Anthosactis pearseae, Daly & Gusmão, 2007

Daly, Marymegan & Gusmão, Luciana, 2007, The first sea anemone (Cnidaria: Anthozoa: Actiniaria) from a whale fall, Journal of Natural History 41 (1 - 4), pp. 1-11 : 3-6

Anthosactis pearseae n. sp.

Figures 1–3

Diagnosis

Column of preserved specimens a stout cylinder, 5–8 mm in diameter, rosy pink to white, with short, bluntly conical tentacles without aboral thickenings ( Figure 1 and 2 ). Tentacles with numerous basitrichs and holotrichs, not concentrated into discrete batteries. Mesenteries hexamerously arranged, first cycle perfect.

Etymology

Named for Vicki Pearse, in honour of her contributions to actiniarian systematics. Material examined

Holotype, NMNH 1096705 ; Paratypes CASIZ 174323–174325 , and NMNH 1096706 ; vouchers CASIZ 174326 .

Base and column. Column stout, of approximately equal diameter throughout in preserved specimens ( Figure 2 ) or slightly flaring proximally, weakly ribbed longitudinally in highly contracted specimens. In life, column flares from base, being wider distally than proximally ( Figure 1 , V. Pearse, pers. comm.). Most specimens uniform opalescent white, a few pale pink. In all specimens, mesenteries faintly visible through column as pinkish lines. No fosse, although distal lip of column may extend beyond base of tentacles in contracted specimens ( Figure 2A ). Distal column of some specimens sparsely scattered with small, poorly demarcated suckers; no specimens had material adhering to these. Proximal column smooth. Limbus may extend past pedal disc, causing pedal disc to look sunken or retracted. Pedal disc adherent, muscular, same colour as column, approximately equal or slightly larger in diameter than oral disc in preserved specimens. Oral disc larger than pedal disc in well-expanded living specimens. Ectoderm of column contains small clusters of gobletshaped basophilic (blue-staining) material without discernible nuclei or other cellular structures surrounded by deeply staining epitheliomuscular cells ( Figure 3A ). Column musculature strong, ectodermal and mesogloeal ( Figure 3E ), concentrated into a mesogloeal marginal sphincter distally ( Figure 3C ).

Oral disc and tentacles. Tentacles partially covered by distal column in contraction; oral disc not visible ( Figure 2B ). Tentacles and oral disc same colour as column. Mouth central, with two prominent siphonoglyphs; lips and siphonoglyphs slightly paler than oral disc in pink specimens, more opaque than disc in white specimens. Tentacles bluntly pointed, longitudinally fluted in preservation, length approximately equal to diameter of oral disc, about 100 in four crowded cycles on outer half of oral disc, those of outermost cycle longest. In life, tentacle length approximately equal to column height ( Figure 1 ). Tentacle musculature ectodermal. Because tentacles are partially retracted inside column, relative thickness of oral and aboral ectoderm at base could not be assessed.

Mesenteries and internal anatomy. Mesenteries arranged hexamerously in three to four cycles, only those of first cycle perfect; two pairs of directives, each attached to siphonoglyph. All mesenteries of first and second cycles including directives bear filaments and gonads; those of fourth cycle weak, lacking filaments and reproductive tissue. All specimens collected in late November sexually mature, with either female or male gametes in any single specimen, some brooding larvae ( Figure 3B ). Mode of larval production unclear: some specimens with male gametes bear young.

Longitudinal muscles of mesenteries weak ( Figure 3D ). Parietal muscle not distinct from mesenterial lamella, consisting of few short processes with no pennon. Retractor muscle circumscribed but not very broad, comprised of few, unramified branches towards the coelenteron and a few larger, more ramified branches closer to the body wall ( Figure 3D ).

Cnidom. Spirocysts, basitrichs, holotrichs, microbasic p -mastigophores ( Figure 4 ). See Table I for size and distribution.

Habitat and biology. We see no evidence that A. pearseae harbours chemosynthetic bacteria, assuming instead that it feeds upon larvae, dissolved and particulate organic matter, and plankton. Although not collected until 2004, Anthosactis pearseae has been present at the type locality since at least 2002, when the carcass was first discovered (C. Braby, pers. comm.). We have examined material collected elsewhere in the northeastern Pacific, including hard substrates away from and peripheral to vents (e.g. sites in Voight et al. 2004; Voight 2005; Daly 2006), in areas of diffuse flow (e.g. sites in Collins & Daly 2005), and at active hydrothermal vents (e.g. site in Voight et al. 2004; Govenar et al. 2005) but have found no animals we can identify as A. pearseae . We expect this description to facilitate the identification of specimens should they occur on other whale carcasses or in other kinds of deep-sea habitats.

Figures

Figure 1. External anatomy and habitus of living Anthosactis pearseae. Note galatheid crabs, and plumes of Osedax protruding from bone. Photo reproduced with permission. Copyright MBARI, 2006.

Figure 2. External anatomy of Anthosactis pearseae. A. Side view of holotype (NMNH 1096705). B. Three-quarter view of paratype (CASIZ 174323). Scale bar55.0 mm.

Figure 3. Internal anatomy of Anthosactis pearseae. A. Column ectoderm. Note hyaline, goblet-shaped structures surrounded by dense and glandular epitheliomuscular cells. B. Cross-section through a tentacle containing a brooded larva. Specimen from which this section was made is male. C. Longitudinal section through the column, showing mesogloeal marginal sphincter. D. Cross-section through column of a contracted specimen, showing one pair of directive mesenteries. Note the absence of any distinct parietal or parietobasilar muscles and the relatively narrow retractor muscle. E. Longitudinal section through the column showing endodermal longitudinal muscle and mesogloeal columnar muscle. The lacunae of the mesogloeal muscles are visible in the inset (E9), taken at higher magnification.

Figure 4. Cnidae of Anthosactis pearseae. See Table I for abundance, distribution, and size. Scale bar520 Mm. A. Robust spirocyst. B. Holotrich. C. Spirocyst. D. Microbasic p-mastigophore. E. Basitrich. F. Basitrich. G. Microbasic p-mastigophore.