Hyalella wakulla, Drumm & Knight-Gray, 2019

Drumm, David T. & Knight-Gray, Julianne, 2019, A new species of the Hyalella ‘ azteca’ complex (Crustacea: Amphipoda: Hyalellidae) from Florida, Zootaxa 4545 (1), pp. 93-104 : 95-102

Hyalella wakulla n. sp.

( Figs 2–7)

Material examined. Holotype: male (♂), 5.2 mm, ( USNM 1480585 ), Wakulla River , 30°9ʹ 49.14ʺN, 84°13ʹ 45.4794ʺW, salinity: 0.2 ppt . Allotype: female (♀), 4.5 mm, ( USNM 1480586 ), same locality as holotype .

Paratypes: 5 females, ( USNM 1480588 ) ; 5 males, ( USNM 1480587 ); all same locality as holotype .

Additional material: 16 females, 19 males, 97 juveniles retained in the author’s ( DTD) collection at EcoAnalysts, Inc .

Diagnosis. Eyes present and pigmented. Pleonites 1 and 2 with dorsoposterior carina. Antenna 1 shorter than antenna 2 but greater than half its length; flagellum with 8–10 articles. Antenna 2, flagellum with 8–11 articles. Maxilla 1, inner plate with two terminal and one (or two?) subterminal pappose setae; palp abruptly narrowing at distal end to acute tip, without setules. Maxilla 2 inner plate with two strong pappose setae on inner margin. Gnathopod 1 propodus length less than twice maximum width, with four pappose setae on inner face. Gnathopod 2 (males), basis ventral margin with two setae; carpus posterior lobe longer than merus width; palm oblique, with angled notch. Pereopod 7, basis posterior lobe ventral margin with several stout spiniform setae. Uropods 1 and 2 without curved setae. Uropod 3, ramus and peduncle subequal in length. Telson slightly wider than long, with two simple terminal setae widely spaced.

Description of male. Size, 5.2 mm ( Fig. 2A). Rostrum absent. Eyes pigmented, black, round, located between insertion of antenna 1 and 2 ( Fig. 3A ). Pleonites 1 and 2 with dorsoposterior carina ( Figs 2, 3B ). Epimerial plates slightly acuminate ( Fig. 3B ). Coxae 1–4 deeper than wide, slightly overlapping; coxa 5 with two subequal lobes; coxa 6 with posterior lobe larger than anterior lobe; coxa 7 with single posterior lobe.

Antenna 1 ( Fig. 3C ) less than half body length, shorter than antenna 2, longer than peduncle of antenna 2; article 1 longer and wider than article 2, article 2 longer than article 3; flagellum with 8 articles.

Antenna 2 ( Fig. 3D ) less than half body length; peduncle articles 4 and 5 subequal in length; flagellum with 9 articles. Upper lip ( Fig. 3E ) rounded, distally setulate.

Mandibles: Left mandible ( Fig. 3F ) incisor process with six teeth; lacinia mobilis with five teeth; setal row with three main pappose setae plus accessory seta. Right mandible ( Fig. 3G ) incisor process with five teeth; setal row with two main pappose setae plus two accessory setae. Molar process large, cylindrical, and triturative, accessory seta present.

Lower lip ( Fig. 3H ) outer lobes rounded, setulate; mandibular lobes distally tapering.

Maxilla 1 ( Fig. 3I ) palp longer than wide, abruptly tapering distally, without setules, reaching to about half the distance between base of palp and tip of setae on outer plate; outer plate with nine stout and serrate setae, inner margin with several simple setae distally; inner plate slender, with two terminal and one subterminal pappose setae, lateral margins setulate.

Maxilla 2 ( Fig. 4A ) inner plate slightly shorter than outer plate, with two strong pappose setae on inner margin.

Maxilliped ( Fig. 4B ) inner plate with three terminal connate setae, medial and distal margins with pappose setae; outer plate with simple setae on distal, medial, and facial margins; palp with 4 articles, article 2 slightly longer than wide, with simple setae on medial margin; article 3 distally with simple setae; article 4 with distal nail and five subterminal simple setae on medial margin.

Gnathopod 1 ( Figs 4C, D ) subchelate, smaller than gnathopod 2; carpus longer than wide, longer than and as wide as propodus, posterior lobe with ten setae and comb scales proximally; propodus length about 1.5 times maximum width, inner face with four pappose setae, comb scales on disto-posterior and disto-anterior margins, palm transverse, posterior distal corner with robust seta; dactylus with comb scales and one sensory seta.

Gnathopod 2 ( Fig. 4E ) subchelate; posterior margin with two setae; merus with four distal simple setae and disto-posterior comb scales; carpus posterior lobe about 1.5 times as long as width of merus, with five distal simple setae and row of about eleven short pappose setae; propodus with comb scales disto-posteriorly, palm oblique, with distinct notch and row of strong setae of differing lengths; dactylus with one sensory seta.

Pereopods 3 and 4 ( Figs 4F , 5A ) similar in size and shape; merus longer than carpus, with disto-anterior lobes extending 1/3 or less length of carpus; dactylus with one sensory seta.

Pereopods 5 and 6 ( Figs 5B, C ) of similar shape and setation, pereopod 6 longer than pereopod 5; basis posterior margin expanded and denticulate, anterior margin with four robust setae; dactylus with one sensory seta.

Pereopod 7 ( Fig. 5D ) subequal to pereopod 6; basis posterior lobe greatly expanded and denticulate, distal margin with three robust spiniform setae.

Uropod 1 ( Fig. 5E ) longer than uropod 2; peduncle longer than rami, with five spiniform setae; inner ramus with two dorsal and four distal/subdistal spiniform setae, without curved setae; outer ramus with three dorsal and four distal/subdistal spiniform setae.

Uropod 2 ( Fig. 5F ) peduncle subequal to rami, with five spiniform setae; inner ramus with two dorsal and five distal/subdistal spiniform setae; outer ramus with two dorsal and five distal/subdistal setae.

Uropod 3 ( Fig. 5G ) peduncle subequal to ramus, with three spiniform setae decreasing in length distally; ramus with three simple and one connate terminal setae.

Telson ( Fig. 5H ) wider than long, with two long simple terminal setae widely spaced and pair of three short plumose setae.

Coxal gills sac-like, present on pereonites 2 to 6. Sternal gills tubular, present on pereonites 3 to 7.

Adult female: similar to male except for the following: size about 4.5 mm ( Fig. 2B); gnathopod 2 ( Figs 6C, D ) similar to size and structure to gnathopod 1 ( Figs 6A, B ) (which is similar to gnathopod 1 of males); propodus slender and longer than propodus of gnathopod 1, about two times longer than wide.

Intraspecific variation: The setation of uropod 3 varied in both males and females and sometimes even in the same individual. In one adult male, the right ramus had four terminal simple setae and no connate setae, and the left ramus had three terminal and one connate seta ( Fig. 7A ). In another male the rami had two simple setae and two (one long and one short) connate setae ( Fig. 7B ). In the same male the terminal setae of the telson ( Fig. 7C ) was more robust than what is typical. In one of the females examined, the right ramus had three simple setae and one connate seta, and the left ramus had four simple setae and one connate seta ( Fig. 7D ). The last article of the maxillipedal palp can have four or five subterminal simple setae on the medial margin. One pereopod 7 examined had only one robust spiniform seta on the distal margin of the basis posterior lobe. One male had three marginal spiniform setae on the outer ramus of uropod 2. All of the specimens examined were adults and around the same size.

Etymology. The species is named after the river in which it was found.

Remarks. Hyalella wakulla n. sp. keys out to H. azteca using Soucek et al. (2015) but can be distinguished by the shape (abruptly tapering distally) and lack of setules of the maxilla 1 palp, the inner plate of maxilla 1 with two terminal and one subterminal setae ( H. azteca has three terminal setae), and the telson having the terminal setae separated (not separated in H. azteca ). Hyalella azteca is also a large-bodied (6–8 mm) ecomorph ( Wellborn 1995), while H. wakulla is a small-bodied (4.5–5.5 mm) ecomorph. We believe the new species is not conspecific with the partially described Hyalella sp. C sensu LeCroy (2007) found in two western Florida bays. Regarding the fact that the setation of uropod 3 rami is variable in H. wakulla , the specimens we examined always had at least three terminal setae, while Hyalella sp. C only has two. Also, the last maxillipedal palp article of H. wakulla has at least four subterminal setae on the medial margin, while Hyalella sp. C only has three. Hyalella wakulla is a freshwater species, while Hyalella sp. C is found in medium to high salinity habitats.

DNA barcoding and phylogeographic research has shown that Hyalella azteca sensu lato is composed of numerous cryptic species ( Witt & Hebert 2000; Witt et al. 2006; Hrycyshyn 2015). Witt et al. (2006) discovered 33 provisional species within Hyalella azteca from the southern Great Basin of California and Nevada. Hrycyshyn (2015) discovered a large-bodied ‘ azteca ’ clade ( Hyalella species 8) occurring throughout freshwater habitats in Florida and parts of Alabama, Mississippi, Tennessee, Arkansas, and Kansas, and he discovered a small-bodied ‘ azteca ’ clade ( Hyalella species 5) occurring in various localities throughout the eastern half of North America including northern Florida, and another small-bodied ‘ azteca ’ clade ( Hyalella species 4) occurring in southeastern USA, including northern Florida. Hrycyshyn (2015) unfortunately did not sample from the Wakulla River, but H. wakulla , n. sp. falls in the small-bodied group, so it is possible that this is his “species 5,” which he sampled from the Apalachicola River and Mosquito Creek west of the Wakulla River. Preliminary examination of specimens from Mosquito Creek revealed no major differences from H. wakulla . One male specimen had four setae (two terminal and two subterminal) on the maxilla 1 inner plate, while another male and a female had three setae, as in H. wakulla . Examination of additional material (plus DNA sequence data from H. wakulla ) will be necessary in order to establish conspecificity. Hrycyshyn’s species 4 differs from H. wakulla . Four of the five specimens examined (Juniper Lake, Florida) had a carina only on pleonite 1, and the fifth specimen had a reduced carina on pleonite 2. The maxilla 1 inner plate had two terminal and no subterminal setae, and the palp was shorter than in H. wakulla . The pereopod 7 basis posterior lobe ventral margin was without stout spiniform setae. Unfortunately, only females were available for examination. While we agree that Hyalella is a taxonomically difficult genus of amphipod crustaceans, we believe that the notion of all ‘morphologically cryptic’ species are diagnosable only with molecular studies ( Witt et al. 2006) is a gross misconception. Subtle, as well as not so subtle, differences are usually found during detailed examinations ( King et al. 2012). Efforts should be made to try and formally describe this diversity, as the exploration of biodiversity starts with taxonomy. However, this is unfortunately rarely accomplished ( Pante et al. 2015), all due to the taxonomic impediment [eg., dwindling taxonomic expertise, lack of funding, low impact factor, etc. ( Coleman 2015)].

Recent morphological work has provided evidence of an exceptionally high diversity of Hyalella in South and Central America ( González 2003; González et al. 2006; Santos et al. 2008; Bueno et al. 2013; Cardoso et al. 2014; Marrón-Becerra et al. 2014; Rodriques et al. 2014; Colla & César 2015). A comparably high diversity in North America is only beginning to be understood ( Hrycyshyn 2015; Soucek et al. 2015). We anticipate that many more species new to science will be discovered in North America, as many of the known species are restricted to specific habitats.

Hyalella wakulla was the most abundant crustacean in the locality where it was discovered, and was collected together with the amphipods Grandidierella bonnieroides Stephensen, 1948 , Gammarus mucronatus Say, 1818 , and Cerapus sp.; the isopods Caecidotea sp., Cyathura polita ( Stimpson, 1856) , and Uromunna sp.; the cumacean Almyracuma bacescui Petrescu & Heard, 2004 ; the midge Cryptochironomus sp.; the leach Gloiobdella elongata ( Castle, 1900) ; the caddisfly Oecetis sp.; the bivalves Pisidium sp. and a species of Sphaeriidae ; and the polychaetes Ceratonereis sp., Hobsonia florida ( Hartman, 1951), and Capitella capitata ( Fabricius, 1780) complex.

Figures

FIGURE 3. Hyalella wakulla n. sp., adult male. A, head and peduncle of antenna 1 and antenna 2 (lateral view); B, pleon (lateral view); C, antenna 1; D, antenna 2; E, upper lip; F, left mandible; G, right mandible; H, lower lip; I, maxilla 1. Scale bars: A, B = 0.2 mm; C, D = 0.1 mm; E–I = 0.05 mm.

FIGURE 4. Hyalella wakulla n. sp., adult male. A, maxilla 2; B, maxilliped; C, gnathopod 1; D, close-up of gnathopod 1 chela; E, gnathopod 2; F, pereopod 3. Scale bars: A, B = 0.05 mm; C, E, F = 0.1 mm.

FIGURE 5. Hyalella wakulla n. sp., adult male. A, pereopod 4; B, pereopod 5; C, pereopod 6; D, pereopod 7; E, uropod 1; F, uropod 2; G, uropod 3; H, telson. Scale bars: A–E = 0.1 mm; F-H = 0.05 mm.

FIGURE 6. Hyalella wakulla n. sp., adult female. A, gnathopod 1; B, close-up of gnathopod 1 chela; C, gnathopod 2; D, closeup of gnathopod 2 chela. Scale bars = 0.1 mm.

FIGURE 7. Hyalella wakulla n. sp., adult male. A, right and left uropod 3; B, uropod 3; C, telson. Adult female; D, right and left uropod 3. Scale bars = 0.05 mm.