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A redescription of the mature larva of Neoporus clypealis (Sharp) (coleoptera: dytiscidae).


Mature larvae of Neoporus were collected from lower Piedmont and upper Coastal Plain lotic habitats in Georgia. Specimens were cultured into the adult stage and identified as N. clypealis. The larval head is characterized by an extended frontoclypeus, a prominent reddish-brown dorsomedial W-shaped marking, and well-developed stemmata. Mesothoracic and lateral abdominal spiracles are absent. The presence of tarsal and tibial natatory sensilla and short secondary sensilla on the proximal urogomphal segment is consistent with the chaetotaxy of previously described Neoporus species.

Key words: Dytiscidae, Neoporus clypealis, larva, morphology, southeastern United States.



The majority of species in the Nearctic genus Neoporus have ranges that either include or that are restricted to the southeastern United States (1). Neoporus is the most specious genus recorded in Georgia with at least 22 species reported from throughout the state, including the Piedmont and Coastal Plain Regions (2). Although Neoporus contains a large number of species, we have been able to find descriptions of immature stages of only nine species. Barman (3) observed oviposition by N. undulatus (Say) and provided brief descriptions of its egg, first, second, and third instars, and pupa. This study also included descriptions of the mature larva of N. dimidiatus (Gemminger and Harold) (as N. solitarius; 4) and N. clypealis (Sharp). Matta and Peterson (5) gave brief descriptions of the mature larvae of N. blanchardi (Sherman), N. carolinus (Fall), N. cimicoides (Sharp), N. lobatus (Sharp), N. shermani (Fall), and N. superioris (Balfour-Browne) based on material collected in the southeast. Alarie (6) identified and described the first, second, and third instars of N. undulatus and the third instar of N. carolinus. The first instar of N. undulatus was included as a reference specimen in the chaetotaxal analyses of the hydroporine last abdominal segment and urogomphi (7) and legs (8). The chaetotaxal analysis of the head (9) included first instars of N. tennetum (Wolfe), N. dimidiatus, and N. undulatus.

Larvae of N. clypealis have been described previously (3), but this study lacks the chaetotaxal detail required by current and more modern nomenclatural standards. The purpose of our study is to redescribe the mature larvae of N. clypealis using chaetotaxal analytical techniques developed by Nilsson (10), Wolfe and Roughley (11), Alarie (6; 9), Alarie and Harper (7), and Alarie et al. (8).


The mature larvae examined in this study were collected in backwater areas of Champion Creek, (Baldwin County), Turkey Creek, (Wilkinson County), and from thick beds of aquatic vegetation in Canoochee Creek, (Emanuel County), Georgia U.S.A., (Fig. 1). The larvae were identified as N. clypealis after culture into the adult stage. This material was compared to preserved larvae (70 percent glycerated ethyl alcohol) of N. undulatus and Hydroporus signatus (Mannerheim) that had also been identified after culture into adults.


Ten larvae were analyzed anatomically, unless noted otherwise. Measurements were obtained from dismembered specimens with head lengths taken dorsally from the posterior margin along the coronal suture to the anterior margin of the frontoclypeus and at the widest region of the cranium. Lengths of the coxa, trochanter, femur, tibia, and tarsus were taken at the longest aspect. Lengths of legs were determined by adding lengths of leg segments, excluding trochanters. A modification of a descriptive system proposed by Wolfe and Roughley (11) was used to enumerate sensilla by position and/or origin on body segments and appendages.


General aspect. -- Body widest at or the near base of first abdominal segment, length (alcohol preserved specimens) about 7.5 mm excluding urogomphi; sclerotized areas of body dark reddish-brown, light yellowish markings medially, and laterally on posterior third of pronotum, and anteriorly on the eighth abdominal segment. Head light yellowish brown with dark reddish brown W-shaped pattern on the frontoclypeus and epicranium (Fig. 2).


Head. -- Prognathic, pear-shaped dorsoventrally, defined cervical region absent, total length 1.01-1.15 mm ([bar.x] = 1.10 [+ or -] 0.06 mm), width 0.80-0.91 mm ([bar.x] = 0.87 [+ or -] 0.05 mm) with a prominent occipital suture. Frontoclypeus, length 0.77-0.89 mm ([bar.x] = 0.82 [+ or -] 0.05 mm), extended well beyond the origins of the mandibles to form a prominent frontoclypeal projection (nasale) with well-developed lateral serrated notches; venter of nasale extensively sclerotized, labrum not evident, coronal suture length 0.21-0.32 mm ([bar.x] = 0.25 [+ or -] 0.04 mm); prominent ocular areas, each with six stemmatal lenses arranged laterally in an elongate oval; gular sutures obscure; posterior tentorial pits visible meso-ventrally; prominent sensilla of the head capsule included temporal spines ranging from eight to ten, lamellae clypeales on anteroventral margin of nasale; antenna four-segmented, total length 0.53-0.62 mm ([bar.x] = 0.58 [+ or -] 0.05 mm), first segment 0.08-0.12 mm ([bar.x] = 0.10 [+ or -] 0.02 mm), second segment 0.18-0.24 mm ([bar.x] = 0.21 [+ or -] 0.03 mm), third segment 0.19-0.22 mm ([bar.x] = 0.21 [+ or -] 0.01 mm), accessory sensorial appendage present, fourth segment 0.05-0.07 mm ([bar.x] = .06 [+ or -] 0.01);

Mouth parts. -- (Fig. 3A) Mandibles slender, falcate, lacking medial teeth, directed dorsomedially to cross beneath anterior margin of the nasale, two small sensilla laterally, one proximal and one medial; maxilla with galea absent, maxillary cardo reduced with one sensillum, stipes short, fingerlike, medial surface without sensilla, two prominent ventral lateral sensilla; maxillary palps three segmented, first segment 0.21-0.28 mm ([bar.x] = 0.26 [+ or -] 0.02 mm), second segment 0.16-0.21 mm ([bar.x] = 0.19 [+ or -] 0.02 mm) with a large distal pore and two distal hair-like sensilla, third segment 0.05-0.08 mm ([bar.x] = 0.06 [+ or -] 0.01 mm) with a proximal hair-like sensillum; labium trapezoidal, narrowest posteriorly, separated from maxillary bases by two low but prominent protuberances, two small proximal spines and two hairlike distal spines at the base of each palp, first segment 0.18-0.29 mm (0.24 [+ or -] 0.03 mm), second segment 0.18-0.24 mm ([bar.x] = 0.21 [+ or -] 0.02 mm) with two ventral hair-like sensilla and two small distal spinulae.

Thorax. -- Pronotum about one and a half times longer than mesonotum and metanotum, widest posteriorly, pronotal venter membranous; meso- and metanotum about equal in length; pronotum with long setae on the margins anteriorly, laterally, and posteriorly. Pronotum, mesonotum, and metanotum with irregularly distributed setae discally, forming fringe on the lateral and posterior margins. Spiracles absent on thorax.

Legs. -- (Tables 1 and 2; Fig. 3). Coxal sutures present; ventral spinulae present on pro- and meso-tarsi and tibiae, absent on metathoracic leg; trochanter with six sensilla; simple and complex spines present, complex spines confined to the femoral and tibial segments, most numerous anteroventrally and distally, and on the metathoracic leg; posterior tarsal claw shorter than anterior claw, tarsal spines present.


Abdomen. -- Segments 1-6 individually shorter than mesosternum, membranous ventrolaterally and ventrally, segments 7 and 8 completely sclerotized; segments 1-7 with sensillar series posteriorly and laterally, segment 8 with numerous sensilla distributed irregularly; spiracles absent on 1-7; segment 8 length 0.32-0.57 mm ([bar.x] = 0.45 mm [+ or -] 0.07); siphon well-defined, length 0.12-0.20 mm ([bar.x] = 0.16 [+ or -] 0.03 mm).

Urogomphus. -- Two segmented; proximal segment length 0.92-1.11 mm ([bar.x] = 1.01 [+ or -] 0.06 mm, n = 7) with 11 sensilla, including one small spine near origin and three long hair-like prominent sensilla arising distally; segment 2 subequal to proximal segment and hair-like with a hair-like sensillum arising distally.


The mature larva of Neoporus clypealis has a distinct W-shaped dorsal head pattern (Fig. 2) similar to that of N. carolinus (5; 6). Both species have ranges that include Georgia (2). If this head pattern is restricted to N. carolinus and N. clypealis, the two species may be separated in Georgia by dramatic differences in the chaetotaxy of the proximal urogomphal segment. The number of sensilla observed on the proximal urogomphal segment on N. clypealis was eleven. In contrast, the number of sensilla on the proximal urogomphal segment of N. carolinus ranges from 20-29 (6).

The basal morphology of the labium of Neoporus clypealis and its relative proximity to the maxillae is significantly different from that of Hydroporus signatus. On H. signatus, the pre- and postmentum are well defined with the base of the prementum proximate to the medial origins of the maxillae. The result is a relatively compact appearance of maxillae and labium when viewed ventrally (Fig. 3B). The prementum of N. clypealis, although shaped somewhat differently, is comparable to that of H. signatus in its relative size; however, the postmentum of N. clypealis has a very different morphology. If it is present on N. clypealis, the postmentum has a relatively wide base that is significantly greater than its height. As a result the distance between the base of the prementum and the medial surfaces of the stipes is almost twice the maximum width of the stipes (3A). The morphology of the mature larva of N. undulatus is similar to that of N. clypealis. This suggests that the relative positions of the labium and maxillae may provide a useful character for separation of Hydroporus and Neoporus larvae in Georgia. Additional sampling of larvae from both genera and further observations of positions of the labium and maxillae will help determine the utility of this character for delimiting Hydroporus and Neoporus.

Table I. Measurements (N=10; in mm) of lengths of thoracic appendages of
Neoporus clypealis (Sharp).

Segment Mean Standard Deviation Range

Procoxa 0.53 0.04 0.48-0.60
Mesocoxa 0.55 0.07 0.41-0.66
Metacoxa 0.63 0.05 0.54-0.69
Protrochanter 0.16 0.01 0.12-0.20
Mesotrochanter 0.19 0.02 0.17-0.23
Metatrochanter 0.23 0.00 0.18-0.27
Profemur 0.51 0.04 0.45-0.57
Mesofemur 0.57 0.05 0.51-0.63
Metafemur 0.67 0.05 0.60-0.72
Protibia 0.24 0.04 0.18-0.30
Mesotibia 0.35 0.04 0.29-0.41
Metatibia 0.45 0.04 0.39-0.50
Protarsus 0.24 0.04 0.18-0.29
Mesotarsus 0.31 0.05 0.20-0.35
Metatarsus 0.45 0.04 0.39-0.50
Proleg 1.51 0.14 1.33-1.69
Mesoleg 1.77 0.12 1.63-2.03
Metaleg 2.20 0.15 2.01-2.39

Table II. Sensillar distribution and patterns on legs of the mature
larva of Neoporus clypealis (Sharp).

Appendage Location Coxa Femur Tibiae Tarsus

 AV 1-4 7-13 1-4 0
 AD 4-6 NA 0 0
Proleg ADi 2 2-3 2-3 1+2 sm
 PD 5-8 0-3 0 1+1 hrl
 PDi 2 1+1 hrl 2+1 hrl 2 sm
 PV 0-2 5-8 2-4 0
 NS NA NA 5-8 1-5
 DAD NA 3-10 NA NA
 AV 1-4 4-14 4-6 4-7
 AD 4-8 NA 3-4 0-1
 ADi 2 2-3 2-3 1+2 sm
Mesoleg APr 6 NA NA NA
 PD 6-8 0-2 0 1+1 hrl
 PDi 2 1+1 hrl 2+1 hrl 2 sm
 PV 0-4 7-11 4-5 0
 NS NA NA 9-14 8-13
 DAD NA 7-12 NA NA
 AV 2-6 11-15 5-7 6-10
 AD 6-8 NA 4-8 0
 ADi 2 3-4 2-3 1+2 sm
Metaleg APr 6 NA NA NA
 PD 4-12 0-2 0 1+1 hrl
 PDi 2 1+1 hrl 2+1 hrl 1+1 sm
 PV 2-4 7-11 4-6 0
 NS NA NA 11-16 11-15

Abbreviations employed include: DAD, dorsal anterodorsal; AV,
anteroventral; AD, anterodorsal; ADi, anterodistal; APr, anteroproximal;
PD, posterodorsal; PDi, posterodistal; PV, posteroventral; PPr,
posterior proximal; NS, natatory sensilla.


Aquatic Coleoptera Laboratory contribution No. 50. This project was supported in part by a Faculty Research Grant awarded by the Office of Research Services, Georgia College & State University. The authors also thank Dr. Melanie DeVore and Ms. Tiffany Shepley, both of this University, for their assistance in completing this study.


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11. Wolfe GW and Roughley RE: Description of the pupa and mature larvae of Matus ovatus ovatus Leech (Coleoptera: Dytiscidae) with a chaetotaxal analysis emphasizing mouth parts, legs, and urogomphus. Proc Acad Nat Sci Phil 137: 61-79, 1985.

Julie Scott

Department of Biological & Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

E. H. Barman

Department of Biological & Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

G. William Wolfe

Department of Biological & Environmental Sciences

Georgia College & State University

Milledgeville, GA 31061

Address Correspondence To:

E. H. Barman
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Article Details
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Author:Scott, Julie; Barman, E.H.; Wolfe, G. William
Publication:Georgia Journal of Science
Geographic Code:1U5GA
Date:Dec 22, 2004
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