Tesserogastria musculosa Beyer 1959

Tesserogastria musculosa Beyer, 1959

Fig. 4 F–G

Tesserogastria musculosa Beyer, 1959: 122, pls 1– 2.

Tesserogastria musculosa – Hesthagen 1971: 3, Fgs 2–10. — Bouillon 1985: 202. — Larson et al. 1992: 284. — Bouillon et al. 2006: 112.

Description

Umbrella bell-shaped, about as high as broad (up to 2.5 mm), with a small, blunt, apical projection surrounded by a circular depression. Exumbrella devoid of radial ridges. Mesoglea rather thin, comparatively thickened at margin, accommodating a belt of chordal cells on which the tentacles insert. Over 300 tentacles, inserted at 3–5 superimposed levels, apparently not forming distinct rows or clusters; solid, core composed of a single row of chordal cells; proximally constricted, leaving tear drop-shaped scars when shed; blunt-ended to pointed distally, and there devoid of adhesive pads; nematocysts evenly dispersed in epidermis, except for the distal tip, where they are comparatively crowded. Manubrium cross-shaped (four perradial lobes are distinguishable), except proximally where it assumes an octagonal shape at the origin of the radial canals; relatively long, though devoid of a peduncle, and extending somewhat beyond the bell margin; mesenteries absent; mouth square, with four simple lips provided with ciliated cells in the epidermis. Eight radial canals with rounded cross sections connect to the broad ring canal, elliptical in cross section, longer axis oral-aboral; centripetal canals absent. A conspicuous nematocyst ring on lower side of umbrella margin. Velum extremely broad and strong. Eight slender, elongated gonads, in four perradial pairs; one pair conFned to each manubrial lobe. Eight small, shortstalked, interradial statocysts with single, spherical statoliths; one statocyst in each octant. Cnidome: almost spherical stenoteles [(7–8) × (6–7) µm], tear drop-shaped microbasic euryteles [(4–7) × (3– 5) µm], and atrichous isorhizas (ca 2 µm); the capsules occur in both tentacles and the marginal ring. Color: umbrella translucent, with white to yellow epidermal spots at junction of radial canals with the ring canal.

Remarks

Although the tentacles were described as “not arranged in distinct rows, nor in clusters” around the bell margin, Beyer (1959) acknowledged that “It is possible, however, to trace some repetition in the arrangement, and this makes 48 groups […]. The pattern is thus not quite unlike that of Ptychogastria polaris Allman […]”. However, no further details were given relative to the position of these groups with respect to the radial canals. Their presence, if conFrmed again, would not be surprising, given that more or less distinct groups of tentacles can be found in both Ptychogastria and Glaciambulata, the sole marked difference in this respect being the total absence of tentacles with adhesive pads in Tesserogastria. Though no such structures have been observed, “The amount of debris so frequently found to be sticking to the tentacle ends indicate that they are adhesive” (Beyer 1959). The so called adhesion is, most probably, due to the crowded condition of the nematocysts in the tentacle tips (Beyer 1959), and the possible glutinant nature of some of them (Hesthagen 1971).

The development from the egg, and the behavior of the medusa were thoroughly documented by Hesthagen (1971).

Ecology

A soft bottom species, never captured in plankton nets or vertical hauls (Beyer 1959). The medusae move extremely slowly, and have never been observed to swim in captivity, unless they were forced to do so and, in this case, their swimming was jerky. Specimens of this species have been collected between 60–350 m (Hesthagen 1971).

Distribution

Only known from the Norwegian coast of the North Sea, between Bergen and Oslo (Hesthagen 1971).