Ptychogastria polaris Allman, 1878

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 : 14-16

Ptychogastria polaris Allman, 1878

Fig. 4 C–E

Ptychogastria polaris Allman, 1878: 290 , Fgs 1–3.

Pectyllis arctica Haeckel, 1879: 266 .

Ptychogastria opposita Vanhöffen, 1912: 386 , Fg. 20, pl. 25 Fg. 6.

Ptychogastria polaris – Fewkes 1888: 43. — Browne 1903: 24, pl. 4, Fgs 1–2, pl. 5, Fgs 6–8. — Maas 1906a: 482, 492, 493, 509. — Linko 1904: 218; 1913: 11. — Broch 1907: 4, 8; 1929: 491, Fg. 6A–B. — Bigelow 1909: 301, 310; 1913: 41. — Mayer 1910: 372, Fg. 212. — Vanhöffen 1912: 387. — Kramp 1914: 386–387, 395–396, 398, 427; 1942: 69, Fg. 21; 1943: 6; 1947: 5, pl. 1, Fgs 1–4, pl. 6, Fgs 1–2; 1955: 158; 1957: 45, 98, 99; 1959: 180, 205, 209–211, 215, 221, 264, 268, 269, Fg. 260; 1961: 241; 1968: 110, 148, 174, Fg. 297. — Foerster 1923: 232, 264. — Kramp & Damas 1925: 316. — Tanasijčuk 1927: 362. — Runnström 1932: 30. — Thiel 1932a: 151; 1932b: 444. — Bernstein 1934: 9, 25. — Yashnov 1940: 112; 1948: 73, pl. 21, Fg. 1A–B. — Dunbar 1942: 74. — Vibe 1950: 103. — Rees 1953: 8. — Chiu 1954: 56. — Naumov 1956: 38; 1969: 610, Fg. 457. — Beyer 1959: 124, 126, 129, 130. — Hesthagen 1971: 16. — Russell 1980: 3, Fg. 6. — Bouillon 1985: 202. — Mackie 1985: 760, 761. — Stepanjants 1989: 416. — Antsulevich 1991: 41. — Larson et al. 1992: 277, 282, Fg. 2C. — Sirenko et al. 1996: 348. — Stübing & Piepenburg 1998: 193, Fg. 1. — Gili et al. 1999: 325. — Panteleeva et al. 1999: 372, Fgs 1–10. — Bouillon & Boero 2000: 68. — Miyake et al. 2004: 40, Fg. 10. — Bouillon et al. 2006: 112. — Antsulevich 2015: 715, Fg. 349.

Pectyllis arctica – Haeckel 1881a: 11, pls 3, 4; 1881b: 10, pls 3, 4. — Maas 1893: 20; 1906a: 482, 492. — Levinsen 1893: 146. — Aurivillius 1896: 194; 1899: 56. — Grönberg 1898: 465. — Browne 1903: 24, 25. — Bigelow 1909: 310. — Mayer 1910: 372. — Kramp 1914: 386–387; 1957: 46. — Beyer 1959: 128.

Ptychogastria opposita – Kramp 1947: 5; 1957: 45; 1961: 241. — Beyer 1959: 128.

Description

Umbrella dome-shaped to hemispherical, up to 12 mm high and 24 mm wide. Mesoglea moderately thick and transparent, conspicuously thickened towards margin of umbrella. Exumbrella with 16 radiating ribs (8 perradial and 8 interradial), alternating with as many grooves; an umbrellar “lobe” to each rib. Manubrium vasiform, about half as long as the height of subumbrella; proximal part divided into 8 lobes, visible as an 8-rayed “star” in an apical view of exumbrella; lower part quadrangular; mouth with four simple lips. Eight radial canals, narrow proximally when leaving the manubrium, then widening distally and becoming very broad and Fat at junction with the ring canal; the latter equally broad, giving rise to 8 interradial, centripetal canals, tapering gradually, and almost reaching the manubrium. Eight mesenteries connect each manubrial lobe to the subumbrella along a radius corresponding to each radial canal. All tentacles with solid cores, and showing a distinctive arrangement around the thickened bell margin: 48 isolated, Fliform tentacles alternate with 48 clusters of additional, smaller tentacles. Filiform tentacles large, with triangular bases in cross section, 3 per umbrellar “lobe”, 16 out of 48 being perradial (with respect to both radial and centripetal canals), while the remaining 32 are interradial. Each of the 48 clusters somewhat triangular in shape and projecting slightly outwards, comprising 16–20 comparatively shorter tentacles in 5–6 superimposed whorls; 3 upper tentacles (composing the two aboral-most rows) Fliform (rounded in cross section, tapering gradually from base to tip), lower tentacles adhesive, with a few scattered nematocysts in epidermis, with narrow base, gradually widening distally, where they bear an adhesive pad. All Fliform tentacles very contractile, epidermis containing numerous, successive rows of nematocysts, more densely crowded distally. Total number of tentacles reaching as many as 700–1000 per medusa. Sixteen small statocysts, 2 in each octant, arising from the inner side of umbrella margin, immediately below a group of adhesive tentacles; short-stalked, with single statolith. A conspicuous, uninterrupted ring of nematocysts along the margin of subumbrella. Velum very wide. Eight pairs of gonads, separated through mesenterial partitions, along the sides of the 8 manubrial lobes, not conFned to the proximal parts of the radial canals, and not developing so as to reach the main body of the manubrium, becoming thus in contact with each other; gonads sac-shaped, elongated, with convoluted surface. Young medusae, 4–8 mm wide, already bear gonads and resemble the adults, thought the number of tentacle groups may be as low as 6. Cnidome: microbasic euryteles and stenoteles. Color: 32 red spots near margin of exumbrella, subumbrella light pink, gonads milky-white to orange, manubrium bright pink to deep red, mesenteries milky-white.

Remarks

According to Kramp (1955), when Haeckel (1879) described his Pectyllis arctica , “he was not aware that in the previous year it had been described by Allman as Ptychogastria polaris ”. Haeckel (1881b), after examining “an incomplete specimen” of Pt. polaris in the British Museum, reached the conclusion that it “appears closely related” to his Pe. arctica . Later, Browne (1903), upon reexamination of the type of Pt. polaris , found it in perfect agreement with Pe. arctica , and included the latter in the synonymy of Allman’s species, an opinion followed later by all subsequent authors.

Though not providing a real description, Vanhöffen (1912) introduced the binomen Pt. opposita for southern specimens of a medusa “that do not markedly differ from the northern P. polaris ”, not excluding that “the two species will eventually prove identical”, the main argument for keeping them distinct being the considerable remoteness of their respective areas of distribution. Kramp (1947), too, although acknowledging their great morphological similarities, kept them provisionally distinct for the same reason. He, however, was subsequently able to identify as P. polaris specimens from the South Shetland Islands, reaching the conclusion that P. opposita could be conFdently sunk into synonymy of Allman’s species ( Kramp 1957).

Miyake et al. (2004) provided beautiful photographs of the medusa in situ, in both dorsal and ventral aspects. Panteleeva et al. (1999) gave comprehensive data on the cnidome composition of medusae from both the PaciFc and Barents Sea.

The tentacle arrangement, as noted by Haeckel (1881b) “is very regular and peculiar. Each of the sixteen marginal lobes bears a principal group, composed of three larger sucking cups [=bases of broken Fliform tentacles] and three triangular sucking-plates alternating with them, and in each sucking-plate we can distinguish sixteen to twenty sucking-cups [=mainly adhesive tentacles] of different sizes”. Their arrangement is well illustrated by Haeckel in his Pl. 3, but his account is somehow misleading: there are, indeed, 3 large Fliform tentacles within each umbrellar “lobe”, but the number of groups of smaller tentacles alternating with them is only 2, while additional groups are common to every two adjacent umbrellar “lobes”. Panteleeva et al. (1999, Fg. 5A–C) provided additional illustrations of the tentacular arrangement, supporting the accuracy of Haeckel’s drawings.

It should be also noted that Allman’s (1878) account (“Each tentacle corresponds to one of the notches which separate the marginal lobes”) is equally erroneous with respect to the arrangement of tentacles. In fact, as stated above, 16 out of the 48 large, Fliform tentacles are perradial, or the umbrellar notches are interradial; consequently, within each notch, there is a group composed of shorter, Fliform and adhesive tentacles.

Ecology

This is an epibenthic species, spending the majority of its time attached to the sea Foor ( Panteleeva et al. 1999), occasionally being involved in short (ca 15 seconds) swimming episodes ( Larson et al. 1992). It forages not only on sediment ( Larson et al. 1992; Stübing & Piepenburg 1998; Panteleeva et al. 1999), but also on hard substrates ( Miyake et al. 2004). According to Panteleeva et al. (1999), P. polaris is deFnitely a cold-water species. Its bathymetric range of occurrence is between 10 m ( Kramp 1947) and 2500 m ( Stepanjants 1989).

Distribution

A mainly boreal-arctic species ( Panteleeva et al. 1999), sporadically recorded from other locations around the world, such as Monterey Bay, California ( Larson et al. 1992), Japan ( Miyake et al. 2004), and Antarctic to subantarctic waters ( Kramp 1957 and Vanhöffen 1912, respectively).

Figures

Fig. 4. — A – B. Ptychogastria asteroides (Haeckel, 1879). A. Lateral view of a medusa. B. Portion of umbrella margin showing the arrangement of tentacles. — C – E. Ptychogastria polaris Allman, 1878. C. Medusa in lateral view. D. Oral view of half of the medusa, showing the arrangement of the marginal tentacles. E. Portion of the bell margin, greatly enlarged. — F – G. Tesserogastria musculosa Beyer, 1959. Medusa in lateral (F) and oral (G) aspects. [A, B redrawn after Gili et al. (1999); C, E redrawn after Panteleeva et al. (1999); D redrawn after Haeckel (1881 b); F, G redrawn after Hesthagen (1971)]. Scale bars: A, B = 500 µm; C = 3 mm; E = 2 mm.