Sphaeronectes christiansonae, 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 : 27-31

Sphaeronectes christiansonae sp. nov.

Diagnosis: Large hemispherical nectophore, c. 10 mm in height, with nectosac extending to 80% of it. Deep hydroecium stretching to half height of nectosac. Small, up to 1.5 mm in length, cylindrical, upright somatocyst, without obvious pedicle. Lateral radial canals looped, with secondary curve on descending part. Somatocyst and phyllocyst deep red in colour.

Material examined: Two specimens collected by the ROV Tiburon during Dives 842 (7 th May 2005; 35°29.96'N, 123°51.99'W; depth of collection 508 m) and 987 (16 May 2006; 35°30.86'N, 122°39.73'W; depth of collection 840 m). The specimens were initially fixed in 5% formalin, and latter transferred to Steedman's preserving fluid. The specimen from Tiburon Dive 987 has been designated the type and is deposited at the Smithsonian's National Museum of Natural History ( USNM1124194 ) .

Description: Each specimen, when collected, consisted of a single nectophore, and the proximal part of the siphosome, which was contracted into the hydroecium. The main part of the siphosome was, unfortunately, broken off during collection.

Photographs of the type specimen, taken on board the R. V. Western Flyer , are shown in Figure 20 .

Nectophore: The single nectophore ( Figure 21) was approximately hemispherical in shape, and in life measured 10–11 mm in height and 9.5– 10 mm in greatest diameter. After preservation the nectophores shrunk in size and became distorted. For the type specimen this resulted in a considerable decrease in the diameter of the specimen, particularly in the anterior and distal parts, where the mesogloea was much thinner, resulting in the nectosac appearing to occupy virtually all of that space and the whole nectophore appearing almost conical. The hydroecium, on the proximal side of the nectophore, extended from the base of the bell up to about two fifths of its height. It was widely open at its base but rapidly narrowed in its upper half. It had a maximum depth of 2.5 mm and was open, proximally, for all its height. In the living specimen its upper, anterior surface was not straight, being deflected posteriorly by a bulge of mesogloea. However, in its preserved state this surface became almost flat, in the type specimen, or bulged convexly up into the mesogloea in the other specimen.

The somatocyst arose from the point of insertion of the siphosomal stem at the distal apex of the hydroecium and, in the live specimens, was directed upwards. For the type specimen, the proximal end of the somatocyst rapidly increased in diameter, and then formed a cylindrical process, 0.5 mm in diameter and 1.1 mm in length. In the Tiburon Dive 842 specimen ( Figure 20) the somatocyst was more club-shaped and reached a length of 1.5 mm. Although in both the living specimens the somatocyst was directed anteriorly, after preservation the somatocyst tended to lie more obliquely, slanting towards the proximal side. The most characteristic feature of the somatocyst, however, was its pigmentation ( Figure 20). It was mainly filled with pigmented granulated material that, where densest, appeared dark, almost brownish, red, but where less dense, at the proximal and toward the distal ends, appeared more yellowish. However, the distal end of the somatocyst appeared to be devoid of any granules and thereby pigmentation. This was particularly noticeable on the Tiburon Dive 842 specimen ( Figure 20, middle right) where there was a clear patch surrounding a central core of pigmented material, but it could also be seen across the whole of the distal end of the type specimen ( Figure 20, upper right). None of this pigmentation was retained after preservation.

In the living specimens, when relaxed, the nectosac extended to almost four fifths the height of the bell and occupied most of its volume apart from on its proximal (ventral) side. However, during normal contractions or when under stress the nectosac could become considerably distorted. As noted above, that is also the case for the preserved specimens. Close to the ostial opening both the nectophore and the nectosac narrowed considerably so that the broad ostial opening measured c. 5.5 mm in diameter, and was equipped with a narrow velum. From the origin of the somatocyst, and the point of attachment of the siphosome, a very short pedicular canal ran to the nectosac. There it gave rise directly to all four radial canals ( Figure 21). The lower radial canal ran directly to the ostial ring canal, while the upper canal passed 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, forming a?-like shape. Close to the ostium, they followed the narrowing of the nectosac and curved inwards toward the ring canal. When observed from certain angles, this could appear as an extra lateral curve.

Siphosome: Unfortunately only the anterior end of the siphosomal stem of both specimens was collected and, for the Tiburon Dive 842, this consisted only of gastrozooids and their tentacles. Fortunately, for the type specimen, a single developing cormidial group, consisting of a bract and gonophore, as well as a gastrozooid and tentacle, was present when the photographs of the living specimen were taken. Unfortunately, this part of the siphosome was then removed and frozen before the specimen was preserved.

The endoderm of the siphosomal stem was chocolate brown in colour ( Figure 20 bottom). The proximal half of the endoderm of the most anterior, immature gastrozooids bore pigmentation very similar in colour to that of the somatocyst, while the distal half was a lighter yellowish-orange colour. The whole was surrounded by a relatively thick layer of mesogloea, encase by the ectoderm, with a milk-white appearance ( Figure 20). For the more mature gastrozooids, the proximal half was entirely orange in colour, while the distal half was a deeper orange-red. As usual their size and proportions varied greatly according to the degree of contraction or relaxation. No pigmentation could be seen in the preserved gastrozooid, whose proximal half appeared clear, while in the distal half there were two bands of denser material separate by a constricted part, with less dense material. The cnidobands and terminal filaments of the tentilla appeared milky white in life ( Figure 20 bottom). The gastrozooid was attached directly to the stem that, on the more posterior remaining cormidia, was often slightly swollen in its preserved state. Immediately posterior to the gastrozooid was a distinct node. The buds of the bract and gonophore lay just anterior to the gastrozooid and could be seen on most of the remaining cormidia; indicating that their development lagged considerably behind that of the gastrozooid. The tentacle bore numerous lateral excrescences, and the small tentilla were borne on long contractile pedicles ( Figure 22). The tentilla were of the basic calycophoran form with two large mastigophores lying on each side of the proximal part of the cnidoband, and large desmonemes, with distinct spines, at its distal end. The other nematocysts were not examined in detail, but it is presumed that anisorhizas constituted the great majority of nematocysts on the cnidoband itself, while smaller desmonemes and anacrophores were present on the terminal filament.

The single cormidial group of the type specimen that included a bract and gonophore can be seen at the posterior end of the siphosomal stem in Figure 20, and is represented, without the gastrozooid and tentacle in Figure 23. The bract was conical in shape and measured about 1.1 mm across and 0.9 mm in height, and on its proximal side there appeared to be a deep groove through which the siphosomal stem passed. The phyllocyst, which was spherical, with an asymmetrically placed excrescence toward its distal apex, occupied the central region of the bract and was c. 0.3 mm in diameter. It had the same granulated appearance as the somatocyst and was pigmented a deep, brownish red.

The immature gonophore, which bore no sign of a manubrium, was about 1.2 mm in height and diameter. Two of its lateral radial canals appeared to be slightly arched close to their point of origin, before passing directly to the ostial ring canal. The photographs ( Figure 20, bottom) seem to indicate that the canals initially arose in pairs, but unfortunately this cannot be confirmed at present. It is presumed that this very young cormidial group would grow considerably in size before being released as an eudoxid.

Distribution: With only two known specimens, both from a limited area of Monterey Bay, California, we can say very little about its geographical distribution. However, given that many of the species described from the Mediterranean have also been found in very different locations, for instance off Chile (see Appendix), Sphaeronectes christiansonae may yet be found in other areas. The main problem for studying Sphaeronectes species is their fragility, which means that they are rarely collected in coarse meshed nets. Even if caught, after preservation the general distortion of the nectophore may conceal important morphological characters. The specimens of S. christiansonae were caught at depths of 508 and 840 m. The only in situ frame grabs of the species that could be found in the VARS Library at MBARI were for the Tiburon Dive 987 specimen. These pictures, although of poor quality, clearly showed the dark red pigmented stem and somatocyst that are so characteristic of this species.

Remarks: Sphaeronectes christiansonae is clearly distinguished from all previously described species not only by its sheer size, although as will be seen that also applies to the two other new species described herein, but by the presence of the deep red, even brownish pigmentation in the somatocyst, phyllocyst and gastrovascular cavity. No such pigmentation has ever been noted on any other Sphaeronectes species.

The surface of the nectophore emitted a bright green fluorescence under blue excitation (S.H.D. Haddock, personal communication).

Etymology: Named for Lynne Christianson of the Monterey Bay Aquarium Research Institute whose help, whether it be during my visits to MBARI or in answering numerous questions, has been so invaluable to me.