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Containing group: Cerylonid Series

Introduction

Discolomatidae is a family of small to moderately-sized (2-4 mm) beetles whose members have generally been considered mycophagous or saprophagous, although little is known about their specific biology.  The family includes 16 genera and ~400 species arranged within 5 subfamilies:  Aphanocephalinae, Cephalophaninae, Discolomatinae, Notiophyginae and Pondonatinae.  Discolomatids are distributed throughout the tropical and subtropical regions of the world, with greatest diversity in the Afrotropics and southeastern Asia.    

Adults and larvae are most often collected from under bark (Lawrence 1982, Cline and Gillogly pers. obs.).  However, Parafallia and Holophygus have also been recovered from leaf litter (Cline and Ślipiński in press), Aphanocephalus and Fallia have been collected feeding on the surface of fungi, and Notiophygus and Discoloma species have been recorded from lichens (Lawrence 1991, Cline & Ślipiński in press). 

Within Discolomatidae, several instances of myrmecophily are known. Cline and Ślipiński (in press) reviewed these associations and discussed some of the morphological adaptations in discolomatids likely exhibited by ant inquilines.  At least 3 genera have been recorded in association with ants (Notiophygus, Katoporus and Holophygus).  Cassidoloma has also been collected in association with ants (Shockley and Robertson pers. comm.).  In addition, several other taxa (e.g., Aphanocephalus, Parafallia) possess features which suggest they may also be myrmecophiles; however, no specific associations have been reported.

Characteristics

Adults of this family are easily recognizable among cucujoid beetles.  The lateral margins of the pronotum and elytra are often broadly explanate, both bearing conspicuous tubular gland openings.  In general, the adults can be characterized by the following combination of characters (based on Lawrence 1982, Lawrence et al. 1999a, Cline & Ślipiński in press): 

• Oval to almost circular habitus, typically dorsoventrally flattened to some degree
• Antennae 9 or 10-segmented (8-segmented in Fallia) with a 1-segmented apical club
• Palpomere II of maxillary and labial palpi swollen
• Prothorax with 2 conspicuous tubular gland openings near front and hind angles
• Lateral margins of elytra often broadly explanate, bearing 6 or more tubular gland openings
• Coxae on all legs appear globular and widely separated, but actually transverse and partially internalized, visible coxal cavities small and round
• Tarsi 3-3-3 in both sexes, all tarsomeres and claws simple
• Often wingless

Larvae for this group are poorly known, but described forms are quite distinct from other cucujoid larvae.  Discolomatid larvae can be distinguished from other similar larvae by the following combination of characters (based on Lawrence 1991, Lawrence et al. 1999b, Cline & Ślipiński in press): 

• Body strongly onisciform and flattened
• Dorsum highly sculptured, tuberculate, or granulate
• Head concealed by pronotum, with epicranial stem short or absent, frontal sutures sinuate
• 3 pairs of stemmata
• Antennae long, 2-segmented (segment III absent), sensory appendage moderately long
• Mandibles with aspirate well-developed mola, bearing a broad hyaline prostheca
• Maxillary and labial palpi 2-segmented
• Legs well-developed, 5-segmented with unisetose tarsungulus
• Urogomphi absent

Taxonomy

The family was first erected by Horn (1878) to accommodate the genera Discoloma and Hyberis (=Notiophygus).  The spelling of the name Discolomidae was later justifiably emended to the grammatically correct spelling Discolomatidae (Pakaluk et al. 1994, Lawrence & Newton 1995).  The classification of Discolomatidae was recently reviewed by Cline and Slipinski (in press).  As with many beetle families, most taxonomic works involving discolomatids have historically been limited to single species descriptions or regional works.  Csiki (1910) produced the first world catalogue for Discolomatidae. Blackwelder (1945) listed the neotropical taxa.  However, the Genera Insectorum fascicle by John (1959) remains the most comprehensive treatment of the family.

Relationship of Discolomatidae to Other Cucujoidea

Crowson (1955) placed Discolomatidae (as Discolomidae) within the Cerylonid Series (CS) of Cucujoidea.  From a morphological standpoint and compared to other CS families, Discolomatidae seems the most likely to form a natural group, based on several unique synapomorphies (listed above) that unite its constituent taxa.  However, discolomatids as a group have been variably classified within many other families including Cerylonidae, Coccinellidae, Colydiidae, Corylophidae, Latridiidae, Nitidulidae and Trogossitidae (see Cline & Ślipiński in press for specific references).  Previous cucujoid workers (Lawrence 1991, Ślipiński 1990) have proposed a possible relationship between Cerylonidae (subfamily Murmidiinae) and Discolomatidae based on several morphological features which may be potential synapomorphies uniting the two groups. 

Despite the inclusion of discolomatids in several recent phylogenetic studies, there have been no specific attempts to resolve internal relationships of the family.  However, these studies have yielded interesting hypotheses of sister group relationships between Discolomatidae and the remaining CS families.  Ślipiński & Pakaluk (1991) recovered Discolomatidae in an unresolved polytomy with Cerylonidae (excluding Euxestinae), and three endomychid subfamilies (Anamorphinae, Eupsilobiinae and Merophysiinae) based on two characters (closed mesocoxal cavities and 5 abdominal spiracles) mapped onto an intuitive phylogeny of relationships between the CS families.

The first formal phylogenetic analysis to include Discolomatidae was that of Hunt et al. (2007) using Bayesian analysis of 3 genes (16S, 18S and COI).  In that study, Discolomatidae was recovered as monophyletic but nested within the family Cerylonidae.  Robertson et al. (2008) also recovered Discolomatidae as monophyletic but sister to Cerylonidae using Bayesian analysis of 2 genes (18S, 28S).  Interestingly, parsimony analyses in that study consistently recovered Discolomatidae as sister to a clade comprising Anamorphinae+Corylophidae.  Ślipiński et al. (2009), using maximum parsimony analysis of adult and larval morphological characters, recovered a monophyletic Discolomatidae with variable sister group associations.  Discolomatidae was recovered as sister to a clade comprising Endomychidae+Coccinellidae based on adult characters alone, however the inclusion of larval characters resulted in Discolomatidae being recovered in an unresolved polytomy with Endomychidae, Coccinellidae and Corylophidae.  At present, sister group affinities of Discolomatidae remain far from resolved. 

Other Names for Discolomatidae Horn 1878

• Discolomidae
• Notiophygidae
• Aphanocephalidae
• Vernacular Names: Discolomatid beetles, Discolomid beetles, Mexican hat beetles

References

Blackwelder, R.E. 1945. Checklist of the coleopterous insects of Mexico, Central America, the West Indies and South America. Part 3. Bulletin of the United States National Museum 185: 343-550.

Cline, A.R. and A. Ślipiński. 10.31. Discolomatidae Horn, 1878. In R.G. Beutel and R.A.B. Leschen (eds.). Handbuch der Zoologie. Band IV, Teilband 38, vol. 2. De Gruyter, Berlin. In Press.

Crowson, R.A. 1955. The Natural Classification of the Families of Coleoptera. Lloyd, London. 187 pp.

Csiki, E. 1910. Coleopterorum Catalogus. Pars 18. Fam. Platypsyllidae, Orthoperidae, Phaenocephalidae, Discolomidae, Sphaeriidae. W. Junk, Berlin.

Horn, G.H. 1878. Synopsis of the Colydiidae of the United States. Proceedings of the American Philosophical Society 17: 555-592.

Hunt, T., J. Bergsten, Z. Levkanicova, A. Papadopoulou, O. St. John, R. Wild, P. M. Hammond, D. Ahrens, M. Balke, M. S. Caterino, J. Gomez-Zurita, I. Ribera, T. G. Barraclough, M. Bocakova, L. Bocak, and A. P. Vogler. 2007. A comprehensive phylogeny of beetles reveals the evolutionary origins of a superradiation. Science 318: 1913-1916.

John, H. 1959. Coleoptera Clavicornia. Fam. Discolomatidae (= Notiophygidae). In P. Wytsman (ed.), Genera Insectorum, Fascicle 213. SPRL Impremerie & Editions Mercurius, Brussels.

Lawrence, J. F. 1982. Lathridiidae, pp. 533-534. In S. P. Parker [ed.], Synopsis & Classification of Living Organisms. McGraw Hill, Inc., New York.

Lawrence, J. F. 1991. Lathridiidae (Cucujoidea), pp. 497-498. In F. W. Stehr [ed.], Immature Insects. Volume 2. Kendall/Hunt Publishing Company, Dubuque, IA.

Lawrence, J. F., and A. F. Newton. 1995. Families and subfamilies of Coleoptera (with selected genera, notes, references and data on family-group names), pp. 779-1006. In J. Pakaluk and S. A. Slipinski [eds.], Biology, Phylogeny, and Classification of Coleoptera: Papers Celebrating the 80th Birthday of Roy A. Crowson. Museum i Instytut Zoologii PAN, Warszawa.

Lawrence, J. F., A. M. Hastings, M. J. Dallwitz, T. A. Paine, and E. J. Zurcher 1999a. Beetles of the World: A Key and Information System for Families and Subfamilies. CD-ROM, version 1.0 for MS-Windows. CSIRO Publishing, Melbourne.

Lawrence, J. F., A. M. Hastings, M. J. Dallwitz, T. A. Paine, and E. J. Zurcher 1999b. Beetle Larvae of the World: Descriptions, Illustrations, Identification, and Information Retrieval for Families and Sub-families. CD-ROM, version 1.1 for MS-Windows. CSIRO Publishing, Melbourne.

Pakaluk, J., S. A. Slipinski, and J. F. Lawrence. 1994. Current classification and family-group names in Cucujoidea (Coleoptera). Genus 5: 223-268.

Robertson, J.A., M.F. Whiting and J.V. McHugh. 2008. Searching for natural lineages within the Cerylonid Series (Coleoptera: Cucujoidea). Molecular Phylogenetics and Evolution 46 (1): 193-205.

Ślipiński, S.A. 1990. A monograph of the world Cerylonidae (Coleoptera: Cucujoidea) Part I—introduction and higher classification. Ann. Mus. Civ. Stor. Nat. ‘‘Giacomo Doria’’ 33: 1–273.

Ślipiński, S. A., and J. Pakaluk. 1991. Problems in the classification of the Cerylonid series of Cucujoidea (Coleoptera), pp. 79-88. In M. Zunino, X. Belles and M. Blas [eds.], Advances in Coleopterology. AEC, Barcelona.

Ślipiński, A., W. Tomaszewska and J.F. Lawrence. 2009. Phylogeny and classification of Corylophidae (Coleoptera: Cucujoidea) with descriptions of new genera and larvae. Systematic Entomology 34: 409-433.