Ptychogastriidae Mayer, 1910

Horia R. Galea, Cornelia Roder, Christoph Walcher, Marco Warmuth, Eberhard Kohlberg & Philipp F. Fischer, 2016, Glaciambulata neumayeri gen. et sp. nov., a new Antarctic trachymedusa (Cnidaria: Hydrozoa), with a revision of the family Ptychogastriidae, European Journal of Taxonomy 252, pp. 1-30 : 3-4

Family Ptychogastriidae Mayer, 1910

Diagnosis

Trachymedusae with either Fat or dome-shaped umbrella; with four-lobed manubrium, not giving rise to mesenteries, or with eight-lobed manubrium, giving rise to eight mesenterial partitions of the subumbrella; without gastric peduncle; mouth with four simple lips; tentacles marginal, either Fliform, not arranged in groups and inserted at varied levels on the umbrellar margin, or Fliform and adhesive occurring simultaneously, and grouped into more or less well-deFned clusters composed of several superimposed rows; eight radial canals joining the circular canal; centripetal canals either absent or present; gonads either simple, elongated and attached to the body of manubrium, or in pairs resulting from the mesenterial partitions and developing on either side of the manubrial lobes; with or without a velum; with either 8 or 16 free, ecto-endodermal statocysts.

Remarks

Earlier diagnoses ( Mayer 1910; Kramp 1959, 1961, 1968; Bouillon & Boero 2000; Bouillon et al. 2006) are broadened by taking into consideration the shape of the umbrella, the presence/absence of a velum, and of centripetal canals. Indeed, unlike both Ptychogastria Allman, 1878 and Tesserogastria Beyer, 1959 , the medusae belonging to the so far monotypic genus Glaciambulata gen. nov. (see below) have Fattened rather than dome-shaped umbrellas, and they also lack a velum. The presence of centripetal canals was curiously excluded from earlier diagnoses of the family, though they are present in P. polaris Allman, 1878 . The occurrence of the gonads is henceforth restricted to the manubrium only, because Pectis antarctica Haeckel, 1879 , formerly assigned to the genus Ptychogastria by a number of authors, has the gonads on the radial canals and, for this reason, combined with additional characters, does not belong to Ptychogastriidae (see below).

The main distinguishing characters of ptychogastriid genera are listed in Table 1 .

Key to the genera

1. Tentacles exclusively Fliform ………………………………………… Tesserogastria Beyer, 1959

– Tentacles of two types: Fliform and adhesive ………………………………………………………2

2. Umbrella dome-shaped, velum present ……………………………… Ptychogastria Allman, 1878

– Umbrella Fat, velum absent ……………………………………………… Glaciambulata gen. nov.

Tables

Table 1. Main distinguishing characters of the genera belonging to the family Ptychogastriidae Mayer, 1900.

Umbrella	Glaciambulata gen. nov. Flat	Ptychogastria Allman, 1878 Dome-shaped	Tesserogastria Beyer, 1959 Dome-shaped
Manubrium	Eight-lobed	Eight-lobed	Four-lobed
Mesenteries	8	8	Absent
Tentacles	Filiform + adhesive; forming contiguous groups; inserted in superimposed rows on umbrella margin	Filiform + adhesive; forming contiguous groups; inserted in superimposed rows on umbrella margin	Filiform; reportedly not arranged in groups; inserted at varied levels on umbrella margin
Centripetal canals	Absent	Present/absent	Absent
Gonads	Ovoid; in pairs, on either side of the manubrial lobes	Ovoid; in pairs, on either side of the manubrial lobes	Elongated; simple; attached to the body of manubrium
Velum	Absent	Present	Present
Statocysts	16	16	8
Ability to swim	No	Yes	Yes