Foregut and reproductive tract anatomy of three species of the Strombina-group (Buccinoidea: Columbellidae)

14 Pages·2003·6.4 MB·English

by  Helena Fortunato

© SociedadEspañola deMalacología ~— Iberus,l\ i¿): 109-122,2003
Foregut and reproductive tract anatomy of three species of
the Strombina-group (Buccinoidea: Columbellidae)
Anatomía del tubo digestivo y del tracto reproductor en tres especies
del grupo Strombina (Buccinoidea: Columbellidae)
Helena FORTUNATO*
Recibidoel13-IX-2002.Aceptadoel16-VI-2003
ABSTRACT
This paper reports for the first time anatomical data for three species of the Strombina-
group sensu Jung, 1989: Bifurcium bicanaliferurrij^ Sincola (Dorsina) gibberula and Clav-
istrombino clavulus. Anatomical data for the foregut and reproductive tracts were deter-
mined from gross dissections mainly of living specimens. Both the anterior digestive tract
and the reproductive systems of the three species are similar in their general plan and con-
form with v/hat is known for columbellids and neogastropods ¡n general.
Differences among the three species are mostly within accessory structures. Nona of them
presentseithera bursa copulatrixora prostate gland. The ingestivegland is also absent. C.
clavulus males present an open reproductive system v/ith a diverticulum communicating the
vas deferens with the body cavity. This species also presents a separated albumen gland,
whereas in both S. gibberula and 6. bicanaliferum only an internal septum separates this
gland from the capsule gland. Bifurcium and Sincola both appearduring theearlyMiocene
ofDominican Republic,whichcould bearontheiranatomicalsimilitude,whereasClavistrombina
is a Recent genus of the eastern Pacific. More studies of other species of these genera are
needed in orderto better understand possible evolutionaryconnections ofthese body plans.
RESUMEN
Se describe por vez primera datos anatómicos de tres especies del grupo Strombina sensu
Jung, 1989: Bifurcium bicanaliferum^Sincola {Dorsina)gibberulay Clavistrombinaclavulus. Los
datos anatómicos se determinaron a partir de disección de especimenes vivos. Los tractos
digestivoy reproductorde lastresespeciesestudiadas son similaresen su estructura general y
se corresponden con los conocidos para columbellidosy neogasterópodosen general.
Lasdiferencias seconcentran en lasestructurasaccesorias. Ninguna especie presenta bolsa
copulatriz, próstata oglándula ingestiva. Los machosde C. clavulustienen un sistema repro-
ductorabiertocon un divertículoquecomunica elvasodeferentecon la cavidad del cuerpo.
Esta especie tiene una glándula del albumen separada, mientras que en S. gibberula y en
6. bicanaliferum sólo un septo la separa de la de la cápsula. Tanto Bifurcium como Sincola
aparecieron durante el Mioceno temprano en la República Dominicana, lo cual puede
explicarsusimilitudanatómica, mientrasque Clavistrombinaesunaespecierecientedel Pací-
fico este. Se precisan más estudios sobre otras especies de estos géneros para una mejor
comprensión de las posibles conexiones evolutivas entre estas características anatómicas.
KEYWORDS: Gastropods,Strombina-group,anatomy,foregut, reptoductivetract
PALABRAS CLAVE: Gasterópodos,grupoStrombina,anatomía, tractodigestivo, tracto reproductor.
*CenterforTropicalAnthropologyandPaleoecology,SmithsonianTropicalResearchInstitute,P.O.Box 169,
Balboa, PanamáRP,e-mail: [email protected]
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Iberus, 21 (2), 2003
INTRODUCTION
Neogastropods are generally consid- columbellid species. Later, Houston
ered the most highly evolved proso- (1976) and Houston and Hatfield
branch gastropods. This large order, (1981) described a couple more species.
with more than 1000 recent and fossil Several other species were studied inre-
genera and subgenera (Taylor and lation to evolution of herbivory in gas-
SOHL, 1962), is characterized by a shell tropods (Hatfield,1979; Harasewych,
with an elongate siphonal canal and 1990; Kantor and Medinskaya, 1991;
rachiglossate or toxoglossate radula. Medinskaya, 1992; Medisnkaya, 1993;
Theclassificationandbiologyofneogas- GuRALNiCK AND De Maintenon, 1997;
tropods has been the focus of many DeMaintenon, 1999).
authors as it contains several extremely The Panamic province has a rich
important groups, both economically assemblage of columbellids many of
and biologically (Adams and Adams, whichhavea veryinterestingevolution-
1858; Thiele, 1929; Risbec, 1954; ary history related to the rise of the
Fretter and Graham, 1962; Ponder, Central American Isthmus . This is the
1973; Harasewych, 1984; Bright and case with the Sírombnjfl-group sensu
Ellis, 1990;KooL, 1993). Jung, 1989. The group consists of five
Neogastropods have a rather similar genera and includes most taxa classified
anatomical organization. This was as Strombina by earlier workers. Jung
shown to be true for the reproductive (1989) splits this genus and proposes
Systems of the Muricidae, Buccinidae, several new genera. Despite the split-
and Nassaridae (Fretter, 1941; Fretter ting, the group is still known in the
and Graham, 1962). Families such as malacological jargon as the Strombina-
Olividae, Columbellidae, Fasciolaridae group, following Jung's (1989) designa-
and Turridae are less studied (Marcus tion. The group needs extensive system-
AND Marcus, 1959, 1960, 1962; Smith, atic revisión (De Maintenon, 1994) and
1967; HousTON, 1976; Kantor, 1991; the relations of these genera to other
Sysoev, 1991). The foregut of some of tropical American columbellids and to
these groups shows signs of simplifica- each other is still poorly unknown
tion, as in the Muricidae (Graham, (Radwin, 1977a, 1977b; Jung, 1989).
1949), whereas others have features of Nevertheless, preliminary cladistic
the Archaeogastropoda (Brown, 1969; analyses based on shell morphology
Ponder, 1972), or have become secon- and anatomy strongly support the
darilycomplex (Ponder, 1970). hypothesis of a sepárate columbellid
The family Columbellidae, one of clade composed by these five genera, as
the groups traditionally included in the well as the validity of Jung's (1989)
buccinoid neogastropods, appears dur- major genera and subgenera (Fortu-
ing the Eocene (Radwin, 1977a). Al- natoANDJung, 1995).
though relatively younger than most The Strombina-group is amongst the
other neogastropod taxa, which appear most abundant and diverse Neogene
in the Cretaceous, is one of the most di- gastropods, and is represented by more
verse and abundant, with almost four than 30 living species in the eastern
hundred recentspecies (Taylor,Morris Pacific but only four in the Caribbean,
AND Taylor, 1980). Contrasting with where they suffered a inassive extinc-
this, there aren't that many works deal- tion at the end of the Pliocene (Jung,
ing with the anatomy of this group, as 1989; Jackson, Jung, Coates and
stated above. Thiele (1929) and Radwin CoLLiNS, 1993;Jackson,Jung and For-
(1977a, 1977b) use radular features to tunato, 1996;Fortunato, 1999).
.subdivide the family into two subfami- The Strombiiia-group has been used
lies. RiSBEC (1954) and especially Mar- as a model taxon to study changing
cus AND Marcus (1962, 1964) give the species morphology and diversity dur-
first anatomical descriptions of several ing the gradual emergence of the Isth-
Fortunato: Foregut and reproductive tract anatomyofthree Strombina-^roup species
Figure 1.Portraitsofthespeciesstudied.A:Bifiírciumbicanaliferum(B.G.SowerbyI, 1832);B:Sincola
{Dorsina)gibberula(B. G. SowerbyI, 1832); C: Clavistrombinaclaviúus(B. G. SowerbyI, 1834).
Figura 1. Especies estudiadas. A: Bifurcium bicanaliferum (B. G. Sowerby I, 1832); B: Sincola
(Dorsina) gibberula (B. G. SowerbyI, 1832); C:Clavistrombinaclávalas (B. G. SowerbyI, 1834).
mus of Panamá (Jackson, Jung and 1832) and Clavistrombina clavulus (G. B.
Fortunato, 1996; Fortunato, 1998, Sowerby I, 1834). B. bicanaliferum is the
1999). In spite of this, very little is only living species of this genus other-
known of the biology of these gas- wise known from Miocene deposits of
tropods (CiPRiANí AND Penchaszadeh, the Caribbean. S. gibberula is one of the
1993; CiPRiANí, Fortunato and Ro- three extant species of this genus, also
dríguez, 1996; Fortunato, Pen- known from Miocene deposits of the
chaszadeh AND MlLOSLAVICH, 1998; Caribbean. C. clavulus is theonlyspecies
Fortunato,2002). Therearenoanatom- of this monotypic genus and has no
ical studies of any of its species, except known fossil record (JUNG, 1989). All
for some referentes to the type of radu- three species inhábil the shallow water
m
lae (Radwin, 1978; Houbrick, 1983; (up to 40 deep) coasts of the eastern
Emerson, 1993). The objective of this Pacific. Whereas the first two species
papar it is to present the gross anatomy can be found in muddy and sandy
of the digestive and reproductive sys- beaches, thethird prefers rockyenviron-
tems of three species: Bifurcium bicanal- ments. In spite of the fact that all three
iferum (G. B. Sowerby I, 1832)^ Sincola species have a very wide distribution,
(Dorsina) gibberula (G. B. Sowerby I, ranging from the Gulf of California
11
Iberus, 21 (2), 2003
Table I. Summary ofdimensions ofseveral organs for the three species discussed here. Measure-
mentsweremadewithfixedspecimensusinglightmicroscopy.
TablaI. Resumendelasdimensionesdevariosórganosdelastresespeciesestudiadas. Lasmedidasfueron
hechasapartirdeespecímenesfijadoscon un microscopioóptico.
Length Lengthof Rodulae Opercula
ofpenis proboscís Length N.of Sízeof N.of Sizeof Length Width
Genusandspecies (mm) (mm) (mm) lateral lateral medial medial (mm) (mm)
teeth teeth(pm) píate píate(pm)
Bifurciumbicanaliferum 11 10 12 360 79 180 30 1.2 1
Sincolagibberula 7 5 15 450 53 225 20 1.5 1
Clavistrombinadavulus 12 7 10 418 68 209 26 4 2
through Perú, C. davulus is much less dissecting, material was submerged in
abundantthantheothertwo species.AU Methylene blue to delinéate tissues and
three species are scavengers and have organs for gross anatomy study. Histo-
planktotrophic larvae (Fortunato et logical sections were done to study the
AL., 1998;Fortunato,2002). proboscises. Standard histological tech-
niques were used, the tissues infiltrated
with paraffin and sectioned at 7 pm.
MATERIALANDMETHODS Transverse sections of of the proboscis
were stained with Hematoxylin/eosin
AllworkwasdonewithUvecoUected (HUMASON, 1962). Measurements of
specimens. Collections were done by penises, proboscises, and radular teeth
hand during low tides and by trawling weredoneinfixedspecimensusinglight
fromsmallboats.Bothliveandpreserved microscopy and a millimeter ocular
.
in 5% buffered formalin material was Radulaewereremovedandcleanedwith
used for this study. About 10 specimens warm 10% KOH until completely free of
ofboth sexes from each studied species tissue. Opercula were treated with 37%
were dissected. Soft parts were removed hydrogen peroxyde. Both radulae and
from the shells with a vise after the opercula were coated with gold-palla-
animáis havebeen relaxed with menthol dium,andexaminedunderaJEOLHMS-
crystals added to the seawater. Before 5300LVScanningElectronMicroscope.
RESULTS
1. Morphology of the anterior ali-
mentarytract
Bifurcium bicanaliferum (Fig. lA)
The operculum (Fig. 2A) is yellow- like mouth opening (mo) (Fig. 4). When
mm
ish, rounded, and small (1 long and resting, the basal part of the proboscis
mm
1.2 wide) (Table I). It is very thin retractsintoatubularfoldofthebodywaU,
and transparent with a proteinaceous the proboscis sheath. The proboscis mea-
mm
consistency. Thegrowthringsareevenly sures about 10 (in a fixed animal)
spaced and it has an antero-posterior (TableI)andisofpleurembolictype,typi-
locatednucleus. calofascavengerandpredatoryUfestyle.
Theanimalhasalong,verymobüepro- The mouth leeds to thebuccal cavity
boscis (prb) taperingtowardsasmallsht- which occupies the first portion of the
112
Fortunato: Foregut and reproductive tract anatomy ofthree Strombina-group species
Figure 2. Scanning electrón micrographs oi opercula. A: Bifurcium bicanaliferum; B: Sincola
{Dorsina)gibberula; C: Clavistrombinaclavulus. Scalebar50 pm.
MEB
Figura2. Microfotografiasal de opérenlos. A: Bifurcium bicanaliferum; B: Sincola (Dorsina)
gibberula; C:Clavistrombinaclavulus. Esealas50j^m.
proboscis. Here the odontophore and of Leiblein (vle) or oesophageal bulb.
the radular sac are located. The The valve has a reddish natural col-
rachiglossate type radula (1+1+1) (Fig. oration and a pear shape. The
mm
3A) is about 12 in length (Table I). oesophageal bulb is surrounded by the
The radular ribbon is typically collum- large salivary glands (sgl). These are
bellid in shape, narrow, and has two paired, yellowish glands and they are
lateral rows of 180 teeth. The median not attached to the valve. These glands
píate, or rachidian tooth, is almost rec- are lobed and the lobes are held
tangular, long and has rounded edges. togetherby strong strands oftissue. The
Each median píate is 30 pim in length. salivary ducts (sd) leave the glands and
The lateral teeth have a sigmoid shape enter the lateral walls of the anterior
and are separated from the rachidian by oesophagus just before the expansión
a large inter-space. Each lateral tooth that represents the oesophageal bulb.
measures 79 pm in length. They have a The ducts follow the anterior oesopha-
wide base, a shaft and two hooked gus and discharge their secretions in the
cusps at the tip. A single blunt hook buccal mass. The oesophageal bulb
appears in the middle ofthe tooth shaft. signáis the beginning of the mid-
Theradula and several layers ofthe sur- oesophagus (moe). This bulbous expan-
bradular membrane together form the sión prevents the food from being
radular sheath at the end of which the suckedforward.
radulaissecreted. The beginning of the mid-oesopha-
The anterior oesophagus, (Fig. 4; gus is narrow. After traversing the
aoe), starts at the posterior end of the neural ring, it makes an S-shape curve
buccal cavity after separating from the after which it begins to engross. The
radular sac. Inside the proboscis, the large Gland of Leiblein (gle), or foregut
anterior oesophagus has a ventral posi- gland, enters directly into the mid-
tion. Once itleaves the proboscis, it con- oesophagus without a delimited duct.
tinúes towards the neural ring. This This unpaired gland has a V-shape and
section ofthe oesophagus is adhered up is darkbrown. After the insertion of the
toitsmiddlethrougha connectivetissue foregutgland,theoesophaguscontinúes
layer to the proboscis sheath. Just after to enlarge becoming the posterior
the neural ring, the anterior oesophagus oesophagus (poe) that ends in the
expands in diameter forming the Valve stomach.
13
Iberus, 21 (2), 2003
Theproboscisisverylonganditswall located within the radular sac (rs), have
iscomposedofathinouterlayerofcuticle bigcellswithacentralnucleus.Theante-
(cut)(Fig.5).Thecellsherearecubicwith rioroesophagus(aoe)islinedwithalayer
a big central nucleus. The next layer is ofcolumnarepitheliuminterspersedwith
composed oflongitudinal muscles (Iml) mucous ciliated cells. The salivary ducts
foUowedbyalayerofheUcalmuscletissue (sd) are located laterally relative to the
(hml). The subradular cartilages (se). anterioroesophagus.
Sincola (Dorsina)gibberula (Fig. IB)
The operculum of this species (Fig. the neural ring has a reddish natural
2B) is very similar to the anterior one. It coloration and a pear shape and is sur-
is oval shaped, small for the overall size rounded by the large salivary glands
ofthe animal (Imm long, 1.5 mm wide) (sgl). These paired, creamy glands are
(Table I), and yellowish. Its consistency not connected in any way to the valve.
is proteinaceous and itis somewhat thin These glands arelobed and thelobes are
and transparent. The growth rings are held together by strong strands of
evenly spaced and it has an antero- tissue. The long and curved salivary
laterallocated nucleus. ducts (sd) leave the glands and enter
Figure 6 shows a short (5 mm) directly into the anterior oesophagus
pleurembolictypeproboscis (prb) (Table through theposteriorlateral walls ofthe
I) that ends in a small slit-like mouth proboscis. The ducts run laterally inside
opening (mo). The proboscis in this the oesophagus and discharge their
species is almost translucent. Its basal secretions into the buccal mass. The
part retracts into a tubular fold of the mid-oesophagus (moe) begins after the
bodywall, theproboscissheath. oesophageal bulb. The mid-oesophagus
The mouth leeds to the buccal mass is thick in most of its length. The Gland
where the odontophore and the radular ofLeiblein (gle), orforegut gland, enters
sac are located. The rachiglossate type into the mid-oesophagus through a
mm
radula (1+1+1) (Fig. 3B) is about 15 small, narrow duct. This is a small, light
in length (Table 1). The typically colum- brown, unpaired organ, with a conic
bellid radular ribbon is narrow, and has shape. The posterior oesophagus (poe),
two lateral rows of 225 teeth. The that starts after the insertion of the
rachidian tooth is almost square in foregutgland,endsinthestomach.
shape, narrow, with rounded edges. It The proboscis walls have an outer
measures 20 ]im. The sigmoid lateral layer ofcuticle (cut) (Fig. 7). The cells of
teeth are separated from the median the cuticle are big, cubic, and have a
píatebyalargeinter-space. Lateral teeth prominent central nucleus. The next
have a wide base and a shaft with two layer is composed of helical muscles
hooked cusps at the tip. Lateral teeth (hml) followed by a layer of longitudi-
measure 53 pm. The hook in the middle nalmuscletissue (Iml).
of the tooth shaft is better delineated The presence of abundant connec-
here than in the previous species. The tive tissue (ct) is noticeable at this level.
radula is constantly being secreted at The subradular cartilages (se), located
theend oftheradularsheath, formedby within theradularsac (rs), havebigcells
the radula itself and the layers of the with a prominent nucleus. Remnants of
subradularmembrane. radular teeth can also be observed
The anterioroesophagus (Fig. 6; aoe) inside the radular sac. The salivary
begins at the posterior end of the buccal ducts (sd) are located on both sides of
mass and runs dorsally inside the pro- the anterior oesophagus (aoe). The later
boscis. The Valve of Leiblein (vle) or has an internal layer of columnar
oesophageal bulb consists of a small epithelium interspersed with mucous
expansión of the oesophagus just before ciliated cells.
114
Fortunato: Foregut and reproductive tract anatomy ofthree Strombina-^ranp species
Figure 3. Scanning electrón micrograph of radulae. A: Bifurcium bicanaliferum; B: Sincola
{Dorsind)gibberula; C: Clavistrombinaclavulus. Scalebar 100 [jm.
MENB
Figura3- Microfotografias al de rádulas. A: Bifurcium bicanaliferum; B: Sincoia (Dorsina)
gibberula; C:Clavistrombinaclavulus. Escalas 100fím.
Clavistrombina clavulus (Fig. IC)
The operculum (Fig. 2C) of this length. The lateral tooth is composed of
species is quite different from the i\\ro a narrow base, a shaft with a single
described before. It has a lenticular hook in the middle, and two hooked
shape, brownish color, and is four mil- cusps at the tip. The radular teeth are
limeters long and two millimeters wide secretedattheend oftheradularsheath.
(Table I). It is relatively thick with a cor- The later is formed by the radula itself
neous consistency. The growth rings are and several layers of the surbradular
evenly spaced and it has an antero-pos- membranabundled together.
terior located nucleus, and exhibits a The short anterior oesophagus (Fig.
ridgeinthemiddlewhichgivesita very 8; aoe) starts at the posterior end of the
uncommonaspect. buccal cavity after separating from the
Figure 8 shows a short proboscis radular sac. It runs laterally and
(prb) thatends in a small slit-like mouth expands into the oesophageal bulb or
opening (mo). At rest, the basal part of Valve of Leiblein (vle) shortly after
the proboscis retracts into the proboscis leaving the proboscis. The valve is
sheath formed by a tubular fold of the small, somewhat elongated, and
body wall. The proboscis measures translucent. The paired salivary glands
seven millimeters (in a fixed animal) (sgl) have a yellowish color and sur-
(TableI) and isofpleurembolictype. round the oesophageal bulb. The lobes
The mouth ends in the buccal mass of the salivary glands are quite big.
located in the first section of the pro- They are held together by connective
boscis, and where the odontophore and tissue. The salivary ducts (sd) are long
theradularsacarelocated. Theradulais and curved. They leave the glands and
mm
10 in length (Table I) and is enter the lateral walls of the proboscis,
rachiglossate (1+1+1) (Fig. 3C). The almost at one third of its length. They
radularribbonhasa collumbellid shape, continué on the inside of the proboscis
is narrow, and is composed of two until they reach the buccal cavity where
lateral rows of 209 teeth. The median they discharge their secretions. The
píate, or rachidian tooth, is almost oesophageal bulb delimits the begin-
square, with rounded edges. The ningofthemid-oesophagus (moe).
median píate is 26 pm in length. The The mid-oesophagus is quite narrow
lateral teeth are sigmoid, and separated up to the sectionwhere theshortduct of
from the median píate by a very large theGland ofLeiblein (gle) enters it. This
inter-space. These teeth are 68 pm in gland is dark brown and elongated.
115
Iberus, 21 (2), 2003
accompanyingtheposterioroesophagus muscular. The walls have a thick outer
(poe) almost in its entirely length. The layer of cuticle (cut). Inside the pro-
posterior oesophagus thickens sHghtly boscis (prb) large mucous glands (glm)
beforeenteringinthestomach. can be seen. The anterior oesophagus
The foot (ft) is very thick and short (aoe) has on both sides the large open-
(Fig. 9). The short proboscis is quite ingsofthesalivaryducts (sd).
2. Morphology of the reproductive
systems
Bifurcium bicanaliferum (Figs. 10, 13)
Thebright yellow ovary (Fig. 10; ov) the visceral cavity. The testis are located
is located laterally relative to the diges- laterally to the digestive gland and from
tive gland from which is separated by a it the short testicular duct (ted) runs
layer of connective tissue. The oviduct parallel to the stomach; after a short
(é^d) is relatively short; it runs parallel while it becomes extremely convoluted
tothebodywalland enters thealbumen and becomes the seminal vesicle (sev).
gland (alb) located near the kidney. The Intheposteriorregión ofthebodymass,
capsule gland (cgl) follows. At first theseminalvesicle straightens outagain
glance, the two glands are almost indis- and becomes the vas deferens (vd), a
tinguishable from each other. Neverthe- very thin and quite long duct that runs
less, transversal and longitudinal sec- parallel to the rectum and thebody wall
tions ofboth organs show the presence until it reaches the base of the penis
ofasmallinfernal septumdividingboth (pen). It enters the penis becoming the
glands. Histological sections show the penial duct (pd), which runs centrally
presence ofmore glandular tissue in the inside it. It is a convoluted tube that
section corresponding to the albumen opens at the tip of the male organ. In
gland than after the infernal septum. resting animáis, the penis is curved
The vestibule (vsb) is very short and is backwards along the right side of the
located at the end of the capsule gland, body and rests in the penial pouch. The
mm
followed by the female aperture (fop) penismeasures 11 longand isthick-
which drains directly to the mantle ened in its middle part, tapering
cavitynexttotheanus. towards the tip. Its ventral side is some-
The testis (Fig. 13; tes), share with what wrinkled and dorso-ventrally flat-
the digestive gland the posterior part of tened.
Sincola (Dorsina)gibberula (Figs. 11, 14)
Theyellowishcolored ovary (Fig. 11; than the second. Both organs arelocated
ov) is lateral to the digestive gland, and near the kidney. The vestibule (vsb) is
separated from these by connective well delineated in this species and runs
tissue. Follows a short and somewhat from the anterior región of the capsule
sinuous oviduct (ovd) that runs parallel gland parallel to therectuinuntilitends
to thebodywalland entersthealbumen in the female opening (fop) located con-
gland (alb). A small external membrane tiguoustotheanus.
connects the albumen and the capsule The testis (Fig. 14; tes) are located in
glands (cgl). Histological sections show the visceral cavity near the digestive
thepresenceofarelativelydeepinfernal gland, in a lateral position. The testicu-
septum dividing the two regions. The larduct (ted) isrelativelylong, runspar-
tissuespresentinboth are also different, allel to the stomach and, soon after
the first being much more glandular leaving the testis, starts to convolute.
16
Fortunato: Foregut and reproductive tract anatomyofthree Stromhina-group species
Figures 4, 5. Bifurcium bicanaliferum. 4: macromorphology ofthe anterior alimentary tract; 5:
transverse section ofproboscis. Figures 6, 7. Sincola (Dorsina)gibberula. 6: macromorphology of
theanterioralimentarytract; 7: transversesectionofproboscis. Figures 8, 9. Clavistrombinaclavu-
lus. 8: macromorphologyoftheanterioralimentarytract; 9: transversesectionofproboscis.Abbre-
viations. aoe: anterioroesophagus; ct: connectivetissue; cut: cuticle; ft: foot; gle: glandofLeiblein;
glm: gland ofmucus;hml: helical muscle; Iml: longitudinal muscle; mo: mouth; moe: middle
oesophagus; poe: posterioroesophagus; prb: proboscis; rs: radularsac; se: subradularcartilages; sd:
salivaryduct;sgl: salivarygland;vle:valveofLeiblein. Scalebars,4, 6, 8: 2 mm; 5,7, 9: 250 pm
Figuras4, 5- Bifurcium bicanaliferum. 4: macromorfologíadeltracto alimentario anterior;5:sección
transversalde laprobóscide. Figuras 6, 7. Sincola (Dorsina) gibberula. 6: macromorfología deltracto
alimentario anterior; 7:sección transversaldelaprobóscide. Figuras8, 9. Clavistrombina clavulus. 8:
macromorfología deltracto alimentario anterior; 9: sección transversalde laprobóscide. Abreviaturas.
aoe: esófago anterior; ct: tejido conectivo; cut: cutícula;ft:pie;gle:glánduladeLeiblein;glm:glándula
delmucus;hml: múscula helicoidal; Iml: múscula longitudinal; mo: boca; moe: esófago medio;poe:
esófagoposterior;prb:probóscide; rs: saco radular; se: cartílagossubradulares; sd: conducto salivar; sgl:
glándulasalivar; vle: válvuladeLeiblein. Escalas, 4, 6, 8:2mm;5, 7, 9:250}im
117
Iberus, 21 (2), 2003
forming the seminal vesicle (sev). This that runs along and inside the penis,
has a whitish coloration and is located opening at its tip. The penis of this
laterallyto the stomach. At theposterior species is quite short, only seven mil-
end, the gonadal duct becomes straight limeters long, and thickened throughout
againformingthevasdeferens (vd). The most of its way. Its surface is smooth
later is thick, not very long and runs and flattened in the dorso-ventral
parallel to the rectum along the body región. At rest, it is tucked in the penial
walls and enters the base of the penis pouchlocated in thedorsalregiónofthe
(pen). Hereitforms thepenial duct (pd) bodywall.
Clavistrombina clavulus (Figs. 12, 15)
The female ducts ofthis species (Fig. duct (ted) curves once after leaving the
12) show several differences from the testis, and soon becomes coiled forming
two previous species. The ovary (ov) is theseminalvesicle (sev). Both the testic-
yellowand hasalateralpositionrelative ular duct and the seminal vesicle are
to the digestive gland, from which it is locatedparallel tothestomach.Afterthe
separated by a layer of connective seminal vesicle, the duct becomes
tissue. Thelongoviduct (ovd) issinuous straight again forming a long conduct,
and divided into two parts. It runs par- the vas deferens (vd) which runs paral-
allel to the body wall, curves and enters lel to the rectum and ventrally gives
the completely delimited albumen origin to a short diverticulum (dv). The
gland (alb), which is located laterally to later connects with the mantle cavity
thekidney Aftertraversingthealbumen through an opening (omc). Immediately
gland, the gonadal duct leaves it, curves after the diverticulum, the vas deferens
again and enters the capsule gland (cgl). enters the base of the penis (pen) and
The later has a bean shape and is becomes the penial duct (pd), running
located anteriorlytothekidney. Fromits centrally and appears as a convoluted
posterior section starts the long and and long tube which opens at the tip of
plain vestibule (vsb), which runs paral- the penis. The penis is very long, over
mm
lel to the rectum and opens near the 12 in length, smooth, and flattened
anusinthefemaleopening (fop). dorso-ventrally. As in the two previous
Both the testis (Fig. 15; tes) and the species, the penis rests in the penial
digestive gland are located posteriorly pouch located in the posterior dorsal
in the visceral mass. A short testicular regiónofthebody.
DISCUSSION
Both the anterior alimentary tract than the other two species, in spite of
and the reproductive systems of the the fact that the animal in itself is
three studied species are similar in their smaller in size (range size for B. bicanal-
general plan. In what concerns the ante- iferum: 9-13 mm; S. gibberula: 9-12 mm;
rioralimentarytract, themostimportant C. clavulus: 14-25mm).
differenceliesintheinsertionofthesali- At the level of the reproductive sys-
vary ducts, which in B. bicanaliferum oc- tems, C. clavulus shows several differ-
curs in the anterior oesophagus just be- ences mostly within the accessory struc-
fore the Valve of Leiblein, whereas in tures. Of particular interest is the exis-
both S. gibberula and C. clavulus it hap- tenceofa welldefined albumin gland in
pens in the posterior región of the pro- témalesandamantleopening(thediver-
boscis. B. Bifiirciiim also presents amuch ticulum) intheinales. Thelaterisofspe-
longer proboscis and anterior oesopha- cial interest as it bears on the evolution
gus,aswellasalargeroesophagealbulb of the open reproductive system. This
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