Lynceus grossipedia, Sigvardt & Shu & Alonso & Ventura & Sanoamuang & Rogers & Palero & Olesen, 2020

Sigvardt, Zandra M. S., Shu, Shusen, Alonso, Miguel, Ventura, Marc, Sanoamuang, La-orsri, Rogers, D. C., Palero, Ferran & Olesen, JØrgen, 2020, A new Northeast Asian Lynceus (Crustacea: Branchiopoda: Laevicaudata) with uniquely modified thoracopods and an evaluation of DNA barcoding for clam shrimp species identification, Nauplius (e 2020013) 28, pp. 1-25 : 5-18

Lynceus grossipedia n. sp.

( Figs. 1–9 )

Zoobank: urn:lsid:zoobank.org:act:B0FBCC1D-782A-4FE3-8946-3E58AC73EE51

Etymology. The species epithet grossipedia is a combination of the word “grosso” from Italian meaning “big/fat” and the Latin word pedes meaning “legs”, referring to the male’s left side thoracopods III– VI, which have enlarged muscular bases.

Type locality. MONGOLIA: Tuv Province: Uguu nuur (Lake), 47°40’26.1”N 108°21’22.8”E, 1307 m a.s.l., coll. Miguel Alonso, 24 August 2017 .

Type material. Holotype: Male, from type locality (NHMD-615874). Allotype: Female, from type locality (NHMD-616085). Paratypes: 11 males and 7 females, same collecting data as for holotype : 2 males and 2 females prepared on SEM stubs; 1 male and 1 females prepared on microscope slides (few larger parts still in ethanol); 2 males used for DNA extraction (voucher specimens); remaining 6 males and 4 females in ethanol (NHMD-616086, 554 TU [ TU and DUG codes from the Limnological Catalogue of Mongolian Lakes (see website: http://oslo.geodata. es/mongolian_lakes)].

Other material examined. MONGOLIA: Dundgovi Province: Khar debrin khudagiin toirom (lagoon), 45°31’00.6”N 105°50’00.4”E, 1398 m a.s.l., 1 male (NHMD-616088, 578 DUG) . Delgerekhiin toirom (lagoon) 15, 46°28’03.0”N 107°55’07.0”E, 1250 m a.s.l., 5 males and 6 females (NHMD-616087, 1197 DUG) . Delgerekhiin toirom (lagoon) 14, 46°28’04.0”N 107°54’56.0”E, 1240 m a.s.l., 1 male and 2 females (NHMD-615923, 1196 DUG) . All specimens collected by Miguel Alonso, August 2017 . CHINA: Jilin Province: Qianguo County: Songyuan City: Chaganhua Town : DongPao Lake , 44°36’10.6”N 124°15’38.2”E, 177 m a.s.l., 14 September 2017, 10 males, 12 females (8 males, 10 females in KIZ; 2 males, 2 females NHMD-615880) . Qian’an County: Daozixiang Town: Busu Lake , 44°53,38.8”N 123°44’45.3”E, 138 m a.s.l., 16 September 2017, 5 females ( KIZ) . Inner Mongolia Autonomous Region: Keyou Zhongqi County: Xing’anmeng City : Haoyaosumu Town : a pond near the road of G111, 44°30’47.6”N 122°02’26.3”E, 174 m a.s.l., 19 September 2017, 2 males, 8 females ( KIZ) . All specimens collected by S. Shu.

Diagnosis

Male. Left side thoracopods III– VI modified as follows:thoracopods III– VI with broad muscular bases; thoracopod V with endopod and distal part of exopod explanate; exopod lamellar, biramal; thoracopod VI with endopod, endite 4 and 5 posteriorly directed (on limb posterior side), and exopod flabelliform, margin with ~7 lobiform processes (further details in description). Right side thoracopods unmodified (= right–left asymmetry). Male claspers: palm with scale patch laterally; movable finger (endopod) base with small knob, anteriorly with band of minute setae; two prominent bumps/protrusions laterally between “palm” and exopod. Rostrum bicarinate, distal margin truncate with setal row and minor distolateral corners.

Female. Rostrum bicarinate and distally broadly rounded with marginal denticles, distolateral corners indistinct. Lamina abdominalis with three dorsal extensions and three marginal extensions.

Both sexes: Rostral shape broad. Head in lateral view smoothly curving with compound eyes on ocular tubercle; compound eyes smaller than frontal setal fields. Description

Male (holotype, 4.2 mm, Fig. 2 ; paratypes Figs. 1 , 4 , 6–9 ).

Length range. Mongolian material: 3.4–4.7 mm (based on 10 specimens). Chinese material: 4.3–5.2 (based on 10 specimens).

Head ( Figs. 1A, B , 2B, C, E , 4A–C, E–H ). Large, ~25–30% of body, rostrum extending to thoracopod I. Head in lateral view arcuate, evenly curving with region of compound eyes protruding on ocular tubercle. Dorsal organ oval, near occipital condyle. Frontal setal fields oval, distally narrower, with short, dense setation, frontal pore dorsal. Compound eyes subcircular, ~50% smaller than setal fields. Rostrum bicarinate, protruding distally between frontal setal fields. Carinae parallel in proximal half, diverging in distal half, each branch terminating near rostral apex, but not reaching it. Rostral apex truncate with distal transverse setal row, distolateral corners not projecting, denticles absent. Rostrum in anterior view broad with minor constriction approximately at second antennae insertion. Fornices present where rostral marginal rims bend anteriolaterally, from above second antenna insertion to distolateral corners. Rostral apex broad in lateral (and apical) view.

First antenna ( Fig. 4E, G, K ). With two antennomeres. Proximal antennomere short, about twice as long as broad. Distal antennomere cylindrical, length ~5x> breadth, with numerous simple setae in two longitudinal rows.

Second antenna ( Figs. 2B, C , 4C–G ). Biramous, extending to around thoracopod IX. Peduncle proximal coxa with transverse row of ~4–5 long plumose setae ventrally and transverse row of ~4 short setae dorsally. Peduncle basis with 6–8 short setae dorsally. Exopod (anterior flagellum) with ~20–22 flagellomeres; short acute seta dorsally and long, plumose seta ventrally. Endopod (posterior flagellum) longer than exopod, with ~24–26 flagellomeres; long, plumose seta ventrally.

Labrum ( Fig. 4G ). Large, lobiform. With fine setae around apex and posteriorly. Minute setae in clusters of 1–3, most dense around apex.

Mandible ( Fig. 4L–N ). Molar surface with ~21–22 transverse ridges. Posteriormost three ridges broadly spaced. Distalmost ridge projecting as single spine, previous two ridges bispinose without ornamentation (maybe due to wear). Remaining ridges closely placed, bispinose with hamulate spines and anterior transverse rows of tubercles (see female description). Ridges broadest around mandible middle, decreasing in size anteriorly. Fine setae present anteriorly, longer ones in cluster near ridges, shorter ones scattered on anterior surface.

Paragnath. Posterior to maxilla I, posterior surface covered with fine setae.

Maxilla I. Elongate, distally semicircular. Posterior surface covered with fine setae. Medially with ~10 long plumose setae, distalmost surface with 2–3 short robust setae with denticulae.

Maxilla II. Absent.

Carapace ( Figs. 1C , 2A–D, G , 4A, C ). Shape subspherical, longer than broad, smooth, without ornamentation. Rounded anteriorly (near attachment of adductor muscle), more arcuate posteriorly. Ducts of maxillary gland transversely surrounding adductor muscle. Oval in dorsal and ventral view, dorsally with depression at attachment site. [Open space around the body within the carapace on SEM images ( Figs. 4A , 5A ) is likely an artefact of drying].

Thoracopods ( Figs. 6–9 ). 10 pairs, becoming smaller from anterior to posterior. First pair modified as claspers, left side thoracopods III– VI modified (see further below).

Thoracopod I (clasper limb) ( Figs. 6 , 8A, B , 9A ): claspers equal in size and shape, with parts as typical for Lynceus present: endite 3 = “palm” with “gripping area”, endite 4 = small palp, endite 5 = large palp, and endopod = “movable finger”. Endite 1 lobiform, elongate, dorsal margin with multiple (~12) long setae, apex with 3–5 pectinate spines and ventrally a single long seta (similar found on remaining thoracopods). Endite 2 transverse, broad, long setae along margin. Endite 3 (palm with gripping area) suboval, in close proximity to endite 2; small protrusion (“knob”) near base of endopod (movable finger)( Figs.6B , 8B , 9B ); laterally with larger area with scales ( Fig. 6B, F, I ); posteriomedially with minor, discrete area with scales (difficult to see on images). Endite 3 medially with longitudinal gripping area with diverse setation (setae types sensu Sigvardt and Olesen, 2014): anterior margin with numerous (>25) long, robust setae (type 4); posterior margin with two rows of setae: five long setae, distally plumose (type 1), 7–8 conical peg-like spines (type 2), apex with prominent denticles in two parallel rows. Setae type 3 and 5 absent. Endite 4 (small palp) lobiform, anterioposteriorly flattened. Distal half with 3–4 long setae, some setae distally with bipectinate setulae; margined with>25 long (varying length), simple setae without setulae. Endite 5 (large palp) around twice as long as endite 4, clavate, becoming broader towards apex; long simple setae at apex (a few with setules) extending in dorsal sulcus; dorsal setae (>20) decreasing in size towards termination of sulcus (near palp basis). Endopod (movable finger) digitiform, curved; tapering towards apex, extending to proximal margin of endite 3 (gripping area); anterior side distal half with elongate band of minute setae clustering together 1–4 ( Fig. 6D, G ). Lateral part between palm and exopod bilobed with two prominent protrusions, basal width ~3x> medial length ( Figs. 8A, B , 9A, B ). Exopod proximal lobe broadly oval, distal lobe elongate with acute apex, both with long setae along margin, either simple or with setules. Epipod elongate, lacking setation.

Thoracopod II ( Fig. 8C ): not modified, typical for genus (see Olesen et al., 2016; Sigvardt et al., 2019) however, endite 2 and 3 elongate rounded and epipod relatively long.

Thoracopods III and IV ( Fig. 8D, E ): left side modified with muscular bases enlarged. Exopod proximal part and epipod long. Remaining parts and right side typical for genus ( Fig. 9C, D ).

Thoracopod V ( Figs. 7A, B , 8F ): left side modified with muscular basis enlarged. Endites 4 and 5 adjacent. Endopod explanate, proximally with stout lobiform structure extending posteriorly, setation as follows: dorsally stout setae increasing in length towards apex, ventrally long filiform setae. Exopod distal lobe biramal ( Fig.8F ), with lateral major part explanate, subquadrate with lateral margin undulating, setae absent; medial minor part triangular with setae distally. Remaining parts and right side typical for genus ( Fig. 9E ).

Thoracopod VI ( Figs. 7C–H , 8G ): left side highly modified with: (1) heavily enlarged musculature extending from basis to near apex ( Fig. 8G ), (2) endopod broadly lobiform, together with endite 4 and 5 directed posteriorly (on limb posterior side) ( Figs. 7D, F ), (3) exopod distal part transversely lamelliform, densely covered with robust setae tapering towards apex ( Fig. 7C, D, H ), few (~8) longer setae with setulae distally along margin ( Fig. 7H ). Exopod proximal part a large semicircular lamella with ~7 lobiform processes with deep invaginations between them ( Figs. 7C , 8G ); proximally with cluster of 5–6 long setae with setulae, posterior surface covered with robust elongate setae ( Fig. 7D, E ), anterior surface and margin lacking setation. Right side thoracopod VI typical for genus ( Fig. 9F ).

Thoracopods VII–X ( Figs. 8H–K , 9G–J ): left and right side typical for genus.

Unmodified structures of thoracopods II–X ( Figs. 8 , 9 ): endite 1 lamelliform, elongate, dorsal margin with multiple long setae, apex with ~3 pectinate stout spines, ventral margin with short setae and a single long prominent seta. Endite 2 transversely broad, with different setal types along margin, some long, slender with setules at distal half, others short, robust, without setulae. Endite 3 similar to endite 2, however less transversely broad. Endite 4 broadly digitiform, margin with ~6 prominent setae together with other setae of varying length. Endite 5 and endopod similar to endite 4, but distally with characteristic stout setae, distally pectinate serrate. Towards posterior thoracopods, all endites and endopod become of more similar shape. Epipod long, slender, without setation, present in thoracopods I–VIII. Exopod proximal lobe broadly oval, flattened, setation along entire margin; exopod distal lobe elongate with acute apex, setation along margin.

Telson ( Figs.1G ). Broad, dorsal lobes with elongate, filiform telsonal setae. Ventral surface finely hirsute except medially. Opercular lamella (thin membranous fold under telson) cordate with minute setae covering surface and margin.

Female (allotype, 3.9 mm, Fig. 3 ; paratypes Figs. 1 , 5 ).

Length range. Mongolian material: 3.2–4.4 mm (based on 8 specimens). Chinese material: 4.2–5.3 mm (based on 23 specimens). Generally similar to male in appearance.

Head ( Figs. 1K, J , 3B, E , 5A–C, E–H, L ). Larger than male head, ~35–40% of body, rostrum extending to thoracopod III. Head in lateral view roundly/evenly curving with region of compound eyes extruding (on ocular tubercle). Dorsal organ oval, with 4 circular elevations. Frontal setal fields and compound eyes as in male. Rostrum bicarinate, carinae parallel around 2/3 proximally, expanding last 1/3 distally with branches terminating near rostral apex but not reaching apex. Rostral apex broadly rounded, almost truncated similarly to male, with denticles, distolateral corners obsolete. Rostrum in anterior view broad with fornices following constriction around second antenna insertion to rostral apex (as in male). Minute setae along rostral margin from lower constriction to apex. Rostral apex broad in lateral view.

Antennae, first and second ( Figs. 3B, E , 5D–G, K ). As in male.

Mandible ( Fig. 5M–O ). Similar to male, with all bispinose ridges ornamented with hamulate spines, anterior row of ~12–16 tubercles, middle row of ~6 larger tubercles, and posterior row of ~4 tubercles (can be due to lack of wear).

Remaining mouthparts. As in male.

Carapace ( Figs. 1L , 3A–D, G , 5A, C ). As in male.

Thoracopods ( Figs. 3B , 5A, I, J ). 12 pairs, serially similar, unmodified, claspers absent; typical for genus (see Olesen et al., 2016; Sigvardt et al., 2019). Thoracopods IX and X with exopods distally modified into curved lobes, dorsally with minute setae clustering together in groups of ~4, apex with tuft of setose setae used to attach egg clutches.

Lamina abdominalis ( Fig. 5A, I ). Broad lamellar structure dorsal to thoracopods X–XII. With three marginal extensions and three dorsal extensions, all with small dentiform spines in minor clusters. Dorsal extensions: digitiform, hamulate, tapering towards apex, anterior extension longest, posterior shortest; all three directed anteriorly.Marginal extensions:anterior and medial extension similar to dorsal extensions but smaller, posterior extension broadly triangular, short; all directed anteriorly.

Eggs ( Figs. 3A, B, F, G , 5A ). Spherical, surface smooth, ~100 μm in diameter.

Telson ( Figs. 1H, I , 3F , 5I ). As in male.

Figures

Figure 1. Line drawings of Lynceus grossipedia n. sp., A–G: male, H–M: female. A. Head, anterior view. B. Head, left lateral view. C. Carapace, left lateral view. D. Left clasper, posterior view. E. Right clasper, anterior view. F. Opercular lamella, ventral view. G. Telson, left lateral view.H. Telson, ventral view. I. Telson, dorsal view. J. Head, left lateral view. K. Head, anterior view.L. Carapace, left lateral view. M. Lamina abdominalis, left lateral view. Scale bars 1 mm.

Figure 2. Lynceus grossipedia n. sp., male, stereo microscopy (holotype, NHMD-615874). A. Left lateral view, intact animal.B. Left lateral view, carapace valve removed. C. Ventral view, carapace valves apart. D. Dorsal view, carapace valves slightly apart. E. Head close-up (from B). F. Left side thoracopods, showing enlarged muscular bases. G. Carapace, left valve interior.

Figure 3. Lynceus grossipedia n. sp., female, stereo microscopy (allotype, NHMD-616085). A. Right lateral view, intact animal. B. Right lateral view, carapace valve removed. C. Ventral view, carapace valves slightly apart. D. Dorsal view. E. Head close-up (from B). F. Telson close-up (from B). G. Carapace, right valve interior.

Figure 4. Lynceus grossipedia n. sp., male, scanning electron microscopy (paratype, NHMD-616086). A. Left lateral view, carapace valve removed.B. Frontal setal fields.C. Left ventrolateral view.D. Left secondantenna.E. Head, lateralview.F. Head, anterior view. G. Head,anteroventral view.H. Dorsal organ.I. Telson,dorsal view.J. Telson, ventral view.K. First antennae.L. Left mandible,lateral view. M. Mandible close-up, dorsolateral view. N. Mandible close-up, dorsal view.

Figure 5. Lynceus grossipedia n. sp., female,scanning electronmicroscopy (paratype,NHMD-616086).A. Left lateral view, carapace valve removed. B. Frontal setal fields. C. Left ventrolateral view. D. Left second antenna. E. Head, lateral view. F. Head, anterior view.G. Head, anteroventral view.H. Dorsal organ.I. Telson and lamina abdominalis, dorsolateral view.J. Egg-carrying exopods of thoracopods IX and X. K. Distal part of right first antenna. L. Serration of rostral distal margin, lateral view (gap at edge likely due to drying artifact).M. Left mandible, lateral view. N. Left mandible, dorsal view. O. Mandible close-up (from N).

Figure 6. Lynceus grossipedia n. sp., male, scanning electron microscopy of claspers (same specimen as on Figs. 4, 7; paratype, NHMD-616086).A. Right clasper, anterior view.B. Left clasper, posterior view.C. Movable finger (endopod), large palp (endite 5), and gripping area (part of palm, endite 3), left clasper, apical view. D. Movable finger with band of minute setae, gripping area with type 4 setae, left clasper. E. Small palp (endite 4) and large palp (endite 5), right clasper. F. Palm with scales (encircled area in B), lateral view, right clasper.G. Setation on movable finger (endopod). H. Setation on posterior side of gripping area. I. Magnification of scales on clasper palm.

Figure 7. Lynceus grossipedia n. sp., male, scanning electron microscopy of modified thoracopods, broad muscular bases highlighted by coloring (same specimen as on Figs. 4, 6; paratype, NHMD-616086). A. Dorsolateral view of thoracopods, broad muscular bases of thoracopods III–VI colored.B. Modified exopods of thoracopod V and VI. C–H: all of thoracopod VI. C. Thoracopod VI in posterolateral view, note exopod with ~7 knob-shaped processes.D. Thoracopod VI in posterior view with endites, endopod and exopod labelled.E. Exopod,knob-shaped processes and posterior surface with long setae (magnificationof D).F. Endopod, broadly lobiform (magnification of D). G. Setae of endopod (magnification of F). Distal part of exopod densely setose.

Figure 8. Lynceusgrossipedia n. sp., male, light microscopy of left side thoracopods, seen from anterior (paratype, NHMD-616086). A. Thoracopod I (male clasper). B. Higher magnification of clasper.C–K. Thoracopods II–X of which III–VI (D–G) are modified, not least with notably enlarged muscular bases.F. Thoracopod V with endopod and distal part of exopod explanate.G. Thoracopod VI with exopod proximal part with ~7 knob-shaped processes and distal part highly setose (seen better on SEM images, Fig. 7H), endites 4–5 and endopod non-visible as folded behind thoracopod. Arrows indicate broken/hidden parts.

Figure 9. Lynceus grossipedia n. sp., male, light microscopy of right side thoracopods (unmodified) (paratype, NHMD-616086).A. Thoracopods I (male clasper) and II, seen from posterior. B. Higher magnification of clasper. C–K. Thoracopods III–X, seen from anterior; all of “regular” Lynceus type (= unmodified). Arrows indicate broken/hidden parts.