Travisia sp. (NHM_1244)

Wiklund, Helena, Neal, Lenka, Glover, Adrian G., Drennan, Regan, Muriel Rabone, & Dahlgren, Thomas G., 2019, Abyssal fauna of polymetallic nodule exploration areas, eastern Clarion-Clipperton Zone, central Pacific Ocean: Annelida: Capitellidae, Opheliidae, Scalibregmatidae, and Travisiidae, ZooKeys 883, pp. 1-82 : 1

Travisia sp. (NHM_1244) Fig. 30 A–G

Material examined.

NHM_1244 NHMUK ANEA 2019.7183, coll. 01 Mar. 2015, 12°15.44N, 117°18.13W, 4302 m http://data.nhm.ac.uk/object/f6906eae-67ec-4d37-83c6-590f3c53df76; NHM_1863 NHMUK ANEA 2019.7184, coll. 13 Mar. 2015, 12°02.49N, 117°13.03W, 4094 m, http://data.nhm.ac.uk/object/fa708aca-6dd1-4b53-8d54-c76a93f43363.

Description.

This species is represented by two specimens only. It is a small species 5.5-6 mm long and 0.7 mm wide for 24 segments, 20 of which chaetigerous and four posterior-most achaetigerous. Preserved specimens pale yellow ( Fig. 30A ), live specimens milky, semi-transparent ( Fig. 30B ). Body robust, compact, grub like, anteriorly half enlarged, particularly over chaetigers 11-13, tapering posteriorly, but remaining relatively thick. Body surface rugose, with transverse rows of small, tightly packed squarish lobes.

Prostomium short, smooth, conical ( Fig. 30C, D ). Peristomium trapezoidal, rugose, with small, tightly packed squarish papillae, appearing in two rows dorsally. Mouth as a transverse slit between chaetigers 1 and 2 ( Fig. 30D ).

Branchiae absent. Parapodia biramous, located on row with largest lobes, both rami well separated ( Fig. 30E ). Parapodial lappets present, observable from chaetiger 1 and well developed from chaetiger 6. Chaetigers in anterior half distinctly triannulate, with three transverse rows of small, squarish lobes, subsequent segments becoming less distinctly annulated, with the last four achaetigerous segments uniannulate; lobes always largest on the ventral most row. Interramal sense organs present, best observed on stained specimen ( Fig. 30E ). Chaetae all long, smooth, slender capillaries ( Fig. 30F ).

Pygidium very short, thick (slightly longer wide); in distal view with a tightly packed circlet of around 11 lobes ( Fig. 30G ), of these five large, thick and tightly packed with the ventral most single lobe thickest, dorso-laterally bordered by about six much smaller lobes ( Fig. 30G ).

Shirlastain pattern.

Stain retained uniformly. Interramal sense organs observed as darkly red stained spots ( Fig. 30E ). Specimen stain within few (about 5) days.

Genetic data.

GenBank MN217468-MN217469 for 16S and MN217511 for 18S. Travisia sp. (NHM_1244) is sister to Neolipobranchus sp. and fall within a clade consisting of Travisia zieglerae sp. nov. as well as other Travisia species from GenBank ( Fig. 32 ).

Remarks.

Both UKSR-collected species are morphologically very similar, in having a similar number of segments and in being abranchiate. They can be distinguished by a suite of subtle characters, which in case of Travisia sp. NHM_1224 is represented by only two specimens, so caution is needed. The two species differ somewhat in body shape as Travisia zieglerae sp. nov. is more slender in the posterior half, while Travisia sp. NHM_1224 is thicker ( Fig. 31A ). The rugosity of transverse rows differs, as the lobes are more tightly packed in Travisia sp. NHM_1244 and looser in Travisia zieglerae sp. nov., at least in the anterior region ( Fig. 31B ). Another difference is the arrangement of pygidial lobes ( Fig. 31C ). Finally, difference can be detected upon staining with Shirlastain, where prostomium of Travisia zieglerae sp. nov. stains darkly unlike that of Travisia sp. NHM_1244 ( Fig. 31B ) and the stain is retained after even 5 days since staining.

Of the known species of Travisia , only five were described as completely abranchiate, with four of these currently valid: T. glandulosa McIntosh, 1879; T. gravieri McIntosh, 1908; T. nigrocincta Ehlers, 1913 and T. fusus (Chamberlin, 1919) with T. abyssorum (Monro, 1930) considered a subjective synonym of T. glandulosa . Type specimens of McIntosh (1879; 1908) and the specimen of Monro (1930) were examined as part of this study. These can be distinguished from the UKSR species as follows:

T. fusus : has a larger body size of 14 mm and 28 chaetigers. Pygidium is divided into 12-14 inconspicuous lobes. Type locality: Pacific Ocean, towards the Marquesas Islands, 0°60'N, 137°54'W, 4504 m.

T. glandulosa ( Fig. 31D ): similar number of chaetiger to UKSR species (tentatively around 20 chaetigers counted), posteriorly thick, pygidium with circlet of about 12 small lobes; of these inner 4 or 5 also small. Original description of not much help, and McIntosh (1879) expressed doubt about naming the species due to its poor condition. Type locality: Arctic Ocean, Davis Strait, Greenland, 3264 m.

T. gravieri ( Fig. 31E ): very compact, grub-like, not thinner in posterior half; tentatively about 16 or 17 chaetigers observed. Type locality: North Atlantic, 986 m.

T. nigrocincta : much larger species, up to 34 mm long and 6 mm wide for 25 segments (the smallest specimen reported by Ehlers was 6 mm long and about 2 mm wide for 17 chaetigers), with dark transverse bands; pygidium not described in detail. Type locality: Southern Ocean, Wilhelm II Coast, 2725 m.

Figures

Figure 30. Travisia sp. NHM _ 1244. A Lab images, whole specimens (specimen NHM _ 1244, unstained [top], specimen NHM _ 1863, faded stain [bottom]) B Live image, whole specimen (specimen NHM _ 1863) C Lab image, dorsal anterior (specimen NHM _ 1863, stained, pr = prostomium) D Lab image, ventral anterior, (stained) (specimen NHM _ 1863, m = mouth) E Lab image, lateral posterior (specimen NHM _ 1863, stained, pp = parapodia, io = interramal organs) F Lab image, detail of capillary chaetae (specimen NHM _ 1244) G Lab image, pygidium, distal view (lower left) and lateral view (upper right), with pygidial features outlined in a fine white line (specimen NHM _ 1863, stained, vl = ventral lobe). Scale bars: 1 mm (A); 50 μm (F).

Figure 31. Comparison between Travisia sp. NHM _ 1244 and Travisia zieglerae sp. nov., and holotypes of Travisia glandulosa (BMNH 1921.5.1.2431) and Travisia gravieri (BMNH 1921.5.1.2429). A Lab images, whole specimens (Travisia sp. NHM _ 1244 specimen NHM _ 1863 [left], Travisia zieglerae sp. nov. holotype [specimen NHM _ 1431] [right], stained,) B Lab images, comparison of prostomia (Travisia sp. NHM _ 1244 specimen NHM _ 1863 [left], Travisia zieglerae sp. nov. holotype [right], stained) C Lab images, comparison of pygidia (Travisia sp. NHM _ 1244, specimen NHM _ 1863 [left], Travisia zieglerae sp. nov. holotype [right], stained) D Travisia glandulosa holotype, with detail of pygidium E Travisia gravieri holotype, with detail of pygidium. Morphological features in plates C-E have been outlined with a very fine white line to improve clarity of those features. Scale bars: 1 mm (A, D, E).

Figure 32. Phylogenetic analysis of Scalibregmatidae and Travisiidae. 50 % majority rule tree from the Bayesian analyses using 18 S and 16 S, with posterior probability values on nodes. Twenty taxa from GenBank were included, and Opheliidae was chosen as outgroup following the annelid phylogeny of Weigert and Bleidorn (2016).