Thyroscyphoides sympodialis, Watson, 2003

Watson, Jeanette W., 2003, Deep-water hydroids (Hydrozoa: Leptolida) from Macquarie Island, Memoirs of Museum Victoria 60 (2), pp. 151-180 : 172-173

Thyroscyphoides sympodialis sp. nov.

Figures 22A–D

Material examined. Stn 44, NMV F91330 , holotype, specimen alcohol-preserved, NMV F91350 , malinol-mounted microslide from holotype colony; 20 infertile stems on hydrorhiza of Eudendrium .

Description (of holotype). Hydrorhiza tubular, rather contorted, reptant on substrate. Stems simple, to 12 mm high, proximal part of stem of same diameter as stolon; basal-most part of stem with 2 to 4 broad, indefinite annulations, stem thereafter sympodial, sometimes a side branch given off from lower stem. Internodes long, smooth, tubular, becoming shorter along stem, widening distally to below hydrotheca; nodes usually with 1 or 2 deep, oblique constrictions almost parallel with adcauline wall of hydrotheca, a slight tumescence in perisarc above node, sometimes 1 or 2 additional constrictions along internode.

Hydrothecae alternate, arising just below node, body tubular, wide, most sessile but some pedicellate; in sessile hydrothecae abcauline wall smoothly contiguous with outward bend of internode, free adcauline wall smooth, weakly convex to almost straight, a short length of wall adnate to internode; floor of hydrotheca flat, saucer-shaped or funnel-shaped (depending upon angle of view), hydropore slightly offset, fairly wide, a row of desmocytes above marking place of attachment of hydranth. Pedicellate hydrothecae arising from floor of a broken hydrotheca; pedicels of variable length, smooth to corrugated with some internal thickenings; floor of hydrothecae rounded to sinusoidal. In both forms, hydrothecal margin almost circular (anterior view) with 4 sharply pointed triangular cusps separated by deep embayments; operculum of 4 thin pyramidal valves. Hydranth without diverticulum, but with a distinct annular fold; hydranth with c. 20 tentacles.

Perisarc of lower stems comparatively thick, thinning apically along internodes, hydrothecal margin and operculum extremely thin and fragile.

Colour. Transparent, colourless

Measurements (µm)

Stem internode length 1000–1640

diameter at node 80–96 Hydrotheca length of adnate adcauline wall 168–200

length of free adcauline wall 480–584

length of abcauline wall (to marginal embayment) 336–520

width at margin 248–296

height of marginal cusps 120–184

width of floor 120–136 Distribution. This is the second record of the genus. T. biformis is known from deep water in the northern Pacific Kurile Islands ( Naumov, 1955).

Etymology. Refers to the strongly sympodial habit.

Remarks. The colonies are almost flaccid out of fluid and the thin, almost transparent perisarc of the hydrothecal margin and operculae are so crushed that few remain intact.

Sessile and pedicellate hydrothecae on the same stem and a hydranth lacking a diverticulum places the species in Thyroscyphoides Naumov, 1955 . The only other known species of the genus, T. biformis Naumov, 1955 , differs from T. sympodialis in its alternate hydrothecae and its strongly sympodial habit.

Figures

Figures 22A–D. Thyroscyphoides sympodialis sp. nov., stn 44. A, single stem from colony. B, sessile hydrotheca, C, pedicellate hydrotheca. D, anterior view of hydrothecal operculum. Scale bar: A, 1 mm; B, C, D, 0.5 mm.