Scopelomorpha

Introduction

As currently recognized the Scopelomorpha comprises two lineages of markedly different size; the morphologically generalized Neoscopelidae (blackchins) with only five species, and the highly specialized Myctophidae (lanternfishes) containing some 230-250 species. Together these two lineages comprise a somewhat heterogeneous assemblage of deep-sea pelagic and benthopelagic fishes distributed in tropical and subtropical regions of all three major oceans. Sometimes they are collectively referred to as "lanternfishes" in reference to one of the most immediately striking features of most members of the clade i.e., luminescent organs. The most prominent and widespread of these being the pearl-like photophores that are arrayed in characteristic patterns over their bodies.

What little is known of the biology of the neoscopelids is summarized in Nafpaktitis (1977), while good summaries of the general biology of the far better studied myctophids are to be found in Paxton (1972); Paxton et al. (1984) and Nafpaktitis et al. (1977).

Scopelomorph monophyly

A close association between the neoscopelid and myctophid fishes has long been referenced in the taxonomic literature. Yet it is only relatively recently that there have been any attempts to critically appraise the question of scopelomorph monophyly. Contrary to some dissenting opinions, most notably those of R.K. Johnson (1974, 1982), Okiyama (1984) and Rosen (1985), Stiassny (1996) presents a broad overview of scopelomorph relationships in which she argues that the weight of anatomical evidence overwhelmingly supports the hypothesis of a monophyletic Scopelomorpha (Myctophiformes) as the sister-taxon to the diverse and species-rich Acanthomorpha (Stiassny, 1986).

Characters supporting scopelomorph monophyly discussed by Stiassny (1996) include the presence of a median dorsal keel on the mesethmoid, the reduction or absence of the first levator externus muscle, the presence of a toothplate fused to the proximal face of the fourth ceratobranchial, the presence of a pair of enlarged cone-like parapophyses on the first vertebral centrum, and the presence of an adipose fin support penetrating the supracarinalis posterior musculature.

Other Names for Scopelomorpha

• Blackchins and Lanternfishes

References

Johnson, R.K. (1974). A revision of the alepisauroid family Scopelarchidae (Pisces, Myctophiformes). Fieldiana, Zool. (N.S.) 66: 1-249.

Johnson, R.K. (1982). Fishes of the families Evermanellidae and Scopelarchidae: Systematics, morphology, interrelationships, and zoogeogrphy. Fieldiana, Zool. (N.S.) 12: 1-252.

Moser, H.G., Ahlstrom, E.H., and Paxton, J.R. (1984). Myctophidae: Development. In "Ontogeny and Systematics of Fishes" (H.G. Moser, W.J. Richards, D.M. Cohen, M.P. Fahay, A.W. Kendall, Jr., and S.L. Richardson, eds), Spec. Publ. No. 1: 218-239. American Society of Ichthyologists and Herpetologists, Lawrence, KS.

Nafpaktitis, B.G. (1977). Family Neoscopelidae. In "Fishes of the Western North Atlantic". Sears Found. Mar. Res., Mem. No. 1, Part 7: 1-12. Yale University, New Haven, CT.

Nafpaktitis, B.G., Backus, R.H., Craddock, J.E., Haedrick, R.L., Robinson, B.H., and Karnella, C. (1977). Family Myctophidae. In "Fishes of the Western North Atlantic". Sears Found. Mar. Res., Mem. No. 1, Part 7: 13-265. Yale University, New Haven, CT.

Okiyama, M. (1984). Myctophiformes: Relationships. In "Ontogeny and Systematics of Fishes" (H.G. Moser, W.J. Richards, D.M. Cohen, M.P. Fahay, A.W. Kendall, Jr., and S.L. Richardson, eds), Spec. Publ. No. 1: 254-259. American Society of Ichthyologists and Herpetologists, Lawrence, KS.

Paxton, J.R. (1972). Osteology and relationships of the lanternfishes (Family Myctophidae). Bull. Nat. Hist. Mus. L.A. Cty. 13: 1-81..

Paxton, J.R., Ahlstrom, E.H., and Moser, H.G. (1984). Myctophidae: Relationships. In "Ontogeny and Systematics of Fishes" (H.G. Moser, W.J. Richards, D.M. Cohen, M.P. Fahay, A.W. Kendall, Jr., and S.L. Richardson, eds), Spec. Publ. No. 1: 239-244. American Society of Ichthyologists and Herpetologists, Lawrence, KS.

Rosen, D.E. (1985). An essay on euteleostean cladssification. Amer. Mus. Novit. 2827: 1-57.

Stiassny, M.L.J. (1986). The limits and relationships of the acanthomorph teleosts. J. Zool. (B) 1: 411-460.

Stiassny, M.L.J. (1996). Basal ctenosquamate relationships and the interrelationships of the myctophiform (scopelomorph) fishes. In "Interrelationships of Fishes" (Stiassny, M.L.J., Parenti, L.R. and G.D. Johnson, eds). : 405-426. Academic Press, San Diego, CA.