Scytophorus, HERTWIG, 1882

Gusmão, Luciana C. & Rodríguez, Estefanía, 2021, Two sea anemones (Cnidaria: Anthozoa: Actiniaria) from the Southern Ocean with evidence of a deep-sea, polar lineage of burrowing sea anemones, Zoological Journal of the Linnean Society 193, pp. 1392-1415 : 1402

GENUS SCYTOPHORUS HERTWIG, 1882

Diagnosis (after Carlgren, 1949; modifications in italics). Halcampoididae with elongate body and flat aboral end. Column indistinctly divisible into scapus and scapulus. Cuticle developed chiefly on scapus, with modified weak tenaculi more or less visible to the naked eye. No sphincter. Tentacles 14, with longitudinal muscles ectodermal. A single weak, ventral siphonoglyph without conchula. Mesenteries 14, six pairs plus one couple; individual mesenteries of couple with retractors faced towards dorsal pairs of directives, wherefore there is seemingly a single pair of directives. All mesenteries perfect, with retractors strong, restricted to kidneylike. Parietal muscles well developed. As a rule, all mesenteries fertile. Ciliate tracts of filaments may be discontinuous. Cnidom: spirocysts, basitrichs, p -mastigophores A.

Type species: Scytophorus striatus by monotypy.

Included species: Scytophorus antarcticus ( Pfeffer, 1889) and S. striatus .

Remarks: We modified the generic diagnosis by removing the mention of a physa-like structure in members of Scytophorus . Although Hertwig (1882) described S. striatus as lacking a pedal disc and with a round aboral end, all of the S. striatus specimens examined had a distinct flat aboral end ( Figs 6C , 7A, F ) as seen attached to solid substrates ( Fig. 6A ). Although most of the specimens of S. striatus observed had their distal column and oral disc contracted, when they are relaxed, the scapulus can be easily distinguished from the rest of the column (see Fig. 6D ). We left in the diagnosis the presence of a weak siphonoglyph, but this structure was difficult to observe in dissections ( Fig. 7G ), histological sections or micro-CT scans ( Fig. 7K ), as noted by others (e.g. Carlgren, 1921).

Figures

Figure 6. External anatomy of Scytophorus striatus. A, lateral view of live specimen attached to scleractinian coral; B, lateral view of preserved specimen showing elongate shape, columnar cuticle and sand grains attached to column; C, detail of flattened pedal disc; D, oral view of preserved specimen showing short scapulus (indicated by arrow); E, detail of column showing small tenaculi with attached sand grains and yellow cuticle; note longitudinal columnar furrows (indicated by arrows). Scale bars: A, E, 2 mm; B, 5 mm; C, D, 4 mm.

Figure 7. Internal anatomy and microanatomy of Scytophorus striatus. A, micro-CT scan of longitudinal section through flattened pedal disc; note absence of basilar musculature (arrows); B, cross-section through mid-scapus showing area between furrows; note body layers and bilayered cuticle (indicated by arrow); C, histological longitudinal section through distal column showing strong, circular endodermal musculature; D, detail of distal scapus showing high muscle processes of strong, circular endodermal musculature (indicated by arrow); E, histological longitudinal section through tentacle showing ectodermal longitudinal musculature; F, micro-CT longitudinal scan through a whole specimen showing flattened pedal disc, actinopharynx, tentacles and gastrovascular cavity; note foreign material attached to epidermis of column and pedal disc; G, micro-CT scanning through distal column showing actinopharynx and two indistinct siphonoglyph (indicated by asterisks); H, cross-section through mid-scapus showing 14 macrocnemes (indicated by numbers) arranged in seven pairs; I, histological cross-section through mid-scapus showing arrangement of mesenteries in seven pairs (indicated by numbers); J, micro-CT cross-section scan through scapulus showing 14 mesenteries; K, micro-CT cross-section scan through distal scapus showing actinopharynx and weak siphonoglyphs (indicated by asterisks); note weak parietobasilar musculature of extra mesentery (indicated by arrow); L, micro-CT cross-section scan through proximal column; note all 14 mesenteries with gonads (= macrocnemes); M, detail of retractor of macrocneme with pennon distally (indicated by asterisk); N, detail of strong parietobasilar musculature of macrocneme; O, detail of macrocneme with both oocytes and spermatic cysts. Abbreviations: ac, actinopharynx; d, directive pair; ep, epidermis; ga, gastrodermis; gc, gastrovascular cavity; me, mesoglea; pd, pedal disc; t, tentacles. Scale bars: A, E, M, N, 0.2 mm; O, 0.3 mm; B, F, 4 mm; C, D, 1 mm; G–L, 2 mm.