OOrder Leptothecata

Order Leptothecata Cornelius, 1992

synonyms	Thecata Fleming, 1828; Thecaphora Hincks, 1868; Leptomedusae Haeckel, 1979
diagnosis	Polyps always colonial, hydranth protected by hydrotheca, but the latter can be so short that hydranth is unable to retract into it, hydrotheca can be shed in few species. Tentacles always in one whorl. Gonophores on much reduced hydranths and nearly always in periderm capsule, the gonotheca; exceptionally medusae buds on fully formed hydranths without gonotheca. Gonophores develop either into medusae or sessile sporosacs. Medusae with shallow bell, gonads on radial canals, usually more than four tentacles, mostly with statocysts. Statocysts formed only from epidermal tissue. Cnidome never includes stenoteles.
higher classification	Cnidaria, Medusozoa, Hydrozoa, Leptolinae
species	about 1900

how to recognize?

gonads on radial canals (green arrow)

medusa bell usually relatively flat

usually with statocysts (red arrow)


Hydrothecae: fully formed rigid hydrotheca of the Campanulariidae. The reproductive structures are often in a gonotheca (green arrow).	a shallow hydrotheca of Halecium	the inconspicuous, soft hydrotheca of Aequorea

specific terms

bell margin of a leptomedusa,

the statocysts are always derived from epidermal cells only, they do not include a gastrodermal core as in the Trachylinae

Terms used to describe colonies; for colony forms click here

The polyp stages of several families of Leptothecata have specialized defensive polyps without tentacles. These are like the normal polyps surrounded by a theca, the nematotheca (green arrow).

The red arrow point towards a hydrothecae, the theca of the ordinary hydranth

In the Superfamily Plumularoidea (picture, hydranths not shown), the nematothecae have a characterisitic arrangement relative to the hydrotheca.

some important topological terms.

Examples of hydrothecae forms made by polyps of the Leptothecata.

a) Canpanulinidae, a soft hydrotheca with a pleated operculum (red arrow). b) Lafoeidae, no operculum, no basal floor. c) Syntheciidae, no operculum. d) Campanulariidae, note cusped margin of this species. e) Haleciidae, a very shallow hydrotheca, often with nested secondary hydrothecae (blue arrow). f) Sertulariidae, note lid-like operculum (red arrow). g) Aglaopheniidae, note fused nematothecae (green arrows).

difficult cases

Some scyphoplyps with a theca resemble thecate hydroids. Certain polyp phases of Leptothecata have a very inconspicuous hydrotheca, or the hydrotheca is even shed it during their growth (e. g. Haleciidae, Eirenidae, Aequoridae). They can easily be confounded with polyps of the Anthomedusae.


a scyphopolyp with a theca	Helgicirrha schulzei, a polyp of the Leptothecata, that looks deceptively like a polyp of the Anthomedusae	some polyps of the Anthomedusae (Bougainvillidae and Pandeidae) have a soft, filmy pseudohydrotheca

Classification

Suborder Conica

Leptothecata having polyps with a simple, generally conical or rounded-conical hypostome, without a pregastric cavity.

Suborder Proboscoidea

Leptothecata having polyps with a flared to globose, more or less peduncled hypostome, forming a pregastric cavity.