Elateriformia (Coleoptera) Larvae
(= Elminthidae, Helminthidae).
Elmidae is a cosmopolitan family.
All elmid larvae are fully aquatic, obtaining oxygen through the anal gills, which are extruded when the operculum is opened. They occur in a variety of habitats, but commonly inhabit shallow moving water, where they feed on algae, diatoms and decaying plant material among substrates of gravel and rock. Some species are commonly found on water-logged wood or among roots and moss at the stream edge.
Böving, A. G. and Craighead, F. C. (1931). An illustrated synopsis of the principal larval forms of the order Coleoptera. Entomologica Americana (New Series) 1: 1–351, 125 pls.
Brown, H. P. (1991). Elmidae (Dryopoidea), pp 404–407 in Stehr, F. W. (ed.), Immature Insects. Vol. II. Kendall Hunt: Dubuque, Iowa.
Costa, C., Vanin, S. A. and Casari-Chen, S. A. (1988). Larvas de Coleoptera do Brasil, vi + 282 pp. Museu de Zoologia, Universidade de Sao Paulo: Sao Paulo.
Body. Length less than 3 mm to more than 15 mm. Body not broadly ovate and strongly flattened; relatively straight or only slightly curved ventrally; circular in cross-section to strongly flattened; body, as viewed from above elongate and more or less parallel-sided. Vestiture consisting of fine hairs or setae only, or including bristles, scales, expanded or complex hairs. Dorsal surfaces more or less heavily pigmented or sclerotized; generally granulate or tuberculate. Ventral surfaces more or less heavily pigmented.
Head. Head prognathous or slightly declined; protracted or slightly retracted; not concealed from above by prothorax; narrower than thorax; not forming sclerotized, serrate, wedge-like plate. Head capsule not strongly depressed and wedge-like anteriorly; posterior edge of head capsule not or only slightly emarginate, or distinctly emarginate. Median epicranial region without longitudinal furrow. Epicranial stem absent or very short, or moderately long; straight, not bent to the left. Frontal arms present; V-shaped or U-shaped; not joined anteriorly by transverse line; bases of frontal arms contiguous. Median endocarina absent or coincident with epicranial stem. Paired endocarinae absent or coincident with frontal arms. Number of stemmata one, or five. Number of antennal segments three. Ratio of antennal length to head width 0.15 to 0.50. Sensorium(a) on preapical antennal segment present; shorter than apical segment, or as long as or longer than apical segment. Sensorium(a) on preapical (or apical) antennal segment conical or palpiform. Apex of preapical antennal segment truncate, so that sensorium and apical segment arise together. Antennal base without eversible membranous lobe. Frontoclypeal suture absent or vaguely indicated, or distinct. Labrum separated from head capsule by complete suture; without crenulate emargination. Epipharyngeal rods absent. Mouthparts not forming sucking tube. Mandibles symmetrical; opposable, at least slightly curving mesally at apex; not approximate, diverging and longitudinally divided; broad and stout or more or less wedge-like; without groove or perforation. Apex of mandible broad when viewed from in front (perpendicular to plane of movement); bilobed or bidentate, or trilobed or tridentate. Accessory ventral process of mandible absent. Incisor edge of mandible simple, or with 1 or 2 subapical teeth. Mesal surface of mandibular base with articulated process, or with brush of hairs and articulated process. Mandibular mola absent. Ventral mouthparts retracted. Cardo distinct and sclerotized; undivided; transverse to slightly oblique. Cardines or maxillary bases separated from each other by labium. Stipes longer than wide. Maxillary articulating area absent. Maxilla with articulated galea and fixed lacinia. Mala or galea consisting of a single segment. Apex of mala or galea rounded or truncate; setose or spinose. Apex of lacinia rounded or truncate; setose or spinose. Number of segments in maxillary palp four. First segment of maxillary palp without digitiform appendage. Labium consisting of prementum and postmentum, or consisting of prementum, mentum and submentum. Mentum, postmentum or labial plate completely free or basally connate with maxillae. Postmentum or labial plate subquadrate or trapezoidal, with blunt posterior edge. Postmentum or labial plate not divided longitudinally. Ligula shorter than labial palp, or as long as or longer than labial palp. Ligula simple, not bilobed; without tooth-like sclerome. Number of segments in labial palp two. Labial palps separated by more than width of first palp segment. Hypopharyngeal bracon present. Hypopharyngeal sclerome absent. Hypostomal region present (separating labium from thorax). Hypostomal rods absent. Ventral epicranial ridges present. Gula absent, or wider than long, or longer than wide; gular sutures absent, or separate. Gula or gular region fused to labium, or separated from labium by suture. Occipital foramen not divided by tentorial bridge.
Thorax. Prothorax not or only slightly wider than abdomen; not longer than meso- and metathorax combined. Thoracic terga without patches of asperities; without rows of asperities or carinae. Protergum with 1 or more sclerotized plates. Meso- and metaterga with 1 or more sclerotized plates. Thorax without well-developed lateral tergal processes, or with well-developed lateral tergal processes. Prosternum without armature. Mesocoxae or coxal lobes separated by less than 1 basal coxal diameter, or separated by 1 to 2 basal coxal diameters. Thoracic legs articulated. Number of segments in mesothoracic leg five including pretarsus (claw). Number of segments in mesothoracic leg five or fewer including pretarsus (claw). Legs not highly reduced, more than 0.2 times as long as head width. Metathoracic leg about same size as mesothoracic leg. Meso- and metathoracic legs not forming stridulatory organ. Apical segment of leg acute and claw-like (or consisting of 2 claws). Number of movable pretarsal claws one. Number of setae on pretarsus one. Thoracic spiracles biforous or bilabiate, or reduced and non-functional or absent; not placed at ends of spiracular tubes.
Abdomen. Ratio of length of abdomen (without appendages) to length of thorax 1.2 to 2.0, or more than 2.0. Number of visible abdominal segments ten. Abdominal terga extending laterally beyond edges of sterna; without patches of asperities; without rows of asperities. Abdomen without well-developed lateral processes, or with 1 pair of lateral processes on most segments. Abdominal tergum 3 without transverse dorsal folds or lobes; simple, not divided into transverse dorsal folds or lobes. Paired abdominal glands (openings or porous plates) absent. Dorsal, balloon-like tracheal gills absent. Long and narrow, lateral gills absent. Abdominal sterna without patches of asperities; without rows of asperities. Paired ventral prolegs (or asperity-bearing ampullae) absent. Ventral abdominal gill tufts absent. Abdominal tergum 8 without special armature. Abdominal apex without respiratory chamber. Abdominal segment 9 excluding appendages much longer than segment 8. Abdominal tergum 9 not forming articulated plate; extending onto ventral surface; without paired processes or urogomphi; without median process or terminal disc. Abdominal sternum 9 partly or entirely exposed; simple or apparently absent; not enclosed by sternum 8. Abdominal apex with ventrally hinged operculum. Abdominal segment 10 without oval lobes separated by longitudinal groove; concealed from above, sometimes membranous or more or less fused to segment 9; without asperated, tubular holdfast organs. Paired pygopods on segment 10 absent. Anal region posteroventrally oriented, or ventrally oriented. Anal gill tufts present. Anal hooks 1 on each side. Anterior abdominal spiracles biforous or bilabiate, or reduced and non-functional or absent. Abdominal spiracles not placed at ends of spiracular tubes. Eighth abdominal spiracles functional and about the same size as others on abdomen, or reduced or absent; abdominal spiracle 8 lateral or dorsolateral, facing laterally.
Illustrations. • Austrolimnius.
The interactive key provides access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, and summaries of attributes within groups of taxa.
Cite this publication as: ‘Lawrence, J.F., Hastings, A.M., Dallwitz, M.J., Paine, T.A., and Zurcher, E.J. 1995 onwards. Elateriformia (Coleoptera) larvae: descriptions, illustrations, identification, and information retrieval for families and subfamilies. Version: 9th October 2005. http://delta-intkey.com’.