Platichthys darwiniana Seddon & Witkowski 2015, sp. nov.
Creators: name: Lange-Bertalot, Horst
name: Witkowski, Andrzej
name: Seddon, Maxim S. Kulikovskiy Alistair W. R.
name: Kociolek, John P.
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Pleuronectiformes
Pleuronectidae
Platichthys
Platichthys darwiniana

description: Platichthys darwiniana Seddon & Witkowski, sp. nov. (Figs 1–38)   
 Frustules in girdle view 23–33 μm long, 7–8 μm broad (Figs 1–13). Valves 4.0–5.5 μm broad, not including copulae. The dorsal valve margins are slightly concave in the middle, becoming convex towards the apices. The ventral valve margin is convex and tapers towards the apices (Figs 14–18). The valve face is compressed laterally to form a narrow keel, the valve surface is steep. The valve mantle is very narrow in the form of structureless band (black arrow in Fig. 26, arrow in Fig. 30). The fibulae are very large, 5.5–7.5 in 10 μm, the two median ones are somewhat wider spaced than the others implying the presence of a central nodule. The striae are not visible in LM (Figs 1–18). The raphe in LM is barely observable, although in LM phase contrast optics both central external and apical endings are detectable. EM: the girdle is composed of a few, open bands perforated with 50–60 pores in 10 μm. The number of rows of pores amounts to ca. 10 for a single copula (Figs 19, 20, 29). The raphe is positioned in a very narrow axial area (Figs 22, 23, 25 and white arrow in Fig. 26), the external central endings are close to each other (arrow in Figs 22 and 23), the apical endings strongly bent in one direction (arrow in Fig. 23, 27, 28). Internally, the raphe is slit-like with internal central raphe endings close to each other and very slightly expanded (arrow in Fig. 36) terminating in a small, double helictoglossa (arrowhead in Fig. 37). Likewise the internal apical raphe endings terminate in a small helictoglossa (Fig. 38). The transapical striae are only measurable on EM images and number 48–61 in 10 μm, whereas the number of areolae within a stria range from 56 to 72 in 10 μm. The striae are composed of straight, uniseriate rows of areolae (arrowheads in Fig. 25). The areolae are in the form of simple poroids (Figs 30–32). Areolar occlusions have not been observed thus far. Internally, the fibulae are massive, column-shaped, short and arched (arrows in Figs 33–35, arrowheads in Fig. 36). They are positioned in a single row at the same height within the valve interior and separate the raphe canal from the valve lumen. The fibulae are positioned at some distance from the raphe (arrowheads in Fig. 26, Figs 33–38). As the fibulae are so large usually a few striae merge into one fibula (cf. Fig. 37). Wave crests begin at the basis of fibulae while wave troughs continue into the portulae (white arrows in Figs 37 and 38). The portulae are very simple and are formed as a result of a slight broadening of the base of the fibulae (Figs 34–38).   
 Type: —GALAPAGOS ISLANDS. Island Isabela: Diablas Lagoon, littoral, a sample from the Late Holocene sediment core, a sample from the Late Holocne sediment core collected in 2005, subsampled by A Seddon, 2007 (holotype: individual in slide no. MCCDRS 7862 at the Charles Darwin Research Station, Puerto Ayora, Galápagos, illustrated in Fig. 4).   
 Etymology: —this species is named in honor of Charles Darwin.   
 Ecology: —so far only found at the type habitat from a lagoon that is changing in salinity from brackish-water to marine close to the inlet of the sea water. The new species occurred abundantly and was very well preserved and associated with brackish-water to marine representatives of Navicula Bory (1822: 128), Amphora Ehrenberg ex Kützing (1844: 107), Fragilaria Lyngbye (1819: 182) sensu lato and Nitzschia. All were benthic, halophilouseuryhaline species, containing genera typifying isolation basins in the littoral zone (Seddon et al. 2011 a, 2014a).
description: Published as part of Lange-Bertalot, Horst, Witkowski, Andrzej, Seddon, Maxim S. Kulikovskiy Alistair W. R. & Kociolek, John P., 2015, Taxonomy, frustular morphology and systematics of Platichthys, a new genus of canal raphe bearing diatoms within the Entomoneidaceae, pp. 135-149 in Phytotaxa 236 (2) on pages 137-141, DOI: 10.11646/phytotaxa.236.2.3, http://zenodo.org/record/13630533