Spiracles of Adult Scarabaeoidea (Coleoptera) and Their Phylogenetic Significance. II. Thoracic Spiracles and Adjacent Sclerites1

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Abstract
The concealed mesothoracic spiracles of adult Scarabaeoidea have the same types of immobile filter apparatusas abdominal spiracles but usually differ in having amedial extension of the peritreme and have a different type of closing device. Associated with the mesothoracic spiracles are 1 or more setiferous intersegmentalia. Meta thoracic spiracles are simple in structure, have movablelips, and are unlike either mesothoracic or abdominal spiracles. Evolutionary trends found in mesothoracic spiracles are the development of a porous or solid filter apparatus from separate atrial spines, a reduction in the size of the spiracular opening, and a reduction in the number of intersegmentalia from several on each side to a median, setiferous sclerite. Many of the structures found in both mesothoracic spiracles and intersegmentalia appear to have taxonomic value. The degree of specialization found in both mesothoracic and abdominal spiracles and in adjacent structures is summarized. Pleocoma and the Lucanidae are the least specialized Scarabaeoidea; other less specialized groups are Passalidae, Troginae, Geotrupinae, Taurocerastinae, Oncerinae (Oncerus), Acoma, Podolasia, Glaphyrinae, Acanthocerinae, Ochodaeinae, and Allidostominae. Melolonthinae, Dynastinae, Rutelinae, and Cetoniinae are the most specialized groups.

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