Oecetis densoni Rasmussen & Harris, 2025

Rasmussen, Andrew K., Denson, Dana R., Orfinger, Alexander B. & Harris, Steven C., 2025, Diversity and distribution of the Trichoptera of Florida, United States, with descriptions of five new species, ZooKeys 1263, pp. 389-439 : 389-439

Oecetis densoni Rasmussen & Harris sp. nov.

Figs 12 , 13

Oecetis sp. nov. (nr. cinerascens ); collection records, Rasmussen et al. (2008 a).

Oecetis sp. nov. (nr. cinerascens ); collection records, Denson et al. (2016).

Type material.

Holotype male ( CMNH) • Florida, Lake County: Sellars Lake, Ocala National Forest, southeast lobe of lake, near canoe launch , 28 April 2007, D. Denson, A. Rasmussen, UV pan trap . Paratypes • Same data as holotype, 39 males, 1 female ( CUAC) • unnamed lake, Ocala National Forest, jeep trail South off State Road 40, just East of Wildcat Lake , 17 May 2009, D. Denson, A. Rasmussen, UV pan trap, 84 males and 21 females ( CMNH) ; Marion County • Lake Delancy, Ocala National Forest, Lake Delancy campground , 27 April 2007, D. Denson, A. Rasmussen, UV pan trap, 14 males and 1 female ( USNM) • Fore Lake, Ocala National Forest, Fore Lake Recreation Area , 16 May 2008, D. Denson, A. Rasmussen, UV pan trap, 6 males ( FAMU) ; Calhoun County • Wildcat Creek at State Road 20 , 30°25'34"N, 85°08'34"W, 6 May 2011, D. Denson, 1 male ( FAMU) • Page Pond at Page Pond Assembly of God , 30°32'21"N, 85°11'51"W, 7 May 2011, D. Denson, UV pan trap, 6 males ( FAMU) ; Jackson County • Porter Pond at Pittman Hall Road , 30°35'17"N, 85°16'34"W, 20 May 2010, D. Denson, A. Rasmussen, UV pan trap, 1 male ( FAMU) ; Leon County • Lofton Ponds, Apalachicola National Forest, at Sam Allen Road , 30°21'40"N, 84°23'25"W, 24 April 2007, M. Heyn, A. Wilson, UV-Light, 1 male ( FAMU) • same as above except 25 June 2007, D. Denson, UV pan trap, 1 male ( FAMU) ; Liberty County • Camel Pond, Apalachicola National Forest, Camel Pond campground, Forest Road 105 , 30°16'37"N, 84°59'20"W, 16 May 2006, R. Flowers, A. Rasmussen, B. Richard, Mercury-vapor light, 3 males ( UMSP) ; Washington County • Lucas Lake at boat landing, Lucas Lake Road , 30°32'37"N, 85°41'26"W, 17 April 2013, N. Miller, A. Rasmussen, UV pan trap, 4 males ( UMSP) .

Diagnosis.

Oecetis densoni sp. nov. belongs to the subgenus Pleurograpta , defined by Chen (1993) based on males having a very short IX th tergum and long IX th sternum. The new species is most similar to Oecetis ( Pleurograpta) cinerascens in general appearance and shared characteristics of the male and female genitalia. The male of O. densoni sp. nov. and O. cinerascens differ from most species in the subgenus by the presence of one or no paramere spines in the phallus, versus many paramere spines typical of the subgenus. The new species differs from O. cinerascens in the absence of honeycomb sculpturing on the abdominal terga VI and VII and the dorsal margin of the inferior appendages having a less abrupt downturn midlength, as seen in lateral view. Females of both species have large circular gonopod plates with an anterior arcuate band of sclerotization and a posterior pair of concave sclerites. The new species female differs in having a more prominent mid-dorsal hump on segment IX and triangular preanal appendages versus in O. cinerascens a much less produced mid-dorsal hump on segment IX and less prominent, broadly rounded preanal appendages (in lateral view).

Description.

Fig. 12 . Forewing length male 8.4–10.2 mm (mean = 9.1 mm, n = 10), female 7.8–8.9 mm (mean = 8.1 mm, n = 10). Forewing with transverse base of MA and MP stem crossveins aligned diagonally at approximately 60 o angle, veins slightly darkened at forks. Nigma of fore and hind wings located near crossvein forks. In alcohol, head, wings, thorax, and legs reddish brown in males and grayish brown in females. Antennal scapes and pedicels reddish brown, flagella pale brown. Abdomen cream color, without honeycomb sculpturing on abdominal terga V – VIII.

Male genitalia. Fig. 13 A – D . Segment IX narrow dorsally, widened dorsolaterally, posterior margin somewhat angulate in lateral view, ventrally with thick line of sclerotization separating posterior sternal area; in dorsal view sclerotized papillae resembling rabbit ears posteriorly; in ventral view each posterolateral corner with line of heavy sclerotization diagonally directed anterad. Preanal appendages ovoid in lateral view, digitate in dorsal view, flared posterolaterally. Segment X consisting of sclerotized mid-dorsal process subequal in length to preanal appendages, subtended on each side by longer membranous ventral process; in lateral view dorsal process arising from under base of preanal appendage, ventral process curved posteroventally, far surpassing dorsal process; in dorsal view apical margin of dorsal process variable among populations, grading from entire to deeply incised. Inferior appendages symmetric; in lateral view base with dorsomesal point, dorsal margin irregularly scalloped anteriorly, posteriorly angled downward and smoothly tapered, apically upturned; in dorsal view ridge separating lateral area from excavated mesal area; in ventral view mesal margins scalloped, slightly concave, outer margins parallel basally, distally tapered, curved inward. Phallus without paramere spines; in lateral view phallobase sharply angled anteriorly, rectangular along mid-length, sharply downturned distally with lip upturned apically, tear drop-shaped phallotremal sclerite near ventral downturn of phallobase dorsal margin.

Female genitalia. Fig. 13 E – G . Segment IX in lateral view narrow, truncate posteroventral extension above concave emargination; in dorsal view broadly rounded median hump with rabbit ear-like papillae produced posteriorly; in ventral view posterolateral corners each with triangular projection with sclerotized line connecting apex to perpendicular sclerotized line at base. Preanal appendages prominent, subtriangular in both lateral and dorsal views. Lamellae ovate in lateral view; in ventral view each with ear-like projection. Gonopod plate (sternum IX) in ventral view large, subcircular with anterior arcuate band of sclerotization, posterior pair of concave sclerites. Bursa copulatrix [spermathecal sclerite of Chen (1993)] in ventral view with median elongate ring surrounded by deltoid sclerite anteriorly, posterior margin sclerotized forming inverted V.

Larva and pupa. Unknown. Based on the high similarity of adults of Oecetis densoni sp. nov. with O. cinerascens and the collection of the two species from similar lake habitats in Florida, the larva of the new species is likely to also be similar to O. cinerascens , as described and illustrated by Floyd (1995).

Distribution.

Oecetis densoni sp. nov. appears to be endemic to Florida’s clear lakes and ponds where its known geographic range extends from the Ocala National Forest northward into the Florida panhandle as far west as Washington County.

Etymology.

This species is named in honor of Dana R. Denson, who helped discover the species and has contributed greatly to the study and protection of Trichoptera biodiversity in Florida.

DNA Barcoding.

To visualize putative phylogenetic relationships, a Neighbor Joining ( NJ) tree was constructed (Suppl. material 3) based on barcoding sequences of mitochondrial cytochrome oxidase I ( COI) nucleotides using the built-in tree-builder of the Barcode of Life Database ( BOLD) using Florida specimens examined in the course of this study. Based on this tree and morphological affinity, O. cinerascens (Hagen) is hypothesized to be the sister species of Oecetis densoni sp. nov. For O. densoni sp. nov. and O. cinerascens , pairwise divergence distances (p-distances) of COI sequences were calculated in MEGA 11 ( Tamura et al. 2021) using the Kimura 2 - parameter evolution model ( K 2 P) ( Kimura 1980) and pairwise deletion of missing sites. Sequences were mined from BOLD and include both available Oecetis densoni sp. nov. sequences from specimens included in the present study ( BOLD FLCAD 120-09 and FLCAD 140-09) as well as specimens of O. cinerascens from the Ocala National Forest ( FLCAD 130-09), northwest Florida ( FLCAD 148-09 and FLCAD 056-08), and Virginia ( PKCAD 021-07), to account for population-level genetic variation. Nucleotide sequences were aligned using ClustalW using default settings ( Larkin et al. 2007). All COI sequences used consist of 658 bp and were generated from vouchered specimens identified by taxonomic experts. Interspecific pairwise p-distance between O. densoni sp. nov. and O. cinerascens ranged from 6.4 % to 6.9 % (Suppl. material 2). These values are substantially larger than intraspecific p-distance ranges for O. densoni sp. nov. (0.08 %) and O. cinerascens (0.2 % to 0.5 %), demonstrating a clear barcoding gap indicative of significant genetic differentiation between the congeners.

Remarks.

The presence of honeycomb sculpturing on abdominal terga V – VIII has been used to place Oecetis ( Pleurograpta) species in the Testacea species group ( Chen 1993). However, phylogenetic analysis by Quinteiro and Almeida (2021) of Neotropical Oecetis suggested that the Testacea species group is paraphyletic and that the honeycomb sculpturing of the abdominal terga probably originated more than once due to convergent evolution. In this study, the other Testacea species group members found in Florida, Oecetis georgia and O. persimilis , were shown to be closely related to each other (Suppl. material 3) but in a separate clade from O. cinerascens and O. densoni sp. nov. This is further evidence that honeycomb sculpturing is of limited use for placement of species into monophyletic groupings. Additionally, the presence of abdominal tergal sculpturing in O. cinerascens and the absence of it in O. densoni sp. nov, along with the relatively high degree of genetic and morphological similarities between the two species, further underscore the probable high evolutionary plasticity of abdominal tergal sculpturing in Trichoptera .

Figures

Figure 12. Oecetis densoni sp. nov. Wings, male: forewing, top; hind wing, bottom. Photographs by Alexander Orfinger.

Figure 13. Oecetis densoni sp. nov. Male genitalia: A lateral B dorsal, showing variation in the dorsal process of segment X C segment IX and inferior appendages, ventral D phallus, lateral. Female genitalia: E lateral F dorsal G ventral, showing internal bursa copulatrix. Abbreviations: dp. = dorsal process of segment X; inf. = inferior appendage; lam. = lamella; pap. = papillae; pre. = preanal appendage; psc. = phallotremal sclerite; vp = ventral process of segment X.