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NAOSITE: Nagasaki University's Academic Output SITE Taxonomy and identification of the armored dinoflagellate genus Title Heterocapsa (Peridiniales, Dinophyceae) Author(s) Iwataki, Mitsunori Citation Plankton and Benthos Research, 3(3), pp.135-142; 2008 Issue Date 2008-08 URL http://hdl.handle.net/10069/23074 Right Copyright (c) 2008 The Plankton Society of Japan This document is downloaded at: 2020-09-18T01:23:45Z http://naosite.lb.nagasaki-u.ac.jp Plankton Benthos Res 3(3): 135–142, 2008 Plankton & Benthos Research © The Plankton Society of Japan Taxonomy and identification of the armored dinoflagellate genus Heterocapsa (Peridiniales, Dinophyceae) MITSUNORI IWATAKI* Institute for East China Sea Research, Nagasaki University, 1–14 Bunkyo, Nagasaki 852–8521, Japan Received 13 September 2007; Accepted 28 January 2008 Abstract: The armored dinoflagellate genus Heterocapsa is composed of relatively small species, including a species responsible for harmful red tides, H. circularisquama. Some Heterocapsa species such as H. rotundata and H. triquetra have been well documented as red tide-forming species, but are not recognized as causing harmful effects. Following sequential shellfish mass mortalities in the coastal waters of western Japan due to H. circularisquama red tides, this species has attracted considerable interest. Many properties of this species, such as its distribution and growth characteristics, have been investigated to better understand the mechanisms involved in harmful red tide formation. Related to the need for unambiguous identification of H. circularisquama, several unidentified (or undescribed) Heterocapsa species, which must be distinguished from the harmful taxon, have been detected sympatrically in regions where H. circularisquama blooms occur. However, the taxonomic affiliation of these Heterocapsa species have not yet been deter- mined because several characteristics of Heterocapsa (e.g. body scale ultrastructure) have not yet been reported from all described species due to the changing taxonomic criteria. After the taxonomic ambiguities in this genus were re- solved, cellular and body scale morphology of Heterocapsa were reinvestigated and several new species were described. In the present paper, the taxonomic history and morphological characters of the genus Heterocapsa are summarized. Key words: body scale, dinoflagellate, Heterocapsa, morphology, nucleus, pyrenoid, red tide, taxonomy, thecal plates to Japan (Yamaguchi et al. 1997, Honjo et al. 1998, Iwataki Introduction et al. 2002b, Iwataki & Matsuoka 2007). The continued The genus Heterocapsa is composed of armored dinofla- harmful impacts on aquaculture have promoted numerous gellates represented by relatively small planktonic species. investigations of the distribution and optimum conditions Some Heterocapsa species such as Heterocapsa rotundata for growth of this species (e.g. Matsuyama et al. 1997, Ya- (Lohmann) Hansen and Heterocapsa triquetra (Ehrenberg) maguchi et al. 1997, Nagai et al. 2000, Yamaguchi et al. F. Stein have long been recognized to be cosmopolitan, red 2001, Shiraishi et al. 2007). During previous studies of H. tide-forming taxa. In 1988, Heterocapsa circularisquama circularisquama, several undescribed species superficially Horiguchi was first found in Uranouchi Inlet, Kochi Prefec- resembling H. circularisquama had been observed; how- ture, Japan, and has since spread along the coast of western ever, it was difficult to define their taxonomic status at that Japan accompanied by tremendous damage to bivalve aqua- time. culture (Horiguchi 1995, Matsuyama 1999). Since this The genus was originally described more than one hun- harmful species and its noxious effects, specifically on bi- dred years ago (Stein 1883), and about 20 species have so valves, had never been reported it was described as the new far been assigned to Heterocapsa. Since the presence of a species H. circularisquama (Horiguchi 1995). The previous resting cyst is unknown in Heterocapsa (Fensome et al. distribution of this novel harmful species remains unclear, 1993), species have been distinguished based on the mor- however, its relatively higher optimum temperature for phology of the motile cell. Nonetheless, the generic criteria growth and a report of its occurrence from Hong Kong for species assignment within Heterocapsa have continued imply a recent transfer from tropical or subtropical waters to change, resulting in some species descriptions unsuitable for inclusion the genus, according to our present knowl- * Corresponding author: Mitsunori Iwataki; E-mail, iwataki@nagasaki- edge. Moreover, some of the morphological characters of u.ac.jp Heterocapsa that should be compared and contrasted, e.g. 136 M. IWATAKI body scale ultrastructure, have not been reported in all the the hypotheca (Lindemann 1924), but this plate tabulation described species. For taxonomic assignment of unidenti- still differed from later reports that have more recently been fied species and unambiguous identification of H. circular- accepted (e.g. Morrill & Loeblich III 1981). During this pe- isquama, reliable criteria are required. Reinvestigations of riod, cell shape was treated as the most fundamental or con- common morphological characters for the genus such as served character of Heterocapsa and the original criterion typical thecal plate arrangement (Po, cp, 5Ј, 3a, 7Љ, 6c, 5s, of the genus was neglected. 5ٞ, 2ЉЉ) and ultrastructure of the triradiate body scales cov- In the 1960s, all thecal plates were investigated in detail ering the cell surface have been carried out recently, and the by light microscopy and their arrangements were adopted taxonomy of this genus was reassessed (Iwataki et al. 2003, as a criterion of the genus. Loeblich III (1968) described 2004). As a result of this work, fifteen species are now rec- the new species Cachonina niei Loeblich III as the type ognized as possessing morphological characters common to species of a new genus Cachonina (CachoninaϭHetero- Heterocapsa. In the present paper, the taxonomic history capsa) with the thecal plate arrangement illustrated as p.p. -and present status of the genus Heterocapsa are summa- (apical pore plateϭPo), 5Ј, 3a, 8Љ, 6c, 4s, 5ٞ, 2ЉЉ. Subse rized and this reliability of morphological characters for quently, von Stosch (1969) reanalyzed the entire plate species identification is discussed. arrangement of H. niei; Po, 6Ј, 3a, 8Љ, 6c, 4s (s.a. (anterior sulcal plate), t (transitional plate), s.l. (left sulcal plate), s.p. Taxonomic history of Heterocapsa (posterior sulcal plate)), 5ٞ, 2ЉЉ. A tiny canal plate was then discovered and mentioned as the sixth apical plate 6Ј (von The genus Heterocapsa was originally established by Stosch 1969). This was the first report of a complete thecal Stein in 1883 with the proposal of a new combination of the plate tabulation to be worked out in detail for a member of type species H. triquetra from Glenodinium triquetrum the genus Heterocapsa (Loeblich III et al. 1981). Thereafter Ehrenberg (Stein 1883). Two species, H. umbilicata F. Stein the generic affiliation of each species was discussed based and H. quadridentata F. Stein, were simultaneously de- on its thecal plate arrangement. scribed as new species (Stein 1883). In the systematics of The next Cachonina species, C. illdefina Herman et dinoflagellates at this time, two thecate genera, Peridinium Sweeney, was described from a red tide sample collected in and Glenodinium, were distinguished based on whether the California (Herman & Sweeney 1976). This species name thecal plates (or sutures) were visible under a light micro- was based on the English term “ill-defined” due to the frus- scope. As Stein (1883) could find the sutures only on the tration over its classification. The thecal plate tabulation of epitheca of G. triquetrum and the other two taxa, he tenta- C. illdefina was identical to C. niei; however, the configura- tively established a new genus Heterocapsa, to include the tion of the sulcal series and cell size were different. Trans- species having a sutured epitheca and a flimsy hypotheca. mission electron microscopy then revealed that C. illdefina The original etymology of the genus Heterocapsa, there- had tubular cytoplasmic invaginations within the pyrenoid fore, denoted different types of the hemitheca. The cell matrix, resembling those of H. triquetra as reported by shapes and thecal plate arrangements of the epitheca were Dodge & Crawford (1971). In 1977, Balech analyzed in de- sufficiently different to distinguish each of these three tail the thecal plates of C. illdefina, and considered it to be species from the other. These morphological and thecal synonymous with C. niei based on the similarity of their plate variances represent the generic differences that are arrangements. In contrast to the opinion of Balech (1977), presently accepted. Morrill & Loeblich III reported a difference in cell size The next description of a Heterocapsa species was Hete- range between C. niei and C. illdefina (Morrill & Loeblich rocapsa pacifica Kofoid (Kofoid 1907). The cell shape of III 1981). They also re-observed the complete thecal plate this species was somewhat similar to H. triquetra, but it dif- ,arrangement of H. triquetra, 2pr, 5Ј, 3a, 7Љ, 6c, 7s, 5ٞ, 1p fered in several ways, including having a broader cell 2ЉЉ, and argued that the arrangements of Heterocapsa and width, in the position of the nucleus and in possessing a Cachonina were almost identical. Moreover they indicated prominent antapical spine. However, it contradicted the

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