Caecidotea tridentata Hungerford 1922

Caecidotea tridentata Hungerford

Caecidotea tridentata Hungerford, 1922:175–181, p. 15.—Creaser, 1931:5,6.—Hoffman, 1933:26–33, fig. 1.—Miller, 1933:102.—Van Name, 1936:473, 474, fig. 299.—Mackin and Hubricht, 1940:394.—Leonard and Ponder, 1949: 168, 169, 194, 195, 198, 199, fig. 37.

Asellus tridentatus.—Hubricht, 1950:17.—Pennak, 1953: 434.—Bresson, 1955:51.—Mackin, 1959:875.—Minckley, 1961:452.—Seidenberg, 1969:52, 81, 84, 90, 91.—Steeves, 1969:52.—Williams, 1970:1.—Fleming, 1973 [in part].

Asellus (Conasellus) tridentata.—Birstein, 1951:52, 53, 111.

Conasellus tridentatus.—Henry and Magniez, 1970:356.

[Not Asellus tridentatus.—Dexter, 1954:256.—Black, 1971:6, 38.—Holsinger, 1971:323.—Fleming, 1972a:254 (Illinois, record).—Page, 1974:91.—Craig, 1975:4.—McDaniel and Smith, 1976:58.]

[Not Caecidotea tridentata.—Peck and Lewis, 1978:45.]

HISTORY.—The first record of Caecidotea tridentata is the original description by Hungerford (1922) of isopods pumped from a cistern in Lawrence, Kansas. Hungerford also examined 4 lots of specimens from Topeka, Kansas, in the USNM collections identified as Caecidotea stygia and found them to be conspecific with the Lawrence specimens. Accompanying Hungerford's description and illustrations of C. tridentata was a key to the 6 known species of Caecidotea. The species were divided into 2 groups: (1) those with processes on the gnathopod palm (C. nickajackensis, C. alabamensis, C. tridentata, and C. stygia);(2) those without processes (C. smithii, and C. richardsonae).

Creaser (1931) included C. tridentata in another key to the species of Caecidotea accompanying his description of C. antricola and pointed out the possible taxonomic significance of the “club shaped setae” (= esthetes) on antennae 1 of C. smithsii, C. richardsonae, C. tridentata, and C. antricola. Miller (1933) included C. tridentata in a table of asellid species comparing characters in an evaluation of the validity of the genus Caecidotea.

Hoffman (1933) reported observations on structure of the brood pouch, number of marsupial young (40–70), molting, longevity, and food habits.

Van Name (1936) published Hungerford's (1922) illustrations and excerpts from his description.

Mackin and Hubricht (1940) compared C. tridentata to the Oklahoma species C. acuticarpa (Figure 26).

In an annotated checklist of the Crustacea of eastern Kansas, Leonard and Ponder (1949) supplied a number of characters that they felt reliable for the recognition of the species. C. tridentata was reported to be “fairly common in cisterns, wells, springs and shallow rocky streams in eastern Kansas,” but new specific collection localities were not given. In another checklist of invertebrates known from Ozark caves, Hubricht (1950) reported the range of Asellus tridentatus to consist of an area “along the northern fringes of the Ozarks.”

Birstein (1951) divided Asellus into subgenera, placing C. tridentata in the subgenus Conasellus.

Pennak (1953) included A. tridentatus in his key to the asellids and repeated Hubricht's (1950) range information.

Bresson (1955) put A. tridentatus in a checklist of Nearctic asellids and listed the range as “Kansas.” Mackin (1959) likewise included A. tridentatus in a checklist of Asellus associated with a key to North American Malacostraca.

In a paper concerned with the occurrence of subterranean isopods in epigean waters, Minckley (1961) stated his belief that “highly modified cavernicolous asellids” such as Asellus tridentatus are found in surface situations only as accidentals. Seidenberg (1969) repeated some of Hoffman's (1933) observations on the ecology of A. tridentatus. Steeves (1969) took note of Hungerford's (1922) attempt to group the species into related assemblages.

Henry and Magniez (1970) resurrected Conasellus and listed species which they included in the genus, including Conasellus tridentatus.

In his revision of the North American epigean Asellus, Williams (1970) noted that A. tridentatus may be found in surface waters, but is typically subterranean, and he did not deal with the species further.

Black (1971) compiled an annotated checklist of cave life in Oklahoma, listing records for the species from a cave and a spring. The species was classified as a troglophile. Two species, Asellus tridentatus and the amphipod Allocrangonyx pellucidus, were thought to share a range comprised of a region including south-central Oklahama and the Arbuckle Mountains. Holsinger (1971) also noted the occurrence of the 2 species together in an Oklahoma cave.

Fleming (1972a) listed determinations of A. tridentatus from localities in Illinois, Missouri, Arkansas, Oklahoma, and Kansas. The following year Fleming (1973) included A. tridentatus in a checklist and key to the genus Asellus. In the same paper Fleming presented a diagnosis of the species. Fleming also examined several collections of Asellus acuticarpus and concluded that this species is conspecific with A. tridentatus.

MATERIAL EXAMINED.—KANSAS. Douglas Co.: Lawrence, drain tile runoff stream in town park, leg. Julian J. Lewis, 8 Jul 1977, 15, 9. Lawrence, drain tile mouth under slab of concrete at head of lake on University of Kansas Campus, leg. Julian J. Lewis, 8 Jul 1977, 1. Franklin Co.: abandoned well, Wheeler Farm, 5 mi (8 km) SSE Ottawa, leg. Leslie Hubricht, 31 Aug 1941, 12 (USNM 108604). Miami Co.: Yates well, 4 mi (6.4 km) SW Osawatomie, leg. Leslie Hubricht, 31 Aug 1941, 3 (USNM 108605). Shawnee Co.: Topeka, 1 (USNM 44479). Topeka, gift of E. A. Popenoe, 9 Apr 1912, 15 (USNM 4480).

DESCRIPTION.—Large, eyeless, slightly pigmented. Length up to 19 mm (Hungerford, 1922), largest specimen examined 16.5 mm; body slender, linear, about 3.7× as long as wide; coxae visible in dorsal view. Margins of head, pereonites, and telson moderately setose. Head about 2.2× as wide as long, anterior margin concave; postmandibular lobes produced, rounded. Telson 1.7× as long as wide, sides parallel; caudomedial lobe slightly produced, broadly rounded.

Antenna 1 reaching almost to last segment of peduncle of antenna 2; flagellum of about 11–13 segments; esthete formula 3-0-1. Antenna 2 reaching to telson, last segment of peduncle about 1.4× length of preceding segment; flagellum of about 80 segments.

Mandibles with 4-cuspate incisors and lacinia mobilis; spine-row with 13 spines in left mandible, 16 in right mandible. Maxilla 1, apex of outer lobe with 13 robust spines (12 shown in Figure 24h) and 2 subterminal seta, plus 1 medial seta; inner lobe with 5 apical plumose setae and about 5 very slender subterminal lateral setae. Maxilliped with 6–7 retinacula.

Male pereopod 1 propus about 1.4× as long as wide; palm with 3 processes, large finger-shaped proximal process, cone-shaped mesial process crowding lower bidentate distal process. Dactyl with about 6 distal lateral weak spines. Pereopod 4 more spinose distally than proximally, dactyl with 2 lateral spines and 1 medial seta.

Male pleopod 1 larger than pleopod 2; protopod about 0.65 length of exopod, with 5 retinacula. Exopod about 0.6× as wide as long, with 6 long setae on distal margin, with several shorter setae interspersed and lining distal part of concave lateral margin, and 1 medium sized proximal seta. Male pleopod 2, protopod with about 3–4 setae along medial margin; proximal segment of exopod with 6 short setae, distal segment oval with about 11 lateral plumose setae on margin and 5 shorter nonplumose setae; endopod of moderate size, proximal bosses well developed, tip ending in 3 processes, mesial process curved, beak-shaped, distally rounded; cannula cone-shaped, shorter than mesial process, apically rounded; caudal process large and broadly rounded, with 2–3 small lobes at lateral margin proximally. Pleopod 3 with about 9 setae on lateral margin of proximal segment, distal segment with about 12 long setae along margin of apex with shorter setae interspersed, many setules on inner surfaces of both segments. Pleopod 4 exopod type A, with about 6 setae along proximal part of lateral margin. Pleopod 5 exopod with about 5 setae along proximal part of lateral margin.

Uropod about 1.3× as long as telson; protopod about 3.4× as long as exopod, about 1.3× as long as endopod; endopod spatulate, triangular in cross section.

ETYMOLOGY.—The specific name refers to the 3 processes on the palm of the gnathopod.

RELATIONSHIPS.—Caecidotea tridentata is similar in many respects to C. spatulata, especially in the pleopods 1 and 2, but C. spatulata has small eyes, and the mesial process on the gnathopod is more proximal in position and separated by a wide gap from the distal process. In C. tridentata the 2 processes are quite close.

Fleming (1973) synonymized Caecidotea acuticarpa Mackin and Hubricht (1940) with C. tridentata after comparing type-material and other specimens of both species. Fleming gave no descriptions or illustrations, stating only, “All comparisons were of the four reliable diagnostic characters: gnathopod, uropod, and first and second pleopods of the male. These structures examined in all specimens of both nominal species were found to be identical.”

Since Fleming's opinion is undocumented, we have made our own comparisons, using syntypes of C. acuticarpa from Byrd's Mill Spring, Pontotoc Co., Oklahoma (Figure 26) and specimens of C. tridentata from Topeka, Kansas. The gnathopods are similar, but the long proximal process in C. tridentata is represented in C. acuticarpa by 1 or 2 stout spines. Mackin and Hubricht (1940) state that both species lack a mesial process, but they interpreted the juxtaposed mesial and distal processes together as a bidentate distal process. The acutely produced carpus in C. acuticarpa, from which the specific name is derived, is blunt and not produced in C. tridentata. The pleopod 1 is similar, but the spinules on the exopod lateral margin extend to the proximal end of the concavity in C. acuticarpa and only to the distal end in C. tridentata. The pleopod 2 endopod tips differ. The mesial process is beak-shaped in C. tridentata and blunt with only a faint indication of a point in C. acuticarpa, although Mackin and Hubricht show it as bluntly hooked.

Caecidotea acuticarpa is known only from caves and springs in the Ouachita province of NE Oklahoma, a distinctly different habitat and range from those of C. tridentata.

HABITAT.—Many of the published records of C. tridentata are, like those given herein for C. kendeighi, from drain tiles and ditches (Figure 11c). The species should be termed a phreatobite, since it inhabits saturated soil interstices and not caves, and references to it as a troglophile (Black, 1971) or troglobite (Craig, 1975) are inaccurate.

RANGE.—Examination of numerous USNM collections labeled “Asellus tridentatus” has led us to the conclusion that this species is endemic to northeastern Kansas, although it may also occur in the plains of adjacent Missouri or Nebraska. All verified localities are from the unglaciated part of the Central Lowlands Province directly south of the margins of the Nebraskan and Kansan glaciations, along the Kansas and Marais de Cynes rivers, both tributaries of the Missouri River (Figure 27). Many of the records given in our synonymy of C. tridentata will probably prove to be misidentifications, but they are included pending reexamination of the specimens reported or of specimens from the same localities.