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| Duobrachium sparksae Ford, Bezio & Collins, 2020 |
Abstract
On April 10, 2015, three individuals of an undescribed species of ctenophore were observed moving just above the seafloor in the Arecibo Amphitheater inside the Guajataca Canyon, north-northwest of Puerto Rico at a depth of approximately 3,900 m. The ctenophore is distinctive; having two prominent tentacle arms, a body that is rectangular when observed laterally along the tentacular plane, and rounded when observed laterally along the stomodeal plane. The tentacle arms each give rise to an extensible tentacle bearing short tentilla of uniform length and distribution. One ctenophore appeared to be anchored to the seafloor by its two long flexible tentacles, as well as by two filaments exiting its oral end. The overall form of the ctenophore suggests classification within the problematic, non-monophyletic order Cydippida, but the robust tentacle arms are more reminiscent of benthic species of Platyctenida, particularly those of families Lyroctenidae and Ctenoplanidae. Whereas most platyctenid ctenophores do not possess ctene rows in their adult forms, features that are possessed by the new species described herein, species of Ctenoplanidae retain comb rows as adults and are capable of limited swimming. The species described herein is easily distinguishable from all other known species of Ctenophora and may trace its origin to a lineage diverging near the origin of Platyctenida.
Keywords: Aricebo Amphitheater, Ctenophora, Duobrachium sparksae gen nov. & spec. nov., Puerto Rico, Cydippida
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| Still captured from video observation of Duobrachium sparksae n. gen. n. sp. 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. |
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| Digital illustration of the habit of Duobrachium sparksae n. gen. n. sp. A. tentacular view B. stomodeal view. Illustrations by Nicholas Bezio. |
Phylum Ctenophora Eschscholtz, 1829
Class Tentaculata Eschscholtz, 1825
Order Cydippida Gegenbaur, 1856
Family Cydippida incertae sedis
Genus Duobrachium gen. nov.
Diagnosis. Tentaculate cydippid ctenophores with two thick, aboral, conical tentacle arms. Tentacle arms emerge from the center of the body and extend aborally. Body rectangular in the tentacular plane, oblong in the stomodeal plane. The tentacle arms are as long as the body is tall. Tentacles retractile, with simple tentilla of uniform length. Filaments can exit orally, anchoring it to the sediment. Stomodeum darkly pigmented. Gonads globular, not extending the length of the meridional canals.
Etymology. From the Latin “two-arms”, a name reflecting the two prominent arms. The Latin “brachium” is of common gender, but shall be treated as feminine, in accordance with ICZN article 30.1.4.2.
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| 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 Nicholas Bezio. |
Duobrachium sparksae spec. nov.
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
Michael Ford, Nicholas Bezio and Allen Collins. 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 and Benthos Research. 15(4); 296-305. DOI 10.3800/pbr.15.296
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