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.
[Illustration: 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.
The development of the Narcomedusae is in the main similar to that of
the Trachomedusae, but shows some remarkable features. In _Aeginopsis_ a
planula is formed by multipolar immigration. The two ends of the planula
become greatly lengthened and give rise to the two primary tentacles of
the actinula, of which the mouth arises from one side of the planula.
Hence the principal axis of the future medusa corresponds, not to the
longitudinal axis of the planula, but to a transverse axis. This is in
some degree parallel to the cases described above, in which a planula
gives rise to the hydrorhiza, and buds a polyp laterally.
In _Cunina_ and allied genera the actinula, formed in the manner
described, has a hypostome of great length, quite disproportionate to
the size of the body, and is further endowed with the power of producing
buds from a stolon arising from the aboral side of the body. In these
species the actinula is parasitic upon another medusa; for instance,
_Cunoctantha octonaria_ upon _Turritopsis_, _C. proboscidea_ upon
_Liriope_ or _Geryonia_. The parasite effects a lodgment in the host
either by invading it as a free-swimming planula, or, apparently, in
other cases, as a spore-embryo which is captured and swallowed as food
by the host. The parasitic actinula is found attached to the proboscis
of the medusa; it thrusts its greatly elongated hypostome into the mouth
of the medusa and nourishes itself upon the food in the digestive cavity
of its host. At the same time it produces buds from an aboral stolon.
The buds become medusae by the direct method of budding described above.
In some cases the buds do not become detached at once, but the stolon
continues to grow and to produce more buds, forming a "bud-spike"
(_Knospenähre_), which consists of the axial stolon bearing medusa-buds
in all stages of development. In such cases the original parent-actinula
does not itself become a medusa, but remains arrested in development and
ultimately dies off, so that a true alternation of generations is
brought about. It is in these parasitic forms that we meet with the
method of reproduction by sporogony described above.
In other Narcomedusae, e.g. _Cunoctantha fowleri_ Browne, buds are
formed from the sub-umbrella on the under side of the stomach pouches,
where later the gonads are developed.
_Classification._--Three families of Narcomedusae are recognized (see
O. Maas [40]):
[Illustration: After O. Maas, _Craspedoten Medusen der Siboga
Expedition_, by permission of E. S. Brill & Co.