Crangonyx pseudoephemerus Cannizzaro & Sawicki 2019, n. sp.
Creators: name: Cannizzaro, Andrew G.
name: Sawicki, Thomas R.
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Crangonyctidae
Crangonyx
Crangonyx pseudoephemerus

description: Crangonyx pseudoephemerus Cannizzaro and Sawicki n. sp.
(Figs. 10–16)
Type material. Holotype, female 6.24 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; Florida Museum of Natural History; catalog number UFID 52591. Allotype, male 4.16 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; catalog number UFID 52594. Paratype, female 7.30 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; catalog number UFID 52592. Paratype, female 6.94 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; catalog number UFID 52593. Paratype, female 5.52 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; Yale Peabody Museum of Natural History; catalog number: YPM IZ 105552. Paratype, male 3.36 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; catalog number UFID 52595. Paratype, male 3.21 mm: St. Marks Headwaters Greenway, Leon County, Florida; Collector: Andrew G. Cannizzaro, 16 March 2018; catalog number YPM IZ 105553.
Diagnosis. Medium sized epigean species distinguished from all other members of the genus Crangonyx except C. ephemerus n. sp. by the combination of the following characteristics: palmar margins of gnathopods 1 and 2 with more than 10 robust setae; pereopod 6 dactylus relatively short, ~30% length of propodus; pereopods 5–7 (especially pereopod 7) possessing numerous deep serrations on posterior margins of bases; strongly produced distoposterior corners of epimera 1–3; posterior margins of epimera 1–3 with 1 seta; ventral margin of epimeron 2 lacking paired robust setae; pleopod 1 peduncle 30–45% length of rami; inner ramus of female uropod 3 with 2 robust setae; comb-spines, but no ventral spines on the inner margin of the outer ramus of male uropod 2; and male uropod 3 inner ramus armed with a single robust seta. Distinguished from C. ephemerus n. sp. by mandibular palp second segment <1.5 times the third in length; meri of female pereopods 6 and 7 up to 70% length of corresponding carpals with up to 3 posteromarginal setae; female uropod 1 peduncle with 1 to 2 inner robust setae and 8 to 9 outer robust setae; female telson 45–50% cleft; male uropod 1 peduncle with 1 inner robust seta; male uropod 2 peduncle with 2 unpaired outer robust setae; male uropod 2 outer ramus inner margin with large comb-spines, reaching half the length of the margin; and male telson 45–50% cleft. Females 5.8–7.1 mm, males 3.7–4.3 mm.
Description of female. Holotype (UFID 52591) 6.24 mm in length. Eyes full, pigmented; interantennal lobe narrow, with rounded and upper lower margins (Fig. 2C). Integumentary pigment bluish grey when alive.
Antennae: Antenna 1 (Fig. 10A): approximately 68% body length, 2.4 times longer than antenna 2; peduncle segment 1 with 1 lateral seta; primary flagellum with 22 segments, aesthetascs present on distal segments, aesthetascs shorter than respective segments; accessory flagellum 2-segmented, subequal in length to first segment of primary flagellum. Antenna 2 (Fig. 10B): gland cone distinct; peduncle 2 times longer than flagellum, with 2 anterior robust setae and 1 lateral robust seta on segment 3, and plumose setae placed on antero/posterodistal margins of segments 4 and 5, peduncular segment 4 subequal in length to segment 5; calceoli absent on both peduncle and flagellum; flagellum 8-segmented.
Mouthparts: Mandibles (Fig. 10C, D): left mandible incisor 4-dentate, lacinia mobilis 4-dentate, with 6 robust and plumose accessory setae; molar process well developed with 1 plumose seta; palp 3-segmented, segment 2 1.3 times longer than segment 3, with 4 Alpha setae and 4 Beta setae, inner margin of segment covered in fine setae; segment 3 rounded distally with 1 C-seta, 4 E-setae, 1 B-seta, and 9 plumose D-setae, A-setae lacking; face of segment covered in numerous pubescent setae. Right mandible, incisor 4-dentate, lacinia mobilis bifurcate, proximal lobe with 8 dentations, distal lobe branched with numerous dentations; accessory setae row with 5 robust and plumose setae; molar process and palp as in left mandible. Upper Lip (Fig. 11A): rounded, apical margin of labrum with numerous fine setae. Lower Lip (Fig. 11B): inner lobes highly reduced, outer margins of both inner and outer lobes covered in numerous fine setae; face of lip covered in pubescence. Maxilla 1 (Fig. 11C): inner plate with 5 plumose marginal setae and fine pubescence covering entire plate; outer plate with 7 apical comb-spines, pubescence covers entire plate, decreasing laterally; palp 2-segmented, distal segment covered in pubescence; apical margin of distal segment with 9 setae. Maxilla 2 (Fig. 11D): both inner and outer plates covered in pubescence; outer plate subequal in length to inner plate, with 15 apical setae; inner plate narrowing distally, with 13 apical setae and 5 plumose facial setae. Maxilliped (Fig. 11E): inner plate much shorter than outer plate, with 3 unarmed spine-teeth, 1 armed spine-tooth along apical margin and 2 plumose inner marginal setae, surface of plate covered in fine pubescence; outer plate armed with 20 setae, several of which are plumose or robust; palp 4-segmented, second segment with 20 marginal/submarginal setae on inner margin, and 1 distal outer marginal seta, third segment with numerous distal setae, lateral surface pubescent; dactylus with 1 outer seta and 1 inner seta.
Gnathopods: Gnathopod 1 (Fig. 12A): coxal plate with 9 apical setae and sparse amounts of short facial setae; basis with numerous long setae inserted along anterior, posterior, lateral and medial margins, along with shorter anterodistal setae, a small patch of pubescence is present on the posterodistal corner; ischium with 3 setae and pubescence along posterior margin; merus with pubescence covering posterior surface and 11 plumose posterodistal setae; carpus 87% length of propodus, with 3 anterior setae, 2 groups of medial setae and 7 plumose posterior setae; propodus 1.5 times longer than broad with 2 marginal anterior setae, 4 inferior medial setae, 2 proximally placed superior medial setae, 6 posterior setae; palm transverse with 7 rows of short robust setae and 6 long setae; defining angle armed with 3 inner and 2 outer robust setae; dactylus with 1 to 2 outer seta(e) and 5 inner setae. Gnathopod 2 (Fig. 12B): coxal plate with 7 apical setae and sparse amounts of short facial setae; basis with numerous long setae inserted along anterior and posterior margins, shorter setae arise distally from anterior margin, a small patch of pubescence is present on the posterodistal corner; ischium with 3 short setae and pubescence along posterior margin; merus with pubescence covering posterior surface and 3 posterior setae; carpus 80% length of propodus with 5 anterior setae, 1 group of medial setae and 5 groups of plumose posterior setae; propodus 1.8 times longer than broad, with 1 marginal anterior seta, 7 superior medial setae, 3 inferior medial setae and 4 groups of plumose posterior setae; palm oblique with 7 outer and 5 inner robust setae and 6 long outer setae; defining angle armed with 3 inner and 1 outer robust setae; dactylus with 1 outer seta and 5 inner setae.
Pereopods: Pereopod 3 (Fig. 12C): coxal plate with 8 apical setae and sparse facial setae; basis with numerous anterior and posterior setae; merus 1.3 times longer than carpus, carpus subequal to propodus in length; dactylus 40% length of propodus, with 1 plumose seta on outer margin, a stout seta on distal corner of inner margin followed by a thin seta on distolateral margin. Pereopod 4 (Fig. 13A): subequal to pereopod 3 in length; coxal plate slightly longer than broad, with distinct excavation along the posteroproximal margin, armed with 12 apical setae and numerous facial setae; merus 1.4 times longer than carpus, carpus subequal to propodus in length; dactylus approximately 40% length of propodus, setation similar to pereopod 3. Pereopod 5 (Fig. 13B): coxal plate large, bilobate with distinct anterior and posterior lobes, posterior lobe with 1 seta on distal corner; basis posterior margin straight with 9 shallow serrations and a rounded distal corner, anterior margin with 6 split-tipped robust setae, 3 distal setae and 1 proximal seta, face of segment with sparse setae; merus 80% length of carpus; carpus subequal to propodus in length, dactylus approximately 38% length of propodus, setation similar to other pereopods. Pereopod 6 (Fig. 13C): coxal plate bilobate, with produced posterior lobe, posterior lobe bearing 1 apical seta; basis posterior margin weakly convex with 8 shallow serrations and a straight distal corner, anterior margin with 7 split-tipped robust setae, and 2 distal robust setae, face of segment with sparse setae; merus 70% length of carpus; carpus subequal to propodus in length, dactylus approximately 33% length of propodus, setation similar to other pereopods. Pereopod 7 (Fig. 13D): coxal plate lobes indistinct, with 2 posterior setae; basis posterior margin convex with 10 serrations (increasing in depth distally) and a straight distal corner, anterior margin with 5 split-tipped robust setae, 2 distal robust setae, and 1 proximal seta, face of segment with sparse setae; merus 70% length of propodus; carpus subequal to propodus in length, dactylus approximately 33% length of propodus, setation similar to other pereopods.
Gills and brood plates (Figs. 12 B–C, 13A–D): coxal gills present on somites 2–6, somite 7 with pereopod 7 gill, subequal in size to coxal gills. Large, setaceous brood plates present on somites 2–5, decreasing in size posteriorly. Sternal gills present on somites 6 and 8.
Pleosome: second and third segments with 1 to 2 setae arising on dorsodistal margins and shorter pubescence weakly covering dorsal surface. Pleopods (Fig. 13 E–G): peduncle of pleopod 1 short, 35% length of rami, lacking setae, with 2 coupling hooks and a patch of pubescence on distal corner of outer margin; outer and inner rami with 14 and 16 segments respectively; pleopod 2 peduncle lacking setae, with 2 coupling hooks and a patch of pubescence on distal corner of outer margin; outer and inner rami with 13 and 14 segments respectively; pleopod 3 peduncle lacking setae, with 2 coupling hooks and a patch of pubescence on distal corner of outer margin; outer and inner rami with 12 segments each. Epimera (Fig. 14A): first epimeron ventral margin unarmed, distoposterior corner distinctly produced, with tooth-like extension, posterior margin with 1 seta placed proximally from distoposterior corner, face of epimeron with 1 seta; second epimeron ventral margin with 3 robust setae, distoposterior corner distinctly produced, with tooth-like extension, posterior margin with 1 seta placed halfway up margin; third epimeron ventral margin with 2 robust setae, distoposterior corner weakly produced, with weaker tooth-like extension, posterior margin with 1 seta placed proximally from distoposterior corner.
Urosome: mostly bare, with sparse setae covering dorsal surface. Uropod 1 (Fig. 14B): peduncle 1.25 times length of rami with 2 robust setae along the inner margin and 8 robust setae on outer margin; rami narrowing slightly distally, outer ramus 88% length of inner ramus, with 3 robust setae on inner margin, 5 robust setae on outer margin, and 4 apical robust setae; inner ramus with 3 robust setae on inner margin, 4 robust setae on outer margin, 4 apical setae, and 1 small seta placed proximally on ventral margin. Uropod 2 (Fig. 14C): peduncle subequal in length to outer ramus with 4 outer and inner robust setae, distal-most inner setae inserted in a pair; rami not narrowing distally, outer ramus 88% length of inner ramus, with 3 robust setae on inner margin, 4 robust setae on outer margin and 3 apical robust setae; inner ramus with 4 robust setae on inner margin, 4 robust setae on outer margin and 4 apical robust setae. Uropod 3 (Fig. 14D): peduncle 60% length of outer ramus, with 1 robust seta on inner and outer margins and 3 robust setae placed apically; inner ramus reduced, scale-like with 2 marginal robust setae; outer ramus 4.5 times longer than broad, 4 times longer than inner ramus, with 4 groups of robust, split-tipped setae on outer and inner margins, apex with a slender seta paired with a short robust seta.
Telson (Fig. 14E): quadrate, as broad as long, lobes fused, cleft approximately 50% of length, apices armed with 3 robust setae and 1 plumose seta, 2 additional plumose setae arise dorsolaterally from outer margins of both lobes.
Description of male: Allotype (UFID 52594) 4.16 mm in length, differing from female in smaller body length; shorter antennae; presence of calceoli on the peduncle and flagellum of antenna 2; presence of more robust gnathopods with enlarged propodi and more robust setae on the palmar margins; gnathopod 1 lacking superior medial setae; pereopods 5–7 with fewer posterior serrations on bases; uropod 1 setation; uropod 2 setation, including presence of comb-spines on inner margin of outer ramus; uropod 3 setation; and telson shape. Brownish in coloration when alive. Structures not described below as in female.
Antennae: Antenna 1 (not illustrated but see Fig. 2D): approximately 75% body length, 1.9 times longer than antenna 2; primary flagellum with 16 segments; accessory flagellum 2-segmented, shorter than first flagellar segment in length. Antenna 2 (Fig. 15A): gland cone distinct, peduncle 2 times longer than flagellum, segment 3 lacking robust setae, plumose setae present on anterior and posterior margins of segment 4 and on anterior margin of segment 5, segments 4 and 5 subequal in length; elongate calceoli present on both peduncle and flagellum; flagellum 5-segmented, calceoli absent on final two segments.
Gnathopods: Gnathopod 1 (Fig. 15B): coxal plate with 5 apical setae and sparse amounts of short facial setae; basis with a few long setae inserted along anterior and posterior margins, a small patch of pubescence is present on the posterodistal corner; ischium with 3 plumose setae and pubescence along posterior margin; merus with pubescence covering posterior surface, with 6 plumose setae and 1 smooth seta along anterior margin; carpus 50% length of propodus with 1 anterior seta, 1 group of plumose medial setae and 1 group of plumose posterior setae; propodus robust, 2 times longer than broad with 2 marginal anterior setae, 1 inferior medial seta and 4 plumose posterior setae (superior medial setae lacking); palm oblique with 7 inner and outer bifid robust setae and 3 long outer setae; defining angle armed with 4 inner and 3 outer robust setae; dactylus with 1 outer seta and 1 inner seta. Gnathopod 2 (Fig. 15C): coxal plate with 6 apical setae and sparse amounts of short facial setae; basis with a few long setae inserted along anterior and posterior margins; ischium with 1 seta and pubescence along posterior margin; merus with pubescence covering posterior surface and 1 distal seta; carpus 50% length of propodus with 1 anterior seta, 1 group of medial setae, and 11 plumose posterior setae; propodus powerful, 2 times longer than broad with 3 singlyinserted superior medial setae, 1 inferior medial seta and 3 groups of plumose posterior setae; palm oblique with 8 outer and 9 inner bifid robust setae and 2 long outer setae, defining angle armed with 3 inner robust setae and 2 large outer robust setae; dactylus with 1 outer seta and 1 inner seta.
Pereopods: Pereopod 5 (Fig. 16A): basis posterior margin with 6 extremely shallow serrations. Pereopod 6 (Fig. 16B): basis posterior margin with 6 shallow serrations. Pereopod 7 (Fig. 16C): coxal plate lobes indistinct, with 2 apical setae; basis posterior margin with 9 serrations (increasing slightly in depth distally), and a convex distal corner, anterior margin with 3 marginal split-tipped robust setae, 1 proximal seta, and 2 setae on distal corner, face of segment with sparse setae.
Urosome: mostly bare, with sparse setae covering dorsal surface. Uropod 1 (Fig. 16D): peduncle subequal to rami in length with 1 inner and 6 outer robust setae; outer ramus 75% length of inner ramus, with 3 robust setae on inner margin, 4 robust setae on outer margin and 5 apical robust setae; inner ramus with 3 inner robust setae, 3 outer robust setae, a ventroproximal seta and 5 apical robust setae.
Uropod 2 (Fig. 16E): peduncle 1.2 times length of inner ramus with 2 unpaired inner robust setae and 2 thin simple outer setae; outer ramus 80% length of inner ramus with 6 outer robust setae and 2 apical setae, inner margin with 10 short comb-spines which reach approximately 50% the length of the ramus; inner ramus with 3 outer and inner robust setae, apex with 5 robust setae. Uropod 3 (Fig. 16F): peduncle 50% length of outer ramus, with 3 robust setae on outer margin; inner ramus reduced, scale-like, with single robust seta; outer ramus elongate, 5 times longer than broad, 5 times longer than inner ramus, with 3 to 4 groups of short robust setae on outer and inner margins, apex with a slender seta paired with a short robust seta.
Telson (Fig. 16G): elongate, with a width to depth ratio of 0.66, lobes fused, cleft 45% of length, apices armed with 3 large robust setae, 2 additional plumose setae arise dorsolaterally from outer margins of both lobes.
Type locality. St. Marks Headwaters Greenway (30.46089, -84.10570), Leon County, Florida, ephemeral pool at edge of cypress swamp (Fig. 1B).
Variation. Individuals examined were shown to vary in several morphological characteristics (Table 2).
Etymology. The specific epithet pseudoephemerus is given in reference to the species’ occurrence in ephemeral pools and its co-occurrence with the morphologically similar Crangonyx ephemerus n. sp.
Distribution and Ecology. In a similar fashion to Crangonyx ephemerus n. sp., C. pseudoephemerus n. sp. is currently only known from near the headwaters of the St. Marks River in Leon County, Florida, where it has been collected from ephemeral pools at the edges of a cypress swamp (Fig. 1). It occurs syntopically with the similar C. ephemerus n. sp. at this locality. In the adjacent St. Marks River proper it is either absent or rare, with the only macro-crustaceans appearing in repeated collections being Caecidotea spp. and Procambarus spp.
During the months of March and April seven individuals of C. pseudoephemerus n. sp. were collected, four were females and of those females two (50%) were ovigerous. Additional collections during different times of the year will be needed to better understand potential breeding seasonality and population sex ratios.
Morphological analyses. Individuals of both Crangonyx ephemerus n. sp. and C. pseudoephemerus n. sp. appear similar in overall morphology but are readily distinguishable (see Table 4). A principal component analysis (PCA) based on 15 characters (Table 3) exhibited distinct separation between the two new species and the closely related C. floridanus, with only minimal overlap (Fig. 17). The first principal component (PC 1 on x-axis of Fig. 17) explained 59.2% of the variation with an eigenvalue of 0.07 and separated the species predominately based on uropod 1 peduncle outer robust setae number. The second principal component (PC 2 on the y-axis of Fig. 17) explained 16.8% of the variation with an eigenvalue of 0.02 and separated species predominately based on body length.
Although a PCA was able to show differentiation between the two species using a combination of quantitative characteristics, only 4 out of the 15 characters examined exhibited statistical significance (P <0.05) between Crangonyx ephemerus n. sp. and C. pseudoephemerus n. sp. when examined using the Student’s t -test (Table 3). Nevertheless, the two species can be readily distinguished via the use of several qualitative morphological characters commonly used for specific level differentiation within the genus Crangonyx, including uropod armament and telson cleft (Table 4).
Molecular analyses. All phylogenetic trees reconstructed using four genes (the nuclear 18S rDNA, 28S rDNA, the mitochondrial 16S rDNA and COI) clearly identify individuals of Crangonyx ephemerus n. sp. and C. pseudoephemerus n. sp. as separate, well-supported clades (Figs. 18, 19). With both C. ephemerus n. sp. and C. pseudoephemerus n. sp. showing more affinity to separate species than to each other.
Species delimitation. Species delimitation performed using three methodologies (GMYC, bPTP, and ABGD) identify the phylogenetic divergence between these clades as specific level, identifying C. ephemerus n. sp. and C. pseudoephemerus n. sp. as separate, well-supported species (confidence>95%) from each other and the morphologically similar C. floridanus in all cases (Fig. 18).
description: Published as part of Cannizzaro, Andrew G. & Sawicki, Thomas R., 2019, Two new species of the genus Crangonyx Bate, 1859 (Amphipoda: Crangonyctidae) from the St. Marks River Basin with notes on the " Crangonyx floridanus complex ", pp. 301-332 in Zootaxa 4691 (4) on pages 316-328, DOI: 10.11646/zootaxa.4691.4.1, http://zenodo.org/record/3527317