Genus Description:
Cells discoid to slightly pear-shaped, rarely naviculoid, undulate in girdle view. Plastids reported as numerous discoid bodies.
Valves shaped like watch-glasses (b), without a distinct valve mantle; some species slightly extended along one radius to give an obovate form. The valve has very distinctive plain rays (see Gombos, 1980. for terminology) alternating with areolate areas. The broad inner parts of the plain sectors abut at the center or off-center on the valve face; one ray differs from the others (the median ray of Greville, 1860) having a thinner distal section (a) and forming a focus from which the others radiate. At the marginal (outer) end of each ray is a thin plate which is usually lost leaving a large aperture (ray hole) (b,c); below this is a smaller opening, representing the external aperture of a rimoportula. This is absent on the median ray but here the thin plate is missing, the outer part of the process is morphologically different and the rimoportula must open into the ray itself for a process can be seen on the inside (d,f,g). The rays are long chambers opening internally by ray slits which taper towards the margin. The valve edge is plain usually with a notch offset from the end of the thin ray (arrow, d). The areolae are loculate. Externally their apertures are variable, though basically cribrate (e, h-j). Internally they have simple foramina. Flattened kidney-shaped rimoportulae occur marginally, opposite the ends of the ray slits (d,f,g); the rimoportula opposite the narrow ray slit is often larger. In some species small rimoportulae also occur near the central plain area (f). Copulae not investigated.
This genus and Asterolampra are clearly closely related and both are found in tropical oceans. The rare 'naviculoid' forms were described by Kolbe (1955) as Liriogramma but are only boat-shaped species of Asteromphalus - they occur in the Gulf of California (Round, unpublished observation).
Emmended Description (Rattray 1890):
Circular, more rarely flabelliform, oval, or suboblong. Colour pale grey or subhyaline, inconspicuous. A centro-lateral area distinct, extending to or slightly beyond the middle of the clear area, rarely quite across the latter- ovate, clavate, or with sides somewhat deeply constricted. Markings: rays distinct, simple or dichotomous, extending from the apex or also from the sides of the centro-lateral area, straight, arcuate, flexuous or sharply bigeniculate, sometimes with short lateral rami passing obliquely outwards from the geniculations; interradial spaces hyaline, or with a subdistinct median area, continuous with the intervals between the compartments; the compartments equal or unequal, their inner ends convex, obliquely to transversely truncate or concave; areolae distinct or inconspicuous, the outermost row most manifest; intervals between the compartments tapering slightly outwards, or of uniform width, their outer ends rarely expanded, sometimes not reaching border; a subobsolete interval distinct, straight, rarely distinctly arcuate; sometimes an obscure granule (apiculus?) at outer ends of intervals. Border narrow, hyaline.
Synonymy:
Spantagidium de Brebisson, 1857.
Asterolampra Greville, 1860 (part).
Mesasterias Ehrenberg, 1872.
Actinogramma Ehrenberg, 1872. |
