Lecane zhanjiangensis, Wei & Jersabek & Yang, 2019

Wei, Nan, Jersabek, Christian D. & Yang, Yufeng, 2019, Rotifers from China (Western Guangdong Province), with description of Lecane zhanjiangensis sp. nov. (Rotifera: Monogononta: Lecanidae), Zootaxa 4603 (1), pp. 66-80 : 66-80

Lecane zhanjiangensis sp. nov.

( Figs 2–3 )

Diagnosis. Lorica longer than wide; dorsal plate anteriorly narrower, medially wider than ventral plate; head aperture margin of dorsal lorica plate protruding significantly beyond ventral plate, with antero-lateral corners forming large semicircular projections, serrated anteriorly with three to five minute spines; antero-lateral corners of ventral plate with large acutely pointed projections; ventral transverse fold incomplete; foot pseudosegment trapezoidal, non-projecting; two relatively short toes, parallel-sided proximally, tapering to acute tips in distal third, no claws; trophi modified malleate; rami asymmetrical, with rounded alulae; unci with one major and two or three minor teeth.

Type locality. Littoral zone of the Shimenhe River outlet in Shimenhe Bay (N21° 24' 2.05", E110° 23' 12.30"), under the Shimen Bridge of Shenyang-Haikou Expressway (G15), Potou district, Zhanjiang City, Guangdong Province, China, distant from shore about 1.5 m, depth about 0.6 m, salinity 18.3‰, temperature 25.1?, pH 7.22, DO 3.86 mg /L, transparency 0.55 m, chlorophyll-a 5 µg /L, on 13 April, 2017.

Holotype. A female in a permanent glycerine glass slide mount deposited in the Museum of Biology , Sun Yatsen University, Guangzhou, China ( SYS ROT 00016).

Paratypes. Four females from type locality, in a glycerine permanent slide mount each. Two females in the Museum of Biology , Sun Yat-sen University , Guangzhou , China (SYS ROT 00017, SYS ROT 00018); one female in the Museum of Hydrobiological Sciences , Institute of Hydrobiology , Chinese Academy of Sciences , Wuhan , China ( MHBS R GD 2019010002); one female in the Academy of Natural Sciences of Drexel University, Philadelphia, USA ( ANSP 2138 ) .

Etymology. This species is named after the city of Zhanjiang, Guangdong, where the new species was found.

Description of female. Lorica ( Fig. 2 ) relatively soft, easily deformed. Head protruding significantly in imperfectly contracted specimens, with two or three pairs of acute spines bilaterally. Head aperture margins ventrally and dorsally almost straight in the middle, dorsal head aperture margin clearly protruding beyond ventral plate. Antero-lateral parts of dorsal plate with large semicircular projections, each with a series of three to five minute, more or less acute spines medially; antero-lateral corners of ventral plate with broad-based, acutely pointed projections with smoothly curved, medially convex inner margins. Dorsal plate smooth, near elliptical in wellcontracted animals. Ventral plate weakly ornamented, near parallel-sided and longer than wide; anteriorly wider, medially narrower than dorsal plate. Posterior margins of dorsal and ventral plate convex, without projections. Deep lateral sulci in well-contracted specimens. Ventral plate with weak, incomplete transverse fold. Foot pseudosegment trapezoidal, sub-terminal, non-projecting. Prepedal fold broad, rounded posteriorly. Coxal plates rounded triangular. Two parallel-sided, relatively short toes, with straight inner margins and curved external edges, then tapering to pointed tips in distal third, no claws.

Trophi modified malleate ( Fig. 3 ). Fulcrum short and plank-shaped in lateral view, rounded distally, broadly curved dorso-ventrally. Rami weakly asymmetrical, both with rounded alulae. Unci slightly asymmetrical, with one major ventral, and two or three minor teeth dorsally. Manubria elongate, with posterior chambers extending up to curved tips.

Male and eggs unknown.

Measurements. Body (N = 10 females): lorica ventral plate length 87–95 µm (mean = 91± 3 µm), ventral plate width 52–60 µm (mean = 55± 3 µm), dorsal plate length 83–92 µm (mean = 88± 3 µm), dorsal plate width 59–70 µm (mean = 65± 3 µm), anterior aperture width 40–53 µm (mean = 45± 5 µm), toe length 29–32 µm (mean = 30± 1 µm); trophi (N = 5): right ramus length 8.9–11.4 µm (mean = 10.0± 1.1 µm), manubrium length 25.2–28.4 µm (mean = 26.3± 1.2 µm), first right uncus tooth length 11.4–12.0 µm (mean = 11.7± 0.3 µm).

Distribution and ecology. Lecane zhanjiangensis sp. nov. was found in two locations in South China, one from the type locality with small numbers collected on 13 April, 2017 ( Tab. 1 ) and one from another brackishwater site (N20° 1' 6.5", E110° 23' 17.45") in the Nandujiang River Estuary, Haikou City, Hainan Province with one specimen collected on 7 April, 2017. The ecological characteristics of the waters were: salinity 18.3 and 14.7 ‰, water temperature 25.1 and 26.4°C, pH 7.22 and 7.9, DO 3.86 and 6.70 mg /L, transparency 0.55 and 1.50 m, chlorophyll-a 5 and 4 µg /L respectively. The high salinity in the localities clearly indicates it is a true brackishmarine Lecane . It co-occurred with two other saltwater species, viz. Trichocerca marina (Daday, 1890) ( Fig. 9 ) and a species from the Brachionus plicatilis - complex ( Tab. 2 ) in the type locality and one Synchaeta sp. in the Nandujiang River Estuary site.

Comments. The new species possibly is closely related to Lecane insulaconae Fontaneto, Segers & Melone, 2008 , a marine Lecane described from the Adriatic Sea, near the outlet of the Isonzo River, Northern Italy. Main differences between the two species are as follows: (1) dorsal plate near elliptical with average ratio of length/ width 1.37 (1.27–1.47) in L. zhanjiangensis sp. nov. vs. almost circular in L. insulaconae with the ratio about 1.05, calculated from Fontaneto et al. (2008: Fig. 2 ), (2) antero-lateral projections on the ventral lorica plate drawn out into a single acutely pointed spine in the new species vs. bifid antero-lateral projections in L. insualconae , (3) foot pseudosegment trapezoidal, sub-terminal, never projecting in the new species vs. terminal, near rectangular, scarcely projecting in L. insulaconae , (4) toes smoothly tapering to acute tip in L. zhanjiangensis sp. nov., but with incompletely separated claws in L. insulaconae .

Lecane zhanjiangensis sp. nov. also superficially resembles L. yatseni Wei & Xu, 2010 , a brackish-water species described from Qi’ao Island in the Pearl River Estuary, Southern China, and recently also recorded from the Nandujiang River Estuary (N19° 59' 25", E110° 23' 34"), Hainan Province, Southern China. The two species have clearly different anterior lorica margins and shapes of toes, however, so can hardly be confused.

The record of a previously undescribed Lecane from a freshwater river in Kansas, USA, misidentified as a “small form of L. levistyla (Olofsson) ” ( Turner, 1996) ( Fig. 2E ), bears a striking resemblance to the newly discovered Chinese species. The only morphological differences between specimens from the U.S. and from China are in the relative proportions of lorica plates (dorsal plate relatively shorter in U.S. animals), and slightly shorter toes in the American animals. Such differences may well result from the observer’s perspective, e.g. if seen from a more posteriorly view, or if specimens are not studied in a perfectly horizontal position. We therefore tentatively identify the U.S. specimens as belonging to the same morphospecies, L. zhanjiangensis sp. nov., notwithstanding that different ecology (brackish vs. freshwater) and disjunct distribution across different continents and biogeographical realms make assuming genetically distinct sibling species equally plausible.

Figures

FIGURE 2. Lecane zhanjiangensis sp. nov. A. Habitus, dorsal view. B. Habitus, ventral view. C. Not well-contracted head with spines, dorsal view. D. Light microscope photograph of Holotype, ventral view. E. Habitus, dorsal view, U.S. specimen modified from Turner (1996). Arrows indicate the spines on the outside of head. Scale bars: A–E: 50 µm.

FIGURE 3. Lecane zhanjiangensis sp. nov., scanning electron microscope photographs of trophi. A. Complete set, ventral view. B. Complete set, dorsal view. C. Unci and rami, ventral view. D. Unci and rami, dorsal view. Scale bar: 5 µm.

FIGURE 9. Trichocerca marina, scanning electron microscope photographs of trophi. A. Complete set, ventral view. B. Complete set, laterodorsal view. Scale bar: 10 µm.