The chaenopsids are an eclectic
group of specialized blennies including the flag, tube, sailfin, arrow and pikeblennies.
They tend to be tiny fishes and are rarely noticed on rocks and pilings as well
as in coral, sand, and grassbeds around Caribbean reefs. Nevertheless, they form a large
family with numerous genera and identifications can be difficult. Many species
have precise habitat requirements and peculiarly narrow geographic ranges and
thus most species' larvae are relatively uncommon and mostly undescribed.
Larval
chaenopsids can be recognized by their often pointed snout, long and continuous
dorsal and anal fins with flexible spines, a very short and narrow caudal peduncle,
long strand-like pelvic fins (usually straight, not curled up over the body),
the absence of spines on the head, and light markings (basically a row of melanophores
along the anal fin base). Larval chaenopsids usually have large round eyes, in
contrast to larval scarids,
labrids, and gobies
in which the eye is often small or narrowed.
Chaenopsids
and their scaled blenny relatives (Labrisomidae)
can share fin ray counts; nevertheless, most chaenopsids have more than 13 dorsal
fin soft rays and 34 or more total dorsal fin elements while regional labrisomids
always have 13 or fewer dorsal fin soft rays and fewer than 34 total dorsal fin
elements. The few Caribbean chaenopsid exceptions that share the low dorsal fin
soft ray count with labrisomids are Coralliozetus
cardonae, Acanthemblemaria
johnsoni (Tobago only?) and A.
rivasi (from the SW Caribbean), Emblemaria
vitta, and the Emblemariopsis
spp.
The genus Stathmonotus
is still considered a chaenopsid even though their dorsal fin is made up of all
spines.
Other similar-appearing
families include the dactyloscopids
with very similar larvae, but with curled pelvic fins, blenniids
with blunt snouts and fewer dorsal fin spines than soft rays (chaenopsids other
than Chaenopsis spp. have
more spines than rays), and tripterygiids
with three separated dorsal fins. Many larval gobies
fit the general labrisomid gestalt, but have separate and very short spinous dorsal
fins with spindly spines, and many have a fused pelvic fin disk as well.
Stathmonotus stahli
Diagnosis:
Modal fin ray counts of D-XLIII-XLIV A-II,24-25 indicate Stathmonotus
stahli. The range of counts can be wide: from 39-45 dorsal fin spines,
23-28 anal fin elements and 8-9 pectoral fin rays. S.
gymnodermis is separated from the other two species by having slightly
fewer anal fin rays (A-II,22-24) and having the dorsal and anal fin membranes
merging only with the base of the caudal fin, not halfway up the fin. There is
an easy separation later in development since S.
gymnodermis is scaleless. S. hemphilli is
separated from the other two species by not having head cirrhi and having more
dorsal spines and fewer pectoral fin rays (45-53 dorsal spines, 25-31 anal fin
elements and only 4-5 pectoral fin rays). (U)
Analogues:
Description:
Body thin long and narrow with a medium eye and a short pointed snout (becoming
blunted at transition). Pectoral and pelvic fins very short, dorsal and anal fin
bases very long, the membranes merging with the caudal fin well above the base
of the caudal rays. Lightly marked: melanophores on the ventral midline at the
isthmus and the pelvic fin insertion and along the base of the anal fin, typically
one for each anal fin soft ray. Internal melanophores occur at the rear of the
brain just below the surface and around the sacculus, along the dorsal surface
of the swim bladder and around the gut near the vent. ((As transition approaches
two irregular rows of large deep melanophores develops in the musculature below
the dorsal and anal fins (diff species?)). Series of transitional larvae show
that the eye remains round. Transitional larvae lose the anal fin row of melanophores
((starting at the front and develop a patch of melanophores at the base of the
central caudal fin rays. A fine uniform speckling appears over the body and the
fins. Patches of fine melanophores develops on the top of the head and behind
the eye and in a bar below the eye, as well as over the mandibular and angle of
the jaw)).
Stathmonotus sp. larva,
7.9
mm SL
(San Blas, Panama, SB86-401)
Stathmonotus sp. larva,
6.8
mm SL
(internal melanophore pattern)
(San Blas, Panama, SB86-827)
Stathmonotus sp. early transitional larvae
7.3 and 7.7 mm SL
(note
caudal fin melanophores and rows of deep body melanophores)
