Crangonyx stinei Sisco and Sawicki 2023, sp. n.
Creators: name: Sisco, Joshua M.
name: Sawicki, Thomas R.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Crangonyctidae
Crangonyx
Crangonyx stinei

description: Crangonyx stinei Sisco and Sawicki sp. n.
(Figures 2–9)
Material examined
Holotype, female, 5.57 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Rodney J. King, 16 July 2022; catalogue number: UFIZ 70388. Allotype, male, 5.27 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70383 (Figure 2).
Paratype, female, 5.98 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70378. Paratype, female, 5.72 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70379. Paratype, female, 5.45 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70382. Paratype, female 4.27 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70384. Paratype, female, 6.27 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70386. Paratype, female, 3.81 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70387. Paratype, female, 5.33 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Rodney J. King, 16 July 2022; catalogue number: UFIZ 70389. Paratype, female, 5.62 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Nicholas Coppock, 24 September 2022; catalogue number: UFIZ 70393. Paratype, male, 3.68 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Rodney J. King, 16 July 2022; catalogue number: UFIZ 70391. Paratype, male, 3.5 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Joshua M. Sisco, 27 August 2022; catalogue number: UFIZ 70392. Paratype, male, 3.26 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70385. Voucher, male, 3.61 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70380. Voucher, male, 3.94 mm: Peacock Springs, Suwannee County, Florida; collector: Michael Stine, 28 April 2019; catalogue number: UFIZ 70381. Voucher, male, 5.12 mm: Peacock Springs, Suwannee County, Florida; collectors: Thomas R. Sawicki and Rodney J. King, 16 July 2022; catalogue number: UFIZ 70390.
Diagnosis
Small to medium-sized epigean species distinguished from other members of the genus Crangonyx by the combination of: female posterodistal margins of pereopods 5–7 (particularly 7) with deep serrations; male pereopod 7 posterodistal margin with only moderately deep serrations; strongly produced posterodistal corners of epimera 1–3; first epimeral plate with ventral seta; male uropod 1 outer margin of outer ramus without setae; comb spines on outer ramus of male uropod 2 (comb-spine row weakly formed); lacking ventral spines on inner margin of outer ramus of uropod 2; outer ramus of uropod 2 not significantly deflected laterally; male uropod 3 outer ramus with seta on inner margin.
Description of female
Female. (Figures 3–7) Holotype (UFIZ 70388) 5.57 mm in length. Eyes full, pigmented, ovate to weakly reniform. Interantennal lobe narrow, with rounded upper, lower margins. Clear/yellowish in live specimens (Figure 2 (a)).
Antennae. Antenna 1 (Figure 3a): approximately 57% body length, 2.1 times longer than antenna 2; peduncle segment 1 with small lateral seta and multiple small plumose setae along the anterior margin; primary flagellum with 20 segments, aesthetascs present on most segments, shorter than respective segments; accessory flagellum 2-segmented, slightly longer than first flagellar segment in length. Antenna 2 (Figure 3b): gland cone distinct; peduncle 1.8 times longer than flagellum, with plumose setae placed on anterior and posterior margins of peduncle segment 4, and plumose setae placed on antero/ posterodistal margins of peduncle segment 5; peduncular segments 4 and 5 subequal in length; calceoli absent on both peduncle and flagellum; flagellum 7-segmented.
Mouthparts. (Figures 3 and 4) Mandibles: left mandible (Figure 3c): incisor 5-dentate, lacinia mobilis 5-dentate, with 6 serrate robust setae and plumose accessory seta(e); molar process well developed; palp 3-segmented, segment 2 with 6 alpha setae, inner margin of segment covered in fine pubescent setae; segment 3 narrowing distally, with 2 C-setae, 4 E-setae, B-seta, and 10 plumose D-setae, A-setae lacking; entire face of segment covered in fine pubescent setae. Right mandible (Figure 3d): incisor 4-dentate, lacinia mobilis bifurcate, both lobes branched with numerous protuberances; 6 serrate robust and plumose accessory seta(e); molar process similar to left mandible. Palp with 3 articles, relative article lengths and setation patterns as in left mandible. Upper lip (Figure 4a): rounded, apical margin of labrum with numerous fine setae. Lower lip (Figure 4b): inner lobes reduced, outer margin of both inner and outer lobes covered in numerous fine setae; face of lip covered in pubescence. Maxilla 1 (Figure 4c): inner plate with 4 plumose marginal setae and numerous fine, pubescent setae covering entire plate; outer plate with 7 apical comb spines, pubescence broadly covers entire plate, decreasing laterally and proximally; palp 2-segmented, distal segment covered in pubescence; apical margin of distal segment with 4 submarginal setae and 5 marginal robust setae. Maxilla 2 (Figure 4d): both inner and outer plates covered in pubescent setae; outer plate narrower than inner plate, not narrowing distally, with numerous apical setae; inner plate broad, narrowing distally, with numerous apical setae and 5 plumose facial setae. Maxilliped (Figure 4e): inner plate much shorter than outer plate, apical margin with 5 serrate and naked cuspidate seta(e), 3 long naked setae; 4 large plumose submarginal setae placed medially; surface of plate covered in fine pubescence; outer plate inner margin armed with 2 robust serrate setae; 2 plumose setae and numerous long naked setae; palp second and third segments inner margins with numerous marginal/submarginal setae; dactyl with outer seta and 2 inner setae placed at base of nail.
Gnathopods. Gnathopod 1 (Figure 5a): coxal plate with 4 distal setae; basis with long seta along anterior margin, and several long setae inserted along posterior and medial margins; ischium with 4 setae and pubescence along posterior margin; merus with pubescence covering posterior surface and 7 plumose posterodistal setae, 3 medial setae along anterior margin; carpus approximately 79% length of propodus, with 2 setae along anterior margin, 3 setae inserted at anterodistal corner, posterior margin with numerous plumose setae; propodus approximately 1.5 times longer than broad, with 2 marginal anterior setae, 3 superior medial setae, 8 setae inserted at anterodistal corner, 3 inferior medial setae and 5 plumose posterior setae; palm weakly oblique with 11 setae along inner and outer margins; 3 outer and 3 inner robust setae; inner margin of defining angle with 3 bifid robust setae, large robust split-tip seta, outer margin with 5 bifid robust setae; dactyl with outer seta. Gnathopod 2 (Figure 5b): coxal plate with 6 distal setae; basis with 4 long and 2 short setae along the posterior margin, anterior margin with long seta and 5 short setae, posterodistal corner with 2 short setae; ischium with seta and pubescence along posterior margin; merus with pubescence covering posterior surface and 3 posterodistal setae; carpus approximately 95% length of propodus, with 2 anterior setae, 2 medial setae, 3 setae placed distally, and 6 groups of setae along posterior margin; propodus approximately 2.1 times longer than broad with marginal anterior seta, 5 superior medial setae, 8 setae at anterodistal corner, 3 inferior medial setae and 4 groups of posterior plumose setae; palm oblique with 11 setae and 4 inner and 3 outer robust setae; defining angle armed with 3 inner robust bifid setae and large robust split-tip seta, outer margin with 3 plumose setae, large robust split-tip seta; dactyl with outer seta, and serrations along inner margin.
Pereopods. Pereopod 3 (Figure 6a): coxal plate with 7 distal setae, lacking facial setae; basis with 4 setae inserted proximally along anterior margin and seta near anterodistal corner, 7 setae along posterior margin, 2 setae along posterodistal corner; merus approximately 1.2 times longer than carpus; carpus approximately 87% length of propodus; dactyl approximately 45% length of propodus, with plumose seta proximally on anterior margin, stout seta placed distally along posterior margin, proximal to nail. Pereopod 4 (Figure 6b): subequal to pereopod 3 in length; coxal plate longer than broad, with distinct excavation along posteroproximal margin, armed with 13 distal setae and sparse facial setae; merus approximately 1.4 times longer than carpus, propodus approximately 1.1 times longer than carpus; dactyl approximately 44% length of propodus, with stout seta placed distally along posterior margin followed by thin seta placed at base of nail, plumose seta placed proximally along anterior margin. Pereopod 5 (Figure 6c): coxal plate large, bilobate with distinct anterior and posterior lobes, each with seta on respective distal corners; basis posterior margin with 8 shallow serrations and a weakly convex distal corner, proximal anterior margin with 2 long setae, anterior margin with 7 split-tipped robust setae, 4 setae along anterodistal margin; merus approximately 76% length of carpus; carpus approximately 1.3 times longer than propodus, dactyl approximately 32% length of propodus, with plumose seta placed proximally on posterior margin, stout seta on distal corner of anterior margin, followed by thin seta placed at base of nail. Pereopod 6 (Figure 6d): coxal plate weakly bilobate, with produced posterior lobe, bearing seta along posterodistal margin; basis posterior margin weakly convex with 9 serrations and rounded distal corner, anterior margin with 7 split-tipped robust setae, 3 distal robust setae, lacking proximal setae; merus approximately 80% length of carpus; carpus approximately 1.1 times propodus in length, dactyl approximately 31% length of propodus, setation like pereopod 5. Pereopod 7 (Figure 6e): coxal plate small, subtriangular, with posterior seta; basis posterior margin convex with 9 serrations increasing in depth distally and with weakly rounded distal corner, anterior margin with 6 split-tipped robust setae, 3 distal robust setae, proximal setae absent; merus approximately 80% length of carpus; carpus approximately 1.1 times propodus in length, dactyl approximately 35% length of propodus, setation similar to pereopods 5, 6.
Gills and brood plates. Gills (Figure 6a–e): coxal gills present on somites 2–6, somite 7 with a small pereopod 7 gill. Slender sternal gills present on somites 6 and 7. Brood plates (Figure 5c): large, setose brood plates present on segments 2–5, decreasing in size posteriorly (only drawn for gnathopod 2).
Pleon. Pleopod 1 (Figure 7a): peduncle of pleopod 1 approximately 34% length of rami, lacking setae, with 2 coupling hooks; outer and inner rami with 16 and 17 articles respectively; pleopod 2 (not figured) peduncle lacking setae, with 2 coupling hooks (Figure 7b), outer and inner rami with 11 and 13 articles respectively; pleopod 3 (not figured) peduncle lacking setae, with 2 coupling hooks (Figure 7c), outer and inner rami with 11 and 12 articles respectively. Epimera (Figure 7d): first epimeron ventral margin armed with seta, strongly oblique, posterodistal corner distinctly produced, with tooth-like extension, posterior margin with seta placed proximally from posterodistal corner; second epimeron ventral margin with 3 robust setae, posterodistal corner distinctly produced, with tooth-like extension, posterior margin with seta; third epimeron ventral margin with 3 robust setae, posterodistal corner produced, with weaker, rounded tooth-like extension, posterior margin with seta placed near posterodistal corner.
Uropods. Uropod 1 (Figure 7e): peduncle 1.4 times length of rami with 7 outer and 3 inner robust setae; rami narrowing slightly distally, outer ramus subequal in length to inner ramus, with 2 robust setae on inner margin, 4 robust setae on outer margin, and 5 apical robust setae; inner ramus with 3 robust setae on inner margin, 4 robust setae on outer margin, and 6 apical robust setae. Uropod 2 (Figure 7f): peduncle 1.16 times inner ramus with 5 robust setae on inner margin, 3 on outer margin, distal-most setae on inner margin inserted as a pair; rami narrowing slightly distally, outer ramus approximately 77% of inner ramus, with 2 inner and 3 outer robust setae, apex with 4 robust setae; inner ramus with 2 robust setae on inner margin, 4 robust setae on outer margin and 5 apical robust setae. Uropod 3 (Figure 7g): peduncle approximately 67% length of outer ramus, with 2 robust setae on outer margin, 2 robust setae on inner margin and 2 robust setae inserted distally; inner ramus reduced, scale-like with marginal robust seta; outer ramus 3.5 times longer than broad, approximately 3.7 times longer than inner ramus, with 9 robust split-tipped setae on outer and 4 on inner margins, apex with slender seta paired with short robust seta.
Telson. (Figure 7h). Slightly broader than long, lobes fused, cleft approximately 39% of length, with a depth to width ratio of 0.96, left apical lobe with 3 large robust setae and small seta, right apical lobe armed with 3 large robust setae and plumose seta, 2 plumose setae arise dorsolaterally from outer margins of both lobes.
Description of male
Male. (Figures 8–9) Allotype (UFIZ 70383) 5.27 mm in length (Figure 2b). Differing from female in smaller body length, range 3.26–5.27 mm (females 3.81–6.27 mm); shorter antennae, presence of calceoli on the peduncle/flagellum of antenna 2; more robust gnathopods with enlarged propodi and more robust setae on the palmar margins; pereopod 7 posterodistal serrations not as deep; uropod 1 setation; uropod 2 presence of comb spines on inner margin of inner ramus; and uropod 3 setation. Structures not described below as in female.
Antennae. Antenna 1 (not illustrated, but see Figure 3a): 63% body length, primary flagellum with 17 segments, aesthetascs on most segments, aesthetascs shorter in length than their respective segments; accessory flagellum 2-segmented, shorter than the first flagellar segment in length. Antenna 2 (Figure 8a): gland cone distinct, peduncle approximately 2.3 times longer than flagellum, 2 plumose setae present along posterior margins of segment 4, segment 4 approximately 1.3 times length of segment 5; elongate calceoli present on both peduncle segments 4 and 5 and second segment of flagellum; flagellum 5-segmented.
Gnathopods. Gnathopod 1 (Figure 9a): coxal plate with 5 distal setae; basis with long seta inserted along anterior and medial margins, 3 long setae along posterior margin, 2 groups of paired setae on antero/posterodistal margins, weakly pubescent along posterodistal corner; ischium with 3 setae and pubescence along posterior margin; merus with pubescence covering posterior surface with 4 long plumose setae, short plumose seta, and robust seta placed distally; carpus approximately 53% length of propodus with seta along anterior margin, posterior margin with numerous plumose setae and 3 submarginal setae directed distally; propodus robust, approximately 1.4 times longer than broad with 2 setae placed at anterodistal corner, 4 superior medial setae, inferior medial seta and 5 plumose setae along the posterior margin; palm oblique with 11 outer and 6 inner robust setae and long seta; defining angle armed with 7 inner and 4 outer robust bifid setae and 2 long setae; dactyl with outer seta. Gnathopod 2 (Figure 9b): coxal plate with 4 distal setae; basis with 2 long setae inserted along anterior and 3 long setae along posterior margins, posterodistal margin weakly pubescent; ischium with seta and pubescence along posterior margin; merus with pubescence covering posterior surface and 2 distal setae; carpus approximately 48% length of propodus with 3 groups of setae along the posterior margin, seta inserted along anterior margin; propodus approximately 2.2 times longer than broad with 4 superior medial setae, inferior medial seta, 4 groups of plumose posterior setae; palm strongly oblique with 9 outer and 14 inner robust setae and long inner seta, defining angle armed with 4 inner and 3 outer robust setae, naked seta, and 2 plumose setae; dactyl with outer seta, inner margin without noticeable serrations.
Pereopods. Pereopod 5 (Figure 9c): basis posterior margin with 7 shallow serrations. Pereopod 6 (Figure 9d): basis posterior margin with 8 serrations. Pereopod 7 (Figure 9e): coxal plate lobes indistinct (not illustrated), with distal seta; basis posterior margin weakly convex with 10 serrations (increasing in depth distally), distal corner sharply rounded, anterior margin with 5 robust split-tipped setae and 3 setae inserted along anterodistal corner (not illustrated).
Uropods. Uropod 1 (Figure 8b): peduncle approximately 1.4 times length of rami with 2 inner and 5 outer robust setae; outer ramus approximately 83% length of inner ramus, with 3 robust setae on inner margin, 3 robust setae on outer margin and 5 robust setae on apex; inner ramus with 3 outer robust setae, inner margin robust setae lacking, and small seta placed proximally on ventral margin, apex with 4 robust setae. Uropod 2 (Figure 8c): peduncle 1.07 times length of inner ramus with 3 robust setae on outer margin and 2 robust setae on inner margin; outer ramus approximately 73% length of inner ramus with 6 outer robust setae, 3 apical setae, inner margin with 8 comb spines (comb-spine row weakly formed) reaching approximately 38% length of ramus; inner ramus with 3 outer and 1 inner robust seta(e), apex with 6 robust setae. Uropod 3 (Figure 8d): peduncle approximately 41% length of outer ramus, with a robust seta placed distally; inner ramus reduced, scale-like, lacking setae; outer ramus approximately 5.5 times longer than broad, approximately 4.3 times longer than inner ramus, with 3 groups of paired robust, split-tipped setae on outer and split-tipped seta on inner margin, apex with a slender seta paired with a short robust seta.
Telson. (Figure 8e) 1.14 times longer than broad, cleft approximately 42% of telson length, with a cleft depth to width ratio of 1.06, apices with 2 large robust setae, left lobe with plumose seta, 2 plumose setae arise dorsolaterally from outer margins of both lobes.
Variation
Crangonyx stinei sp. n. varies morphologically in several nondiagnostic characteristics (see Table 2).
Type locality
Wes Skiles Peacock Springs State Park, Suwannee County, Florida (30.123°N, 83.133°W); all dives into the cave were through the Peacock Springs I entrance. Specimens were collected from the silt and sediments of the cave benthos.
Etymology
The specific epithet stinei is in honour of Michael and Bonnie Stine, who first noticed and collected the species from the bottom sediments of Peacock Springs Cave, and to acknowledge their years of effort assisting with scientific collections across the Floridan aquifer.
Distribution and ecology
Peacock Springs is a large subterranean karst system with more than 10 km of explored cave passages and five second-magnitude springs (Florida DEP, 2023). This cave system has been biologically explored for decades by one of us (TRS), who has documented the presence of a variety of stygomorphic fauna within the cave including the crayfish Procambarus pallidus Hobbs, 1940, the isopod Remasellus parvus Steeves, 1964, and the amphipods Crangonyx grandimanus and C. parhobbsi (Cannizzaro et al., 2020; see also Franz et al. 1994).
Crangonyx stinei sp. n. was first observed and collected by cave divers on 28 April 2019. Because C. stinei sp. n. had not been previously recorded from the cave, and given its epigean morphology, it was assumed to have washed into the cave from the open-water spring run or nearby Suwannee River. Additionally, cave divers had reported the presence of tannic and green surface water entering into the cave system during the weeks prior to the initial observation of C. stinei sp. n., providing a plausible scenario for its movement from nearby epigean water into the cave. To determine the distribution of C. stinei sp. n., attempts to collect using dip nets and baited traps occurred within the Peacock Springs spring run and nearby Suwannee River. Baited traps were employed as C. floridanus sensu lato from a spring fed, pond in Jackson County, Florida, had been observed scavenging a crayfish carcase (Cannizzaro et al. 2019a). However, the only amphipod species collected from these attempts was Hyalella cf. azteca, which was collected in the spring run, but not the Suwannee River. Other animals collected included ostracods, insect larvae, and other freshwater invertebrates. Additional collecting from nearby epigean habitats and from other regional cave systems are needed to gain a better understanding of the biogeographic distribution of C. stinei sp. n. Additional dives within the Peacock Springs system resulted in the collection of an ovigerous female in September 2022. Females with sexually mature brood plates were collected in April 2019, July 2022 and September 2022. These data strongly suggest that C. stinei sp. n. is completing its life cycle within the cave.
Little is known about the ecology of Crangonyx stinei sp. n. Crangonyx stinei sp. n. has been observed deep into the cave, hundreds of metres from surface connections. Additionally, they appear to strictly inhabit the cave̍s benthic sediments and have never been observed swimming into the water column. Individuals exhibit a rapid ‘corkscrew̍ movement, subsequently burrowing into the sand/silt bottom sediments during collection efforts. This behaviour likely represents a flight response.
Given that Crangonyx stinei sp. n. has not been observed outside of the cave, is broadly distributed throughout and completes its life cycle within the cave, and has been documented to occur in the habitat over a three-year period, it is plausible that the species is stygobitic. However, its lack of stygomorphism suggests that it is likely in the early stages of its hypogean evolution. The only other stygobitic member of the floridanus complex, C. manubrium, lacks exoskeletal pigment, and individuals within the population exhibit varying degrees of eye reduction, with some individuals possessing eyes slightly reduced as compared to epigean species, and some an almost complete loss of eyes (Cannizzaro et al. 2019a).
Of the 16 individuals examined, nine were female and seven were male. These data are not suggestive of a strong female-biased sex ratio within the species, as has been documented in other stygobitic members of the genus Crangonyx that occur in the Floridan aquifer (Cannizzaro et al. 2018, 2019a, 2019b, 2019c, 2020). This fact provides additional support to the idea that if C. stinei sp. n. is stygobitic, it is likely early in its evolution.
description: Published as part of Sisco, Joshua M. & Sawicki, Thomas R., 2023, Molecular and morphological analyses reveal a new hypogean species of amphipod in the genus Crangonyx Bate, 1859 (Crustacea: Crangonyctidae) within the floridanus species complex, from Suwannee County, Florida, pp. 1257-1286 in Journal of Natural History 57 (21 - 24) on pages 1257-1286, DOI: 10.1080/00222933.2023.2247155, http://zenodo.org/record/10015548