Agalma clausi (Bedot, 1888)

Mańko, Maciej K. & Pugh, Philip R., 2018, Agalma clausi (Bedot, 1888) (Siphonophora: Physonectae) - complementary description with notes on species distribution and ecology, Zootaxa 4441 (2), pp. 311-331 : 315-316

Agalma clausi (Bedot, 1888)

Synonyms.

Agalma sarsii ( Fewkes, 1880) p. 628.

Crystallodes Clausi (Bedot, 1888, post-scriptum) p. 20.

Stephanopsis Clausi ( Bedot, 1896) p. 406.

Stephanomia sarsii ( Schneider, 1898) p. 121–122.

? Agalma eschscholtzii (Haeckel, 1888) p. 226 and Plate XVIII, Fig. 8–17 .

? Agalma haeckeli ( Bigelow, 1911) p. 274–277.

Systematics. Agalma clausi belongs to the Family Agalmatidae Brandt, 1834 that is nested within the historically recognized Physonectae, a suborder that groups all siphonophores sharing particular body plan i.e., possessing pneumatophore, nectosome, and siphosome. However, Physonectae were shown to be polyphyletic (Dunn et al. 2005) and following the most recent phylogeny ( Munro et al. 2018) agalmatid siphonophores are placed within a newly erected, monophyletic clade Euphysonectae. Although this phylogenetic hypothesis is well supported, as the International Commission on Zoological Nomenclature ( ICZN 1999) does not recognise clades we decided to maintain the name Physonectae throughout this text.

Type specimens. There is no known type specimen, thus we designate the specimen from BWP Dive 1044-15 as a neotype. It will be deposited at the United States National Museum ( Smithsonian Institution ), Washington, DC under accession number USNM 1422474 . It was collected close to the surface by a SCUBA diver on 14th July, 1983 at 3°56.9'N, 37°15.8'W.

Diagnosis. Rigid-stemmed, monoecious agalmatid siphonophore of prismatic appearance, with nectophores arranged biserially and some bracts showing carmine pigmetation in living animal. Nectophores with short axial wings and size-dependent ridge pattern, incomplete laterals discernible only in younger zooids, but upper and lower lateral ridges present throughout development, but very weak in largest nectophores. No vertical lateral ridges. Thrust block small on mature nectophores; lateral ostial processes also small and packed with nematocysts. Typical Agalma course of lateral radial canals. Cormidia bearing gastrozooids (often flask-shaped), with tentacle, several gonophores of both sexes, bracts and palpons. Involucrum of tentillum voluminous, able to contain the cnidoband, the two terminal filaments and the central ampulla. Palpacle of palpon originates not at its base but, on the fully mature palpon, almost at its mid-length. Six types of bracts, of which one is able to discharge a coloured, probably fluorescent, fluid when stimulated.

Figures

FIGURE 8. Nectophores of Agalma clausi drawn at different developmental stages, based on specimen JSL I Dive 2929-DSI. A. Young nectophore; B. Upper (left) and lower (right) views of medium-sized nectophore; C. Upper (left) and lower (right) views of largest nectophore. Scale bars: A. 2 mm; B. 2 mm; C. 5 mm.

FIGURE 9. Different types (A–F) of Agalma clausi bracts. All drawings represent bracts of similar size i.e., 3.0 ± 0.5 cm in length except for type E bracts, which measured c. 1.3 cm in length.

FIGURE 10. Loose Type D bract of Agalma clausi from BWP Dive 1044-11. Scale bar: 1 mm. (With grateful thanks to Ron Gilmer).

FIGURE 11. Palpons of Agalma clausi. A. Early bud; B. Tip of mature palpon with amorphous droplet; C. Tip of mature palpon with nematocysts arranged differently; D. Surface of mature palpon with regularly scattered opaque cells; E. Developmental sequence of palpons of specimen BWP 1044-22. Scale bars: A. 100 µm; B. 100 µm; C. 200 µm; D. 100 µm; E 50 µm.

FIGURE 12. Morphology of gastrozooid. bas—basigaster, hs—hepatic stripes, tc—tentacle, tn—tentillum. Scale bar: 500 µm.

FIGURE 13. Developmental sequence of gastrozooids (A), showing tentacle bud for each of the gastrozooid growth stage respectively (B–D). Scale bars: A. 500 µm; B. 50 µm; C. 100 µm; D. 200 µm.

FIGURE 14. Development of tentillum. A. Early stages; B. Later stages. gvc—gastrovascular canal, inv—involucrum, nc—nematocyst cluster, pa—primordial ampulla, rtf—rudiment of terminal filament Scale bars: A. 50 µm; B. 200 µm.

FIGURE 15. Gonophores of Agalma clausi. A. Portion of stem showing arrangement of male gonophores; B. Developmental sequence of male gonophores with zooid axis; C. Mature female gonodendron showing gonophores at different stages of development being arranged along three axes; D. Growth sequence of female gonophores with zooid axis. brl—bracteal lamella, D—distal, mgon—male gonophores, P—proximal, pal—palpon, st—stem. Scale bars: A., B. 0.8 mm; C., D. 0.5 mm.

FIGURE 16. Distribution map of Agalma clausi (dots) and A. haeckeli (star).

FIGURE 17. Details of amphipod placements within zooids of Agalma clausi specimen BWP 1044-22. A. Two Eupronoe sp. (squared) living inside nectophore mesoglea; B. Close-up of picture A showing one of Eupronoe sp. in the axial wing of the Agalma clausi nectophore, and the damage it caused to the radial canal; C. Close up of picture A showing another Eupronoe sp. that lives in the central part of the nectophore, presumably ingesting pre-digested food directly from the radial canal; D. Two Eupronoe sp. (arrowed) living in the lateral part of the nectophore, close to the ostium; E. Exuviae of an amphipod (arrowed) inside the Agalma clausi bract. Scale bars: A. 1 mm; B., C., D. 500 µm; E. 250 µm.