Duobrachium sparksae, Ford & Bezio & Collin, 2020

Ford, Michael, Bezio, Nicholas & Collin, Allen, 2020, Duobrachium sparksae (incertae sedis Ctenophora Tentaculata Cydippida): A new genus and species of benthopelagic ctenophore seen at 3,910 m depth off the coast of Puerto Rico, Plankton & Benthos research 15 (4), pp. 296-305 : 298

Duobrachium sparksae spec. nov.

( Figures 1–3 , 5)

Material examined. Holotype video, USNM 1607331 ; two paratype videos, USNM 1607332-3 . Collection was impossible at this location due to vehicle capabilities.

Diagnosis. Same as for genus.

Description. Bodies semi-transparent with two tentacles sheathed in two large conical tentacle arms extending aboral of the body ( Table 1 ). Based on ROV-mounted lasers being 10 cm apart, the estimated length of one specimen (USNM 1607332) from the oral end to the tips of the tentacle arms is 6–8 cm, with the tentacle arms about one-third as long as the body. Lasers were not used to measure the other two animals observed, but contextual scaling objects suggest they were similar in size to the laser-measured animal. Body forms roughly rectangular as viewed laterally in the tentacular plane, but a more oblong rounded shape in the stomodeal plane ( Figs. 1–3 ). Stomodeum dark-colored, oval in shape when viewed from the tentacular plane and goblet-shaped on the stomodeal plane ( Figs. 1–3 ). Eight ctene rows, consisting of 28 to 32 combs per row as counted in the high-definition video, ascend from the apical organ approximately halfway to the oral end, originating from the apical organ unbranched ( Fig. 2C ). At the oral end, opposite the apical organ, an irregularly undulating bright line with a visible cavity is interpreted as a wide mouth ( Fig. 1A , Fig. 2B ). Blue to whitecolored gonads (eight in total) located under each of the eight ctene rows near their oral ends, presumably within meridional canals ( Fig. 1–3 ), which cannot be directly discerned through the high definition videos. Gonads contain distinct round bodies, eggs or embryos, estimated to be 1.5–2.0 mm in diameter ( Figs. 1C, D , 2A , 3 ).

Tentacle arms encase retractile tentacles within tentacle sheaths ( Figs. 1–3 ). Tentacles thick, opaque white, estimated to be five to seven times the length of the body (including tentacle arms), or approximately 30–56 cm, and appear to be capable of adhering to the seafloor. Tentacles are tentilla-bearing and originate from a tentacle bulb near the stomodeum. Tentilla are simple, uniform, approximately 0.5 cm in length, regularly-spaced at roughly 4 mm intervals along extended tentacles. When retracted, tentacles form a coil inside the translucent tentacle sheath and just outside the tentacle arm ( Fig. 1A , 3A ). Tentacle sheaths form a wing-like shape that connects to the stomodeum right above the gonads ( Fig. 2A ). Two fine filaments extend from the oral end of the body ( Fig. 5 .)

Etymology. The specific epithet “sparksae ” honors Elizabeth Ann Sparks, the wife of Michael Ford.

Common name. Sparks’ two-armed ctenophore.

Distribution. Only known from Guajataca Canyon, north-northwest of Puerto Rico at a depth of approximately 3,900 m, within meters of the seafloor.

Electronic Registration: This published work and the nomenclatural acts it contains have been registered in ZooBank under LSID: urn:lsid:zoobank. org:pub:B1BD0C96-F9A8-47A0-BA3F-F42A32B4B91D.

Figures

Fig. 1. Stills captured from video observations of Duobrachium sparksae n. gen. n. sp. A. First sighting (USNM 1607331), showing body shape in stomodeal plane and tentacles coiling within tentacle sheath inside the arms. 16:30:40 UTC; B. First sighting (USNM 1607331), showing body shape in tentacular plane and gonads beneath all ctene rows. C and D. Second sighting (USNM 1607332) showing regular tentilla of tentacles and large embryos/eggs within gonads, highlighting the quality of the HD video. 17:37:36 UTC.

Fig. 2. Line drawing schematic of Duobrachium sparksae n. gen. n. sp. A. Tentacular view of the main body of the animal. B. Oral view. C. Aboral view. ct - ctene row, g - gonads, m - mouth, ta - tentillum, tent - tentacle, stat - statocyst, sto - stomodeum. Illustrations by NB.

Fig. 3. Digital illustration of the habit of Duobrachium sparksae n. gen. n. sp. A. tentacular view B. stomodeal view. Illustrations by NB.

Fig. 5. Artist’s interpretation of the configuration of tentacles and filaments of Duobrachium sparksae n. gen. n. sp. as observed during the second sighting (USNM 1607332 at 1:14–2:36). The specific insertion point near the mouth and attachment to the seafloor were not observed and are represented here by dashed lines. Illustration by NB.