Form elongate oval. Labrum and mandibles prominent, produced beyond apex of clypeus, clypeus with or without weak horn. Antenna with 9 segments, antennal club with 3 segments, segments not tomentose. Anterior coxae transverse. Pronotum with or without anterior projections. Scutellum exposed. Metasternum longer than abdominal sternites. Metatibia with apical spines separated by basal metatarsal segment (Aclopus) or not (mesad and adjacent in Neophaenognathus). Tarsal claws on all legs not independently movable, claws equal in length or size, claws with a weak basal tooth. Onychium cylindrical with 2 setae. Pygidium exposed beyond apices of elytra. According to Arrow (1909) the genitalia are poorly sclerotized and do not provide characters for identification.

Classification Status
The subfamily Aclopinae was established by Blanchard 1850. It originally included two genera, Aclopus Erichson and Phaenognatha Hope. These two genera were placed in Glaphyridae by Erichson (1845-1847) and moved to the Melolonthinae by Lacordaire based on the position of the spiracles. Later Arrow (1909) found that the spiracles of one species Aclopus brunneus Erichson were of the laparostict type, condition in which most of the spiracles are on the pleural membrane between on the tergites and sternites and it is characteristic of scarabs that feed on dung, carrion hides or feathers (i.e. Scarabaeinae, Aphodiinae); the alternative is the pleuristic condition where most of the abdominal spiracles are situated in the upper portion of the sternites present in scarabs that feed primarily on leaves, roots, or decaying wood (i.e. Rutelinae, Dynastinae, and Cetoniinae). However, Ohaus (1909) found that the spiracles of the male were situated in the membranes connecting the dorsal and ventral segments (laparostict type), but the last four spiracles of the female were situated in the chitin of the ventral segments (pleurostict type). According to Arrow (1909) this difference may be due to the possible fact that the females are flightless. In 1915 Arrow described a third genus, Xenaclopus, with one species, X. borneensis Arrow, from Borneo. Iablokoff-Khnzorian (1977) hypothesized that the Aclopinae are most closely related to the Hybosorinae, Ochodaeinae, and "Loxsticti" (Euchirinae, Cetoniinae, Dynastinae, Rutelinae). Allsopp (1981, 1983) revised the Australian species and created a new genus, Neophaenognatha, for the New World species of Phaenognatha. Nikolajev (2004-2005) was the last to treat the group, he divided the subfamily in two tribes, Aclopini includding all extant taxa plus two monotypic genera from the Jurassic and Cretaceous respectively, and Holcorobeini that includes four genera and 17 fossil species. These records make the Aclopinae among the oldest groups of Scarabaeoidea. Although the systematic placement of the fossil taxa (at least some) included in Nikolajev´s paper as Aclopinae (Nikolajev 1992, 2004, 2005) are very doubtfull, if they are in fact aclopines, Aclopinae would be among the oldest scarabs ever recorded in literature. These fossil records place the origin of the subfamily Aclopinae and Scarabaeoids back to minimum of 144 mya (see Krell 2000).

The subfamily includes four genera and 19 species that are distributed in northern Australia, Borneo, and southern South America (Allsopp 1983). Two genera occur in the New World: Neophaenognathus (4 species) and Aclopus (6 species). Catalog: Arrow 1912.

New World Genera of Aclopinae
Neophaenognatha Allsopp 1983
Includes four species distributed in Argentina (Allsopp 1983).

Erichson 1835
Includes six species that are distributed Brazil and Argentina.

Little is known of the ecology and biology of this small group of scarabs. In Australia, adults of Phaenognatha are usually taken at lights (Lawrence and Britton 1991). Although few female specimens of Aclopinae are known and no literature exists regarding females, Arrow (1909) noted that certain morphological characters suggest that females may be flightless. Allsopp (1983) also noted character similarities that the Aclopinae share with other scarabaeoids that spend most of their lives below ground, including reduced posterior wings and posterior tarsi, inflated abdomen, and absence of a clypeal horn.

Larvae of the Aclopinae have not been described.

References Cited
ALLSOPP, P. G. 1981. Revision of the Australian species of Phaenognatha Hope (Coleoptera: Scarabaeidae: Aclopinae). Journal of the Australian Entomological Society 20: 185-195.

ALLSOPP, P. G. 1983. Neophaenogantha, a new genus for the Neotropical species of Phaenognatha Hope (Scarabaeidae: Aclopinae) with the description of N. capella n. sp. and designation of lectotypes. Coleopterists Bulletin 37(3): 208-211.

ARROW, G. J. 1909. XV. On the characters and relationships of the less-known groups of Lamellicorn Coleoptera, with descriptions of new species of Hybosorinae, etc. Transactions of the Entomological Society of London 57: 479-507.

ARROW, G. J. 1912. Scarabaeidae: Pachypodinae, Pleocominae, Aclopinae, Glaphyrinae, Ochodaeinae, Orphninae, Idiostominae, Hybosorinae, Dynamopinae, Acanthocerinae, Troginae. Coleopterorum Catalogus pars 43, W. Junk, Berlin. 66 pp.

BLANCHARD, E. in MILNE-EDWARDS ET AL. 1850. Museum d'Histoire Naturelle de Paris: Catalogue de la Collection Entomologique. Classe des Insectes, Ordre des Coleopteres. Vol. 1. Gide & Baudry, Paris. 240 pp.

ERICHSON, W. F. 1845-1847. Natureschichte der Insecten Deutschlands. Erste Abtheilung, Coleoptera, Vol. 3: 1-800. Verlag der Nicolaischen Buchhandlung, Berlin.

Uber die Phylogenie der Lamellicornia (Insecta, Coleoptera). Entomolo. Abh. (Dresden) 41: 135-200.

LAWRENCE, J. F. and E. B. BRITTON. 1991. Coleoptera. The Insects of Australia, 2nd edition, Volume 1, , pp. 543-683. Melbourne University Press, Carlton.

LAWRENCE, J. F. AND A. F. NEWTON, JR. 1995. Families and subfamilies of Coleoptera (with selected genera, notes, and 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. Muzeum i Instytut Zoologii PAN, Warszawa, Poland.