Apolemia rubriversa, Siebert, Stefan, Pugh, Phil R., Haddock, Steven H. D. & Dunn, Casey W., 2013

Siebert, Stefan, Pugh, Phil R., Haddock, Steven H. D. & Dunn, Casey W., 2013, Re-evaluation of characters in Apolemiidae (Siphonophora), with description of two new species from Monterey Bay, California, Zootaxa 3702 (3), pp. 201-232 : 213-220

Apolemia rubriversa sp. nov.

Material examined: Doc Ricketts Dive D331-D4, 0 7 Dec 2011, 36°41.99’N, 122° 5.99’W, depth 650m.

Doc Ricketts Dive D195-D5, 0 7 Oct 2010, 36º 35.97’N, 122º 8.928’W, depth 780m.

Ventana Dive V 908, 20 June 1995, 36° 42.34’N, 122° 02.24’W, depth 609m.

Only the anterior parts of the colonies, including the pneumatophore, nectosome, and anterior siphosome were collected. In situ high-definition videos were recorded for both Doc Ricketts specimens (Supplementary video, for Doc Ricketts D311-D 4 specimen). The following observations were made on the holotype and on live tissue if not stated otherwise.

Holotype: The specimen from Doc Ricketts dive D311-D4 has been designated as the holotype. The specimens from Doc Ricketts dive D195-D5 and Ventana Dive V 908 have been designated as paratypes. All three specimens have been deposited at the National Museum of Natural History, Smithsonian Institution, Washington DC ( USNM 1207947, USNM 1207948 and USNM 1207949, respectively).

Diagnosis. Nectophores, with upper and upper lateral surfaces densely covered in patches of nematocysts. Refractile cells sparsely scattered between, but not within, these patches. Lateral radial canals with up to three distinctive diverticula extending along the wall of the nectosac and not penetrating into the mesoglea. Two median patches of red pigmentation present on the lower surface; one in the vicinity of the thrust block and the other, more prominent, one in the ventral groove.

Siphosomal growth zone with pronounced horn. Cormidia pedunculate. All siphosomal zooids borne on the peduncle of the gastrozooid, with naked stem between them. The cormidia with distinct biserial arrangement and peduncles attach left and right from the midline. Upper surface of bract entirely covered with patches of nematocysts, with refractile cells present outside of nematocyst patches predominately at the margins of the upper bract surface. Bracteal canal usually with distinct diverticula penetrating into the mesoglea. One type of palpon.

General appearance: The overall appearance of the colony was brown-red in color. This was mainly caused by colored gastrovascular fluid within the gastric system ( Fig. 2 B,D). The bracts were nearly transparent and gave the siphosome a ragged appearance rather than a well-defined outline ( Fig. 2 B,D).

Pneumatophore: The pneumatophore of the holotype was oval, approximately 3.3 mm in height and 1.7 mm as maximum diameter ( Fig. 11 A). The gas-filled pneumatosaccus was covered with orange pigment.

Nectosome: All but one of the mature nectophores of the holotype specimen became detached from the nectosome during the sampling procedure ( Fig. 11 B) but were retained in the sampler. The youngest nectophores were each accompanied by a single palpon ( Fig. 11 A). The nectophores were attached to the ventral side of the stem, i.e. on the same side that the siphosomal zooids were attached. Up to three palpons were associated with a single mature nectophore for the holotype and specimen D195 ( Fig. 11 B,C). The palpons in the nectosome were translucent white, and were up to two times the length of associated nectophores in relaxed state. The nectophoral palpons were attached to a protruding tissue fold at the posterior end and, in ventral view, left of the nectophoral lamella ( Fig. 11 C).

Nectophores: In the growth zone, the more developed nectophores were densely covered with opaque nematocysts ( Fig. 11 A). In older nectophores these nematocysts were organized in distinct patches. The largest nectophore of the holotype had a length of 14 mm, and a width of 10 mm. Mature nectophores had large axial wings ( Fig. 12 ). Whereas immature nectophores were widest at mid-height of the nectophore, mature ones were widest at the apical tips of the axial wings ( Fig. 12 A,N). Patches of nematocysts covered the upper and upper-most lateral surfaces, including the axial wings ( Fig. 12 ). There were no lateral nematocyst patches below the lateral furrows. Refractile cells were sparsely scattered between but not within these patches of nematocysts.

Deep lateral grooves approached the upper side at approximately half the length of the nectophore, which resulted in indentations in the sides of the nectosac. On the upper side of live nectophores these grooves ran slightly in the ostial direction before they met in the mid-line ( Fig. 12 A,D). In fixed nectophores, however, the grooves were even more pronounced ( Fig. 12 G–N). On the upper side close to the midline they bent through almost 90° to turn in the ostial direction and ran around the axial wing margins before turning toward the mid-line and uniting with the opposite groove. Laterally the grooves continued along the lower lateral sides of the nectophore and ended below the ostium ( Fig. 12 F).

Nectophores had a wide ostium, and the nectosac was broad at the distal end of the nectophore, occupying most of its width. Slightly proximal to this region, the nectosac narrowed considerably, before expanding in width just before the lateral furrow. The nectosac was indented by the lateral furrows and expanded again to reach its maximum or equivalent width proximal to the lateral grooves ( Fig. 12 ).

In lower view, the inner margin of the axial wings of the nectophore gradually curved toward the mid line and tapered out well apart from each other before reaching the mid-length of the nectophore ( Fig. 12 B,E). Some red pigmentation was present in the region of the thrust block ( Fig. 12 B). The outer wing margins curved inwards at about the mid-length of the nectophore and met below the ostium. On the lower side of the nectophores the mesoglea formed pillows on either side of the median lower furrow. Where the furrow was deepest and narrowest, red pigmentation was present on its walls ( Fig. 12 B). In living nectophores the distal part of the lower surface only slightly protruded below the ostium ( Fig. 12 A,D). In fixed nectophores this protrusion was very pronounced ( Fig. 12 J–N). This suggests a stabilizing or antagonistic function of the lower mesoglea pillows flanking the lower furrow. This structural element seems to be less affected by the fixation procedure, whereas other parts of the nectophore might have a greater tendency to shrink, causing the differences in appearance between fixed and living nectophores.

The ascending pallial canal arose from the pedicular canal at about 1/4 the height of the nectosac and then ran toward the upper surface for a short distance to end half way up the thrust block ( Fig. 12 F). The pedicular canal also gave rise to the upper and lower radial canals. The upper radial canal was fairly straight on the upper surface. Just distal to where the lateral furrows joined, the canal widened slightly, kept a larger diameter and ran down to the ostial ring canal ( Fig. 12 D). Within the region where the lateral furrows joined small protuberances could be observed occasionally on the irregular wall of the upper radial canal.

The lateral radial canals arose at the same level from the upper radial canal at mid-height of the nectosac ( Fig. 12 F). They ran away from the midline and slightly up to reach the sides of the nectosac just above its widest point. In mature nectophores, in this region the lateral radial canals had up to three distinct diverticula. The outermost, on the proximal-lateral margin, was the longest and pointed towards the ostium ( Fig. 12 E,F). The other two were shorter, if present at all, with the one closest to the junction of the lateral canals ascending and the next descending. Presence or absence of diverticula was not a solely function of ontogenetic stage. In the holotype specimen, medium-size nectophores could be found without a single diverticulum whereas diverticula were clearly present in smaller and larger nectophores. At the position where the outermost diverticulum branched off, the lateral radial canal turned upwards and curved over onto the upper surface of the nectosac and eventually, in a slightly undulating manner, down. The canal either descended along the base of the lateral furrow, or more usually crossed that furrow and then began to descend parallel with it ( Fig. 12 F). Before reaching the lower margin of the nectosac the canal then curved upwards and ran obliquely to join the ostial ring canal ( Fig. 12 F).

In specimen V908, only one mature nectophore was available. It had all three characteristic diverticula (not shown).

Siphosome: The full length of the siphosome of the holotype prior to collection was about 1.2m in the state of relaxation as pictured in Fig. 2 B. After relaxation, the siphosome of the partial holotype fragment that was collected measured 1.8 cm in length ( Fig. 2 D).

Siphosomal growth zone and early zooid organization. The siphosomal growth zone of the holotype had a massive horn that bent, in ventral view, to the left side of the colony ( Fig. 13 ). The horn was covered with a thin layer of orange-red pigment, which was easily detached when the horn was manipulated ( Fig. 13 B,C). The anterior end of the horn was free of zooids ( Fig. 13 C). The first observable buds became gastrozooids, which were alternately displaced to the left and right off the ventral midline resulting in a pronounced biserial organization ( Fig. 13 A, B). Additional buds became visible on the peduncle of the fourth-youngest gastrozooid ( Fig. 13 B). At the distal end of the peduncle, the diameter of the developing gastrozooid widened and its body had a cone-shaped appearance (gastrozooids 3–7, Fig. 13 B). Just distal to the base of the cone, a constriction became apparent in gastrozooid 6 which generated a ring-like structure (gastrozooid 7, Fig. 13 B). The opaque appearance of this structure indicated a site of nematogenesis and thereby the formation of the basigaster region. By gastrozooid 9, it was obvious that the buds on the peduncle of the gastrozooid gave rise to palpons. No tentacle formation could be observed in early gastrozooids.

Bracts: Bracts were mottled with irregular shaped patches of nematocysts distributed across their upper surface ( Fig. 14 ). These patches formed early in bract development and the distance between them increased as the bracts matured ( Fig. 14 A). Refractile cells were scattered sparsely and predominantly on the periphery of the upper surface outside of the opaque nematocyst patches ( Fig. 14 B,C). The bracteal canal ran close to lower surface throughout its length. At the distal end, however, it bent into the mesoglea ( Fig. 14 D). The wall of the bracteal canal in young bracts was irregularly shaped, giving it a rough appearance ( Fig. 14 B). Older bracts frequently, but not always, had diverticula penetrating into the mesoglea ( Fig. 14 D). Mature bracts had a distinct keel ( Fig. 14 E). Bracts were associated either with a palpon or a gastrozooid (see below). We found no morphological differences between the bracts attached at these different locations.

Palpons and gastrozooids: The body column of gastrozooids was colored by a deep red pigment. This pigment gradually faded out close to the distal end so that the oral region was white. Multiple clusters of zooids were attached to the gastrozooid peduncle ( Fig. 15 A). At the base of each gastrozooid peduncle a single curled lamella frequently could be observed, indicating the point of attachment of a single gastrozooidal bract ( Fig. 15 A). The secondary branches themselves were branched. Palpons sat on and budded off these secondary branches. Each palpon had a palpacle and was accompanied by a bract. Mature palpons were translucent with a distinct white tip. The palpacle originated at the very base of the palpon ( Fig. 15 B). A distinct basigaster region could not be observed. In the holotype, cells with red pigment were visible in live or freshly fixed tissue in the distal region where the obvious gastric cavity ended, and the proboscis region began ( Fig. 15 C). A region with very large cells could be frequently observed along one side of the palpons ( Fig. 15 B,C). Tentacles associated with gastrozooids could be found in fixed tissue, but these tentacles were difficult to distinguish in live tissue ( Fig. 15 D).

Gonodendra: Male gonodendra were found along the siphosomal stem of specimen V908 ( Fig. 16 ). The tissue was highly contracted and detailed studies of cormidial organization could not be conducted. However, branches exclusively bearing gonophores, attached by thin peduncles, could be removed from the colony. Young palpons at the base of these branches indicated palpon bearing secondary branches as the point of their attachment ( Fig. 16 B).

Nematocyst complement: Four different types of nematocysts were found on the different zooids of the colony ( Fig. 17 ).

Spherical isorhizas of two distinct sizes.

Macroisorhizas, with a mean diameter of 21.0 µm ( Fig. 17 A) found exclusively in nematocyst patches on nectophores and bracts. Refractile cells were not observed within these patches.

Microisorhizas, with a mean diameter of 5.8 µm. These nematocysts were found predominantly at the distal ends of gastrozooids, palpons and nectophoral palpons and scattered along the body columns of these zooids and in very high densities at the tip of the nectophoral palpons ( Fig. 17 G,H).

b) Stenoteles, with a mean length of 14.1 µm and a mean width of 11.2 µm. These were regularly found interspersed between the macroisorhizas of the bracts and nectophores ( Fig. 15 A). Stenoteles were also found predominantly at the distal ends of gastrozooids, palpons and nectophoral palpons and scattered along the body columns of these zooids ( Fig. 17 B,E,G).

c) Unknown type, with a mean length of 26.7 µm and a mean width of 16.1 µm.

Microbasic mastigophores as described for Apolemia lanosa ( Fig. 10 C,E) were not found. The unknown capsule type was, however, found in corresponding locations at the tips of gastrozooids and palpons ( Fig. 17 C,E). It was smaller than the mastigophores of A. lanosa and was ovoid in shape. Unfortunately, no discharged capsules of this type were found.

d) Capsules of tentacles and palpacles, mean length 15 µm in length and mean width 9.1 µm ( Fig. 17 D,F).

The ovoid capsules of the tentacles and palpacles were similar in appearance to the rhopaloids found on the palpacles and tentacles of Apolemia lanosa but, unfortunately, their true identity could not be established as no discharged capsules were found. For the palpons, the base of the palpacle was found to be a nematogenic region. No mature capsules were found there, whereas they could easily be identified more distally, but developing nematocysts were identified.

Distribution. The holotype and paratype specimens all came from the vicinity of Monterey Bay, California. Several other specimens from the same region have either been collected or identified from in situ photographs, as listed below in Table 2 . One specimen, however, was collected at the southern end of the Gulf of California, Mexico. The mean depth for all these specimens was 649 ± 151 m. Similar morphology has been reported for nectophores collected off Vancouver Island ( Mapstone 2009, p. 83, Fig. 13 ) and described as “ Apolemia sp.”, raising the possibility that they are the same species. Mapstone (2009) also reported more findings of this particular Apolemia sp. from Bahamian waters taken by manned submersibles JSL I and JSL II, which would extend the geographic distribution of A. rubriversa if they prove to belong to that species. There are, however, critical differences between the nectophores of these samples and those of A. rubriversa . The nectophores described by Mapstone (2009) did not have diverticula on the lateral canals or nematocyst patches. Thus it will be necessary to have more complete material in order to make a definitive statement about the identity of those samples.

Etymology. The specific name rubriversa is derived from the Latin for red furrow, indicating the red pigmentation in the lower furrow of the nectophore.

Figures

FIGURE 2. (A – B) In situ photographs of holotype specimens. (A) Apolemia lanosa sp. nov., approximate length 2 m. (B) Apolemia rubriversa sp. nov., approximately 1.2 m in length. (C – D) Anterior regions of the collected, unfixed specimens of (C) A. lanosa, which had already lost most of its bracts (Scale bar 2 cm); and (D) A. rubriversa, whith most of its mature nectophores detached (Scale bar 2.5 mm).

FIGURE 10. Apolemia lanosa sp. nov. Nematocyst complement of the holotype. (A) Nematocyst patch of macroisorhizas on the upper surface of a nectophore. Refractile elements on nectophores and bracts were cellular as indicated by the presence of nuclei. (B) Stenoteles at the distal end of a gastrozooid. (C) Microbasic mastigophores at the distal end of a gastrozooid. (D) Ovoid capsules of the gastrozooidal tentacle. (E) Stenoteles and microbasic mastigophores at the distal ends of palpons. (F) Ovoid capsules of a palpacle, apparently identical to those on the gastrozooid tentacles. (G) Stenoteles at the distal end of a nectophoral palpon. (H) Microisorhizas at the distal tip of a nectophoral palpon. Scale bar 25 µm. (I) Discharged capsule from a palpacle. Arrow indicates a single dilation on the tubule. (J) Discharged microbasic mastigophores. Scale in I, J is 50 µm. Scale bar in A (50 µm) applies to A – G.

FIGURE 11. Apolemia rubriversa sp. nov. Nectosome of the holotype (live, A, B) and specimen D 195 (fixed, C). (A) Nectosomal growth zone and pnematophore. Older nectophores, densely covered in nematocysts, are at the bottom of the frame. Scale bar 1 mm. Anterior is pointing out of the page, ventral to the lower right of the pane. (B) Contracted nectosome and anterior portion of the siphosome. Anterior is to the left, ventral is down. 1, 2, 3: nectophoral palpons accompanying a single nectophore. Nectosomal palpons with colored gastric content. Scale bar 2 mm. (C) Ventral view of posterior part of the nectosome showing nectophoral palpon attachment scars (dashed circles) to the left of the posterior end of the associated nectophore lamellae. Dashed line indicates one nectophore lamella. Scale bar 2 mm.

FIGURE 12. Apolemia rubriversa sp. nov. (A – F) Medium sized nectophore of the holotype (live). Canals were colored red by prey pigment. Photographs and drawings of upper (A, D), lower (B, E) and lateral (C, F) views. Lower view of type specimen (B) revealed red pigmentation within the ventral furrow and on the thrust block. Scale bar (5 mm) in C applies to all figures A – F. (G – N) Available fixed nectophores of sample D 195 shown in upper view. Scale bar (1 cm) in J applies to G – N.

FIGURE 13. Apolemia rubriversa sp. nov. Early siphosomal organization of the holotype (live). Ventral view, anterior up. Numbers indicate gastrozooids starting with the youngest. (A) Anterior part of the siphosome. Frame indicates region shown in B. (B) Close-up of siphosomal growth zone. Gastrozooids (numbered) become arranged in a defined biserial organization. Palpon buds are first visible at the base of the gastrozooid and later on the gastrozooidal stalk. An indentation forms at the proximal end of the gastrozooid body separating the future basigaster region from the main body. Nematocysts become visible as opaque cells in basigaster of gastrozooid 7. (C) Siphosomal horn bending towards the right side of the siphosomal stem. Pigment has been lost as a result of tissue manipulation. Scale bars in (A) 2 mm, (B, C) 1 mm.

FIGURE 14. Apolemia rubriversa sp. nov, Bracts of the holotype (living A, B, C) and specimen D 195 (fixed, D, E). (A) Change of nematocyst patch distribution during bract maturation. Anterior to the left. Scale bar 3 mm. (B) Young bract with irregularly shaped bracteal canal. Scale bar 1 mm. (C) Refractile cells (white dots) scattered in between but not within nematocyte patches. Scale bar 400 µm. (D) Bracteal canal with diverticula, and the distal end (at bottom) of the canal penetrating into the mesoglea. Scale 2 mm. (E) More mature bract with distinct keel. Scale bar 2 mm.

FIGURE 15. Apolemia rubriversa sp. nov. Palpons, gastrozooids and siphosomal organization of the holotype (A, C) and specimen D 195 (B, D) (fixed tissue). (A) SEM of branched cormidium with primary branch (red) bearing the gastrozooid. Secondary branches (blue) branch off the primary branch and branch further (green). Palpons bud off branches of higher order and could be found at all different stages of development. Each palpon was accompanied by a bract and a palpacle. Scale 500 µm. (B) Mature palpons. Scale 2 mm. (C) Close-up of palpon showing highly prismatic cells and red pigmented cells in the distal region where the main gastric cavity ends. Scale 1 mm. (D) Mature gastrozooid with tentacle. Scale 2 mm.

FIGURE 16. Apolemia rubriversa sp. nov. Gonodendra of specimen V 908. (A) Gonophores protruding from palpon clusters. Scale 2 mm. (B) Gonodendron. Branch exclusively bearing gonophores with young palpons at the proximal end indicating branches with palpons as the point of attachment. Scale 2 mm.

FIGURE 17. Apolemia rubriversa sp. nov. Nematocyst complement of the holotype. (A) Nematocyst patch on the upper bract surface. Patches on nectophores were of identical composition. Stenoteles were interspersed between spherical macroisorhizas. (B) Stenoteles from the hypostome of the gastrozooid. (C) Stenotele to the left and an unidentified capsule in the hypostomal region of the gastrozooid. (D) Ovoid capsules on the proximal part of the gastrozooidal tentacle. (E) Tip of the palpon with the unidentified capsules also seen in the hypostomal regions of gastrozooids (F) Ovoid capsules on palpacle. (G) Tip of the nectosomal palpon with stenoteles and spherical microisorhizas in very high densities. (H) Close-up of microisorhizas from the tip of the nectosomal palpons with the coiled tubule visible inside. Scale in (A) applies to (A – G) and is 50 µm. Scale in (H) is 25 µm.