Apolemia lanosa, 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 : 205-213

Apolemia lanosa sp. nov.

Material examined: Doc Ricketts Dive D327-D4, 4 Dec 2011, 35°56'N, 122°55'W, depth 636 m.

Doc Ricketts Dive D329-SS6, 6 Dec 2011, 36°6.99'N, 122°54.01'W, depth 1030 m.

Doc Ricketts Dive D423-D12, 1 Oct 2012, 36°15.02'N, 123°9.98'W, depth 1325 m.

Due to their lengths, only the anterior parts of the specimens D327-D4 and D329-SS6, including the pneumatophore, nectosome, and anterior siphosome, could be collected. A posterior part of the siphosomal stem bearing gonophores was collected for D423-D12. In situ high definition (HD) videos were recorded for specimen D327-D4 and D329-SS6, and are provided as supplementary video (Supplementary video).

Holotype: The specimen D327-D4 has been designated as the holotype and specimens D329-SS6 and D423- D12 as paratypes. All three specimens have been deposited at the National Museum of Natural History, Smithsonian Institution, Washington DC ( USNM 1207944, USNM 1207945, and USNM 1207946, respectively). All of the following observations were made on the holotype and on living tissue, unless explicitly stated otherwise.

Diagnosis. Large nectophores with patches of nematocysts covering their upper and upper-lateral sides. Refractile cells scattered in and around these patches. No distinct diverticula on lateral radial canals. Number of nectosomal palpons per nectophore increasing in posterior direction, with an observed maximum of four. Bracts with similar patches and refractile cells on distal two-thirds of upper surface. Siphosomal growth zone with inconspicuous horn. Cormidia dispersed, each with one type of palpon. Cormidia with one primary gastrozooid and an increasing number of secondary gastrozooids in more posterior parts of the colony.

General appearance: The orange-white tinge of the siphosome, with deep red gastrozooids, contrasted with the complete lack of color in the nectosome ( Fig. 2 A,C). The zooids of the siphosome were densely packed, without any obvious bare stem between them. The bracts were conspicuous. Bracts, gastrozooids and numerous palpons gave the siphosome a relatively thick and well-defined fleece-like outline (Supplementary Video).

Pneumatophore: The pneumatophore of the holotype specimen was ovoid, 2.2 mm in height and 1.4 mm in maximum diameter, with a silvery appearance and no obvious pigmentation ( Fig. 3 A).

Nectosome: The colorless nectosome of the holotype measured 6 cm in length after relaxation ( Figs. 2 C, 3). The nectophores were attached, in a single line, on the ventral side of the stem. In vivo the nectosomal stem was twisted. A 180º turn of the stem between two adjacent nectophores resulted in a biserial arrangement of nectophores ( Fig. 3 D). Fourteen attachment lamellae were found on the nectosome of the holotype, including the ones with nectophores still attached. The youngest nectophores, toward the anterior end of the nectosome, were each accompanied by a single nectosomal palpon ( Fig. 3 B). Further to the posterior, with the increasing age of the nectophores, the number of palpons per nectophore increased, such that there were four associated with the oldest nectophore of the holotype ( Fig. 3 C). The nectosomal palpons lacked a palpacle and were attached directly to the stem to the posterior end and, in ventral view, left of the nectophore lamella. In a relaxed state these palpons were about three times as long as the associated nectophore. Nematocysts, occurring as small opaque spots, were scattered over the surface of the palpon, but were mainly concentrated in its distal region.

Nectophores: No sign of any pigmentation was seen on the nectophores ( Figs. 2 C, 3A, 4A–C, 4G–U). The largest nectophore of the holotype specimen had a length of 21.4 mm and a width of 17.6 mm ( Fig. 4 P). Living and fixed nectophores differed in appearance. In general, furrows tended to be more pronounced in fixed tissue. The appearance of a fixed nectophore varied with the presentation in the dish (compare Figs. 4 R, 4S). In vivo, the state of contraction influenced nectophore appearance, which in consequence might influence the resulting nectophore morphology at the time point of fixation (compare Figs. 4 T, 4U). The youngest nectophores (n1–2, Fig. 3 B) within the growth zone had very prominent canals and a translucent epidermis, while older ones (n3) were slightly opaque. The upper and upper lateral surfaces of the latter were densely covered with nematocysts, which were organized into defined patches in older nectophores ( Figs. 3 A, 4A–C, 4G–U). The distance between these patches was correlated with the size of the nectophore ( Figs. 4 G–P). This suggests that the patches have a similar total area through the course of maturation, and that the patches become further separated as the nectophore grows. On the axial wings of more mature nectophores these patches tended to be more rounded, while those on the main body of the nectophore were more elongate ( Figs. 4 A–C). In addition, refractile cells were sparsely scattered between and within these patches of nematocysts.

The large, flared axial wings occupied about one third the total length of the younger nectophores and about one fourth of the mature ones ( Figs. 4 G–P). The central thrust block was very narrow in early nectophore development and well developed in mature nectophores ( Fig. 4 G–P). A broad, relatively shallow lateral furrow extended almost vertically up each side of the nectophore, from the lateral margins of the lower surface to the upper surface. In most of the nectophores it reached the inner, upper margins of the axial wings ( Figs. 4 A,D, 4G–P). On the lower surface of the nectophore, i.e. that which is closest to the stem, the lower margins of the axial wings began to approach each other from above the level of the proximal side of the nectosac, but each petered out well short of the mid-line ( Fig. 4 B,E). There was a pair of small, slightly thickened cushions of mesoglea on the lower surface of the nectophore that delineated a shallow lower furrow, overlying the lower radial canal. The nectosac mostly filled the main body of the nectophore ( Fig. 4 ). It was broadest just above the ostium and at about half of its length.

No descending pallial canal was present. From its origin from the pedicular canal, the ascending pallial canal ascended towards the top of the thrust block and ended at about two thirds of the total height of the nectosac ( Fig. 4 C,F). The lower radial canal was frequently torn in the region where it ran in close contact with the lower part of the muscular attachment lamella, after which it passed along the base of the lower groove to reach the ostial ring canal ( Fig. 4 B,E).

The upper radial canal gave rise symmetrically to the lateral radial canals close to the mid-height of the proximal side of the nectosac ( Fig. 4 E,F). It then continued over onto the upper side of the nectosac and to the ostial ring canal. Although straight for the most part, just above the ostium it had a series of small bends ( Fig. 4 D). The lateral radial canals, from their point of origin, curved away from the midline and upwards to the apico-lateral margins of the nectosac and passed, slightly undulating, over onto the upper surface before curving outwards to run obliquely downwards toward the lower surface of the nectosac, but curving upwards again before reaching that surface and then bending to run directly to the ostium, reaching it at about half its height ( Fig. 4 D, F). No distinct diverticula could be observed on the lateral canals but occasionally small protrusions were observed.

Siphosome: The full length of the siphosome prior to collection was about 2m in the state of relaxation as pictured in Fig. 2 A. After relaxation, the siphosome of the partial holotype fragment that was collected measured 12 cm in length ( Fig. 2 C). The stem and the attached palpons were milky-white, while the basal region of the palpacles had a faint red tinge. The body columns of the gastrozooids were of deep red color.

Siphosomal growth zone and early zooid development: The siphosomal growth zone had an inconspicuous horn that pointed in the anterior direction ( Figs. 5 , 6 A). Gastrozooid buds originated on the horn. Gastrozooid morphology, with a peduncle, ring-like basigaster, and proboscis was apparent at very early stages ( Fig. 5 B). These primary gastrozooids were alternately displaced to the left and right slightly off the ventral midline resulting in a biserial organization that was most conspicuous in the youngest cormidia ( Fig. 5 B). To the anterior of the gastrozooid peduncle, attached directly to the siphosomal stem, was a compound palpon bud. Each compound palpon bud gave rise to a palpon cluster. Key aspects of palpon morphology were in place by cormidium eight ( Fig. 5 B). Developing palpacles had an opaque appearance ( Fig. 6 B), first of a yellowish coloration, while older palpacles showed an intense orange at their proximal ends ( Fig. 6 C, Fig. 8 A,E). In the case of the gastrozooids, no tentacle formation could be observed during early zooid development. Palpacle formation, therefore, preceded gastrozooidal tentacle formation. Bract formation was first observed in association with gastrozooids ( Fig. 6 B). Each gastrozooid was accompanied by a single bract attached to the ventral midline just to the posterior of the gastrozooid ( Fig. 6 B). This gastrozooidal bract marked the posterior end of each cormidium. A stem sphincter is located just posterior to the gastrozooidal bracts ( Fig. 6 C). Removal of the gastrozooidal bract left a curled attachment lamella ( Fig. 6 D,E). A second type of bract was associated with the palpons. These were located laterally. The first of these lateral bracts to form arose toward the posterior end of each palpon clusters. As the palpon clusters grew, more bracts were added in the anterior direction. In older parts of the colony new secondary gastrozooids formed in between primary gastrozooids ( Fig. 6 F) indicating that the distance between the latter increased with the age of the cormidium. The addition of new zooids, therefore, occurred along the siphosomal stem and was not restricted to the siphosomal growth zone.

Bracts: As the ROV approached, the colony rapidly began to autotomize its mature bracts, and so it was difficult to document their in vivo arrangement. In addition, a large fraction of the bracts were lost during the sampling procedure. Thus, by the time the colony was examined, few mature bracts remained attached directly to the siphosomal stem. Developing gastrozooid and palpon lateral bracts were very similar, though they became more distinct as they matured. Mature gastrozooid bracts were very elongate and straight without an obvious keel ( Fig. 7 A). Mature palpon bracts tended to be more ovoid in shape and more curved, and they tapered to form a more rounded proximal end on the upper surface. In this case the mesoglea was generally thicker and, on the lower surface, it bulged out slightly to form a small, but distinct, keel. The bracteal canal arose from the proximal end of the bract. Nematocyst patches were scattered over the distal two-thirds of the upper side of the bracts ( Fig. 7 A). As observed in the case of nectophores individual large refractile cells could be found scattered between and within these nematocyst patches ( Fig. 7 B). In all bracts the bracteal canals extended distally along the lower surface in the mid-line. At their distal ends they bent into the mesoglea and then back towards the lower surface ( Fig. 7 A,C). However, the distinctiveness of this arch varied considerably, and it was in many cases difficult to detect.

Palpons: Only a single type of siphosomal palpon was observed. The maximum length of the palpon was 22 mm when fixed. In vivo, however, palpons could reach twice the length of gastrozooids ( Fig. 2 C). Palpons were slightly opaque and of a milky-white color, with a more opaque, white region at their distal ends ( Figs. 2 C, 6F). In older cormidia, new palpon cluster formation was inferred at the anterior end of each cormidium ( Fig. 8 A) based on differences in the sizes of palpons. The individual palpon clusters were clearly separated from each other on the siphosomal stem ( Fig. 8 A) even though this separation was not obvious when the specimen was observed macroscopically. The very proximal part of the palpacle was tinged orange, while distally it was a translucent white ( Fig. 8 A–D). Particularly in fixed material a ring-like basigaster region of the palpon became obvious just distal to the palpacle attachment point ( Fig. 8 C). Developing nematocysts were discerned in this region. Proximally, nematocysts were densely packed on one side of the palpacle, but more distally they were separated into pairs and continued as such along the remainder of its length ( Fig. 8 D).

Gastrozooids: The maximum length of fixed gastrozooids was 18 mm. The peduncles of the mature gastrozooids were short, translucent and did not bear other zooids ( Fig. 8 E). The proximal portion of the gastrozooid was deep red in live animals ( Fig. 8 E). Gastrozooids had a ring-like basigaster just distal to the peduncle, where developing nematocysts were found. The distal end of the gastrozooid was milky-white. Stripes were visible in many cases, which were reflected by ectodermal grooves in the distal parts of the gastrozooids ( Fig. 8 E). The diminutive gastrozooid tentacles were not conspicuous in macroscopic images, and were only apparent in fixed gastrozooids that were separated from the stem ( Fig. 8 F). As in other apolemiids, they bore no tentilla.

Gonodendra: Female gonophores were found along the siphosomal stem of specimen D423-D12 ( Fig. 9 ). Gonodendra inserted directly on the siphosomal stem laterally to palpon clusters. There were several gonophores in different stages of maturation per gonodendron. Each gonophore was attached to the stalk of the gonodendron via a peduncle ( Fig. 9 B). The stalks of the gonodendra were small and inconspicuous. Each gonophore contained a single egg.

Nematocyst complement: Four types of nematocysts were documented across the different zooids of the colony ( Fig. 10 ). These were:

a) Spherical isorhizas of two distinct sizes.

Macroisorhizas, with a mean diameter of 22.2 µm ( Fig. 10 A). The evaginated tubule was isodiametric and holotrichous. These nematocysts formed the patches on nectophores and bracts. Spherical refractile spots (mean diameter 47.2 µm, n=12) present in between and within patches were cellular, as indicated by the presence of nuclei ( Fig. 9 A).

Microisorhizas, 7.2 µm (mean) in diameter ( Fig. 10 E,H) that were found at the distal ends of gastrozooids, palpons and nectophoral palpons, and were scattered along the body columns of these zooids in lower numbers.

b) Stenoteles, with a mean length of 17.9 µm and a mean width of 13.7 µm ( Fig. 10 B,E,G). These were found in the same locations as the microisorhizas and were highly abundant at the distal ends of the three types of zooid.

c) Microbasic mastigophores ( Fig. 10 C,E) could be found at the tips of gastrozooids, palpons and nectophoral palpons with densities being highest on gastrozooids and palpons. They were elongate (mean length 57.8 µm, mean width 21.9 µm) and slightly banana-shaped.

d) The capsules of tentacles and palpacles were ovoid in shape with a mean length of 22 µm and a mean width of 14.6 µm ( Fig. 10 I). They were found on the palpacles and gastrozooidal tentacles. The evaginated tubule was isodiametric and holotrichous with a single dilation at the end of the shaft close to the distal end of the capsule. This was in contrast to the two dilations in birhopaloids as described for Apolemia uvaria ( Claus 1863; Totton 1965).

Distribution. The holotype and paratype specimens, described above, both 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 in Table 1 . The mean depth for all these specimens is 1193 ± 285.7 m. The species has also been pictured in Burton and Lundsten (2008) at the Davidson Seamount over a depth range 439– 1159 m. Photographic material strongly suggests that A. lanosa has been collected off Japan ( Lindsay 2005, 2006). The probability that there are further records is discussed below.

Etymology. The specific name lanosa , derived from the Latin lana, meaning woolly, refers to the fleece-like appearance of the siphosome of the living colony.

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 3. Apolemia lanosa sp. nov. Nectosome of the holotype specimen (live, A – C) and specimen from Doc Ricketts dive D 329 (live, D). (A) Nectosomal growth zone with young nectophores still attached. The pneumatophore is at center and posterior at the bottom. (B) Close-up of the nectosomal growth zone. The pneumatophore is just out of frame to the upper left. (C) Posterior part of nectosome and anterior part of siphosome after removal of nectophores, with nectosomal palpons still attached to the ventral side of the stem. Anterior is up. (D) Close-up of twisted nectosomal organization with nectophores still attached. Anterior is up. Scale bars in A – D 5 mm.

FIGURE 4. Apolemia lanosa sp. nov. Medium sized nectophore from the holotype specimen (living, A – C). Photographs and drawings of upper (A, D), lower (B, E), and lateral (C, F) views. Scale bar (5 mm) in C applies to figures. (G – S) Photographs of “ upper ” view of nectophores from the holotype and lateral view of the paratype specimen (T – U). All the nectophores had been fixed apart from those shown in Q, T and U. (G – P) Photographs showing change in nectophore morphology and proportions during growth. Axial wings were close to each other in young nectophores and widely apart in mature ones. The thrust block was well developed and the axial wings were proportionally shorter in older nectophores. (Q – S) Photographs of the same nectophore after relaxation while living (Q), and after fixation (R – S). Appearance of nectophore morphology in fixed state varied significantly with viewing angle and how the nectophore was presented in the dish. In S the nectophore was gently stretched in the longitudinal direction. T – U show the same nectophore, while living, of specimen D 329 - SS 6 freshly detached from the stem in an uncontracted (T) and fully contracted (U) state. Scale bar (1 cm) in (S) applies to nectophores in G – S. Scale bar (1 cm) in (U) applies to T – U.

FIGURE 5. Anterior portion of Apolemia lanosa sp. nov. siphosome, including the siphosomal growth zone, photographed while living. Ventral view, anterior is up. (A) Scale bar 5 mm. (B) Close-up of the first eight cormidia from the region framed by the dashed box in (A). Scale bar 1 mm. Numbers indicate primary gastrozooids starting with the youngest.

FIGURE 6. Apolemia lanosa sp. nov. Cormidial organization of the holotype specimen (live). Anterior is to the left, ventral is up. (A – C) Sequential photographs of the anterior part of siphosome. Scale bar in (A) 2 mm applies to (A – C). (B) Early palpacles and a young bract associated with a primary gastrozooid. (C) Sphincter region posterior to a primary gastrozooid. (D) Developing gastrozooidal bract associated with primary gastrozooid 10. Scale bar 1 mm. (E) Curled bracteal canal and attachment lamella that remained after detachment of the gastrozooidal bract. Scale bar 1 mm. (F) Secondary gastrozooids intercalated between primary gastrozooids in older cormidia. Scale bar 5 mm.

FIGURE 7. Apolemia lanosa sp. nov. Gastrozooid bracts of the holotype specimen (fixed). (A) Upper view of bracts. Bract at bottom with discharged nematocyst tubules visible. Scale bar 5 mm. (B) Close-up of nematocyst patches. Refractile cells appear as larger white specks within nematocyst patches. Scale bar 400 µm. (C) Distal end of bracteal canal bends into the mesoglea and back towards the lower bract surface (end of canal at bottom). Scale bar 1 mm.

FIGURE 8. Apolemia lanosa sp. nov. Palpons and gastrozooids. (A) The most anterior palpon cluster of a cormidium. The arrow indicates bare stem in between youngest palpon clusters and the next older cluster. Scale bar 1 mm. (B) Mature palpon. Scale bar 2 mm. (C) Close-up of proximal end of palpon in B showing basigaster and the proximal end of palpacle. Scale bar 1 mm. (D) Distal regions of palpacles with pairs of nematocysts. Scale bar 200 µm. (E) Gastrozooid of the holotype (live). Scale bar 2 mm. (F) Gastrozooid of specimen D 329 - SS 6 with tentacle. Scale bar 2 mm. A, D, E holotype (living). B, C, F specimen D 329 - SS 6 (fixed).

FIGURE 9. Apolemia lanosa sp. nov. Female gonophores (live). (A) Ventral view of palpon clusters framed by two gastrozooids (g). A cluster of female gonophores (go) is attached laterally. Scale bar 2 mm. (B) Close-up of a single female gonophore. Two smaller gonophores can be seen to the right. Gonophores sit on peduncles which attach to the stalk of the gonodendron (not visible) which itself is a small protrusion on the stem of the colony. Scale bar 1 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.