periostracum produced between external and
middle fold. Mantle lobes totally free except for siphonal
area. Anterior mantle fusion occurring at ~45% of ante-
rior adductor muscle height; posterior mantle fusion oc-
curring at ~68% of posterior adductor muscle height (Fig.
11). Siphonal area corresponding to ~42% of total mantle
lobe length. Mantle lobes mostly free from each other,
except for siphonal area, relative to 42% of mantle lobe
total length (more details below).

Pallial cavity (Figs 8, 10-14, 16): Occupying about
half of inner shell volume. Palps small, occupying ~30%
of total shell volume. Pair of hemipalps triangular (Figs
11, 16), ~20% shorter but same width of insertion area
of anterior adductor muscle; pair of external hemipalps
(op) connected at mantle lobe by hemipalp dorsal bor-
der, in half of hemipalp length; pair of internal hemipalps
(ip) connected at visceral mass by dorsal border, in ~30%
of total hemipalp length. Internal surface of both palps
covered by ~24 transverse folds; internal hemipalp folds
high and rounded, covering ~90% of hemipalp internal
surface, forming thin smooth area at hemipalp borders
corresponding ~1% of total hemipalp internal area, folds
decreasing towards mouth, forming shallow channels to-
wards mouth (mo). Gills area ~30% of total valve area;

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Valentas-Romera, B.L. et al.: A new species of Cyreno/da from Brazil

outer demibranch (od) fusiform, twice longer than wide,
folded on ~30% of total demibranch extension, covering
pericardium and kidney areas, connected to mantle lobe
by ~15% of total length of dorso posterior border of de-
mibranch. Inner demibranch (id) triangular, ~twice longer
than wide, folded on half of demibranch total extension,
~40% of internal demibranch area covered by external
demibranch (Fig. 8); presenting food groove (fg); demi-
branchs connected to each other by tissue at posterior
end, in ~20% of total gill length (Fig. 12). Suprabran-
chial chamber volume ~60% of infrabranchial chamber
volume. Incurrent (is) and excurrent (ex) siphons orig-
inated by inner mantle fold; length ~30% of total shell
length; each one ~3 times longer than wide in retracted
condition; externally fused with each other; internally
separated by thick, smooth muscular wall. Inner siphonal
openings directly to pallial cavity (Figs 11, 14). Incurrent
siphon length ~20% of total shell length, height ~1% of
total shell height. Excurrent siphon length ~80% of inhal-
ant siphon length; same width. Distal opening of incur-
rent siphon flanked by three rows of papillae (Fig. 14: ir,
mr, or); papillae length equivalent ~5% of total inhalant
siphon length. Distal opening of excurrent siphon with
single row of flattened papillae (Fig. 14: 9p). Siphon at-
tached to mantle by 2 pairs of muscle described above.

Visceral mass (Fig. 11): Visceral sac occupying half
of inner shell volume; shape triangular. Slightly flattened;
twice wider than muscular base; located dorsally at foot
retractor muscles; ~20% of anterior portion filled with di-
gestive diverticula of brown color; remaining areas with
gonad of cream color. Stomach and style sac located ver-
tically at central region.

Circulatory and excretory systems (Figs 11, 15, 23):
Pericardium located dorsally in posterior half of visceral
sac, between posterior portion of umbonal cavity and dor-
sal surface of kidney; twice longer than wide; occupying
~25% of total visceral sac volume. Pair of auricles (au)
antero posteriorly long; connected to central axis of gill in
~30% of total auricle length; walls thin, translucent walls
thin; located at central portion of pericardium; surround-
ing ~50% of intestinal portion crossing pericardium; con-
nected to auricles in median portion of lateral walls. Kid-
ney (ki) located postero ventrally at visceral mass (Figs
11, 15), below posterior end of pericardium and dorsal sur-
face of posterior foot retractor muscles, color light brown;
shape triangular, occupying ~25% of visceral mass vol-
ume. Gonopore (gp) rounded, located at posterior portion
of visceral mass, at ~25% of visceral mass height, opening
in suprabranchial chamber, next to nephropore (np).

Digestive system (Figs 16, 20-22): Palps and diges-
tive diverticula described above. Mouth small, located
in central portion at intersection of palps (Fig. 16), lips
small. Esophagus (es) elongate, narrow, cylindric; length
and height respectively ~16% and 1% of total visceral sac;
no contact with anterior adductor muscle; passing through
anterior portion of foot anterior retractors; internal surface
with low longitudinal folds (fo); low esophageal rim (er)
at stomach entrance; stomach (Figs 20-21: st) occupying

Zoosyst. Evol. 100 (2) 2024, 543-553 547

Paired apertures to digestive caeca located ventro-laterally
of gastric anterior portion, in transition with esophagus;
turned to ventral side of visceral sac. Dorsal hood (dh)
narrow, thin, length ~25% of total stomach length, distally

~25% of total visceral sac volume; shape elliptical, fun-
nel-like; located slightly posteriorly to umbones; length
~80% of total visceral sac length, ~30% of visceral sac
heigh; posterior portion ~60% wider than anterior portion.

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Figures 8-12. Cyrenoida implexa, anatomical drawings. 8. Right view, valve removed, structures seen by transparency of mantle
lobe; 9. Mantle border, transverse section in its ventromedial portion; 10. Gill, transverse section in its central portion; 11. Right
view, right mantle, and gill removed; 12. Postero-ventral visceral region, ventral view, showing fusion of inner demibranchs in

siphonal base and mantle fusion at siphonal area. Scale bars: 2 mm.

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548

pointed. Left pouch (Ip) located below anterior portion
of dorsal hood, anteriorly to connection of digestive di-
verticula; shallow and wide; occupying ~20% of total
area of left external wall of stomach. Internal surface of
stomach (Fig. 22) mostly smooth, covered by three sort-
ing areas well defined. First sorting area starting at left
side of esophageal rim, running along dorsal wall of an-
terior stomach chamber, penetrating dorsal hood, narrow,
comprised of small transverse folds (sal). Second sorting
area originating ventral to first sorting area, at left side of
esophageal rim, running along left wall of anterior stom-
ach chamber, entering left pouch and dorsal hood, both
on their ventral surfaces, broad, formed by thickening
of stomach wall (sa2). Third sorting area starting inside

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Valentas-Romera, B.L. et al.: A new species of Cyreno/da from Brazil

dorsal wall of dorsal hood, running along dorsal and right
walls of posterior stomach chamber, until diffusing on
ventral portion of right wall (sa3). Gastric shield (gs) lo-
cated at central dorsal wall, occupying ~30% of total gas-
tric area, with two anterior projections, one dorsal at left
border, penetrating dorsal hood, and one left ventral, pen-
etrating left pouch. Two narrow, tall gastric ridges running
along ventral stomach chamber, forming major and minor
typhlosoles at style sac opening. Longer ridge originating
at ventral surface of stomach, surrounding left digestive
diverticula, penetrating style sac at its right side, forming
major typhlosole (mt). Shorter fold originating at style sac
entrance, at region of major typhlosole penetration into
style sac, forming rim bordering style sac entrance and

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Figures 13—16. Cyrenoida implexa anatomical drawings. 13. Incurrent and excurrent siphons, anterolateral view, right mantle lobe
partially removed, some adjacent structures shown; 14. Siphon tips; right view, both partially sectioned longitudinally; 15. Pericar-
dial region and kidney, right view, right mantle wall partially removed; 16. Labial palps, ventral view, outer hemipalps deflected

dorsally. Scale bars: 2 mm.

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Zoosyst. Evol. 100 (2) 2024, 543-553

ultimately minor typhlosole (nt). Style sac (ss) connecting
ventrally to dorsal portion of stomach; conical; tapering
in ventral surface of visceral sac; ~3.5 times longer than
wide; occupying ~16% of total visceral sac volume; height
equivalent to half of visceral sac total length, length ~1%
of visceral sac length. Intestine (in) narrow, long; starting
in style sac; performing an inverted U-shaped loop under
the anterior portion of the stomach, reaching the style sac
high (Fig. 20), running towards dorso-posterior region of
visceral sac parallel to style sac; leaving posterior portion
of visceral sac, crossing pericardium and kidney; passing
between posterior ends of foot posterior retractor muscles.
Flanking entire posterior surface of posterior adductor
muscle. Anus (an) on ventral surface of posterior adductor

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muscle; intestine total length ~9 times longer than style
sac. Anus simple, sessile.

Genital system (Figs 11, 15): Gonads described above.
Pair of gonoducts receiving sort of gonad acini along
length along anterior portion of visceral sac. Genital pore
simple, located at posterior region of visceral sac (Fig. 11:
gp), opening next to nephropore (Figs 11, 15: np).

Central nervous system (Figs 17—19): Pair of cerebral
ganglia (Fig. 17: cg) surrounding anterior dorsal half of
esophagus, dorsally to labial palps; shape slightly trian-
gular; longer than wide; size ~50% of esophagus width;
cerebral commissure (cc) length ~60% of each ganglion
length; from anterior portion connecting anterior adductor
muscle nerve, bifurcating in two branches, internal branch

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Figures 17-23. Cyrenoida implexa anatomical drawings. 17. Cerebral ganglia, ventral view; 18. Pedal ganglia, right view;
19. Visceral ganglia, ventral view; 20. digestive tubes and main musculature as in situ, right lateral view; 21. stomach, left lateral
view; 22. Pericardial region, posterodorsal view, dorsal mantle wall partially removed; 23. stomach, right lateral view, right wall
opened and deflected to show inner gastric surface. Scale bars: 2 mm.

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550

penetrating dorso posterior third of muscle and leaving at
ventral surface of muscle; other branch bordering posteri-
or surface of anterior muscle, both branches fusing at ven-
tral region of anterior muscle; two connectives originating
dorsally in ganglia, anteriorly to cerebro-visceral connec-
tive crossing visceral mass, touching gonopore dorsal-
ly, bordering anterior portion of kidney and connecting
dorsally at visceral ganglia, connecting posteriorly cere-
bro-pedal connective running immersed at pedal muscles,
connecting to anterior region of pedal ganglia. Pair of vis-
ceral ganglia (Fig. 19: vg) fusiform; each ganglion slightly
longer than wide; ~80% of cerebral ganglia size; partially
fused at median portion, with presence of shallow central
groove; located ventrally at kidney, parallel to posterior
adductor muscle; in dorsal tip connecting cerebra-visceral
connective and renal nerve, penetrating into kidney area;
laterally originating ctenidial nerves running thought cen-
tral axis of posterior portion of gills; dorsally originating
posterior adductor muscle nerve, penetrating median re-
gion of anterior surface of posterior muscle; at ventral

Valentas-Romera, B.L. et al.: A new species of Cyrenoida from Brazil

tip originating pallial nerve, touching anterior surface of
ventral portion of posterior adductor muscle, running par-
allel to inhalant and exhalant apertures and mantle border,
diffusing at mantle lobe board. Pair of pedal ganglia (Fig.
18: pg) 40% larger than pair of cerebral ganglia; shape
elliptic; longer than wide; totally fused with each other,
without vestigial commissure; located immerse on foot
retractor muscles, above foot insertion; in anterior tip con-
nects cerebro-pedal connectives from cerebral ganglia; in
posterior tip connecting two pairs of nerves, dorsal pair
running towards posterior region inside posterior foot re-
tractor muscles; postero-ventral nerves curved to ventral
region, running internally.

Etymology. The specific epithet implexa is a Latin
word for “tangled,” referring to species commonly found
between the roots of estuarine and mangrove plants.

Distribution. Brazil, Maranhao to Sao Vicente, Sao
Paulo (Fig. 24).

Habitat. Mangroves in brackish water, buried until
15 cm in muddy sand.

Atlantic Ocean

Caranguejos Island 7

Tropic of Capricorn

30°

Branco river
mangroove

Atlantic Ocean }

§ 3°38" |
Atlantic Ocean

Ceara river estuary

Atlantic Ocean

Figure 24. Cyrenoida implexa distribution along the Brazilian coast.

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Zoosyst. Evol. 100 (2) 2024, 543-553

Discussion

At first glance, the external shell features of C. im-
plexa closely resemble those of Diplodonta punctata
(Say, 1822), which may strongly indicate misidentifica-
tions along the Brazilian coast (e.g., Barroso and Mat-
thews-Cascon 2009). Both species exhibit rounded shells
covered by a thin periostracum, displaying a light color,
a posteriorly pointed shape, and living infaunally. De-
spite these initial similarities, differentiation differences
between the two species are evident. C. implexa is found
in estuaries and mangroves, featuring a slightly wrinkled
and light brown periostracum (noticeable on dried speci-
mens that retain it) and a fragile shell, while D. punctata
inhabits a predominantly marine environment, burrowing
into muddy or sandy bottoms, and possesses a hinge den-
tition composed exclusively of cardinal teeth (Mikkelsen
and Bieler 2007; Rios 2009).

The classification of C. implexa within the genus
Cyrenoida is primarily based on limited studies com-
paring it to C. dupontia, the type species of Cyrenoida
(Joannis 1835; Deshayes 1836), as well as comments
made on C. d’ Ailly, 1869 (Taylor et al. 2009). These three
species share several distinguishing features, including a
hinge dentition characterized by fused laminar and car-
dinal teeth, the absence or faint presence of muscle scar
impressions on the internal shell surface, valves covered
with a brownish periostracum, a larger inner demibranch
in the gills, paired triangular labial palps located at the
anterior part of the ctenidia, and a pair of incurrent and
excurrent siphons (Joannis 1835; Deshayes 1836; Taylor
et al. 2009; Valentas-Romera et al. 2019). Furthermore,
it is important to note the habitat of C. implexa, as these
organisms are typically found thriving in freshwater to
brackish environments, often intertwined among plant
roots. Similar cyrenoidids with these characteristics are
prevalent in both African and American ecosystems.

Most of the knowledge about the six Cyrenoida spe-
cies stems from studies focusing on C. floridana in the
Western Atlantic. Taylor et al. (2009), through molecu-
lar analysis of C. floridana, identified similarities among
the families Cyrenoididae, Corbiculidae, and Glauco-
nomidae. This finding led to the proposal of removing
Cyrenoidindae from the superfamily Lucinoidea and as-
signing it to the superfamily Cyrenoidoidea, now known
as Cyrenoidea. Subsequently, Wu et al. (2023) conducted
another molecular analysis involving various Cyrenoida
species, including C. floridana, and concluded that the
family Cyrenoididae also encompasses Geloina J. E.
Gray, 1842, Cyanocyclas Blainville, 1818, and Polyme-
soda Rafinesque, 1820.

Regarding C. floridana specifically, Valentas-Romera
et al. (2019) undertook an extensive anatomical study
comparing this species with others within Cyrenoidea,
unveiling new morphological and anatomical insights,
such as microtubules within shell walls, pairs of stpho-
nal retractor muscles, the first description of the species’
stomach, and evidence of shell parasitism in this species.

551

Given that additional studies involving the sequencing
of C. implexa material are planned, the species is cur-
rently described based on its shell morphology and soft
parts anatomy. These features are deemed comparable to
those of C. floridana, as the available data is sufficient-
ly convincing. Regarding the shell characters, both spe-
cies are similar in outline and the characteristics of the
left hinge teeth, especially the shape of the lateral tooth
complex (t4) and cardinal teeth (t4 and t5). The studied
specimens of C. implexa are also similar to C. floridana
in size, as they fall within the species size range. The larg-
est specimen documented in this study measures 8 mm,
while C. floridana exhibits a length range of 10 to 14 mm
(Valentas-Romera et al. 2019). Notably, reproductive
populations of C. floridana described by Leathem et al.
(1976), Kat (1982), and Wingard et al. (2022) include
smaller individuals with average shell sizes of 9 mm, 3.5
to 4.5 mm, and less than 5 mm, respectively.

However, C. implexa and C. floridana can be differen-
tiated by two sets of characteristics: a) right hinge teeth;
b) internal anatomy; and c) ecological requirements.

a) The hinge in C. implexa is composed of three
teeth: two lateral teeth, forming a single inverted
V-shaped tooth, along with a solitary cardinal tooth
(Fig. IF, H). In contrast, C. floridana displays a
different pattern with four teeth: two cardinal and
two lateral teeth, creating two inverted V-shaped
structures, where the smaller one is positioned be-
neath the larger one (Valentas-Romera et al. 2019).
Notably, in C. implexa, only the larger or superior
inverted V-shaped tooth (sv) is present, while the
smaller one consists solely of the lateral tooth (t3)
(Valentas-Romera et al. 2019).

b) Anatomically, C. implexa differs from C. floridana in
the following features: the anterior and posterior ad-
ductor muscles in C. implexa are respectively ~12%
and ~7% smaller than those in C. floridana (Valen-
tas-Romera et al. 2019). However, this discrepancy
in adductor muscle size could represent a specific
trait or may be influenced by ontogenetic stages. C.
implexa is also characterized by a sizable pair of si-
phons and a well-defined siphonal area at the mantle
border. It also possesses a single pair of dorsal siph-
onal retractors muscles, whereas C. floridana has a
smaller pair of dorsal siphonal retractors muscles,
separated into two bundles (Valentas-Romera et al.
2019). Notably, C. implexa is further differentiated
by the presence of three rows of papillae at the tip of
the incurrent siphon and one row of papillae at the
tip of the excurrent siphon. Additionally, the mantle
borders of C. implexa lack papillae.

c) The salinity range of C. floridana varies from 0.25 to
20.7 practical salinity units (psu), while C. implexa
tolerates salinities between 20.3 and 30 psu (Brew-
ster-Wingard and Ishman 1999; Gaiser et al. 2006;
Barroso and Matthews-Cascon 2009; Rodrigues et
al. 2016; Saad et al. 2019; Wingard et al. 2022).

zse.pensoft.net

552

According to Wingard et al. (2022), C. floridana is
a stenohaline species that inhabits oligohaline zones
and can be used as an indicator of low-salinity en-
vironments. However, this feature apparently is
not found in C. implexa, as samples were absent in
Ceara’s river estuary, where the salinity was below
5 psu. This might indicate that C. implexa tolerates
higher salinities than C. floridana.

The differentiation between both species is further
substantiated by the consistent presence of these traits
in all samples of C. implexa collected from the Brazil-
ian coast, whereas the attributes of C. floridana remain
uniform across Caribbean and North American samples.
Given that the southernmost occurrence of C. floridana
is observed on the coast of Guyanas (Valentas-Romera et
al. 2019), it is plausible to suppose that the Amazon River
Plume may have functioned as a reproductive barrier, as
seen in mollusk groups (Giachini-Tosseto et al. 2022).

Conclusions

Based on the present findings, it is evident that the newly
identified species, Cyrenoida implexa sp. n., 1s a member
of the Cyrenoididae family. This species exhibits distinct
morphological and anatomical characteristics in both
shell morphology and soft parts anatomy, setting it apart
from C. floridana. Furthermore, Cyrenoida implexa sp.
n. represents the first documented record of the genus in
the South region of the Western Atlantic, specifically in
Brazilian mangroves and estuaries.

Acknowledgements

We thank Lara Guimaraes (MZSP) for assistance with
scanning electron microscopy; Luiza Saad (Instituto de
Biociéncias da USP); Inés Xavier Martins (Universidade
Federal Rural do Semi Arido); and Cristiane Xerez Barro-
so (Universidade Federal do Ceara) for granting material.
This project was partly supported by Fapesp (Fundacao
de Amparo a Pesquisa) proc. #2010/11401—8 and CNPq
(Conselho Nacional de Desenvolvimento Cientifico e
Tecnologico) proc. #134425/2010-3, #159490/2012-0,
and #203533/2014-3.

References

Adams H, Adams A (1853-1858) The Genera of Recent Mollusca: Ar-
ranged According to their Organization (Vol. 2). John van Voorst,
London, 661 pp. https://doi.org/10.5962/bh1.title.4772

Barroso CX, Matthews-Cascon H (2009) Distribuigao espacial e
temporal da malacofauna no estuario do rio Ceara, Ceara, Brasil.
Pan-American Journal of Aquatic Sciences 4: 79-86. https://panam-
jas.org/pdf_artigos/PANAMJAS 4(1) 79-86.pdf

zse.pensoft.net

Valentas-Romera, B.L. et al.: A new species of Cyrenojda from Brazil

Brewster-Wingard GL, Ishman SE (1999) Historical trends in salinity
and substrate in central Florida Bay: A paleoecological reconstruc-
tion using modern analogue data. Estuaries 22(2): 369-383. https://
doi.org/10.2307/1353205

Cavalcante ER, Ribeiro VV, Taddei RR, Castro IB, Alves MJ (2024) High
levels of anthropogenic litter trapped in a mangrove area under the
influence of different uses. Marine Pollution Bulletin 200: 116045.
[ISSN 0025—326X] https://doi.org/10.1016/j.marpolbul.2024.116045

Coan EV, Valentich-Scott P (2012) Bivalve Seashells of Tropical West
America — Marine Bivalve Mollusks from Baja California to North-
ern Peru (2 vols). Santa Barbara Museum of Natural History, Santa
Barbara, 1258 pp.

Deshayes M (1836) Sur la cyrénoide de M. de Joannis. Suivie d’une
lettre de M. Joannis. (Cl. V, n°64). Magasin de Zoologie 6, Classe V:
1-3. https://biodiversitylibrary.org/page/2633064

Duarte LFA, Ribeiro RB, Medeiros TV, Scheppis WR, Gimiliani GT
(2023) Are mangroves hotspots of marine litter for surrounding
beaches? Hydrodynamic modeling and quali-quantitative anal-
yses of waste in southeastern Brazil. Regional Studies in Marine
Science 67: 103177. [ISSN 2352-4855] https://doi.org/10.1016/j.
rsma.2023.103177

Gaiser EE, Zafiris A, Ruiz PL, Tobias FAC, Ross MS (2006) Track-
ing rates of ecotone migration due to salt-water encroachment us-
ing fossil mollusks in coastal south Florida. Hydrobiologia 569(1):
237-257. https://doi.org/10.1007/s10750-006-0135-y

Giachini-Tosseto E, Bertrand A, Neumann-Leitéo S, Nogueira-Junior
M (2022) The Amazon River plume, a barrier to animal dispersal in
the Western Tropical Atlantic. Scientific Reports 12(1): 537. https://
doi.org/10.1038/s41598-021-04165-z

Gray JE (1840) Shells of molluscous animals. In: British Museum
(Ed.) Synopsis of the contents of the British Museum. ed 42. G
Woodfall, London, 105-152. https://www.biodiversitylibrary.org/
page/55287672

Huber M (2015) Compendium of Bivalves 2. A Full-Color Guide to the
Remaining Seven Families. A Systematic Listing of 8’500 Bivalve
Species and 10’500 Synonyms. ConchBooks, 907 pp.

Joannis [L.] De (1835) Cyrénoide. Cyrenoida. Joannis. Magasin de Zo-
ologie 5. Classe V, 2 pp. [pl. 64] https://www. biodiversitylibrary.org/
page/37121825

Kat PW (1982) Reproduction in a peripheral population of Cyrenoi-
da floridana (Bivalvia, Cyrenoididae). Malacologia 23(1): 47-54.
https://biodiversitylibrary.org/page/13112410

Leathem W, Kinner P, Mauer D (1976) Northern range extension of
the Florida marsh clam Cyrenoida floridana (superfamily Cyrenoi-
dacea). The Nautilus 90(3): 93-94. https://biodiversitylibrary.org/
page/8276463

Lemer S, Bieler R, Giribet G (2019) Resolving the relationships of clams
and cockles: dense transcriptome sampling drastically improves the
bivalve tree of life. Proceedings of the Royal Society B: Biological
Sciences 286(1896): 1-9. https://doi.org/10.1098/rspb.2018.2684

Lugo AE, Medina E, McGinley K (2014) Issues and challenges of man-
groves conservation in the Anthropocene. Madera y Bosques 20:
11-38. https://doi.org/10.21829/myb.2014.200146

Mariano Neto M, da Silva JB, de Brito HC (2024) Carbon stock es-
timation in a Brazilian mangrove using optical satellite data. En-
vironmental Monitoring and Assessment 196(9): 9. https://doi.
org/10.1007/s10661-023-12151-3

Zoosyst. Evol. 100 (2) 2024, 543-553

Mikkelsen PM, Bieler R (2007) Seashells of Southern Florida: Liv-
ing Marine Mollusks of the Florida Keys and Adjacent Regions.
Bivalves. Princetion University Press, Princeton, New Jersey, 503
pp. https://doi.org/10.1515/9780691239453

Moore AC, Hierro L, Mir N, Stewart T (2022) Mangrove cultural ser-
vices and values: Current status and knowledge gaps. People and
culture 4: 1083-1097. https://doi.org/10.1002/pan3. 10375

Rios EC (2009) Compendium of Brazilian Sea Shells. Rio Grande,
RS,668 pp.

Rodrigues CA, Ribeiro RP, Santos NB, Almeida ZS (2016) Patterns of
mollusc distribution in mangroves from the SAo Marcos Bay, coast
of Maranhao State, Brazil. Acta Amazonica 46(4): 391—400. https://
doi.org/10.1590/1809-439220 1600493

Romafiach SS, DeAngelis DL, Koh HL, Li Y, Teh SY, Raja Barizan
RS, Zhai L (2018) Conservation and restoration of mangroves:
Global status, perspectives, and prognosis. Ocean and Coast-
al Management 154(15): 72-82. https://doi.org/10.1016/j.oce-
coaman.2018.01.009

Saad LO, Cunha CM, Colpo KD (2019) How mollusk assemblages re-
spond to different urbanization levels: Characterization of the mal-
acofauna in subtropical Brazilian mangroves. Marine Biodiversity
49(2): 989-999. https://doi.org/10.1007/s12526-018-0883-8

553

Say T (1822) An account of some of the marine shells of the United
States. Journal of the Academy of Natural Sciences of Philadelphia 2:
302-325. https://www. biodiversitylibrary.org/item/113421#page/318/
mode/1lup

Taylor JD, Glover EA, Williams ST (2009) Phylogenetic position of the
bivalve family Cyrenoididae — removal from (and further disman-
tling of) the superfamily Lucinoidea. The Nautilus 123(1): 9-13.
https://biodiversitylibrary.org/page/50438173

Valentas-Romera BL, Simone LRL, Mikkelsen PM, Bieler R (2019)
Anatomical redescription of Cyrenoida floridana (Bivalvia,
Cyrenoididae) from the Western Atlantic and its position in the
Cyrenoidea. Zoosystematics and Evolution 95(2): 517-534. https://
doi.org/10.3897/zse.95.38456

Wingard GL, Stackhouse BL, Daniels AM (2022) Using mollusks as
indicators of restoration in nearshore zones of south Florida’s es-
tuaries. Bulletin of Marine Science 98(3): 351-380. https://doi.
org/10.5343/bms.2022.0004

Wu R, Liu L, Liu X, Ye Y, Wu X, Xie Z, Liu Z, Li Z (2023) Towards
a systematic revision of the superfamily Cyrenoidea (Bivalvia, Im-
paridentia): Species delimitation, multi-locus phylogeny and mito-
chondrial phylogenomics. Invertebrate Systematics 37(9): 607-622.
https://doi.org/10.1071/1S23015

zse.pensoft.net