Biology Reference
In-Depth Information
3.3.2 The elopiformes
The order Elopiformes is composed of two families: the Elopidae
(tenpounders) and the Metalopidae (tarpons) (Nelson, 2006). Adults of
these fi shes have a typical fi sh-like form, rather than being eel-like, but they
possess a leptocephalus larval stage (Fig. 3a). The most notable characteristic
of elopiform leptocephali is the well-developed, forked caudal fi n. The
posterior dorsal and anal fi ns are present and are distinct from the caudal
fi n. The ventral fi ns are formed in the later larval stages. The body height
is relatively narrow. Elopiform leptocephali are the smallest (maximum
length about 3 cm) of the elopomorph groups. The intestine is extremely
long. Myomeres are V-shaped.
3.3.3 The albuliformes
The order Albuliformes is composed of three families: the Albulidae
(bonefi shes), the Halosauridae (halosaurs), and the Nothacanthidae (spiny
eels) (Nelson, 2006). Most of the albulid fi shes are coastal species whereas
fi shes of the other two families are deep-sea inhabitants. The external
appearance of albulid leptocephali resembles that of the elopiforms but
they grow to 60-180 mm, much larger than elopiform leptocephali (Fig. 3b).
Halosaurid leptocephali differ greatly, both in shape and size, compared
with albulid leptocephali. Halosaurid and nothacanthid leptocephali
typically grow to 40-50 cm and, exceptionally, may reach a length of 2 m (Fig.
3c). The caudal fi n is fi lamentous. The body shape is extremely slender. The
base of the dorsal and ventral fi ns is short. The pectoral fi ns are small. The
myomeres are V-shaped. Many halosaurid and nothacanthid leptocephali
remain unidentifi ed at the species level.
3.3.4 The anguilliformes
The Anguilliformes forms the largest group in the Elopomorpha, being
composed of 15 families, 141 genera and 791 species (Table 1, Nelson, 2006),
which includes true eels, moray eels, snake eels, conger eels and so on.
Associated with vast numbers of species, the morphology of anguilliform
leptocephali is diverse (Fig. 3d-f). The size is generally 5-10 cm long, but
may reach 50 cm. The body shape is typically leaf-like. The caudal fi n is
short and round, and is merged with the dorsal and anal fi ns. The ventral fi n
is absent. The myomeres are W-shaped. The intestines are usually straight
and open at the anterior edge of the anal fi n. Some has a pouch-like region
in the intestines or external intestines (Fig. 3f).
