3. Trachynemidae.—Eight radial canals, eight gonads, stomach not prolonged into manubrium; tentaculocysts enclosed. Rhopalonema, Trachynema, &c.
| After E. T. Browne, Proc. Zool. Soc. of London. |
| Fig. 65.—Aglantha rosea (Forbes), a British medusa. |
4. Ptychogastridae (Pectyllidae).—As in the preceding, but with suckers on the tentacles. Ptychogastria Allman (= Pectyllis), a deep-sea form.
5. Aglauridae.—Eight radial canals, two, four or eight gonads; tentacles numerous; tentaculocysts free; stomach prolonged into manubrium. Aglaura, Aglantha (fig. 65), &c., with eight gonads; Stauraglaura with four; Persa with two. Amphogona, hermaphrodite, with male and female gonads on alternating radial canals.
6. Geryonidae.—Four or six radial canals; gonads band-like; stomach prolonged into a manubrium of great length; tentaculocysts enclosed. Liriope, &c., with four radial canals; Geryonia, Carmarina (fig. 26), &c., with six.
7. Halicreidae.—Eight very broad radial canals; ex-umbrella often provided with lateral outgrowths; tentacles differing in size, but in a single row. Halicreas.
Sub-order 2. Narcomedusae.—Margin of the umbrella-lobed, tentacles arising from the ex-umbrella at some distance from the margin; tentaculocysts exposed, not enclosed in vesicles; gonads on the sub-umbral floor of the stomach or of the gastric pouches.
| Fig. 66.—Cunina rhododactyla, one of the Narcomedusae. (After Haeckel.) |
| c, Circular canal. h, “Otoporpae” or centripetal process of the marginal cartilaginous ring connected with tentaculocyst. k, Stomach. l, Jelly of the disk. r, Radiating canal (pouch of stomach). tt, Tentacles. tw, Tentacle root. |
The Narcomedusae exhibit peculiarities of form and structure which distinguish them at once from all other Hydromedusae. The umbrella is shallow and has the margin supported by a rim of thickened ectoderm, as in the Trachomedusae, but not so strongly developed. The tentacles are not inserted on the margin of the umbrella, but arise high up on the ex-umbral surface, and the umbrella is prolonged into lobes corresponding to the interspaces between the tentacles. The condition of things can be imagined by supposing that in a medusa primitively of normal build, with tentacles at the margin, the umbrella has grown down past the insertion of the tentacles. As a result of this extension of the umbrellar margin, all structures belonging to this region, namely, the ring-canal, the nerve-rings, and the rim of thickened ectoderm, do not run an even course, but are thrown into festoons, caught up under the insertion of each tentacle in such a way that the ring-canal and its accompaniments form in each notch of the umbrellar margin an inverted V, the apex of which corresponds to the insertion of the tentacle; in some cases the limbs of the V may run for some distance parallel to one another, and may be fused into one, giving a figure better compared to an inverted Y. Thus the ectodermal rim runs round the edge of each lobe of the umbrella and then passes upwards towards the base of the tentacle from the re-entering angle between two adjacent lobes, to form with its fellow of the next lobe a tentacle-clasp or peronium, i.e. a streak of thickened ectoderm supporting the tentacle. Similarly the ring-canal runs round the edge of the lobe as the so-called festoon-canal, and then runs upwards under the peronium to the base of the tentacle as one of a pair of peronial canals, the limbs of the V-like figure already mentioned. The nerve-rings have a similar course. The tentaculocysts are implanted round the margins of the lobes of the umbrella and may be supported by prolongations of the ectodermal rim termed otoporpae (Gehörspangen). The radial canals are represented by wide gastric pouches, and may be absent, so that the tentacles arise directly from the stomach (Solmaridae). The tentacles are always solid, as in Trachomedusae.