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Revealing enigmatic mucus structures in the deep sea using DeepPIV


Many animals build complex structures to aid in their survival, but very few are built exclusively from materials that animals create 1,2. In the midwaters of the ocean, mucoid structures are readily secreted by numerous animals, and serve many vital functions3,4. However, little is known about these mucoid structures owing to the challenges of observing them in the deep sea. Among these mucoid forms, the ‘houses’ of larvaceans are marvels of nature5, and in the ocean twilight zone giant larvaceans secrete and build mucus filtering structures that can reach diameters of more than 1 m6. Here we describe in situ laser-imaging technology7 that reconstructs three-dimensional models of mucus forms. The models provide high-resolution views of giant larvacean houses and elucidate the role that house structure has in food capture and predator avoidance. Now that tools exist to study mucus structures found throughout the ocean, we can shed light on some of nature’s most complex forms.

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Fig. 1: Giant larvacean, B. stygius, in its mucus feeding structure, which includes an inner and outer house.
Fig. 2: A three-dimensional reconstructed model of a giant larvacean and its inner house yields composite models of the mucus structure.
Fig. 3: Comparison between traditional line sketches and three-dimensional models of a giant larvacean mucus house.
Fig. 4: Laser scanning coupled with particle flow-field measurements reveal the structure and function of the mucus house.

Code availability

The custom MATLAB code developed as part of this study can be downloaded from our public repository at

Data availability

The data reported in this paper are archived and can be openly accessed using MBARI’s Video Annotation and Reference System (VARS) query tool ( with the search term ‘Nature20190609559’. In addition, the data that support the findings of this study are available from the corresponding author upon reasonable request.


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We thank D. Graves, C. Kecy, D. Klimov, J. Erickson and MBARI technical staff for their engineering contributions to the development of DeepPIV, the crews of RVs Rachel Carson and Western Flyer, and the pilots of ROVs Doc Ricketts, Ventana and MiniROV for their contributions to this project. This work is a contribution of the Deep Ocean Inspiration Group and was supported by the David and Lucile Packard Foundation.

Author information

Authors and Affiliations



K.K., B.H.R. and A.D.S. devised the experiments; K.K., G.T. and J.D. conducted the visualizations and processed the data; K.K., J.D., K.L. and R.E.S. analysed the data; K.K., B.H.R. and R.E.S. wrote the manuscript; all authors edited the manuscript.

Corresponding author

Correspondence to Kakani Katija.

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Competing interests

The authors declare no competing interests.

Additional information

Peer review information Nature thanks Cornelia Jaspers, Kelly Sutherland and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data figures and tables

Extended Data Fig. 1 DeepPIV hardware and deployment.

a, DeepPIV is used to visualize gelatinous or mucus structures and conduct in situ three-dimensional scanning laser reconstructions using ROV MiniROV. b, Enlarged view of DeepPIV components affixed to the laser housing to generate a laser-sheet and fluorescent-dye field, as well as components to aid in pilot control of the vehicle during ROV deployments. c, MiniROV being launched in Monterey Bay from RV Rachel Carson.

Extended Data Fig. 2 DeepPIV scans yield cross-sectional structural information.

During a single laser sheet scan using DeepPIV, multiple planes (1–5 from dorsal to ventral) are illuminated to reveal different features in the mucus house structure of B. stygius. Scale bars, 4 cm.

Extended Data Fig. 3 The inner and outer house as well as the connective mucus structures of B. stygius.

a, Line drawing of the typical structure of the outer house and inlet channels with embedded inlet filters near the animal trunk. b, c, Overviews of the outer house structure with the animal–house complex oriented downwards (b) and upwards (c). df, Magnified views of the two inlet channels connecting laterally to the inner house from outside the outer house looking laterally (d), inside the inlet channel looking laterally (e) and inside the outer house looking dorsally (f).

Extended Data Fig. 4 Three-dimensional reconstructions of mucus and gelatinous structures using DeepPIV.

af, White-light illumination (a, c, e) provides two-dimensional snapshots of structures in midwater, where the scanning laser illumination of DeepPIV (b, d, f) can yield three-dimensional reconstructions of floating egg masses (a, b), larvacean bodies (c, d) and other gelatinous or mucus structures such as siphonophore swimming bells (e, f; Desmophyes annectens). Scale bars, 1 cm.

Supplementary information

Supplementary Information

This file contains Supplementary Materials and Methods and Supplementary Table 1.

Reporting Summary

Video 1

Video compilation showing a giant larvacean, Bathochordaeus stygius, illuminated by white light and followed by a DeepPIV laser scan with the ROV approaching the inner house dorsally (Table S1, 3DR4). The red lights shown in the white illumination clip correspond to the DeepPIV laser sheet.

Video 2

Video compilation showing a giant larvacean, B. stygius, illuminated by white light and followed by a DeepPIV laser scan with the ROV approaching the inner house anteriorly (Table S1, 3DR5).

Video 3

Fly around video showing a 3D reconstructed model (Table S1, 3DR4) of a giant larvacean (black) occupying its inner house. The lateral inlet channels are shown along with the inner house, which includes the inlet filters, suspensory threads, ramp, supply chambers, and food concentrating filters.

Video 4

Dye visualizations reveal flow through the inner house being driven by the beating giant larvacean tail (Table S1, Batho3).

Video 5

Compilation of DeepPIV particle videos revealing fluid motion within various features of the giant larvacean inner house.

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Katija, K., Troni, G., Daniels, J. et al. Revealing enigmatic mucus structures in the deep sea using DeepPIV. Nature 583, 78–82 (2020).

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