Trilobodrilus ellenscrippsae

Habitat Subtidal in coarse to silty shell gravel at the surface layer at 9 m depth (subtidal).

Description Measurements given first in the text from holotype, ranges in in parenthesis include measurements taken from the lost specimens. Compact body, light brown tint (fixed specimens, Fig. 3 A). Body length 485 µm (306 – 774 µm, n = 4, Tables 1, 7), width 122 µm (91 – 229 µm, n = 4, Tables 1, 7), body segments indistinct (Fig. 3 A – C). Prostomial shape conical (Fig. 3, Table 7). No eyes. Middle of the mouth located 69 – 88 µm (n = 4) posterior of terminal prostomium (mo, Fig. 3 A, C, F, Table 1). Four compound cilia terminally on prostomium (pcc, Fig. 3, Tables 1, 7), each consisting of approximately 30 cilia (n = 3); dorsal compound cilia spaced 19 µm apart (16 – 29 µm, n = 3), length similar to the cilia in the prostomial ciliary bands (10 – 18 µm long, n = 3). Prostomial compound cilia surrounded by four pairs of semicircular arranged apical ciliary tufts (act, Fig. 3 B, D – E, Table 7). Two prostomial ciliary bands on prostomium and one ciliary band posterior to the nuchal organs, as well as one additional incomplete fourth ciliary band posterior to these bands (cb 1 – 4, Fig. 3 B, E, Table 7). First dorsally continuous ciliary band (13 µm wide, n = 1) encircles prostomium (Fig. 3 A, D – E, Table 7). Several intermediate ciliary tufts located laterally between first and second ciliary band (ict, Fig. 3 B, D – E, Table 7). Second ciliary band (cb 2, Fig. 3 A – B, D – F; 24 µm wide, n = 1) dorsally incomplete with 48 µm wide gap (n = 1) and one mid-dorsal ciliary tuft in center of gap (mdt, Fig. 3 B, E, Table 7, 40 – 60 cilia, n = 1). One lateral pair of nuchal organs located between second and third ciliary band (no, Fig. 3 F). Third ciliary band (10 µm wide, n = 1) dorsally continuous (cb 3, Fig. 3 B – E, Table 7) posterior to nuchal organs. Fourth ciliary band extends laterally approx. 24 µm (n = 1) from the ventral ciliary tract (cb 4, Fig. 3 B, E, Table 7). Ciliary tufts arranged laterally along the body (lct, Fig. 3 B, Table 7). Ventral ciliary tract extends from posterior prostomium to posterior pygidium (vct, Fig. 3 B – C, E; width of tract relative to total body width approximately 0.44 (n = 1 )). Anus opening dorso-anteriorly on pygidium. No eggs present in the investigated specimens. Epidermal inclusions and spindle glands in the epidermis could not be described and measured due to insufficient preservation in the investigated specimens. Molecular information The following sequences were determined by Sanger sequencing from a single, non-type specimen collected on 19 April 2009, for which no morphological voucher remains: 18 S rDNA, MG 588090 (1857 nucleotides (nt), Table 4); 28 S rDNA, MG 588092 (1126 nt, Table 5); COI, MG 588094 (644 nt, Table 6); CytB, MG 588096 (426 nt). In the following, the sequences of T. ellenscrippsae sp. nov. are first compared to the most similar sequences found in T. windansea sp. nov., and the range of similarities with the addition of the respective species are subsequently listed. Trilobodrilus ellenscrippsae sp. nov. 18 S rDNA is 99.9 % similar to the 18 S rDNA of T. windansea sp. nov., and 99.5 % (T. axi) – 99.9 % (T. nipponicus) similar to the other sequenced species (Table 4). Its 28 S rDNA is 99.9 % similar to the 28 S rDNA of T. windansea sp. nov. and 98.5 % (T. axi) – 99.4 % (T. nipponicus) similar to the other species (Table 5). COI is 84.9 % similar to T. windansea sp. nov., and 76 % similar to the T. itoi and T. nipponicus (Table 6). Cytochrome B resembles the sequence of T. windansea sp. nov. to 85.6 %.

Fig. 3, Tables 1, 3 – 7

Trilobodrilus ellenscrippsae sp. nov. further differs in its genetic sequences from all other species, see Molecular information above or Tables 4 – 6.

Diagnosis Short Trilobodrilus with two pairs of prostomial compound cilia encircled by four pairs of intermediate ciliary tufts anterior to first ciliary band. Additional ciliary tufts between first and second ciliary band. Dorsally continuous third ciliary band. Incomplete fourth ciliary band, posterior of third ciliary band with broad dorsal gap.

Remarks Trilobodrilus ellenscrippsae sp. nov. shows closest morphological resemblance to T. nipponicus (but nests with T. windansea sp. nov. in the molecular tree), but is much shorter, has a higher number of apical ciliary tufts on the prostomium, and its ciliary tufts along the body are not arranged in an as distinctive a pattern as in T. nipponicus (Fig. 3, Table 7). Trilobodrilus ellenscrippsae sp. nov. resembles T. windansea sp. nov. by having apical and intermediate ciliary tufts on the prostomium, and a dorsally incomplete second ciliary band with a mid-dorsal tuft (Fig. 3 B, D – E, Table 7). However, T. ellenscrippsae sp. nov. differs from T. windansea sp. nov. in the shape of the prostomium, the additional ciliary row posterior to the second ciliary band, and by having a dorsally continuous third ciliary band as well as an incomplete fourth ciliary band (Fig. 3, Tables 1, 7).

Distribution Trilobodrilus ellenscrippsae sp. nov. is known from La Jolla Cove, La Jolla, San Diego, California only.

Etymology This species is named (as a noun in the genitive case) to honour Ellen Browning Scripps (1836 – 1932), a founding benefactor of the Scripps Institution of Oceanography (McClain 2017) in La Jolla, California. No species have been named for her to date, yet Ellen Browning Scripps’ impact on science has been very important (see McClain 2017).

Material examined Holotype UNITED STATES OF AMERICA: complete adult, 485 µm long (platinum-palladinium-coated and mounted on stub for SEM), La Jolla Cove, La Jolla, California, 32 ° 51 ′ 03 ″ N 117 ° 16 ′ 20 ″ W, 9 m depth, 19 Apr. 2009, K. Worsaae and G. Rouse leg. (SIO-BIC A 8209). Additional specimens mounted on slides were unfortunately lost after conducting the measurements.