Scytophorus striatus, 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 : 1403-1406

publication ID	https://doi.org/ 10.1093/zoolinnean/zlaa176
publication LSID	lsid:zoobank.org:pub:D000BAA9-51C4-46FE-AC9B-BB361B601FA2
DOI	https://doi.org/10.5281/zenodo.5752653
persistent identifier	https://treatment.plazi.org/id/2964E41D-FFB2-FFC3-FF53-C771FB06B547
treatment provided by	Plazi
scientific name	Scytophorus striatus
status

Treatment

SCYTOPHORUS STRIATUS HERTWIG, 1882 View in CoL

( FIGS 6–8 View Figure 6 View Figure 7 View Figure 8 ; TABLE 2 View Table 2 )

Material: AMNH 5268 About AMNH (nine specimens), Nathaniel B. Palmer R/ V, NBP11-03 Expedition , Sta. 14, off Burdwood / Namuncurá Bank, Drake Passage, Antarctica, 54º42.84’S 62º14.99’W, 732 m, 11 May 2011, Hein Dredge, collected by M GoogleMaps . R. Brugler . AMNH 5275 About AMNH (three specimens), ‘ Nathaniel B. Palmer’ R/V, NBP11-03 Expedition, Deep Site – North Grassy Knoll, Sta. 10, Burdwood / Namuncurá Bank , Drake Passage, Antarctica, 54°43.35’S 62°14.21’W, 720 m, 11 May 2011, Blake Trawl, collected by M. R. Brugler. AMNH 5254 About AMNH (20 specimens), Nathaniel B. Palmer R / V, NBP11-03 Expedition, Sta. 16, off Burdwood/Namuncurá Bank, GoogleMaps Drake Passage, Antarctica, 54º48.52’S 62º07.20’W, 1423 m, 13 May 2011, Hein Dredge, collected by M. R. Brugler. AMNH _ IZC 00361338 About AMNH (three specimens), Nathaniel B. Palmer R / V, NBP11-03 Expedition, Sta. 22, off Burdwood / Namuncurá Bank, Drake Passage, GoogleMaps Antarctica, 54º50.50’S 62º07.53’W, 1922 m, 14 May 2011, Hein Dredge, collected by M. R. Brugler GoogleMaps .

Additional material examined for comparison: Scytophorus antarcticus ZMH C1452 (one specimen: holotype); locality: South Georgia. Halcampoides purpureus AMNH 4498 (one specimen); locality: Southern Ocean , Antarctica, Kapp Norvegia, Sta. PS 56/105-1, 10°57’S 12°15.05’W, GKG, giant box corer, collected in 2000 by P. López-González bi-layered cuticle on column with foreign material attached to it, p -mastigophores A in actinopharynx GoogleMaps .

External anatomy ( Fig. 6 View Figure 6 ): Body elongate in preserved specimens ( Fig. 6A, B View Figure 6 ) but with aboral end flattened without a well-defined physa ( Fig. 6A–C View Figure 6 ). Column cylindrical with 14 longitudinal furrows/evaginations ( Fig. 6B View Figure 6 ), divided into scapulus and scapus ( Fig. 6D View Figure 6 ) and tenaculi throughout scapus ( Fig. 6E View Figure 6 ); column with epidermis covered by yellow cuticle distributed on scapus ( Fig. 6B, E View Figure 6 ). Column diameter 5–11 mm distally and 7–9 mm proximally; 18–40 mm length in preserved specimens. Oral disc small, circular, contracted in all specimens ( Fig. 6A, B, D View Figure 6 ); diameter 2–7 mm in preserved specimens. Margin of column tentaculate; tentacles 14, smooth; putatively arranged in a single cycle.

(330–331 m). AMNH 4501 About AMNH (one specimen); locality: Southern Ocean , Antarctica, Bransfield Strait, Sta. PS 56/164-1, 63°04.80’S 59°32.80’W, Agassiz Trawl, collected on 28 April 2000 by P. López-González (858–859 m) GoogleMaps . AMNH 4502 About AMNH (one specimen); locality: Southern Ocean , Antarctica, West Deception Island, Sta. PS 56/183-1, 62°07.15’S 60°22.60’W, Bottom Trawl, collected on 3 May 2000 by P. López-González (200–204 m) GoogleMaps . Halcampoides abyssorum Danielssen, 1890 USNM 53297 (seven specimens); locality: North Pacific Ocean , Bering Sea , Alaska, Punuk Islands, Stranger M /S, collected on 15 July 1937 by W. Williams (27 m) .

Diagnosis: Fourteen mesenteries arranged in seven pairs, 14 tentacles, hermaphrodite, strongly attached, Internal anatomy, microanatomy ( Fig. 7 View Figure 7 ): Aboral end flat, not physa-like, but without basilar musculature ( Fig. 7A View Figure 7 ). Overall body wall thickness varies along column: generally thicker on furrows (epidermis 53–119 µm, mesoglea 33–119 µm, gastrodermis 50–122 µm) than rest of column (epidermis 32–84 µm, mesoglea 19–88 µm, gastrodermis 50–94 µm) ( Fig. 7B View Figure 7 ). Bi-layered cuticle on column (19–35 µm) ( Fig. 7B View Figure 7 ). Longitudinal endodermal musculature of column strong ( Fig. 7C View Figure 7 ); higher muscle processes in distal column, but not forming a differentiated marginal sphincter muscle ( Fig. 7D View Figure 7 ). Longitudinal musculature of tentacles ectodermal ( Fig. 7E View Figure 7 ). Actinopharynx approximately one-third of the length of the column, longitudinally sulcate, more heavily folded proximally ( Fig. 7F View Figure 7 ). Two indistinct siphonoglyphs ( Fig. 7G, K View Figure 7 ).

Mesenteries with unusual arrangement: 14 perfect mesenteries arranged in seven pairs, including a single pair of directives ( Fig. 7H, I View Figure 7 ). Macrocnemes span entire length of body, from proximal ( Fig. 7J View Figure 7 ) to distal column ( Fig. 7L View Figure 7 ). Retractors of macrocnemes small, strong, circumscript, with clear pennon distally ( Fig. 7M View Figure 7 ). Parietal musculature well developed, strong ( Fig. 7N View Figure 7 ), equally developed in all mesenteries ( Fig. 7I View Figure 7 ), more developed proximally ( Fig. 7L View Figure 7 ). Basilar musculature absent ( Fig. 7A View Figure 7 ). The four specimens examined hermaphroditic ( Fig. 7O View Figure 7 ): one to three oocytes per macrocneme (major axis of oocytes 217– 597 µm) and many spermatic cysts (major axis of spermatic cysts 94–311 µm); all specimens collected in May.

Cnidom: spirocysts, basitrichs and p-mastigophores A. See Figure 8 View Figure 8 and Table 2 View Table 2 for size and distribution.

Distribution and natural history: Over a dozen specimens of Scytophorus striatus were collected in the same trawl suggesting they might be locally abundant in the Burdwood Bank (also known as Namuncurá Bank) at 1423 m. Many of these specimens were collected attached to scleractinian corals ( Fig. 6A View Figure 6 ) indicating that at least some of them live burrowed in the sand but attached to solid substrates, which were plentiful in the trawl (e.g. coarse sand and coral gravel). The species was collected in an area in which octocorals and stylasterid hydroids were also trawled. Scytophorus striatus was previously known only from its type locality between the Kerguelen Islands and Heard Island and McDonald Islands (52°4’S, 71°22’E) in somewhat shallow waters (274 m). This new record for S. striatus extends the distribution of the species from the Indian Ocean region of Antarctica (Kerguelen) to the Atlantic portion of the sub-Antarctic region (Burdwood/Namuncurá Bank), a region that connects continental South America to the northern region of the Antarctic Peninsula. We also extend significantly the bathymetric range of S. striatus to 720–1922 m depth. Scytophorus is one of only six genera found in both Antarctic and sub- Antarctic regions (~7% of Antarctic fauna: Rodríguez et al., 2007).

Remarks: Specimens of S cytophorus striatus examined in this study largely agree with the original description in terms of external anatomy and musculature. We document and provide the cnidom and cnidae size ranges of S. striatus for the first time (see Fig. 8 View Figure 8 and Table 2 View Table 2 ) and show that it differs from the one given for S. antarcticus by Carlgren (1927) and our own examination of its holotype (ZMH C1452; see Fig. 9 View Figure 9 ). Both species differ in the size of basitrichs in the column and the actinopharynx, which in the column only overlaps in the lower range of those in S. striatus , and the presence of p- mastigophores in the actinopharynx in S. striatus . Although Carlgren (1927) does not specify the types of nematocysts in S. antarcticus , we confirmed their identity ( Table 2 View Table 2 ), including those of the mesenterial filaments not provided by him (i.e. basitrichs, p -mastigophores A). One of the most consistent differences between S. antarcticus and S. striatus is fertility: S. antarcticus is gonochoric, whereas S. striatus is hermaphrodite. Although hermaphrodite and gonochoric specimens may coexist in a population, hermaphrodites tend to be rare (e.g. Jennison, 1981; Van Praët, 1990; Rodríguez et al., 2013). The fact that all five specimens of S. striatus examined in this study were hermaphrodite leads us to believe that it is a specific character of S. striatus . Likewise, we confirmed that the holotype of S. antarcticus (ZMH C1452) is female, corroborating the reproductive differences between the two species.

References

Figures

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.