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About abnormalities on the number of eyes and the evolution of the possible eye- sight related shell aspects in Strombidae; introducing new shell terms in Strombidae morphology (Gastropoda: Stromboidea, Strombidae)

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  • Independent researcher; CPA at Dekkers Accountants
Article

About abnormalities on the number of eyes and the evolution of the possible eye- sight related shell aspects in Strombidae; introducing new shell terms in Strombidae morphology (Gastropoda: Stromboidea, Strombidae)

Abstract

Aberrations on the number of eyes and strombid notches, the evolution of the eyesight , the use of the anterior canal and other morphological adaptions to the shells of the family are discussed. Animals with 3 and 4 eyes instead of 2 eyes are reported just as shells with 2 strombid notches instead of one strombid notch. The use of the term 'siphonal canal' is discouraged and replaced by 'anterior canal'. A new term is introduced: the strombid lobe for the broadly rounded projection on the outer lip posterior to the strombid notch.
Volume: 53 THE FESTIVUS ISSUE 3
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About abnormalities on the number of eyes and the evolution of the possible eye-
sight related shell aspects in Strombidae; introducing new shell terms in
Strombidae morphology (Gastropoda: Stromboidea, Strombidae)
Aart M. Dekkers
Oasestraat 79, 1448 NR Purmerend, the Netherlands aart.dekkers@wxs.nl
ABSTRACT Aberrations on the number of eyes and strombid notches, the evolution of the eye-
sight, the use of the anterior canal and other morphological adaptions to the shells of the family are
discussed. Animals with 3 and 4 eyes instead of 2 eyes are reported just as shells with 2 strombid
notches instead of one strombid notch. The use of the term ‘siphonal canal’ is discouraged and
replaced by ‘anterior canal’. A new term is introduced: the strombid lobe for the broadly rounded
projection on the outer lip posterior to the strombid notch.
KEY WORDS Strombidae, Strombus, eyes, eye sight, anterior canal, strombid notch, strombid lobe
INTRODUCTION
Strombidae Rafinesque, 1815 is the largest
extant family in the superfamily Stromboidea
Rafinesque, 1815, a family of well-known
marine snails with many colourful and diversely
shaped shells including beautiful shell
morphologies. Although the number of species
is quite limited (over 100 species at present), the
shells are very popular with shell collectors. The
family is important as a food source for the
human race and is abundantly collected almost
everywhere they live, but especially in the
Philippines. Recent Strombidae occur
exclusively in tropical and subtropical seas,
mostly in shallow and very shallow water
(Clench & Abbott 1941; Abbott 1960, 1961)
while for instance, extant members of the family
Aporrhaidae Gray, 1859, also belonging to the
Stromboidea, mainly occur in deeper water in
subtropical to cold water seas (differences in
depth and water temperature).
Most members of the family Strombidae can be
recognized by the presence of a so-called
‘strombid notch’, a sinus of the labrum of the
shell through which the second (right) of its two
long eyestalks extends out from the shell
(Savazzi, 1991). The first (left) eye-stalk
extends out from the sinus at the anterior end of
the shell, often wrongly called ‘siphonal’ canal,
which I will explain in this paper. The strombid
notch is almost exclusively a Strombidae
evolutionary adaption lacking in the other
families in the superfamily Stromboidea; the
only exception being members of the
Rimellidae Stewart, 1927. For example,
Varicospira decussata (Basterot, 1825) from the
Miocene of Dax, Landes Department, France,
has a perfect strombid notch (Plate 2A, C). Also
living members such as Varicospira
cancellata (Lamarck, 1816), a well-known
species from the Philippines, and Varicospira
crispata (Sowerby, 1842) have a clear strombid
notch (Plate 2B, D). The other members of the
family Rostellariidae Gabb, 1868 (and the
Seraphidae Gray, 1853) did not develop a true
strombid notch but have long eye stalks. A
photo of the live Terebellum terebellum
(Linnaeus, 1758) from Guam (Courtesy of Bob
Abela) is shown (Plate 3D), along with an
empty shell from the Philippines showing the
lack of a strombid notch (Plate 3A).
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Eyes are located at the end of the long eye stalks
of the strombid species. The eyes themselves
are almost human at first sight: a central dark
coloured spot with one or more differently
colored circles including white around this
central spot. When the eyes are focused on the
viewer, it almost feels like you are being spied
on (just look at photos of live animals). What
the affected animal is likely to see is not yet
known. It can be black and white, just shades,
but colors can also be the case. This can be a
subject of further (scientific) study, and the
London museum is working on this aspect
(personal communication).
Members of all other families included in
Stromboidea have not developed a strombid
notch in the evolutionary path, though
evolutionary trends towards this phenomenon
can be observed. For example, the recent
members of Aporrhaidae have the head between
the first and the second digitation like Aporrhais
pespelecani (Linnaeus, 1758) and Tibia species
such as Tibia insulaechorab Röding, 1798
(Rostellariidae) have protective spines on the
apertural rim (Plate 1B and A respectively).
The majority of Strombidae snails are found in
fairly shallow waters, often in combination with
seagrass species. A lot of them are burrowers in
clean sand, coarse sand or muddy sand.
Strombids are known to be herbivores or
detritivores (Abbott 1960, 1961). It is therefore
somewhat surprising that strombids are thought
to have excellent vision (due to the peculiar
development of eyes on eye stalks). Unlike most
mobile “higher Caenogastropoda” (like
tonnoideans and Neogastropoda (Simone 2005:
247)), Strombidae do not hunt or prey on other
animals. These other Caenogastropoda probably
don't use the eyes as a primary agent, but other
sensory organs such as smell or vibrations. Why
strombids developed eyes on stalks is therefore
problematical but is likely not necessary for the
feeding process, but possibly to escape
predators.
The shell morphology and the diversity of
stromboid gastropods was the subject of the
research of Savazzi (1991). Especially the
evolution of the shell shape and the snails' way
of life was his main interest.
The extreme diversity in shell form of strombid
gastropods is interpreted by Savazzi (1991: 311)
as the result of three independent factors:
(1) The terminal growth pattern of the
Strombidae allows the circumvention of
geometric constraints on shell morphology
found in gastropods with continuous or periodic
growth patterns;
(2) Shell morphology in the Strombidae is
adaptive to epifaunal locomotion, burrowing,
infaunal or semi-infaunal habits and passive
protection from predators. Specialization for
one of these functions often conflicted with the
others, thus bringing about a forced choice
among mutually exclusive morphological
characters;
(3) Conservatism in life habits and anatomy of
the soft parts has allowed the multiple evolution
of extreme shell morphologies, as well as the
secondary return to relatively unspecialized
morphologies.
Especially factor (2) seems the important driver
of the development of eye sight in the evolution
of Strombidae.
One of the very remarkable facts on
Stromboidea is that the soft parts between the
recognised families in the superfamily do not
vary much (Jung 1974). Perhaps this is due to
the simple diet of the snails, which originates
the successful basis scheme of organs of the
snails, fit for a long period of time involved in
the evolution that led to the diversification into
families of which only a few are still extant.
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Instead of altering the basis scheme of organs,
the snails are highly adaptive to the
environment or habitat, which resulted in a
multitude of shell forms.
METHODS
The discovery of strombid shells with double
strombid notches (coll. AMD) and photos of
live animals with more than 2 eyes were the
trigger for this study. Shell aspects of Strombid
shells are discussed based on personal
observations and related to literature directly or
indirectly involved with 'Eyes on Stalks' unique
development within Gastropoda within the
superfamily. Evolutionary paths of these aspects
are discussed where possible within the scope
and the general knowledge.
ABBREVIATIONS
AMD = Collection of Aarl M. Dekkers,
Purmeiend, the Netherlands.
MNHN = Musée National d’ Histoire Naturelle,
Paris, France.
TERMINAL GROWTH
Almost all Strombidae – and the species in the
other families in the superfamily – are
characterized by terminal (or determinate)
growth. After the shell attains the adult size the
aperture undertakes a change in shape. The
adult conch lip is often flared or wing-shaped.
Shell secretion is subsequently restricted to
selective thickening of the interior of the shell
and thickening of the wing and apertural rim.
Projecting teeth or digitations are formed in
certain clades and species at the edge of the
shell lip. Shell secretion stops completely or
continues very slowly with the deposition of
semi-transparent callus on some parts of the
ventral surfaces. In older snails the thick parietal
callus and the callus on the outer lip sometimes
gets a silvery or purple-blackish hue. This is
especially seen in species without projections on
the outer lip, like members of Laevistrombus
Abbott, 1960. The digitations on the outer lip
are an interesting and attractive aspects of
Strombidae. In the process of terminal growth,
the formation of the labrum (the wing), the
strombid notch is also formed. Before this final
stage, the shell has a more or less conoidal form
with a thin lip, almost mimicking a Conus shell.
DIGITATIONS
Spines are initially built as folded digitations of
the outer lip in species of Lambis Röding, 1798.
Extensions of the mantle occupy the interior of
the spines, and progressively fill them with shell
material. Once the spines are completely filled,
the mantle retracts within the shell aperture,
leaving a slit-shaped scar along the ventral
surface of the spines. This is especially well
visible with the members of the genus Lambis
and related genera Like Ophioglossolambis
Dekkers, 2012 and Harpago Mörch, 1852 with
large digitations.
In many species in other genera, outer lip
thickening occurs in adulthood without large
spines developing. In the shells of these species,
bumps are often visible where the strong ribs of
the body whorl end at the outer lip. This was
also noted by Vermeij (2014: 329) but not
exclusively for Strombidae members.
“Ventrally directed serrations, lobes or spines
occur in many Indo-West Pacific stromboidians.
In Tibia, blunt spines associated with obsolete
spiral cords are oriented ventrally at the edge of
the adult outer lip”. These ‘obsolete spiral
cords’ can be seen in the shell of Tibia species
by the lighter coloured spiral banding. More
directly it is seen in the related Rostellariella
delicatula (Nevill, 1881), which is shown on
Plate 1C. These obsolete spiral cords occur also
in the stromboidian genera Tridentarius
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Kronenberg & Vermeij, 2002 and Terestrombus
Kronenberg & Vermeij, 2002, which are also
remarkable by the very minimal strombid notch
(on Plate 3B). The strombid notch is thought to
be the hallmark of Strombidae, but in these two
genera the evolutionary path made it disappear
(secondary loss) which may be a consequence
of their lifestyle as speedy sand burrowers.
In Terestrombus terebellatus (Linnaeus, 1758),
5 white beams can be seen towards the apertural
rim, 2 of them besides the shallow strombid
notch, resulting in very small rounded dents
(Plate 3B). This is also the case in Tridentarius
dentatus (linnaeus, 1758) (Plate 3C).
Vermeij noted that in Tridentarius dentatus
(Linnaeus, 1758) “there are three ventrally
directed spines, one anterior to and two behind
the strombid notch” hence the chosen name
Tridentarius. But on closer inspection, there are
two more obsolete spirals situated more
posteriorly resulting in knobs on the outer lip
that did not fully develop into little spines. Most
likely all the spiral ribs and obsolete spirals both
ending in either spines or bumps are
reinforcements of the shells as a protection from
predators (new observation). The spines
themselves can be important as protection and /
or for stabilizing the shell on the surface on
which the animal crawls. With Vermeij (2014:
329) I also conclude that these configurations
arose independently in several lineages, but
with hesitation. Vermeij is limiting it to
Strombidae, but it also counts for Tibia
(Rostellariidae Gabb, 1868). The coding in the
DNA of the reinforcements and the spines in
Stromboidea is perhaps very old and on/off in
the lineages as evolution found it of benefit or
due to life habits and perhaps as old as the
Harpagodinae Pchelintsev, 1963 (Aporrhaidae).
The Harpagodinae members (upper Jurassic -
lower Cretaceous) possess angulations, which
strengthen the broadly expanded labrum.
Perhaps it is better to state that the
configurations originated early in Stromboidea
(instead of Strombidae) and switched on or off
in the evolution of the clades. Is this an example
of Atavism? In biology, an atavism is a
modification of a biological structure whereby
an ancestral genetic trait reappears after having
been lost through evolutionary change in
previous generations (definition from
Wikipedia). In short, an 'atavism' is an
evolutionary throwback to more primitive times.
As said, the DNA contains, genomes which
serve as archives of the evolutionary past in
whatever lineage. It only has to be turned “on’’
again, for whatever reason, in the evolution.
We have found no evidence of a link between
the evolutionary development of digitization
and the evolution of vision and long eye stalks
in Strombidae in literature.
The development of strong cords resulting in
digitations is not limited to Stromboidea. A
remarkable radiation of gigantic early
Cypraeidae in the Eocene of western Europe
(Dominici et al. 2020) also show this almost
unique feature. These gigantic Eocene fossil
cypraeid species showing strong dorsal ridges
and spines as prolongation of ridges. No dents
along the aperture as commonly seen in present
day cypraeids. Shells resembling a Lambis
species. Shown here (Plate 4A-D) are the newly
described species Vicetia bizzottoi Dominici,
Fornasiero & Giusberti, 2020. There are several
other species from the European Eocene
(England, France, Spain and Italy) in the genera
Vicetia and Gisortia.Gisortia coombii
(Sowerby in Dixon, 1850) is also such rare
dream fossil shell, with flower-like spines, but
no ridges to reinforce the shell (Pacaud, 2008).
Another species is Vicetia hantkeni (Lefevre,
1878) also on Plate 4E. The development in
these gigantic cowries and the later evolved
strombid species are analogous. The ridges,
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reinforcements and spines in strombids are not
modified versions of a structure present in a
common ancestor with cowries but probably
have developed independently as adaptations to
a likewise shared habitat, probably off shore and
rather soft substrate, not seen in any other group
of gastropods.
Examples of all kind of strombid notches are on
the Plates 5 and 6. The shallow strombid
notches in the big American strombs are
exemplary for the huge species crawling on the
sandy surface soil (Plate 5). Macrostrombus
costatus (Gmelin, 1791) and Titanostrombus
goliath (Schröter, 1805) are illustrated: not
more than 9 mm on a shell of 310 mm large!
The smaller (but still medium size to large)
species on Plate 6 show us deeper incised
strombid notches: smaller and deeper. These
species are all in the same subfamily of the
Strombidae: the Strombinae Rafinesque, 1815.
Exception is Mirabilistrombus listeri (Gray,
1852), which has a very wide and deep strombid
notch. This species is in the other subfamily
Carininae Dekkers, 2008. Dekkers (2008)
named these groupings as tribes in this work,
but the definitions given there are herein
supported as subfamilies. Carininae - definition:
includes all smaller forms of the family
Strombidae. Shells are small to medium sized,
often decorated with small knobs on the
shoulder and mostly decorated on the body
whorl with axial ribbing, strombid notch
shallow to clearly visible; lip thickened
sometimes on the inside and sometimes on the
outside, sometimes flaring and sometimes not
so flaring, columella and inside of lip often
decorated with lizae or teeth. Type genus:
Canarium Schumacher, 1817. In the tree in
Latiolais et al. 2006, the 2-split in the branches
are seen and supported by molecular
comparison.
A real eye-opener is the size and form of the
strombid notch compared to the size and form
of the sinus (=opening) of the anal canal. A
good observer can detect the logically build of
these two structures in a strombid shell: look at
the shell at the anterior end and level the labrum
horizontally. Then you will notice that the
strombid notch is in line with the anal canal in
height and in form. This has not been posted
previously, to my awareness.
STROMBID LOBE
In the stage of adultness an indentation, called
stromboid notch, is often found along the lateral
margin of the adult wing, rather anteriorly. Also,
in most of the larger extant Strombidae, there is
a kind of curtain or flap between the strombid
notch and the anterior canal. I have not found a
name in the literature for this special strombid
shell function and suggest calling it ‘strombid
lobe’. Basically, I found that there are two types
of strombid lobes: fairly large lobes that are
vertically oriented and a second group with
lobes that are quite small and follow the outline
of the labrum. Genera that have shells with a
large, down pointed strombid lobe are:
Harpago Mörch, 1852; Lambis Röding, 1798;
Lentigo Jousseaume, 1886; Ophioglossolambis
Dekkers, 2012; Solidistrombus Dekkers, 2008
(not available ‘synonym’ Sinustrombus Bandel,
2007) and Tricornis Jousseaume, 1886. These
are the larger shelled Indo-Pacific species and
genera. Examples of these strombid lobes are
shown on Plate 6C, D, and F with Tricornis
tricornis ([Lightfoot], 1796), Lambis lambis
(Linnaeus, 1758), Lentigo lentiginosus
(Linnaeus, 1758) and Solidistrombus sinuatus)
showing the strombid lobe with the down
pointed fingers (=ribbing). The smaller shelled
Indo-Pacific genera mostly have the smaller
type of strombid lobe. Curiously, the huge
species in the American radiations have the
smaller kind of strombid lobe or even lacking
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just as the strombid notches are hardly present;
see Titanostrombus goliath (Schröter, 1805)
(Plate 5A-C). Perhaps these differences can be
linked to be evolutionary aspects of the animals.
I have noticed that many of the smaller types
are sand burrows and it is likely that a small
strombid lobe aligned with the outer lip is an
advantage when digging into the sediment. The
larger shelled Indo-Pacific genera with shells
with a large, downward facing strombid lobe are
usually crawlers on the sediment instead of
burrowers and then a larger lobe is an advantage
as it provides better protection for the weak
parts of the animal and especially the vulnerable
eyestalks. The smaller type of strombid lobe
also offers protection to the animal but in a
lesser degree, which is not a real disadvantage
when buried in the sediment. The conclusion is
that the strombid lobe offers protection to the
weak parts of the animals and especially the
eyestalks. It is related to the living habits of the
species.
Note that the strombid lobe is only formed in
adult shells; the juvenile shells have a straight
thin ending of the aperture. Shells of
Strombidae remain thin walled throughout the
late juvenile, immature and subadult stages. The
adult wing is initially built as a very thin and
fragile membrane that gradually becomes
thickened on its internal, ventral, surfaces.
Secondary thickening may also take place on
parts of the internal and external (ventral)
surfaces. This results in a remarkable increase in
shell weight: the shell can be more than doubled
or tripled in weight (Savazzi 1991: 314) from
the almost adult to fully adult stage. Only in this
adult stage the labrum is fully formed with a
strombid notch (not in all species), strombid
lobe and digitations in some species.
THE SNOUT
The head of the gastropods can have one of 3
major varieties for consuming the desired food.
The simplest one is just a plain head without
any elongated parts. One of the more successful
varieties, the proboscis, is a feature developed
in the higher evolutionary lineages in
Gastropods. The highly developed proboscis is
(partly) retractable. This kind developed in the
higher Caenogastropoda starting with
Calyptraeoidea and including all following
superfamilies including Naticoidea,
Cypraeoidea, Tonnoidea and Neogastropoda
(Simone 2019: 28). In Strombidae a proboscis
has not yet developed, but instead the elongated
snout has already a retractor muscle (Simone
2019). The Strombidae seems to be a first step
in the development of the proboscis in
Gastropods. It makes it easier for the animals to
get the food while buried in the sand for the
burying species or in the crawling mode of the
larger species. The development of the
retractable snout is seemingly not related to the
evolution of the eye-sight. I place this
development in the context of the mobility and
lifestyle of the animals.
THE DEVELOPMENT OF THE
ANTERIOR CANAL
Gastropods in which the siphonate condition
arose were mobile, bottom-dwelling,
microphagous animals (Vermeij, 2007: 469).
According to Vermeij, conservative estimates
indicate that the siphonate condition arose the
incredible number of 23 times (and were
secondarily lost again 17 times). Active
predatory habits became associated with the
siphonate condition in for instance many
members of the Neogastropoda.
Many infaunal predatory gastropods have a
short (though often very deeply notched)
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siphonal canal through which a very long
proboscis emerges. Wide, deep siphonal notches
and dorsally deflected canals offer great
flexibility to the siphon and proboscis, and may
enable the gastropod to detect dangers and
opportunities of importance above as well as
ahead of the snail (Vermeij, 2007: 474). The
siphonal canal in most living siphonate
gastropods is associated with organs that
produce a narrow anterior inhalant current of
water. Associated sensory organs detect both
the concentration and direction of chemical cues
released by distant food, enemies, or mates
(Vermeij; 2007: 473, Lindberg and Ponder
2001). Inhalant streams in non-siphonate
gastropods are more diffuse, meaning that
ventilation of the mantle cavity is controlled
passively or actively by other structures than a
siphon. Among the extant siphonate snails are
the ‘higher Caenogastropoda’: cerithioideans,
campaniloideans, and stromboideans. These are
however either herbivorous or microphagous
and not predatory snails. Simone (2001) has
shown that the siphonal canal of cerithioideans
is not associated with a fully differentiated
siphon (Vermeij, 2007:474). Also, a developed
siphon is lacking in Strombidae (Plate 8C,
Macrostrombus costatus (Gmelin, 1791)
aquarium photo); only a simple mantel flap is
present.
The anterior channel in strombid species is
commonly referred to as the ‘siphonal canal’
which is an obvious misunderstanding as the
shell structure is not used by the animal for a
siphon, but is instead used to protrude the left
eye stalk. This is a remarkable invention in the
gastropod lineages and truly unique. There is
not one other gastropod family that uses the
‘siphonal canal’ for one of the eye stalks. Here
we see the evolution of two sinuses used for the
eyes: the anterior channel (or canal) and the
strombid notch. Members of the closely related
family Seraphidae have not developed a
strombid notch, but recent members of this
family use the broad anterior end of the shell to
accommodate both eye-stalks. Here the shell is
adjusted in a different way, likely facilitating
the protection of the head of the animals with a
broad roof and a broad ‘window’ for the eye-
stalks, retaining a very smooth torpedo like
form for fast moving in the sand. Same
intention, different solution. This ‘hooded’
protection is also found in some genera of the
family Ovulidae (personal observation) where
the animals use the extension of the shell as a
kind of hood. This observation is in line with
that of Vermeij: “a long siphonal canal extends
the shell’s passive defence by shielding the
vulnerable anterior organs from above and
below while the gastropod is active” (Vermeij,
2007: 474).
According to Vermeij (2007: table 1) the
siphonate character arose already in the Early
Jurassic (Toarcian) in Stromboidea. The family
of the aporrhaids, a basal family in the
Stromboidea, have been siphonate since their
first appearance in the Early Jurassic, though it
is not very easy to see: it is just the broad sinus
between the 2 front spines.
All early representatives of siphonate gastropod
groups appear to have been microphagous
(Stanley 1977), as are living cerithioideans and
stromboideans, which also have high-spired
siphonate shells. Predatory habits of
tonnoideans and neogastropods have been
possibly the triggers for the evolution of the
proboscis and associated organs of the digestive
system (Kantor 1990, 1996; Riedel 2000) and
the further use and development of the siphonal
canal in these lineages. The ‘bauplan’ was
already invented in the early roots of gastropod
evolution. But the question is why the early
siphonate condition arose.
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The (early) siphonal condition (cerithioideans,
campaniloideans, and stromboideans) seems to
be linked with active crawling animals on a
sand/mud bottom, which have a shell form that
enables the animals to crawl easily and thus fast.
It probably evolved as the front end of the shell
in conjunction with the strong spiral (coiling)
and elongated shell shape. Active predatory
animals evolved later and started using the
existing ‘bauplan’ of the anterior canal with the
development of a siphon which was well
protected by the existing anterior (now truly
siphonal) canal. More sessile snails (an older
bauplan’) as patellids and trochids are non-
siphonate and have a big flat base of the shell or
a more or less rounded aperture, for better
fixture on the hard underground where they
crawl slowly. Conclusion: the (early) anterior
(‘siphonal’) bearing shelled snails are either
herbivorous or microphagous and not predatory,
thus the development of an anterior canal is not
(directly) linked with the feeding habits. The
remaining logic beneficiary lies in the
assumption that it is the result of the
development of fast locomotion and the
assumption of Vermeij that it has evolved for
the benefit of protection. For the head and the
organs there placed, including the eyes. I
herewith like to discourage such an ingrained
term as "siphonal canal" and replace it by the
term "anterior canal" for Strombidae and
Cerithidae. I hope subsequent authors will do
the same.
DEVELOPMENT OF THE STROMBID
NOTCH
The strombid notch is, as said, a development
uniquely in Stromboidea (Strombidae and
Rimellidae) and all other known gastropods lack
this feature on the anterior part of the edge of
the labrum. The strombid notch can be rather
shallow or deeply incised into the labrum,
differentiated on the species or genus, as
discussed before and shown on Plates 5 and 6.
Kollmann (2005) allocated the subfamily
Harpagodinae to the family Strombidae on the
basis of the basal notch. Due to the presence of
an identical small basal notch in the
Aporrhaidae, he later (Kollmann 2009) placed
the Harpagodinae in the family Aporrhaidae.
Perhaps the origin of the strombid notch is
already as early as the Mesozoic era.
As the location of the strombid notch is on the
labrum at the anterior part, the right side of the
animal, one eye is pointing sideways to the right,
leaving the left side of the animal unwatched.
However, watching movements of strombid
species (personal observations), the animal
moves in a straight line using both eyes in
forward direction, thus the head is not in line
with the apex of the shell, but instead the shell
is oblique compared to the head. It seems that 2
eyes through the anterior canal is more logical
to us (as in Terebellum, Seraphsidae) but
apparently there are better evolutionary
arguments for the evolution of the strombid
notch. One argument could be that the smaller
anterior canal is a better protection against
predators like crabs and the shell can be smaller
constructed as part of the head is protected by
the labrum. In the adult stage the mantel just has
to skip a part of the reinforcing of the labrum to
create the strombid notch. This seems to be an
easy adaption, which renders a safe condition
and the possibility to peep out under the roof of
the labrum. Thus, also an evolutionary trend for
the benefit of safety in combination with the
development of the eyes and the unique
development of long eyestalks. The Seraphidae
have developed a torpedo like shell which
enables them to move with high speed through
the clean sand. They lost the broad shell form as
in Strombidae in favour of speed and thus did
not develop a strombid notch for the long eye-
stalks.
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The Rimellidae arose in early Eocene and
already demonstrated strombid notches (in
Ectinochilus Cossmann, 1889; Dientomochilus
Cossmann, 1904; Dasyostoma Stewart, 1927;
Varicospira Eames, 1952) in the Eocene period
and onwards. In genera of the Strombidae,
strombid notches are absent or very obscure in
the Eocene (Oostrombus Sacco, Orthaulax
Gabb, 1873). The evolutionary relation between
the Rimellidae and the Strombidae is not yet
clear.
Early (large) strombids like the very large
Dilatilabrum roegli (Harzhauser, 2001) from
the Chattian (Late Oligocene) of Greece and
Dilatilabrum fortisii (Brongiart, 1823) from the
middle Eocene of Italy lack a strombid notch or
have a very shallow indention but do have the
general bauplan of the larger extant strombid
species. Also, Dilatilabrum trigonus (Grateloup,
1834) from the lower Miocene of France still
lacks a strombid notch. Even Tricornis tricornis
(Lightfoot, 1786) from the Pleistocene (Ras
Doumeira, Djibouti, Gulf of Aden) of the
Arabian Sea has a very shallow strombid notch
(personal observation). Only extant T. Tricornis
of the Egyptian Red Sea have well developed
strombid notches. This is also seen in American
gigantic strombid species like Lobatus
dominator (Pilsbry & Johnson, 1917) from the
Oligocene up to the upper Miocene of the
Caribbean which lacks a strombid notch, even
the extant Titanostrombus goliath (Schröter,
1805) has only a very shallow strombid notch
(Plate 5A-C). These large to gigantic strombid
species are likely not burrowers but remain
surfaced on the sand and therefore did not
develop a strombid notch. The conclusion could
be arrived that strombid notches developed
primarily in the branches of burrowing
strombids and that the very shallow or almost
obsolete strombid notches in the large not
burrowing species could be secondary loss or
the basic situation.
Bandel (2007) also notes that Dilatilabrum (for
which he erected the new family Dilatilabridae)
resemble Strombus in shell shape with an
expended outer lip but do not have a stromboid
notch. As they lived in the Paleogene, he
concludes that they may represent the stem
group to the Strombidae. Strangely, he places
the younger genera Oostrombus and Orthaulax
(Eocene, Oligocene and Miocene), which have
smoothed shells with callus covering the spire
as seen in Calyptraphorus in the family
Thersiteidae Savornin, 1915. Perhaps these
Oostrombus and Orthaulax species were the
early burrowing representatives of the
Strombidae (with smooth shells), but still
lacking a strombid notch. Orthaulax can be a
enlarged version of Calyptraphorus. Further
study is needed on the relations between those
genera.
Whatever the origin of the Strombidae, the stem
group consists of shells without strombid notch.
And even up to present times the large strombid
species that live epifaunal (living on and not in
the substrate) lack strombid notches or have
very shallow ones and strong and rapid small
burrowers as Tridentarius Kronenberg &
Vermeij, 2002 and Terestrombus Kronenberg &
Vermeij, 2002 have secondary lost the strombid
notch. Just as members of Terebellum Röding,
1798 (Seraphidae) with similar life habits do not
have a strombid notch (Plate 3A & D).
In the collection of the author, several strombid
shells are housed with 2 instead of 1 strombid
notch, at least a structure that looks like it, an
anomaly not often seen and not previously
reported to my knowledge. The question that
arises is: (1) is this an occasional anomaly
caused by damage to the mantel, the soft tissue
that builds the shell, or (2) is the second
strombid notch an anomaly to house a third eye-
stalk?
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On Plate 9 several examples of this abnormality
from the authors’ collection are shown. It
concerns three from the genus Euprotomus Gill,
1870 and one from the genus Lentigo
Jousseaume, 1886, which are likely genetically
closely related when molecular tested. Is this a
coincidence?
In the case of Lentigo lentiginosus STR2728
(Figure 9D), no damage to the shell is visible,
thus eliminating the possibility of early damage
to the soft tissue due to e.g. crab attacks. This is
also the case of E. aurisdianae STR3079
(Figure 9C) though this example bears
extraordinary double shoulder knobs. Both E.
bulla (STR1428 and STR2227) (Figure 9B)
have a dorsal situation that might point at tissue
damage, especially STR2227, with raised dorsal
rim which points at an early tissue damage. But
ending in the apertural rim as an almost perfect
second strombid notch. STR1248 (Figure 9A)
has a sharp additional shoulder lacking knobs,
ending in the apertural rim with a narrow
indention looking a bit like a second strombid
notch, but probably is not.
Weather all those abnormal condition of double
strombid notch must be the cause of abnormal
eye-stem number or tissue damage is hard to tell
from only the empty shells.
Table 1. Comparison of characters of recent Stromboidian families (Xenophoridae excluded)
DEVELOPMENT OF EYE-STALKS AND
DEVELOPMENT OF STROMBID NOTCHES
Except Strombidae, the living species of the
stromboidean families Rostellariidae (see e.g.
figures in Man in ‘t Veld & Visser, 1998),
Seraphidae (see e.g. Jung & Abbott, 1967: pl.
319, pl. 321 bottom figure) and Rimellidae
(observation Kronenberg, 2013) also have their
eyes at the tip of long eye-stalks. Thus, this is a
synapomorphy of these families within the
Stromboidea, distinguishing them from
evolutionary older families as the Aporrhaidae
and Struthiolariidae, and suggesting a common
ancestor where the longer eye-stalks and
apparent same usage of the eyes developed
(Maxwell et al. 2019, the construction of
Epifamilies herein). The occurrence of long
eye-stalks is in relation to the development of a
strombid-notch is given in Table 1.
Eye-stalks development is a dominant condition
or trigger of strombid notch development in
both Strombidae and Rimellidae. Most likely
the long eye-stalk is a development that arose as
result of animals' burrowing modes, a chance to
stay safely under the sand / mud while scanning
the area for danger. Strombidae and Rimellidae
probably have shared ancestors, and the genus
Calyptraphorus (at present in the Rostellariidae)
can be the one (Kollmann 2009: 59). Kollmann
(2009: 60) “The Calyptraphorinae Bandel
possess a basal notch. They may have given rise
to the Rimellinae and perhaps other
Stromboidea with a basal notch, while the
Rostellariidae, which generally lack a notch,
Character
Strombidae
Rimellidae
Rostellariidae
Aporrhaidae
Struthiolariiae
Long eye-stalks
present
present
present
-
-
Open anterior canal
present
present
-
-
-
Strombid notch
Present or
absent
present
-
-
-
Short eye-stalks
-
-
-
present
present
First labral digits used
to protect the head
-
-
present
present
-
Average living depth
shallow
shallow
Shallow to
deep water
Shallow to deep
water
shallow
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have evolved from Hippochrenes Montfort”.
These animals (Calyptraphorinae) were
burrowers with a smooth shell with a callus
layer over the shell that lived in the Cretaceous,
Palaeogene and Eocene after which they
became extinct. Shells of this group have a
broad sinus next to the small open anterior canal,
which can be the basic bauplan of the later
strombid notch and anterior canal used for the
long eye-stalks in Strombidae.
ABNORMALITIES IN THE NUMBER OF
EYES
In the normal situation, the number of eyes is
always 2, each eye on a separate eye-stalk. It is
the normal condition; however, deviations are
reported in this document. A Caribbean
strombid species with a doubled (twin) eye on a
stalk (Kronenberg, 2013) has already been
reported. In that case, the eyes stayed together
like Siamese twins. On the accompanying photo
of “Strombus lobatus Linnaeus, 1758” in that
report, it is clear that the twin-eyes at the tip of
the right eye stalk are smaller than the other
normal left eye and that it almost looks a split of
one normal eye into 2 ‘Siamese’ eyes.
Anomalies in living creatures are perhaps not
even rare, but reports about them are. In the past,
all kinds of anomalies were collected and put on
alcohol in special collections or even displayed
as an attraction (especially when it came to
people) at traveling exhibitions. In this paper
two species with anomalous number of eyes are
reported from Turtle Crossing for both, a sandy
plateau with scattered coral heads from 12-14 m
on the south of the island of Roatan, Bay Islands,
opposite of Honduras mainland. This is a clear
and unspoilt area with no pollution or other
suspect circumstances (observation of Mickey
Charteris, the discoverer). It is therefore
unlikely that environmental influences are the
cause of the deviations. The two species are
Queen Conch, Aliger gigas (Linnaeus, 1758)
(Plate 7A) with 4 eyes and the Milk Conch
Macrostrombus costatus (Gmelin, 1791) (Plate
7B) with 3 eyes.
Special attention is also required for the 4-eyed
Conomurex luhuanus (Linnaeus, 1758)
photographed by Shawn Miller (Plate 8A-B).
This snail has a normal left eye-stalk with a
normal eye protruding through the anterior
canal, and the right eyestalk with three eyes of
one has a cleaved stem and two eyes are
connected just in the form of Y. The eyes look
natural and the size is not much different from
normal eyes. Also seen in the photo is the
proboscis, which appears to be normal. The
strombid notch is wider than normal and also
the anterior canal is wider than normal, almost
twice the normal size (compared to collection
material AMD). Thus, there is a relation
between shell aspects and the multiple eyes in
this aberrant example.
Also, Stephen Maxwell, Cairns, Queensland,
Australia once caught a C. luhuanus with an
additional eye but that was years ago and the
animal was discarded, even without taking
photos (personal communication, May 2017).
The author discussed the abnormal multiple
eyes with Maxwell, but he could not recall if the
shell had additional features related to the
multiple eyes; the shell is no longer in his
collection/possession.
In the authors collection, several strombid shells
are housed with 2 strombid notches per shell, as
discussed before (Plate 8). This is an anomaly
that can be caused by damage to the shell
secreting mantle or possibly related to multiple
eye-stalks. With empty shells it is not possible
to determine the cause of the double strombid
notch.
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ACKNOWLEDGEMENTS
We express our great thanks to Mickey
Charteris, Roatan, Bay Islands, Honduras for
making the great photos of the live 3-eyed and
4-eyed Strombus examples from Roatan, his
home town. The same for excellent photos by
Shawn Miller of the live C. luhuanus. Without
these photos it would be impossible for us to
demonstrate the deviations in the number of
eyes in Strombidae. Thanks also to Tammy
Myers, Ormond Beach, Florida, USA, for the
aquarium photo of the Milk Conch. All
involved are thanked for permission to use these
excellent photos. David Berschauer is thanked
for editing, and Stephen Maxwell, Cairns,
Australia, is thanked for mounting the
photographic plates.
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Plate 1. Rostellariidae and Aporrhaidae
A = Tibia insulaechorab Röding, 1798 (as Rostellaria curvirostris) in Kiener, 1843, Vol. 4, Rostellaria pl. 1, fig. 1. Drawing showing the live animal
with the eyes on stalks. Large sinus near the anterior spine for the snout and lacking a stromboid notch.
B = Aporrhais pespelecani (Linnaeus, 1758) in Forbes & Hanley, 1853, pl. II, fig. 3, 3a (as Aporrhais pes-pelecani). Animal showing eyes close to the
body mass, no stalks. A large sinus for the snout and lacking a strombid notch.
C= Rostellariella delicatula (Nevill, 1881); AMD STR0996, Andaman Sea, southern Thailand, trawled by Thai boats, deep water, 1977. Part of the
shell showing the ‘internal’ white bands reinforcement structures resulting in the labral spines.
Plate 2. Rimellidae
A = Varicospira decussata (Basterot, 1825) in Duclos in Chenu, 1844, pl. ?, fig. 5, 6 (as Strombus decussatus). Drawing showing a clear strombid
notch.
B = Varicospira crispata (Sowerby, 1842) in Duclos, 1844, pl. 16, fig. 9, 10 (as Strombus crispatus). Drawing showing the small but well visible
strombid notch.
C = Varicospira decussata (Basterot, 1825), AMDSTR927. H 26 mm. St. Martin d’Oney, France. Self-collected. Miocene – Aquitanien. Clear strombid
notch.
D = Varicospira crispata (Sowerby, 1842), AMD1329. H 22.2 mm. Bohol, Philippines, showing the strombid notch.
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Plate 3. Seraphidae and smooth Strombidae
A = Terebellum terebellum (Linnaeus, 1758); AMD STR3532, H37.5 mm. Olango Island, Philippines, night dive 20-25 meter. Shell side view showing
the lack of strombid notch.
B = Terestrombus terebellatus (Linnaeus, 1758); AMD STR3867, H47.4 mm. Calituban Island, Philippines, from fisherman. November 2006. Side
view of the shell. Towards the apertural rim 5 white beams can be seen, 2 of them besides the shallow strombid notch, resulting in very small rounded
dents.
C = Tridentarius dentatus (Linnaeus, 1758); H51.2 mm. Quezon Baraguy, Puring, Palawan, Philippines. Taken in coral sand at 1-3 meters. 09-2006.
Clearly seen are the 3 dents and another 3 bumps on the apertural rim connected with 5 white banding. Also the indention between the first 2 dents
serve as shallow strombid notch. Also, the anterior canal is open towards the first 2 dents, both ready for the eye-stalks.
D = Terebellum terebellum (Linnaeus, 1758); ~80 ft, Agat Bay, Guam; ~2003-2004; aquarium photo Bob Abela, Guam. Eyes on stalks looking
backwards.
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Plate 4. Eocene gigantic Cypraeidae
A to D = Vicetia bizzottoi Dominici, Fornasiero & Giusberti, 2020. (Holotype MGP-PD 32314, measuring 335 mm in length). (a) Posterior view, (b)
ventral view, (c) dorsal view, (d) anterior view. Gigantic Eocene fossil cypraeid species showing strong dorsal ridges and spines as prolongation of
ridges. No dents along the aperture as commonly seen in present day cypraeids. Shell resembling a Lambis species.
E = Vicetia hantkeni (Lefevre, 1878). MNHN.F.R11785. Specimen with dorsal ridges, measuring approximately 120 mm in length. Gan, La Tuilerie,
France. Collected by Didier Merle. Photo Credit: RECOLNAT (ANR-11-INBS-0004), Jocelyn Falconnet, 2017.
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Plate 5. Big Strombidae with shallow strombid notch
A-C = Titanostrombus goliath (Schröter, 1805); AMD STR3409. H 235 mm. Récife, Brasil, 2000. Depth of the strombid notch ca. 5 mm of this almost
fully adult (not yet thickened lip).
D = Macrostrombus costatus (Gmelin, 1791); AMD STR0379. H 187 mm. Photos showing the very shallow strombid notch.
Plate 6. Strombidae with deep strombid notch or large
strombid lobe
A = Mirabilistrombus listeri (Gray, 1852); AMD STR0573. H 144 mm.
Ranong, SW Thailand. Enormous broad and deep strombid notch.
B = Persististrombus granulatus (Swainson, 1822); AMD STR1275. H
61.1 mm. La Mira, Las Perlas Islands, Panama, on hard sand flats. Bigg
and deep strombid notch.
C = Tricornis tricornis ([Lightfoot], 1786); AMD STR3498. H 68.9 mm.
Coll. by B. Gras, Mah Kabi, Yemen, Red Sea. With periostracm. Very
big and deep strombid notch.
D = Lambis lambis (Linnaeus, 1758); AMD STR2242. H 152 mm.
Pandanan Island, Philippines. Large strombid lobe with 5 fingers of
which one is in the large and deep strombid notch.
E = Solidistrombus sinuatus ([Lightfoot],1786); AMD STR1860. H 86.1
mm. Caubyan Island, Philippines. Strombus lobe with at least 5
downward fingers. Strombus notch also with dents, very deep.
F = Lentigo lentiginosus (Linnaeus, 1758); AMD STR3555. H 80 mm.
South of Mombassa, Keynia, at 2 meter on sand in algae field. Strombid
lobe with 4 downward fingers.
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Plate 7. Certain Strombids displaying bifurcated eye stalks
A = Aliger gigas (Linnaeus, 1758) with 4 eyes. Turtle Crossing, which
is a sandy plateau with scattered coral heads from 12-14-meter-deep on
the south of the island of Roatán, Bay Islands, opposite of Honduras
mainland, Honduras. Photo courtesy of Mickey Charteris (Caribean
Reef Life), Roatán, Islas de La Bahia, Honduras.
B = Macrostrombus costatus (Gmelin, 1791) with 3 eyes. Turtle
Crossing, which is a sandy plateau with scattered coral heads from 12-
14-meter-deep on the south of the island of Roatán, Bay Islands,
opposite of Honduras mainland, Honduras. Photo courtesy of Mickey
Charteris (Caribbean Reef Life), Roatán, Islas de La Bahia, Honduras.
Plate 8. Certain Strombids displaying bifurcated eye stalks
A, B = Conomurex luhuanus (Linnaeus, 1758) with 3 eyes, Okinawa,
Japan. Photo courtesy of Shawn Miller (Okinawa Nature Photography),
Okinawa, Japan.
C = Macrostrombus costatus (Gmelin, 1791). Aquarium photo, courtesy
of Tammy Myers, Ormond Beach, Florida, USA.
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Plate 9. Various Strombid shells displaying growth structures
A = Euprotomus bulla (Röding, 1798). Bohol, Philippines. H. 59 mm AMD STR1428. Sharp additional shoulder lacking knobs, ending in the apertural
rim with a narrow indention.
B = Euprotomus bulla (Röding, 1798). Beni Island, Philippines. H. 58 mm AMD STR2227. With raised dorsal rim which points at an early tissue
damage. But ending in the apertural rim as almost perfect second strombid notch.
C = Euprotomus aurisdianae (Linnaeus, 1758). Beni Island, Philippines. H. 51.7 mm AMD STR3079. Looks like a undamaged shell, but with
elongated or double shoulder knobs.
D = Lentigo lentiginosus (Linnaeus, 1758). Olango Island, Philippines. H 71.5 mm STR2728. Perfect shell, no damage.
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On the status of Tibia melanocheilus (Adams, 1854) and some notes on the appearance of its shell
  • L Veld
  • G J Visser
Man in 't Veld, L. & Visser, G.J. 1998. On the status of Tibia melanocheilus (Adams, 1854) and some notes on the appearance of its shell. La Conchiglia 288(7/9):51-56, 60.