(a) With filiform tentacles; the commonest type, seen in
_Bougainvillea_ (fig. 13), _Eudendrium_, &c.
(b) With capitate tentacles; type of _Clavatella_.
4. Hydranth with tentacles reduced below four; type of _Lar_ (fig.
11), _Monobrachium_, &c.
The _Anthomedusa_ in form is generally deep, bell-shaped. The sense
organs are typically ocelli, never otocysts. The gonads are borne on the
manubrium, either forming a continuous ring (Codonid type), or four
masses or pairs of masses (Oceanid type). The tentacles may be scattered
singly round the margin of the umbrella ("monerenematous") or arranged
in tufts ("lophonematous"); in form they may be simple or branched
(Cladonemid type); in structure they may be hollow ("coelomerinthous");
or solid ("pycnomerinthous"). When sessile gonophores are produced, they
may show all stages of degeneration.
_Classification._--Until quite recently the hydroids (Gymnoblastea)
and the medusae (Anthomedusae) have been classified separately, since
the connexion between them was insufficiently known. Delage and
Hérouard (HYDROZOA [2]) were the first to make an heroic attempt to
unite the two classifications into one, to which Hickson (HYDROZOA
[4]) has made some additions and slight modifications. The
classification given here is for the most part that of Delage and
Hérouard. It is certain, however, that no such classification can be
considered final at present, but must undergo continual revision in
the future. With this reservation we may recognize fifteen
well-characterized families and others of more doubtful nature.
Certain discrepancies must also be noted.
1. _Margelidae_ (= medusa-family _Margelidae_ + hydroid families
_Bougainvillidae_, _Dicorynidae_, _Bimeridae_ and _Eudendridae_).
Trophosome arborescent, with hydranths of _Bougainvillea_-type;
gonosome free medusae or gonophores, the medusae with solid tentacles
in tufts (lophonematous). Common genera are the hydroid
_Bougainvillea_ (figs. 12, 13), and the medusae _Hippocrene_ (budded
from _Bougainvillea_), _Margelis_, _Rathkea_ (fig. 24), and
_Margellium_. Other hydroids are _Garveia_, _Bimeria_, _Eudendrium_
and _Heterocordyle_, with gonophores, and _Dicoryne_ with peculiar
sporosacs.
[Illustration: After Haeckel, _System der Medusen_, by permission of
Gustav Fischer.