Ptychogastria asteroides Haeckel 1879

Ptychogastria asteroides (Haeckel, 1879)

Fig. 4A–B

Pectanthis asteroides Haeckel, 1879: 267.

Pectanthis asteroides – Haeckel 1881a: 17, pls 7–8; 1881b: 20, pls 7, 8. — Browne 1903: 25, 26, 29. — Maas 1906a: 492. — Bigelow 1909: 311. — Vanhöffen 1912: 386. — Beyer 1959: 126–130.

Ptychogastria asteroides – Mayer, 1910: 374. — Thiel 1932b: 478. — Kramp 1947: 5; 1957: 46; 1959: 180, 205, 223, 226; 1961: 241; 1968: 174. — Picard 1955: 68. — Bouillon 1985: 202. — Boero & Bouillon 1993: 266. — Gili et al. 1998: 116, 126, 129, 131, 132; 1999: 232, Fgs 6–7; 2000: 1517, 1526. — Bouillon & Boero 2000: 68. — Bouillon et al. 2000: 92; 2004: 240, Fg. 152A–C; 2006: 112.

Umbrella 1–2 mm high and 4–5 mm wide, dome-shaped in a contracted state, and comparatively Fattened when relaxed. Mesoglea relatively thin, giving rise to a small, blunt, apical projection. Exumbrella with 16 radiating ribs (8 perradial and 8 interradial) alternating with as many grooves, giving the margin a “lobed” appearance. Each umbrellar “lobe” bears a group of 12–16 solid tentacles arranged in a few, horizontally stacked rows; the three large, uppermost tentacles Fliform, borne on a conical projection enveloping their bases; projection crowded with irregular, refringent, likely mineral inclusions, as well as with stenoteles; additional tentacles of two types, Fliform and adhesive; surface of all Fliform tentacles covered with successive rings of spherical stenoteles of varied sizes; adhesive tentacles with a few, scattered stenoteles, ending distally in adhesive pads; a total of 200–260 tentacles per medusa. A free, pendant statocyst in middle of each umbrellar lobe, below the lowest row of tentacles; short, club-shaped, with single, spherical to elliptical statolith. Manubrium about half the length of the subumbrellar cavity; quadrangular proximally and eight-lobed towards middle; mouth with four simple lips crowded with mainly large stenoteles and granular, gland cells. Eight radial canals, bound to the wall of the manubrium through 8 shelf-like mesenteries, connect to the ring canal; centripetal canals absent. A continuous ring of nematocysts below the groups of tentacles. Velum thick and broad. Eight pairs of ovoid gonads on either side of the manubrial lobes; members of a pair separated through a mesentery. Cnidome: only stenoteles in two size classes reported to date. Color: perradial ribs of exumbrella purple-red, expanding distally into an ovoid spot of the same color; umbrella margin between the groups of tentacles yellowish; manubrium gold-yellow; tentacles translucent-yellow; adhesive disks red; gonads red.

The tentacles of this medusa were described and illustrated by Haeckel (1881a, 1881b) as hollow, which made Kramp (1947) doubt about its afFnities with the genus Ptychogastria. Later, Picard (1955) found the species again and stated that all its tentacles were solid. Haeckel also noted that “all sixteen [exumbrellar] ribs are tipped with nematocysts”, but his statement was subsequently invalidated by Gili et al. (1999).

The shape of the manubrium, as well as the position of gonads in Haeckel’s (1881b) account, is highly contradictory. In the legend of his Fg. 1 (pl. 7), he stated: “In the middle [,] the golden-yellow base of the stomach with the surrounding corona of red genitalia shines through the umbrella” and, indeed, a pair of gonads is illustrated on either side of an eight-lobed manubrium. A similar condition is seen in his pl. 7 Fg. 3. In contrast, his Fg. 2, from the same plate, depicts a quadrangular manubrium and eight pairs of gonads originating from the proximal parts of the radial canals, thus apparently Ftting the rather imprecise diagnosis he gave of the species (p. 20): “Eight egg-shaped genitalia in the proximal half of the radial canal (sic!), encircling the basis of the stomach in the form of an eight-rayed star, and halved by long radial mesogonia”. However, Haeckel (1881b: 23) seems to clarify his observations by stating the following: “The eight genitalia […] surround the basis of the stomach like an eight-rayed star”. Although not making speciFc comments, a similar situation is seen in the more recent account by Gili et al. (1999: 324, Fg. 6), who Fgured the gonads around a rather lobed manubrium, the unambiguous shape of which is even more evident in their Fg. 7 (right drawing). It is worth noting that the manubrial lobes in this species are less developed than in P. polaris.

In addition, the position of the marginal “lobes” of the umbrella (and, consequently, of the groups of tentacles) seems to be erroneous in Haeckel’s account. Indeed, he placed two lobes (with their respective tentacle groups) in each octant (pl. 7 Fgs 1–3), while Gili et al. (1999, Fg. 7) illustrate 8 of them as perradial, and the remaining 8 as interradial.

Often recorded in both intermediate waters above submarine canyons and near the sea Foor close to the continental shelf. Owing to the most frequent occurrence of the specimens in traps placed in intermediate waters than in those close to the bottom, lead Gili et al. (1999) to suspect that P. asteroides is a medusa that shows longer swimming periods compared to its congener P. polaris (see below). The specimens obtained by Picard (1955) from 10 m depth over a Posidonia bed are suspected to have been brought there fortuitously after a heavy sea episode. The normal bathymetric range varies between 200 m (Haeckel 1881b) and 1150 m (Gili et al. 1999).

Many recent records are from the northern part of the Mediterranean basin (France and Spain) (Gili et al. 2000), but the species is known to extend its distribution westwards to the Strait of Gibraltar (Haeckel 1881b).