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| Group
2 Gobies: Coryphopterus, Lythrypnus,
and others |
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Six-spined: standard 9,10,
and 11 dorsal and anal fin elements
(mostly similar, lightly-marked species)
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This group
includes many of the abundant small gobies
ubiquitous on and around Caribbean reefs.
They share six first dorsal fin spines and
9, 10, or 11 dorsal and anal fin elements.
Larvae of these gobies are typically small
and lightly marked, usually with only a
ventral midline series of melanophores (at
the isthmus, pelvic fin base, anal fin base
and caudal peduncle). Unfortunately the
larvae of this group and the seven-spined
standard gobies (Group
3) can be similar in appearance and
a challenge to separate, although with the
characters discussed here they should be
able to be quickly identified, at least
to genus.
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The small
lightly-marked goby larvae account for a
major fraction of larval collections in
the region. They are superficially quite
similar, sharing the ventral midline markings
and an otherwise bland appearance. Before
counting fin rays, the basic appearance
of the larvae can distinguish genera efficiently.
The three larvae below are typical, with
Coryphopterus punctipectophorus in the middle, Lythrypnus sp.
below and Microgobius sp. above. The body shape of each is distinctive, with
the differences discussed below.
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The large
genus Coryphopterus
dominates this group of gobies and accounts
for the vast majority of gobies one sees
on a Caribbean coral reef. The largest group
within Coryphopterus are the sand
gobies. These fishes can be found perching
on the bottom along the sandy edges of hard
substrate, seemingly everywhere except in the
most turbid or muddy environments.
The sand gobies are particularly difficult
to identify to the species level in the
field and, even when in the hand, careful
examination of marking patterns is required
to distinguish the species. This becomes
even more difficult for smaller juveniles
that have not developed their species-specific
marking patterns. The other group of Coryphopterus,
the hovering masked and glass gobies, are
also very abundant, although more reef-associated.
They are found in large groups just off
the bottom on almost every coral reef in
the region.
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| Other members
of the Group 2 gobies are less conspicuous,
consisting of the numerous species of Lythrypnus
with a few others such as Priolepis
and Lophogobius
and the unrelated river gobies, Sicydium.
I start the page with the sand gobies and
congeners, then follow with the Lythrypnus
gobies and, in particular, how to separate
their larvae from those of Coryphopterus. |
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Note: Fin ray counts for the second dorsal
fin and the anal fin are total elements (spines
plus rays) and species are listed in rough
order of increasing anal fin rays. |
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| The
large goby genus Coryphopterus contains numerous
species in the Caribbean, several of which are particularly
difficult to distinguish, sometimes even as adults.
The results of my barcode (mtDNA) sequencing for
this group show that many of the important characters
used to separate adults do not apply to larvae or
juveniles. Since the basic markings and morphology
of small juveniles are shared by many of the species
in the group, DNA sequencing is likely the only
reliable way to distinguish species for most larvae
and some juveniles. |
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| One
of the primary causes of the difficulty in identifying
juveniles and adults of Coryphopterus species
in the western Atlantic is is the extreme variability
in the degree of dark markings with habitat. All
of the sand gobies have lightly-marked forms on
white sand in clear water and heavily-marked forms
on darker sediments in more turbid waters, particularly
along continental coastlines. This variation can
become extreme, with some individuals showing almost
no dark markings at all. These occasional super-pallid
individuals can be impossible to identify to species
without DNA sequencing. On the other hand, heavily-marked
populations of some supposedly pallid species, for
example Coryphopterus
eidolon, have not been recognized as conspecific
and are typically assigned to other species in museum
collections. |
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| An
additional problem when using the literature and
field-guides for identifications is the presence
of heretofore cryptic species in the common 10/10
sand-perching bridled-goby group, i.e. the recently
twice-redescribed "pallid" bridled goby C.
tortugae, a new more-offshore species C.
bol (Victor 2008), and the Venezuelan sibling species
C. venezuelae. These species are presently
lumped by most observers as variants of the bridled
goby C.
glaucofraenum. To avoid confusion, I propose
that C.
glaucofraenum retain the original "bridled
goby" common name, while C.
tortugae should be called the "patch-reef goby"
and C.
bol should be called the "sand-canyon goby", after their distinctive habitats.
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| Some
of the more important morphological characters traditionally
used to separate species in this group do not apply
to juvenile or larval stages. For example, the morphology
of the pelvic fin is one of the more important taxonomic
characters separating the regional Coryphopterus
spp. The presence or absence of the pelvic frenum
has been considered diagnostic for some species.
The pelvic fin frenum is the anterior membrane running
from spine to spine that forms the fin into a sucking
disk. My DNA barcoding results, however, reveal
that the pelvic frenum is fully-formed in juveniles
of species that later do not have one (C.
dicrus) and that larvae and some transitional
recruits of species with divided pelvic fins have
fused pelvic fins, such as C.
personatus and C.
lipernes. Furthermore, the degree of joining
of the two pelvic fins and the relative length of
the innermost ray are commonly used taxonomic characters
for adult gobies, however the innermost pelvic fin
rays do not become distinctly shorter or longer
until after the transitional recruit stage. |
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| Finally,
and even more complicating for larval studies, is
that transitional individuals can develop their
metamorphic melanophores in differing sequences,
leading to a proliferation of transitional larval
types that certainly represent the same species.
At least some of this variation may reflect the
marked variability in the degree of markings with
habitat type characteristic of this group, with
lightly-marked juveniles living on white sand and
those on darker backgrounds or more turbid waters
being heavily-marked. The light marking may occur
in larvae as well, where a significant portion of
individuals are missing the melanophores on the
caudal fin base and/or the dorsal caudal peduncle.
Whether the larvae have pre-determined which habitat
to settle onto or whether it is a facultative decision
is an open and very interesting question. |
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The reported fin ray counts for
the genus Coryphopterus in the literature:
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in the order of increasing anal
fin elements, then increasing pectoral fin rays
format= Species: #dorsal/#anal
fin elements #pectoral rays (pelvic fin state)
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fewer than 10 total anal fin
elements
C.
kuna: mode 9/9 pect 15
C.
alloides: mode 10/9 Bohlke:
10, rare 9/9, rare 8 pect 16-17 (divided pelvic
fins)
10/10 group
(total second dorsal and anal
fin elements)
C.
lipernes: Randall: 10/10 pect 16-18 (divided
pelvic fins)
C.
glaucofraenum: Randall: 10/10 pect 17-20
Bohlke: 10/10, rare 9 pect 17-20 usu 19
C.
tortugae: Acero: 10/10 pect 18-20
C. bol:
Victor 2008: 10/10 pect 18-20
C.
eidolon: Randall: 10 (11 was typo)/9-10,
mode 10 pect 19-20, rare 18 Bohlke: 10/10,
rare 9 pect 19-20
C.
thrix: Bohlke: 9-10/10 pect 17-19
C.
dicrus: Randall: 10/10 pect 18-20 Bohlke:
10/10 pect 18-20
10+ group
C. punctipectophorus: Bohlke: 11/10 pect 18-20
(South Carolina to the Gulf of Mexico)
C.
venezuelae: Cervigon: 11/11 pect 18-20
(Venezuela: Cubagua and Isla Margarita; often
12 dorsal and/or anal fin elements)
C.
personatus: divided pelvic fins, Randall:
10-11/10-11 pect 14-16 Bohlke: 10-11, mode
11/10-11, mode 11 pect 14-16
C.
hyalinus: divided pelvic fins, (same as
C.
personatus, although perhaps usu 10/10?)
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the Coryphopterus
"sand-gobies"
pretransitional larval stages: |
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| The
many Coryphopterus gobies that live on sand
share a suite of characters as larvae and most cannot
be separated without individualized barcode sequencing.
Some species do have one more or less in the modal
fin-ray counts, however, given the variation in
fin ray counts within species, this would not be
a definitive character. |
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| Rather
than repeating the same description for all of these
species, I describe the pretransitional larval stages
here and leave the transitional and subsequent stages
to the species entries below. |
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| Analogues:
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| Description:
Body relatively thin, long and narrow with a large
eye and a terminal mouth. Paired fins medium to
long at transition, dorsal and anal fin bases relatively
short, caudal peduncle long and narrow, procurrent
caudal fin rays 7-10 (7-8 spindly). Lightly marked
mostly along the lower body: melanophores on the
ventral midline at the isthmus and the pelvic fin
insertion (usually streaks). Rare variants (sp.?)
have a melanophore on the abdominal midline promontory
just forward of the vent. There is a row of melanophores
along the anal fin base, usually five, paired and
one per side between the third and eighth element
(often merged into a streak on each side). Then,
after a space, there is a row of midline melanophores,
usually seven or eight unpaired (but often merged
into a streak) extending along the ventral caudal
peduncle ending near the start of the procurrent
caudal fin rays. Melanophores are typically present
on the base of several (usually 4 or 5) of the lower
segmented caudal fin rays extending up to halfway
out along the rays. The majority of larvae have
one (often none or two, occasionally three or four)
melanophores on the dorsal midline just after the
last dorsal fin ray (proportions vary greatly between
collections). Some have an additional small melanophore
off-center of the dorsal midline near the base of
some of the mid-soft dorsal fin rays. Many have
melanophores on the distal membranes between the
anal fin rays, usually between the second and sixth
elements (the true frequency cannot be ascertained
since many fins are frayed). Internal melanophores
are present in the head at the base of the saccule
and there is often one above the saccule and sometimes
several around the rear braincase, along the dorsal
surface of the swim bladder and around the gut near
the vent. Most individuals have a melanophore at
the angle of the jaw, however less-developed larvae
are often missing them (but they do have caudal
fin melanophores, separating them from C.
personatus). |
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| Early-stage
larvae before the completion of all of the fin elements
have a dorsal and ventral indentation in the iris,
with some later-stage larvae retaining a dorsal
indentation in the iris. Series of transitional
larvae show development of the eye from a moderately-narrowed
vertical oval, often somewhat squared-off, with
a small posterior-inferior extension of the iris,
to round. The extension has no surface melanophores
overlying it, or, at most, a single small melanophore
at the dorsal edge (vs. C.
personatus, see comparative photograph under
C.
personatus). Rare individuals show abnormal
enlargements of this extension (intriguingly, sometimes
including several in the same collection).
There is often a prominently speckled "eyebrow"
membrane over the upper half and posterior of the
eyeball that appears detached from the pigmented
iris below. |
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| Although
the length of the pelvic rays are an important character
as adults, larvae and juveniles typically have the
innermost pelvic fin ray slightly shorter or about
equal in length to the next ray. The pelvic frenum
is not usually visible, but may develop on all juveniles
in the group (see C.
dicrus). Larvae typically have fused pelvic
fins, and the species with divided pelvic fins likely
develop the division after transition (unknown for
C.
alloides, but confirmed for C.
lipernes and C.
personatus). |
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| Transitional
larvae show a variety of patterns of development
of body and fin melanophores. Most species develop
two stripes of melanophores behind the eye, the
upper eye stripe and the mid-eye stripe, separated
by a patch of small iridophores. There are also
a few large iridophores on top of the brain. Then
a divergence occurs with the most common type developing
an interorbital midline melanophore stripe (some
variants continue to develop other transitional
markings without interorbital melanophores until
later). A patch of melanophores develops at the
top edge of the pectoral fin. Two patches develop
along the dorsal midline of the body between the
head and the dorsal fin (some do not develop these
latter patches until much later). Patches of melanophores
develop along the base of the dorsal fin: three
along the first dorsal and then three patches spaced
out along the base of the second dorsal fin. |
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| Coryphopterus
sp. 10/10 larva |
| 4.2 mm SL |
| early-stage with rounded
eye |
| San Blas, Panama, SB86-927 |
|
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| Coryphopterus
sp. 10/10 larva |
| 6.5 mm SL |
early stage with narrow
eye
and dorsal iris indentation |
| San Blas, Panama, SB86-512 |
|
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| Coryphopterus
sp. 10/10 larva |
| 7.2 mm SL |
| with slightly narrowed
eye |
| San Blas, Panama, SB86-426 |
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| Coryphopterus
sp. 10/10 larva |
| 7.4 mm SL |
| with round eye |
| San Blas, Panama, SB86-426 |
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| Coryphopterus
sp. 10/10 larva |
| 7.2 mm SL |
squarish eye, membrane
above eyeball,
braincase melanophores (left-sided visible) |
| San Blas, Panama, SB87-219 |
|
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| Coryphopterus
sp. 10/10 larva |
| 7.3 mm SL |
| speckled membrane above
eyeball |
| San Blas, Panama, SB86-1103 |
|
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| Coryphopterus
sp. 10/10 larva |
| 7.5 mm SL |
| with anal fin ray membrane
melanophores |
| San Blas, Panama, SB86-1124 |
|
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| Coryphopterus
sp. 10/10 larva |
| 6.6 mm SL |
innermost pelvic fin
ray equal to next,
with abdominal promontory melanophore |
| San Blas, Panama, SB86-1103 |
|
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| Coryphopterus
sp. 10/10 larva |
| 5.9 mm SL |
| internal melanophores |
| San Blas, Panama, SB86-404 |
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| Coryphopterus
sp. 10/10 larva |
| 6.3 mm SL |
| small and thin, but
with round eye |
| San Blas, Panama, SB84-522 |
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| Coryphopterus
sp. 10/10 larva |
| 7.0 mm SL |
| innermost pelvic fin
rays equal to next |
| San Blas, Panama, SB84-617 |
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| Coryphopterus
sp. 10/10 larva |
| 7.0 mm SL |
| variant with short
patch of anal fin melanophores |
| Barbados, HV 8-04-02
SB86-805 |
|
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| Coryphopterus
sp.
10/10 larva |
| 6.6 mm SL |
| San Blas, Panama, SB86-805 |
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| Coryphopterus
sp. 10/10 larva |
| 8.6 mm SL |
| large-sized, extreme
one percent |
| San Blas, Panama, SB86-805 |
|
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| Coryphopterus
sp. 10/10 larva |
| 7.0 mm SL and 7.1 mm
SL |
variant with melanophore
on promontory
forward of vent, pect-18 |
| San Blas, Panama, SB86-1004 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 6.3 mm SL |
| San Blas, Panama, SB83-151 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 7.2 mm SL |
variant with transitional
markings only
at spinous dorsal fin |
| San Blas, Panama, SB87-221 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 6.6 mm SL |
transitional variant?
no anal fin base or caudal fin melanophores:
D-VI,10 A-10 Pect-18 |
| Banco Chinchorro, Mexico,
coll. D. Jones |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 7.6 mm SL |
| San Blas, Panama, SB86-426 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 7.2 mm SL |
| San Blas, Panama, SB86-424 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 6.6 mm SL |
| typical type, head
iridophore pattern |
| San Blas, Panama, SB86-416 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 6.6 mm SL |
| note head neuromasts
developing |
| San Blas, Panama, SB86-1010 |
|
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| Coryphopterus
sp. 10/10 transitional larva |
| 8.6 mm SL |
transitional variant,
the only dorsal body
melanophores along first dorsal fin spine
D-VI,10 A-10 Pect-19 |
| San Blas, Panama, SB86-627a |
|
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| Coryphopterus
sp. 10/10 larva |
| abnormal posterior
extension of the iris |
| San Blas, Panama, SB83-151 |
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| Coryphopterus glaucofraenum |
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| Diagnosis:
Modal fin ray counts of D-VI,10 A-10 and
Pect-18-20 with fused pelvic fins indicate a group
of very similar gobies (the six 10/10 sand gobies)
comprising Coryphopterus glaucofraenum, C.
tortugae, C.
bol, C.
eidolon, C.
thrix, and C.
dicrus. Large
juveniles and adults of the 10/10 sand-goby
clade are separated by the presence or absence of
a pelvic frenum, the relative length of the innermost
pelvic fin rays, and by markings. In C. glaucofraenum,
the pelvic fin has a frenum and the innermost pelvic
fin rays are about equal in length to the next ray
(slightly shorter or longer). The suite of markings
that identify adult C. glaucofraenum include
a two-pronged dorsal projection on the mid-eye stripe,
two round colon-like spots at the caudal-fin base
(sometimes joined by a constricted bridge but with
the tips distinctly rounded), and no 8 o'clock bar
of melanophores to the mid-maxilla. The lower pectoral
fin base marking pattern varies considerably, from
none to some speckling or sometimes a full stripe. |
|
| Juveniles:
The 10/10 sand goby clade share fin ray counts,
morphology, and most markings as larvae and new
recruits. C. glaucofraenum only begin to
diverge when they develop the distinctly-rounded
colon spots at the base of the caudal fin. The diagnostic
two-pronged dorsal projection on the mid-eye stripe
develops only on adults. |
|
| Analogues:
|
|
| Description:
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| Coryphopterus
glaucofraenum juvenile |
| 12.9 mm SL |
| San Blas, Panama, SB82-054 |
|
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| Diagnosis:
Modal fin ray counts of D-VI,10 A-10 and
Pect-18-20 with fused pelvic fins indicate a group
of very similar gobies (the six 10/10 sand gobies)
comprising Coryphopterus tortugae, C.
glaucofraenum, C.
bol, C.
eidolon, C.
thrix, and C.
dicrus. Large juveniles and adults of the
10/10 sand-goby clade are separated by the presence
or absence of a pelvic frenum, the relative length
of the innermost pelvic fin rays, and by markings.
In C. tortugae, the pelvic fin has a frenum
and the innermost pelvic fin rays are about equal
in length to the next ray (slightly shorter or longer).
The suite of markings that identify adult C.
tortugae include a triangular vertex-upward
dorsal projection on the mid-eye stripe, a broken
upper eye-stripe with rounded midline spots on the
head not linked by a chain pattern of melanophores,
no discrete lower pectoral-fin base spot, no rounded
spots at the caudal-fin base, and no 8 o'clock bar
of melanophores to the mid-maxilla. |
|
| Juveniles:
The 10/10 sand goby clade share fin ray counts,
morphology, and most markings as larvae and new
recruits. C. tortugae only begin to diverge
when they develop rounded midline head spots with
a broken upper-eye stripe, without rounded spots
on the base of the caudal fin (vs. C.
glaucofraenum), without an 8 o'clock bar
of melanophores to the mid-maxilla (vs. C.
eidolon and C.
thrix) and without melanophores on the lower
third of the pectoral fin base (vs. C.
bol, C.
eidolon, C.
thrix, C.
dicrus, and some C.
glaucofraenum.) |
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| Analogues:
|
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| Description:
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|
|
| Diagnosis:
Modal fin ray counts of D-VI,10 A-10 and
Pect-18-20 with fused pelvic fins indicate a group
of very similar gobies (the six 10/10 sand gobies)
comprising Coryphopterus bol, C.
glaucofraenum, C.
tortugae, C.
eidolon, C.
thrix, and C.
dicrus. Large
juveniles and adults of the 10/10 sand-goby
clade are separated by the presence or absence of
a pelvic frenum, the relative length of the innermost
pelvic fin rays, and by markings. In C. bol,
the pelvic fin has a frenum and the innermost pelvic
fin rays are about equal in length to the next ray
(slightly shorter or longer). The suite of markings
that identify adult C. bol include a triangular
dorsal projection (vertex-up) on the mid-eye stripe,
a discrete lower pectoral-fin base spot, a complete
upper eye-stripe with a chain pattern of melanophores
along the top of the head, a bar or thick C-shaped mark
(not rounded spots) at the caudal-fin base, and
no 8 o'clock bar of melanophores to the mid-maxilla. |
|
| Juveniles:
The 10/10 sand goby clade share fin ray counts,
morphology, and most markings as larvae and new
recruits. C. bol only begin to diverge when
they develop melanophores on the lower third of
the pectoral fin base (vs. C.
tortugae), without rounded colon-like spots
on the base of the caudal fin (vs. C.
glaucofraenum), without an 8 o'clock bar
of melanophores to the mid-maxilla (vs. C.
eidolon and C.
thrix), and without the upper-eye stripe
broken up into a series of short segments (vs. C.
dicrus). |
|
| Analogues:
|
|
| Description:
|
|
|
| Coryphopterus
bol transitional recruits |
| 9.0 and 9.5 mm SL,
DNA confirmed ID |
| innermost pelvic fin
ray equal to next |
| Noronha, Brazil, FN01 |
|
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| |
 |
| |
 |
Coryphopterus
bol
late transitional recruit |
| 7.4 mm SL |
| Barbados, V05-R20,
coll. H. Valles |
|
 |
| Coryphopterus
bol |
| 7.9 mm SL |
| San Blas, Panama, SB82-050 |
|
 |
| Coryphopterus
bol juvenile |
12.5 mm SL, DNA confirmed
ID |
| Noronha, Brazil FN01 |
|
 |
| Coryphopterus
bol juveniles |
| 12.5 to 15.1 mm SL,
DNA confirmed ID |
no stripe on lower
cheek and
equal innermost and next pelvic fin rays |
| Noronha, Brazil FN01 |
|
 |
| |
 |
| |
 |
| Coryphopterus
bol juvenile |
| 22.5 mm SL, DNA confirmed
ID |
| lower pectoral base
spot, complete upper-eye stripe, no 8 o'clock
bar |
| Panama, n7530a |
|
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| |
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|
|
| Diagnosis:
Modal fin ray counts of D-VI,10 A-10 and
Pect-18-20 with fused pelvic fins indicate a group
of very similar gobies (the six 10/10 sand gobies)
comprising Coryphopterus eidolon, C.
glaucofraenum, C.
tortugae, C.
bol , C.
thrix, and C.
dicrus. Large juveniles and adults of the
10/10 sand-goby clade are separated by the presence
or absence of a pelvic frenum, the relative length
of the innermost pelvic fin rays, and by markings.
In C. eidolon, the pelvic fin has a frenum
and the innermost pelvic fin rays are distinctly
shorter than the next ray (often with a notched
edge outline). The suite of markings that identify
adult C. eidolon include a uniform-width
mid-eye stripe (orange outlined in tiny melanophores
in pallid type), an oblique bar of melanophores
from 8 o'clock on the iris to the mid-maxilla (present
although inconspicuous in the pallid type), a short
oblique upward stripe from the corner of the mouth
(also outlined in pallid type), often a discrete
lower pectoral-fin base spot, and no rounded spots
at the caudal-fin base. |
|
| Juveniles:
The 10/10 sand goby clade share fin ray counts,
morphology, and most markings as larvae and new
recruits. C. eidolon diverges early as they
develop a cluster of melanophores over the brain
with no upper-eye stripe or midline stripe on the
top of the head. Furthermore, a prominent melanophore
develops at the 8 o'clock position next to the eye
very early in transition. CT |
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| Analogues:
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| Description:
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| | |
