Aphanta asiatica X.L. Wang, Z.M. Sun & G.C. Wang, 2020

Aphanta asiatica X.L. Wang, Z.M. Sun & G.C. Wang , sp. nov. ( Figs 1–22 View FIGURES 1–9 View FIGURES 10–14 View FIGURES 15–22 )

Type:— CHINA. Hainan Province: Sanya City, Hongtang Bay (N: 18°18′08.85′′, E: 109°15′56.77′′), on subtidal rocks, August 30, 2019, X.L. Wang, holotype SY94- 1 in AST (Marine Biological Museum, Chinese Academy of Sciences, Qingdao, China) GoogleMaps , isotype SY94-2 GoogleMaps , paratypes SY94-3 , GoogleMaps CJ5-1 , GoogleMaps CJ5-2 , GoogleMaps CJ5-3 , GoogleMaps SY134-1 , GoogleMaps SY134-2 , GoogleMaps SY134-3 , GoogleMaps JPN-X5-1 , GoogleMaps JPN-X5-2 , GoogleMaps and JPN-X5-3 GoogleMaps .

Thalli were 1.8–3.0 cm high, purple-red, comprising a prostrate system and erect fronds ( Fig. 1 View FIGURES 1–9 ). The prostrate system comprised robust, irregularly branched terete stolons bearing peg-like haptera ( Fig. 2 View FIGURES 1–9 ). Stolons were 439.7–1,045.5 μm in diameter with a mean of 711.4 μm. Several uprights sometimes corresponded to the main hapteron on the dorsal side ( Fig. 3 View FIGURES 1–9 ), and a single upright usually developed from the stolon without a dorsal hapteron ( Fig. 4 View FIGURES 1–9 ). Uprights were sometimes anastomosed to the stolon by very short (~ 1 mm long) cylinders ( Fig. 4 View FIGURES 1–9 ), resulting in the fronds being interweaved. Erect axes were lanceolate or ligulate, flattened, 1.4–3.9 mm wide with a mean of 2.0 mm, and 145.0–370.4 μm thick with a mean of 230.8 μm. Young branches were cordate ( Fig. 5 View FIGURES 1–9 ), becoming lanceolate or ligulate when mature, with obvious basal constrictions ( Fig. 6 View FIGURES 1–9 ). Branches were subpinnate to pinnate or lateral in a regular or irregular pattern, with one to two orders ( Fig. 6 View FIGURES 1–9 ). The apex of branches was usually emarginate ( Fig. 7 View FIGURES 1–9 ).

Cross-sections of the central axis showed ovate or elongate cortical cells of two to three layers, and round, angular, or elongate medullary cells ( Fig. 8 View FIGURES 1–9 ). The rhizoidal filaments were grouped at the two distal ends of each axis and on the inner cortex, but were sparsely distributed in the medulla ( Fig. 8 View FIGURES 1–9 ). The outermost cortical cells were regularly arranged, 3.8–8.5 × 1.6–5.4 μm, with a mean of 5.9 × 2.9 μm, whereas the inner cortical cells were arranged loosely, 4.3–14.1 × 2.1–8.8 μm with a mean of 7.8 × 3.8 μm. Medullary cells were uneven in size (17.6–36.3 × 12.3–26.1 μm, with a mean of 26.7 × 17.5 μm). The rhizoidal filaments were round in transection, and 2.9–4.3 μm in diameter, with a mean of 3.7 μm.

Three different forms were observed in the longitudinal sections of stolons and haptera ( Figs 9–11 View FIGURES 1–9 View FIGURES 10–14 ). The section of the node (stolon) connecting the upper axis and the lower hapteron (the main hapteron) resembled a reverse bouquet in appearance with the initial coalesced rhizoidal filaments corticated and then separated into several non-corticated bundles ( Fig. 9 View FIGURES 1–9 ). Many floridean starch grains were observed in the medullary cells of the stolon ( Fig. 9 View FIGURES 1–9 ). Another section showed a cylinder-type attachment with rhizoidal filaments coalesced and non-corticated ( Fig. 10 View FIGURES 10–14 ). Many floridean starch grains were also observed in the medullary cells of the stolon ( Fig. 10 View FIGURES 10–14 ). The third form was a peg-like attachment with rhizoidal filaments coalesced and corticated in a usual way, although the distal end was non-corticated ( Fig. 11 View FIGURES 10–14 ). Rhizoidal filaments were grouped in the inner cortex of the stolon and floridean starch grains were also observed in the medullary cells ( Fig. 11 View FIGURES 10–14 ). Rhizoidal filaments of the hapteron issued from inner cortical cells and were arranged longitudinally ( Fig. 11 View FIGURES 10–14 ).

A tetrasporangial sorus was borne on the terminal end of each branchlet or axis ( Figs 12, 13 View FIGURES 10–14 ), irregularly arranged and cruciately divided on surface view ( Figs 13, 14 View FIGURES 10–14 ). Tetrasporangia developed from the inner cortical cells, surrounded by abnormal cells ( Fig. 15 View FIGURES 15–22 ). A spermatangial sorus was also borne on the terminal part of each branchlet ( Fig. 16 View FIGURES 15–22 ), forming a pale patch with a sterile margin ( Figs 17, 18 View FIGURES 15–22 ). The spermatangia were cut off from surface cortical cells ( Fig. 19 View FIGURES 15–22 ). Female thalli were not observed.

Morphological comparisons with other Aphanta species are provided in Table 2 View TABLE 2 .

Distribution and Habitat:— Aphanta asiatica is currently known from Hainan Island, China and Shirahama, Wakayama City, Japan. It grows on lower subtidal rocks or rocks at a depth of ~ 3 m ( Fig. 20 View FIGURES 15–22 ), usually forming turfs ( Fig. 21 View FIGURES 15–22 ). Thalli growing on higher rocks usually become pale and dead when exposed to the sun ( Fig. 22 View FIGURES 15–22 ). The tetrasporophytes and male plants were collected during late August and early October.

Etymology:—The specific epithet refers to its current geographical distributions, namely Asian waters.

Molecular analyses of COI-5P and plastid rbc L sequences:—Nine COI-5P and nine rbc L sequences were generated from nine A. asiatica specimens in the present study. Eight COI-5P sequences were identical and only one sequence differed from the other sequences by only one base pair (bp). Interspecific divergences between A. asiatica and A. pachyrrhiza ranged from 10.4% to 10.6% (57–58 bp), and divergences between A. asiatica and A. ligulata ranged from 20.6% to 21.3% (112–116 bp). In rbc L, intraspecific divergences of A. asiatica varied from 0 to 1.4% (0–17 bp). Interspecific divergences between A. asiatica and the other two Aphanta species ranged from 3.0% to 3.3% ( A. pachyrrhiza ), and 9.8% to 10.1% ( A. ligulata ). In both the COI-5P and rbc L trees, A. asiatica formed a clade and clustered with A. pachyrrhiza with full support (1.0 BI/100% ML for COI-5P, 1.0 BI /100% ML for rbc L) ( Figs 23 View FIGURE 23 , 24 View FIGURE 24 ).