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Dinoflagellate Glossary

Species Name:

Pyrophacus steinii

Common Name:      Dinoflagellate



Dinophyta Dinophyceae Gonyaulacales Pyrophacus

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Figure 1. Pyrophacus steinii, epitheca under light microscope. Indian River Lagoon at Grand Harbor.

Figure 2. Epitheca plate formula of P. steinii.

Figure 3. Lateral view of P. steinii. From Taylor 1976.

Figure 4. Ventral side, lateral view of P. steinii.

Figure 5. P. steinii, hypotheca under light microscope. Collected from the Indian River Lagoon at St. Lucie Inlet.

Figure 6. Hypotheca plate formula of P. steinii.

Figure 7. P. steinii, epitheca with hachure lines in precingular plates.

Figure 8. P. steinii, line drawing of hypnocyst.


Pyrophacus steinii (Schiller) Wall et Dale 1971


Pyrophacus was first described by F.R. Stein in 1883 as a monospecific genus. Schiller (1935) subsequently recognized two varieties, var. horologium (frequently misspelled as horologicum), and var. steinii. Both varieties were elevated to separate species by Wall and Dale (1971). Another taxon, designated by Steidinger and Davis (1967) as 'Pyrophacus Form B1' was suspected to be an aberrant form of 'Pyrophacus horologicum var. steinii', but later shown to be the thecate stage of the fossil dinoflagellate cyst Tuberculodinium vancampoae (Rossignol) Wall. That fossil is at least lower Miocene (ca. 20 million years ago) in age, and Wall and Dale (1971) established the form described by Steidinger and Davis (1967) as Pyrophacus vancampoae (Rossignol) Wall et Dale. Balech (1979) reassigned vancampoae as a subspecies of steinii, a situation later confirmed on morphological bases by Matsuoka (1985). However, living cells are still occasionally referred to as Tuberculodinium vancampoae (Zonneveld & Susek 2007). In summary, current thinking is that there are two living species of Pyrophacus:  horologium and  steinii, with the later further divided into subspecies (or varieties) steinii and vancampoae.

Species Description:
In apical view (Figures 1, 2) cells are nearly circular, with a small concavity at the ventral surface that corresponds to the sulcus location. In lateral or side view, cells are lenticular and strongly compressed anterior-posteriorly (Figures 3, 4). The epitheca and hypotheca are somewhat unequal in height. The epitheca is conical and occasionally slightly concave. The hypotheca is more rounded and slightly flattened at the antapical end. The cingulum is equatorially located and lacks displacement in its circumference. The thecae are easily separable and, because of their shape, orient themselves in a position where the plates are quite visible (Figures 1, 5, 7).

The cells are thecate, with plates numbered in the Kofoidean system. With a few exceptions, a typical plate arrangement is as follows: the epitheca has a pore plate with two curved slits, seven apical plates and 12 precingular plates; 12 cingular plates and eight sulcal plates; the hypotheca has 12 postcingular plates, three posterior intercalary plates and three antapical plates. The abbreviation of this plate formula is (Po, 7’, 0a, 12’’, 13c, 8s, 12’’’, 3p, 3’’’’). There is considerably more variability in posterior intercalary plates than in others. Consequently, authors have identified the plate affinities differently (Matsuoka 1985, Figure 2). For example, the posterior intercalary plates in Figures 5 and 6 are generally interpreted as (12’’’, 1p, 5’’’’) but could be interpreted as plates as (12’’’, 3p, 3’’’’).   Matsuoka (1985) also reported that cells in culture were more variable in their plate numbers than those from natural samples.  Radially arranged short stripes (hachures) sometimes occur on precingular plates of the epitheca (Figure 7). Most thecate dinoflagellates are fairly conservative in the distribution of hypothecal plates; Pyrophacus is an exception. For the genus as a whole, the plate formula is (Po, 5-8’, 0a, 9-12’’, 9-14c, 8s, 9-14’’’, 1-11p, 3’’’’).

The cells of P. steinii are unicellular and photosynthetic, with numerous golden brown chloroplasts. P. steinii has two heterodynamic flagella, and the diameter is reported to be 82-191µm (Wall & Dale 1971). As in other members of the genus, P. steinii is bioluminescent. There have been no reports of toxicity in this species.



Habitat & Regional Occurence:
In part, the distribution of Pyrophacus steinii depends on one’s view of the taxonomy. Taylor (1976) for example, recognized three separate species, with P. steinii the most common and widespread in Indian Ocean samples, and mostly oceanic in distribution down to 27°S. With a distribution closer to landmasses, P. vancampoae is much less common; likewise for P. horologium. Both P. horologium and P. steinii are widespread and common in the North Atlantic. Though P. steinii has a preference for warmer water, it was recorded from 48°N by Gaarder (probably introduced as part of the North Atlantic Drift). There are also many records of P. steinii from the Pacific Ocean, primarily tropical or subtropical locations. The cysts have been found in surface sediments where the surface water temperature was 12.7-29.5°C and the salinity was 16.9-36.6 psu (Zonneveld & Susek 2007). Its presence in the Baltic Sea (Ostsee) suggests a tolerance for brackish conditions, and Faust (1998) suggests that, at least in mangrove environments, P. steinii is mixotrophic. There is some evidence that P. steinii is sensitive to pollution.  Inhibition of its bioluminescence by anthropogenic contaminants has been suggested as a novel method to determine lethal and sublethal contaminant levels in environmental risk assessment (Lapota et al. 2007).

Indian River Lagoon Distribution:
In the IRL, all observed cells have been vegetative cells of P. steinii: neither horologium cells nor hypnozygotes were seen. Occurrences have been rare, never more than a few cells per liter, and confined to the summer (25°C or higher) and salinities of 30-36 psu. Wherever found, P. steinii is never abundant, though quantitative data are incomplete and cryptic.



Details of the life history of P. steinii have been studied by Faust (1998) and Pholpuntin et al. (1999) and are summarized in Figure 9. Vegetative (asexual) reproduction is by nuclear division binary fission inside the parent cell, with the two (rarely four) daughter cells breaking the parent cell apart and forming new thecae and flagella (Figure 9: 6 & A1). Sexual reproduction is anisogamous and heterothallic (male and female of different size and morphology; Figure 9: 2B,C). Male gametes are smaller and rounder than vegetative cells, with a different plate arrangement, whereas female cells are indistinguishable from vegetative cells. Eight or 16 sperm cells are released from one male cell (Figure 9: 2B). The sperm cell enters the female cell, usually where the cingulum and sulcus meet, and the gametes fuse. This normally takes place in the dark. The resulting cell with two trailing flagella (the planozygote; Figure 9: E) is motile for two or three days, then transforms into an inactive resting cyst, the hypnozygote (Figure 8, Figure 9: 4F). The hypnozygote is the form called Tuberculodinium by micropaleontologists.

In most dinoflagellates, the germination of the hypnozygote (Figure 9: 5) takes place only after a refractory time (obligate dormancy), which varies from weeks to months. The refractory period for P. steinii is unknown, though Faust (1998: 176) implies that it is short. In a series of experiments with cultures grown from cysts isolated from Japanese coastal waters, Zonneveld and Susek (2007) found that cyst production could take place at 16.5-34.8°C, with highest cyst production at 27°C; and at 20-45 psu, with highest cyst production at 35 psu in moderate to strong light conditions.

Figure 9. P. steinii life cycle, based on Pholpunthin et al. 1999. A) vegetative cell; B) male gamete; C) female gamete; D) gamete fusion; E) planozygote; F) hypnozygote (cyst); G) planomeiocyte. 1) formation of gametes; 2) fusion and zygote formation; 3) formation of planozygote; 4) formation of hypnozygote; 5) germination of hypnozygote; 6) first vegetative division after germination.



Balech, E. 1979. El genero Pyrophacus Stein (Dinoflagellata). Physis 38: 27-38.

Faust, MA. 1998. Morphology and life cycle events in Pyrophacus steinii (Schiller) Wall et Dale. J. Phycol. 34: 173-179.

Gaarder, KR. 1954. Dinoflagellatae from the “Michael Sars” North Atlantic Deep-Sea Expedition 1910. Reports of the Scientific Results of the Michael Sars North Atlantic Deep-Sea Expedition, 1910. 2:1-62

Lapota, D, Osorio, AR, Liao, C & B Bjorndal. 2007. The use of bioluminescent dinoflagellates as an environmental risk assessment tool. Mar. Pollut. Bull. 54: 1857-1867.

Matsuoka, K. 1985. Cyst and thecate forms of Pyrophacus steinii (Schiller) Wall et Dale. Trans. Proc. Palaeont. Soc. Japan, N.S. 140: 240-262.

Pholpunthin, P, Fukuyo, Y, Matsuoka, K & Y Nimura. 1999. Life history of a marine dinoflagellate Pyrophacus steinii (Schiller) Wall et Dale. Bot. Mar. 42: 189-197.

Schiller, J. 1935. Dinoflagellatae (Peridineae). In: Rabenhorst’s Kryptogamen-Flora von Deutschland, Oesterreich und der Schweiz, Teil 2 Akademische Verlag, Leipzig. 589pp.

Steidinger, K & JT Davis. 1967. The genus Pyrophacus, with a description of a new form. Florida Board of Conservation Leaflet Series, Vol. 1, Part 1. Dinoflagellates, No. 3: 1-8.

Taylor, FJR. 1976. Dinoflagellates from the international Indian Ocean Expedition. Bibl. Bot. 132: 1-234 + 46 plates.

Wall, D & B Dale. 1971. A reconsideration of living and fossil Pyrophacus Stein 1883 (Dinophyceae). J. Phycol. 7: 221-235.

Zonneveld, K & E Susek. 2007. Effects of temperature, light, and salinity on cyst production and morphology of Tuberculodinium vancampoae (the resting cyst of Pyrocystis steinii). Rev. Palaeobot. Palyno. 145: 77-88.



Unless otherwise noted, all images and text by PE Hargraves
Editing and page maintenance by LH Sweat

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Page last updated: 14 June 2011

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Process of reproduction in dinoflagellates that involves the production of gametes that are fused to create a zygote.


Plates at the antapex of the cell, mostly in contact with sulcal plates, indicated by ('''') in Figure 3A on the Dinoflagellates page.


Plates located between the postcingular and antapical plates, indicated by (p) in Figure 3A on the Dinoflagellates page.

Plates located immediately below the cingulum, indicated by (''') in Figure 3A on the Dinoflagellates page.


Plates located in the sulcus, indicated by (s) in Figure 3A on the Dinoflagellates page.


Plates that are located in the cingular (girdle) groove around the cell, indicated by (c) in Figure 3A on the Dinoflagellates page.


Plates located immediately above the cingulum, indicated by ('') in Figure 3A on the Dinoflagellates page.


Plates that surround and touch the cell apex, indicated by (') in Figure 3A on the Dinoflagellates page.

A furrow encircling the cell that contains the rotatory flagellum. Also referred to as the girdle or transverse groove.

Plates at the antapex of the cell, mostly in contact with sulcal plates, indicated by ('''') in Figure 3A on the Dinoflagellates page.


The part of a dinoflagellate cell below the cingulum. Usually refers to a thecate (with cellulose plates) cell. May also be referred to as the hypocone or hyposome.

The part of a dinoflagellate cell above the cingulum. Usually refers to a thecate (with cellulose plates) cell. May also be known as the epicone or episome.

A longitudinal furrow, often partially enclosing the propulsive flagellum.


Front side of the cell where the sulcus is located, opposite of the back dorsal side.

The diploid zygotic dormant stage in the sexual life cycle. Usually morphologically dissimilar from the haploid motile stage. Also called the ‘dinocyst’ or ‘hypnozygote’.


Dinoflagellates possesing a cell wall comprised of cellulose plates, which have special designations and symbols according to their location on the cell. See glossary for more information.