A Re-investigation of Sarcinochrysis marina (Sarcinochrysidales, Pelagophyceae) from its Type Locality and the Descriptions of Arachnochrysis, Pelagospilus, Sargassococcus and Sungminbooa genera nov.

Systematists increasingly use molecular markers to identify species; however, most microalgae were described before gene sequencing and type specimens were often ink drawings. Cryptic speciation and biogeographic isolation are other potential problems when anchoring an old species name with a modern gene sequence. Therefore when biological type material is absent, the best approach is to recollect the alga from the type locality and sequence genes. Sarcinochrysis marina, described in 1930 by Geitler from the Canary Islands, Spain, is the oldest Pelagophyceae genus. Geitler used two cultures in his study, but these cultures no longer exist. We re-isolated S. marina from the type locality near Las Palmas, Gran Canaria. Furthermore, we included additional Pelagophyceae strains that were isolated from natural habitats for this study or were obtained from culture collections. We produced 85 sequences, representing the nuclear-encoded SSU rRNA and the plastid-encoded rbcL, psaA, psaB, psbA, and psbC genes. The sequences were used to infer maximum likelihood phylogenetic trees. We anchored the name Sarcinochrysis marina using the Las Palmas isolate, and we described four new genera (Arachnochrysis, Pelagospilus, Sargassococcus, Sungminbooa) and nine new species in the Sarcinochrysidales. We also described a new family, Chrysocystaceae, based upon molecular phylogenetic analyses.

Introduction

Sarcinochrysis marina Geitler was first described in 1930, and the cells were illustrated using a photomicrograph and several ink drawings (Geitler 1930). The genus was placed in the class Chrysophyceae even though Geitler pointed out that the unusual zoospores resembled the motile cells of brown algae and differed significantly from typical chrysophyte swimming cells. Forty-seven years later, based on electron microscopic observations of the zoospore, Gayral and Billard created the order Sarcinochrysidales (Chrysophyceae) (Gayral and Billard 1977a). The class Pelagophyceae was described (Andersen et al. 1993) and then based on molecular data, the Sarcinochrysidales was moved to the Pelagophyceae (Saunders et al. 1997). Additional molecular studies have corroborated the placement of Sarcinochrysis in the Pelagophyceae (e.g. Yang et al. 2011). The known diversity of the class is expanding, and a number of new generic names have been proposed for taxa belonging to the Sarcinochrysidales, e.g. Chrysocystis (Lobban et al. 1995), Aureoumbra (DeYoe et al. 1997), Chrysoreinhardia (Hoffmann et al. 2000), Aureoscheda (Wynne et al. 2014), Andersenia (Wetherbee et al. 2015).

During the original description, Geitler (1930) established two enrichment cultures from the type locality, Las Palmas in Canary Islands, Spain. He described Sarcina-type colonies, i.e. cubic packets of cells, and he showed that the cells had two deeply lobed chloroplasts and a new zoospore type. However, Geitler’s cultures no longer exist and cannot be investigated with modern methods. Subsequent studies attributed to Sarcinochrysis, are based on algae collected from other localities (e.g. Billard, 1974, Billard, 1984, Conrad and Kufferath, 1954, Gayral, 1972, West, 1969). However, the descriptions in the newer studies disagreed with Geitler’s description on some important points. For example, West (1969) didn’t observe a sarcinoid stage, Gayral (1972) described zoospores with only a single chloroplast, and Billard (1984) described chloroplasts without deep lobes and zoospores with a much shorter posteriorly directed flagellum. As a consequence of these differences, cultures identified as Sarcinochrysis and studied using molecular techniques (e.g. Saunders et al., 1997, Yang et al., 2011) seemed uncertain or even incorrect to represent Geitler’s organism.

The aims of this study are to (a) re-collect Sarcinochrysis marina from the type locality and establish a culture, (b) use molecular data to precisely identify the “true” S. marina on a phylogenetic tree, and (c) to re-evaluate the identity of culture strains that were previously named Sarcinochrysis. To achieve these goals, we collected new material from Geitler’s type locality. Several cultures were established and others were purchased; these were compared with Geitler’s observations. A culture that closely resembled Geitler’s description is included in molecular phylogenetic analyses using the nuclear encoded SSU rRNA and five plastid genes (psaA, psaB, psbA, psbC, and rbcL). Based on these results, we nomenclaturally anchor the name Sarcinochrysis marina and we describe four new genera and nine new species in the Sarcinochrysidales.