Sphaeronectes haddocki, Pugh, 2009

P. R. Pugh, 2009, A review of the family Sphaeronectidae (Class Hydrozoa, Order Siphonophora), with the description of three new species, Zootaxa 2147, pp. 1-48 : 31-35

Sphaeronectes haddocki sp. nov.

Diagnosis: Large cylindrical nectophore, with rounded apex, up to 11.5 mm in height. Nectosac extensive, occupying 87% of height of nectophore. Hydroecium extending to 45% height of nectosac, but not fully open on proximal side. Ovate vertical somatocyst, without pigmentation, with characteristic, mainly horizontal, pedicle. Lateral radial canals looped, with secondary curve on descending part.

Material examined: Four specimens collected by the ROVs Ventana and Tiburon. Ventana Dive 2623 (7 th February 2005; 36°41.87'N, 122°03.49'W; depth of collection 354 m); Tiburon Dive 987 (16 th May 2006; 35°30.86'N, 122°39.73'W; depth of collection 397 m); Tiburon Dive 1156 (1 st December 2007; 35°42.24'N, 122°34.75'W; depth of collection 412 m); and Tiburon Dive 1157 (2 nd December 2007; 36°41.76'N, 122°04.98'W; depth of collection 433 m). The specimens were initially fixed in 5% formalin, and latter transferred to Steedman's preserving fluid. The specimen from Tiburon Dive 1156 has been designated the type and is deposited at the Smithsonian's National Museum of Natural History ( USNM 1124195).

Description: Each specimen, when collected, consisted of a single nectophore, and the proximal part of the siphosome. The main part of the siphosome was, unfortunately, broken off during collection. Photographs of various specimens, taken shortly after recovery of the ROV, are shown in Figure 24.

Nectophore: The single nectophore ( Figures 24 & 25) present with each specimen was cylindrical in shape with a rounded, convex apex and in life measured from 9 to 11.5 (type specimen) mm in height and c. 10.5 mm in diameter. The nectosac occupied the great majority of the nectophore, and extended to 0.87 of the nectophore height. On its proximal side it was indented toward its mid-line to afford space for the hydroecium and the somatocyst. Slightly above the ostial opening both the nectophore and the nectosac narrowed considerably so that the broad ostial opening measured about 7 mm in diameter but, according to the degree of contraction of the nectosac, occasionally was smaller. It was equipped with a narrow velum. After preservation the nectophores shrunk considerably in size and became distorted. There was a considerable decrease in the diameter of the type specimen, particularly in its upper and distal regions, where the mesogloea was much thinner, resulting in the nectosac appearing to occupy virtually all of that space.

The hydroecium had a maximum depth of 2.5 mm and extended to about two fifths the height of the bell, on its proximal side. It was widely open at its base, forming two large lateral flaps that, in the preserved specimens, tended to fold down and extend below the ostial level. It gradually decreased in width up to its apex and, in the living specimen, it was open on its proximal side for only about two-thirds of its height. The siphosomal stem was attached at the upper distal corner of the hydroecium of the nectophore. Here too was the point of origin of the somatocyst. However, no obvious pedicular canal arose at this point; the wall of the nectosac being closely applied to the apex of the hydroecium in this region. Several other Sphaeronectes also have what Carré (1969 c) described as a "virtuel" pedicular canal. The four radial canals arose together from this point with the lower canal running directly to the ostial ring canal down the median indentation of the nectosac. Similarly the upper canal passed up this median indentation then over the apex of the nectosac and then straight down to the ring canal. The lateral radial canals arched up toward the apex of the nectosac, curved round close to this apex and back toward the mid-line before continuing down to the ostial ring canal. Close to the ostium, they followed the narrowing of the nectosac and curved inwards toward the ring canal. Their course was very similar to that described above for Sphaeronectes christiansonae .

The somatocyst had a very characteristic shape. A broad pedicle arose from its point of origin and, at first, followed the contours of the hydroecium, running a short distance up its distal side to its apex and then bending through 90° and running proximally for a short distance before bending up, again through 90°, and giving rise to the main part of the somatocyst. In all, the pedicle was c. 0.8 mm in length. The main part of the somatocyst expanded into a large ovate structure up to 2 mm in height and 1.3 mm in diameter. In life it had a very pale whitish hue, with apparently homogeneous contents, although occasionally oil droplets were present ( Figure 24D). It was covered with a honeycomb of large, but indistinct cells.

Siphosome: Of all the photographs of the living specimens only those of the Ventana Dive 2623 specimen show any signs of well-developed cormidia, but these pictures are too poor to reproduce. However, they do show a barrel-shaped gonophore, but with little sign of a manubrium, and a hemispherical bract whose phyllocyst appears to be small and globular. Unfortunately that posterior part of the stem was not preserved and so no further details on the arrangement of the bract and gonophore could be elucidated. The other specimens, however, retained quite long pieces of the anterior siphosomal stem that, in the case of the type specimen, included more than twenty cormidia. Most of these consisted of a gastrozooid, with its tentacle, attached directly to the stem and just anterior to it two buds, side by side, which represented the primordial bract and gonophore. However, the posterior most four cormidia on the siphosomal stem of the type specimen showed the beginnings of the development of the bract. The oldest of these is shown in Figure 26. Here the mesogloea of the bract has yet to expand to its full extent and its ultimate shape cannot be gauged. The phyllocyst appears as a slightly asymmetric globular process. The gonophore at this stage remains a bud1.

In the preserved specimens, the stem was slightly narrower at the point where each gastrozooid was attached, but there was no sign of the distinctive node seen in Sphaeronectes christiansonae . The gastrozooids were, as usual, very variable in shape and, in life, appeared to be colourless. Those of the type specimen were narrow and elongate, measuring 1.5–1.8 mm in length. The basigaster, which was the widest part, occupied the proximal quarter of the gastrozooid, while the small distal proboscis region also was slightly inflated. However, the gastrozooid of the Ventana Dive 2623 and the Tiburon Dive 1157 specimens were much shorter, with the main stomach region greatly expanded. In life the cnidobands of the tentilla where pale yellow in colour. The cnidoband ( Figure 27) was of the typical calycophoran form, with a pair of large mastigophore on each side of the proximal part, and some large desmonemes distally. The nematocysts of the long, but highly contracted and convoluted in its preserved state, terminal filament were not examined in detail but were presumed to be the desmonemes and anacrophores typical of other calycophoran species. Both the pedicle of the tentillum and the tentacle itself bore numerous large lateral excrescences.

Distribution: The four specimens of Sphaeronectes haddocki that have been examined, together with a further known specimen from Tiburon Dive 1157, all came from a very limited area in the region of Monterey Bay, California. They were also collected within a relatively narrow depth range between 354 and 488 m. Further specimens can almost certainly be identified from the in situ frame grabs, taken during various dives of Ventana and Tiburon, in the VARS Library at MBARI. These were all taken within the 391 to 498 m depth range; further suggesting that this species has a limited depth range.

Remarks: Although of similar size to Sphaeronectes christiansonae , S. haddocki is easily distinguished from it not least by the absence of deep red pigmentation. In addition, the general shape of the nectophore is different and the presence of the large pale milky-white somatocyst can clearly be seen in some of the in situ frame grabs. The arrangement of the somatocyst is very characteristic of this species. Like S. christiansonae , the surface of the nectophore of S. haddocki was found to emit bright green fluorescence (S.H.D. Haddock, personal communication).

Etymology: Sphaeronectes haddocki is named in honour of Professor Steven Haddock of the Monterey Bay Aquarium Research Institute who has not only kindly invited me to participate in several of his cruises, but has always taken a keen interest in siphonophores.