Stephanacantha
Stephanacantha Thomsen, 1983 (ref. ID; 7700 original paper)
[ref. ID; 7700]
Diagnosis; Small marine collared flagellates. The uniflagellate cell is located in a lorica composed of broad costal strips with a central thickening, and with or without transverse patterning. The transverse costa at the anterior opening of the lorica is composed of costal strips which carry an upright spine at one end. The anterior tip of each longitudinal costa is usually attached to the center of a transverse costal strip thus forming a T-joint. Longitudinal costae show bifurcations in the middle lorica region (each anterior longitudinal costal strip posteriorly adjoins two much smaller diverging costal strips). The posterior part of the lorica surrounding the protoplast, is either a complete armour, which consists of a large number of convering broad costal strips, or composed of a few rather narrow converging costal strips, which emanate from the posterior joints of the short obliquely oriented middle lorica costal strips. All available evidence suggests that each costal strip element (e.g. the anterior longitudinal costal strips) is exterior to the next following element, when examined in sequence from the anterior to the posterior lorica end. A short flattened pedicel is commonly present. Replication tectiform. (ref. ID; 7700)
Etymology; From the Greek stephanos, wreath and acantha, spine. (ref. ID; 7700)
Type species; Stephanacantha campaniformis (Leadbeater, 1973) comb. nov. (= Parvicorbicula campaniformis Leadbeater, 1973). (ref. ID; 7700)
- Stephanacantha campaniformis (Leadbeater, 1973) Thomsen, 1983 (ref. ID; 7700 redescribed paper)
Syn; Parvicorbicula campaniformis Leadbeater, 1973 (ref. ID; 7700)
- Stephanacantha dichotoma Thomsen, 1983 (ref. ID; 7700 original paper)
- Stephanacantha formosa Thomsen, 1983 (ref. ID; 7700 original paper)
- Stephanacantha parvula Thomsen, 1983 (ref. ID; 7700 original paper)
Stephanacantha campaniformis (Leadbeater, 1973) Thomsen, 1983 (ref. ID; 7700 redescribed paper)
Synonym
Parvicorbicula campaniformis Leadbeater, 1973 (ref. ID; 7700)
Descriptions
Lorica morphology: Lorica (9-12 um long) consisting of two chambers. The anterior chamber is formed by six longitudinal costal strips, each posteriorly adjoining two much shorter, diverging costal strips. The anterior tip of each longitudinal costal strip is attached to the center of a costal strip of the anterior ring, thus forming T-joints. The six transverse costal strips usually carry an upright spine at one end of the strip (left hand end when viewed from outside the lorica). The posterior lorica chamber is formed by approximately 12 very broad costal strips which converge posteriorly and join with a short flattened pedicel. The whole lorica thus consists of four different types of costal strips. All are, however, rather broad and show a conspicuous thickened midrib on the introverted side of the strip. The transverse strip patterning is very limited. The mutual position of costal strips, not only as regards the type of interconnection of adjoining strips, but also concerning the interior versus exterior location of each costal element, has been given considerable attention recently (Manton & Bremer 1981; Manton, Bremer & Oates 1981), in the hope that these characteristics may prove useful as generic differentials. It is evident from Plate 17 (Leadbeater 1973) that in S. campaniformis the anterior transverse costa is exterior to the longitudinal costal strips, which are subsequently exterior to the small middle lorica costal strips. (ref. ID; 7700)
Taxonomy
It has been obvious, virtually from the description of this taxon (Leadbeater 1973), that the allocation to the genus Parvicorbicula Deflandre (1960) was only temporarily a possibility. A comparison between the generic type Parvicorbicula socialis (Meunier 1910) (for electron micrographs see Thomsen (1973), Manton et al. (1976), Buck (1980)) and S. campaniformis shows, apart from the presence of T-joints, no points of resemblance, in characters which are generally considered to be of importance in loricate choanoflagellate taxonomy. The finding of a number of species which are definitely closely related to S. campaniformis, by sharing i.a. the following characteristics: (1) lorica composed of broad costal strips, (2) bifurcations of longitudinal costae, (3) unipolar spines on anterior transverse costal strips and (4) flattened pedicel, has clearly emphasized the justification of transferring Parvicorbicula campaniformis to a new genus. The Red Sea specimen illustrated by Thomsen (1978, loc. cit. Fig.7) and reffered to as Parvicorbicula campaniformis is not identical with the Mediterranean type material of this taxon (Leadbeater 1973). In the Red Sea specimen there are no bifurcations of the longitudinal costae in the middle part of the lorica, but rather a number of oblique costal strips. Similar cells have later been observed in material from the Andaman Sea and from the coasts of New Zealand, and will be dealth with in a separate publication (Thomsen and Moestrup 1983). (ref. ID; 7700)
Geographical distribution
S. campaniformis has been recorded from Jugoslavia (Leadbeater 1973) and Algiers (Leadbeater 1974). (ref. ID; 7700)
Diagnosis
Cells solitary. Protoplast when dried ca. 2x4 um, flagellum 8-12 um, surrounded by a collar composed of tentacles (ca. 30). Lorica 12-15 um long, composed of 18 slightly broadened costal strips of three different types. The anterior transverse ring (diameter 6-7 um) consist of 6 costal strips (3-4 um long) each with an upright spine at one end. The diameter of the lorica is calculated assuming a complete collapse of dried loricae. Three longitudinal costal strips (5-6 um long) attach the centres of every second transverse costal strip. Six short costal strips (2-3 um long) form a zig zag shaped belt around the middle part of the lorica, with the three anterior and the three posterior longitudinal costal strips attaching the apices. The insertion of this system of costal strips thus causes a displacement of anterior and posterior longitudinal costal strips and futhermore makes all longitudinal costal strips appear bifurcated. Posteriorly the longitudinal costal strips (5-6 um long) converge and join with a flattened pedicel which is 3-5 um long. (ref. ID; 7700)
Remarks
This species is easily recognized both light and electron microscopy by the shape of the lorica and the arrangement of the costal strips. Stephanacantha dichotoma is distinguished from S. campaniformis on the basis of the number of longitudinal costae (3 versus 6), by the presence of three posterior longitudinal costal strips rather than a large number of very broad costal strips forming a posterior protoplast armour, and finally by the presence of a conspicuous flattened pedicel. Stephanacantha dichotoma is similar to S. campaniformis concerning the mutual position costal elements. The anterior longitudinal costal strips are thus exterior relative to the small costal strips of the middle lorica, while overlaid externally by the anterior transverse costa. (ref. ID; 7700)
Geographical distribution
Andaman Sea (Thailand) and Sargasso Sea (Davis & Sieburth, per. comm.). (ref. ID; 7700)
Type specimen
Type specimen, shown in Fig.6, found in a water sample collected 14 September 1981 at St. 1 near Phuket Island, SW Thailand. (ref. ID; 7700)
Stephanacantha formosa Thomsen, 1983 (ref. ID; 7700 original paper)
Diagnosis
Cells solitary. Protoplast when dried ca. 3x5 um, flagellum 9-13 um long. Lorica (13-20 um long; diameter at anterior end 14-17 um) composed of four types of broad costal strips with a thickened midrib. The anterior transverse costa consists of 13
(11-14) costal strips (3-5.5 um long) each with an upright, slightly twisted spine at one end. Longitudinal costae usually 4 (4-6) each consisting of one anterior costal strip (4.5-7.0 um long), and one posterior costal strip (5.5-7.0 um long) which are interconnected and mutually dislocated through a system of smaller (2.0-3.5 um long) zigzag-arranged costal strips. Posteriorly the longitudinal costae converge and join with a flattened pedicel, 6-8 um long. A membraneous sheath surrounds the cell body and part of the collar, securing the protoplast to the lorica. (ref. ID; 7700)
Remarks
S. formosa was very common in the Andaman Sea, and no less than thirty cells have been photographed. The species is easily recognized by the shape of the lorica and arrangement of costae. The light micrographs show at the recognition of this taxon when viewed air-mounted on cover-slips offers no problems. The number of costal strips in the anterior transverse costa varies between eleven and fourteen, whereas in other Stephanacantha species the anterior ring contains invariably six transverse costal strips. Thirteen costal strips is by far the most common transverse costal strip number encountered in the S. formosa lorica. In sixteen cells examined the distribution was as follows: 11 (2 cells), 12 (2 cells), 13 (11 cells), 14 (1 cell). Also the number of anterior longitudinal costae is variable. In fifteen cells showing this feature adequately, the distribution was the following: 4 (12 cells), 5 (2 cells), 6 (1 cell). Any kind costal strip connection intermediate between a T-join and an end-to-end join may be found at the anterior lorica end. It should be borne in mind that a T-joint is the typical type of connection observed in other species allocated to this genus. The lack of numerical stability in the S. formosa lorica, and the fortuitous linking together of anterior transverse and longitudinal costal strips are obviously coherent phenomena. Stephanacantha formosa is in complete agreement with other species alocated to this genus as regards the mutual position of costal elements. The anterior longitudinal costal strips are overlaid externally by the anterior ring, while the diverging sets of short costal strips attach the introverted face of the longitudinal costal strips at slightly different levels, in that respect very similar to S. campaniformis (Leadbeater 1973; loc. cit. P1. 17 c, d). In some of the empty loricae a delicate membraneous sheath is visible, the function of which is to secure the cell properly to the lorica. (ref. ID; 7700)
Etymology
From the Latin formosus, beautiful. (ref. ID; 7700)
Geographical distribution
S. formosa is known from the Andaman Sea (Thailand) and from the sea around the Galapagos Islands (Manton, per. comm.). (ref. ID; 7700)
Type specimen
Type specimen, shown in Fig.22, found in a water sample collected 10 September 1981 at St. 4 (2 m) near Phuket Island, SW Thailand. (ref. ID; 7700)
Stephanacantha parvula Thomsen, 1983 (ref. ID; 7700 original paper)
Diagnosis
Cells solitary. Protoplast when dried ca. 2.5x4 um, flagellum ca. 12 um long. Lorica 9-10 um long consisting of two chambers; diameter at anterior lorica end ca. 6 um (calculated on the assumption that the dried loricae are completely collapsed). The anterior transverse costa consists of six costal strips (3-4 um long), each with an upright spine at one end. Three longitudinal costal strips (4-4.5 um long) join the centre of every second anterior transverse costal strip (T-joins). The longitudinal costal strips of the anterior chamber posteriorly attach to pairs of short diverging costal strips (ca. 2 um long). The posterior lorica chamber is composed of 3 somewhat broader costal strips surrounding the protoplast. A pedicel has not been observed. (ref. ID; 7700)
Remarks
S. parvula is closely related to S. campaniformis. The only major differences are the number of longitudinal costae (3 versus 6) and a certain difference is costal strip width, those of S. parvula being much more narrow. One cannot preclude the possibility that future investigations may reveal mixed populations of genuine S. campaniformis (so far known from the Mediterranean only) and S. parvula which, if occasion should arise, might result in the decision of treating S. parvula as merely a formtype of S. campaniformis. For the moment, however, it appears relevant to deal with these two types at the species level. To distinguish between S. parvula and S. dichotoma offers no problems. The most useful characteristics for immediate identification is the size and shape of the lorica and the absence (within S. parvula) of a flattened pedicel. It is evident from the transmission and scanning electron micrographs that S. parvula is similar to S. campaniformis and S. dichotoma as regards the mutual position of costal elements. The longitudinal costal strips of the anterior chamber are thus overlaid by the anterior transverse costa, while themselves being exterior relative to the short middle lorica costal strips. Because of the rather sparse material of this taxon (eight cells encountered, of which only two have been studied in the electron microscope), and the fact that the protoplast is in every case retained within the lorica, it has been difficult to analyze in detail the construction of the posterior lorica chamber. A close inspection of the transmission and scanning micrographs of the very same specimen, at least suggests that the costal strips of the posterior lorica chamber are slightly wider than the remainders, and that there is probably three of them, each anteriorly adjoining a pair of diverging middle lorica costal strips. (ref. ID; 7700)
Etymology
From the Latin parvulus, tiny. (ref. ID; 7700)
Geographical distribution
Andaman Sea (Thailand) and Sargasso Sea (Davis & Sieburth, per. comm.). (ref. ID; 7700)
Type specimen
Type specimen, shown in Fig.17, found in a water sample collected 8 September at St. 6 (Fig.1) near Phuket Island, SW Thailand. (ref. ID; 7700)