TAXONOMIC CLASSIFICATION
Taxonomy is the practice and science of classification. Taxonomies, or taxonomic schemes, are composed of taxonomic units known as taxa (singular taxon), or kinds of things that are arranged frequently in a hierarchical structure. Originally the term taxonomy referred to the classifying of living organisms (now known as alpha taxonomy); however, the term is now applied in a wider, more general sense and now may refer to a classification of things, as well as to the principles underlying such a classification.

HIGHER CLASSIFICATION OF BIOLUMINESCENT BEETLES
Representing 40% of all insects, beetles are one of the most successful organisms on the planet. All beetles belong to the order Coleoptera and a number of physical features define beetles but most prominent is the presence of elytra, heavily sclerotized forewings which protect the hindwings and abdomen. There are approximately 370,000 described species which makes Coleoptera the largest order of organisms. This vast number of species makes classification a particular problematic discipline.

Currently the order Coleoptera is divided into four principle groups or suborders which are:
• The Archostemata is the smallest suborder of beetles comprising of less than 50 specialized wood boring species.
• The Myxophaga are a small enigmatic group of around 65 species with specialized aquatic and semi-aquatic lifestyles. These are minute beetles often no more than 2mm in length.
• The Adephaga include the predaceous ground beetles and aquatic beetles and comprise 10% of all beetles or 36,000 known species.
• The Polyphaga is the largest group comprising 90% of all beetle species. These species as the name suggests exhibit a diversity of feeding habits.

All bioluminescent beetles are members of the Poylphaga.

ELATERIFORMIA
Subdivided into some 40 extant families the series Elateriformia is one of the major groups of beetles within the suborder Polyphaga containing around 40,000 species. All bioluminescent beetles, with the exception of one species are contained within the Elateriformia. Bioluminescence in the series Elateriformia is currently classified as occurring in Elateridae and four other families: Omalisidae, Rhagophthalmidae, Phengodidae and Lampyridae which originally belonged to the superfamily Cantharoidea. Originally a part of the Malacoderma the superfamily Cantharoidea was revised by Crowson in 1972 and latter combined into the Elateroidea when Lawrence (1988) redefined Elateriformia. As a result all bioluminescent beetles, with the exception of the single staphilinid species, are now currently contained within a single superfamily - Elateroidea.

FAMILY LAMPYRIDAE
The majority of bioluminescent beetles are found in the family Lampyridae containing approximately 2000 species divided into 100 genera. The Lampyridae are commonly known as the fireflies, lightning bugs or glow-worms and are probably the most conspicuous of all biolumienscent beetles. With the exception of the antarctic, they are found throughout all the ecozones of the world.

In 1966 McDermott, in his revision of E. Olivier’s Lampyridae Catalog of 1910, listed 1891 lampyrid species and 92 genera. These were divided by Mcdermott into seven subfamilies: Lampyrinae, Photurinae, Luciolinae, Otottretinae, Mathetinae, Pterotinae and Rhagophthalminae. The current classification of the subfamilies within the Lampyridae is based upon gross similarities e.g. the degree of retractability of the head under the pronotum or the morphology and the position of adult light organs, if indeed they are present.

FAMILY RHAGOPTHALMIDAE
Within the cantharoid group the Lampyridae, Phengodidae and Rhagophthalmidae have often been regarded as closely related. This is illustrated by the history of species within the Rhagophthalmidae. Olivier (1910) erected the family Rhagophthalmidae for Rhagophthalmus and the similar genera Dioptoma and Ochotyra (now synonymized with Rhagophthalmus). Olivier moved Rhagophthalmus to the Lampyridae in 1911 which was accepted by McDermott and subsequently the members of the Rhagophthalmidae were contained within a new subfamily of Lampyridae the Rhagophthalminae (McDermott, 1964, 1966). However Crowson in 1972 moved Rhagophthalminae to the Phengodidae which was accepted by Lawrence and Newton (1995) and supported by recent phylogenetic data (Bocakova et al., 2007).

It was not until much later that Wittmer and Ohba resurrected the Rhagophthalmidae as a separate family (Wittmer & Ohba, 1994). This was supported by morphological observations (Branham & Wenzel, 2001; 2003) and luciferase gene data (Ohmiya et al. 2000). However, analysis of the mitochondrial 16S gene sequence (Suzuki, 1997) and embryonic data (Kobayashi et al., 2001; 2002; 2003) support McDermott's proposal that Rhagophthalmidae should be treated as a subfamily of Lampyridae. However, Suzuki excluded any members of the Phengodidae and was also dependent on a single locus for his phylogeny. Despite the controversial placement of Rhagophthalmidae species it is undisputed that there is a close relationship between these three families.

FAMILY PHENGODIDAE
All members of the family Phengodidae are bioluminescent and are limited to a Nearctic and Neotropical distribution ranging from southern Canada to Chile. Known as glowworm beetles, due to the larviform females, they are also referred to as railroad worms due to their spectacular paired photic organs located on each body segment which resemble the windows of train carriages.

The Phengodidae was first listed as a family by Leng (1920) who listed four tribes: Pterotini, Phengodini, Mastinocerini and Omethini. Green (1948) removed the Pterotini and placed it into the Lampyridae. The Omethini were later removed to its own family, the Omethidae, by Crowson (1972). The Phengodidae contain approximately 25 genera of which six genera are found in the Nearctic. Around 181 species are currently described. More information on the Phenogidae can be found here.

References

Bocakova, M., Bocak, L., Hunt, T., Teraväinen, M., Vogler, A.P. (2007) Molecular phylogenetics of Elateriformia (Coleoptera): evolution of bioluminescence and neoteny. Cladistics 23, 477-496.
Branham MA, Wenzel JW (2001) The evolution of bioluminescence in cantharoids (Coleoptera: Elateroidea). Florida Entomologist 84, 565-586.
Branham MA, Wenzel JW (2003) The origin of photic behavior and the evolution of sexual communication in fireflies (Coleoptera: Lampyridae). Cladistics 19, 1-22.
Green JW (1948) Two new species of Lampyridae from southern Florida, with a generic revision of the Nearctic fauna. Transactions of the American Entomological Society 74 61-73.
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McDermott FA (1966) Lampyridae. In: Steel WO Coleopterorum Catalogus, Suppleminta (9), pp 1–149. W. Junk, Gravenhague.
Ohmiya Y, Sumiya M, Viviani VR, Ohba N (2000) Comparative aspects of a luciferase molecule from the Japanese luminous beetle, Rhagophthalums ohbai. Science Report of the Yokosuka City Museum 47, 31–38.
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