Plankton Benthos Res 13(2): 41–45, 2018 Plankton & Benthos Research © The Plankton Society of Japan First record of the mesopelagic narcomedusan genus Solmissus ingesting a fish, with notes on morphotype diversity in S. incisa (Fewkes, 1886) 1,2, 1,2 MITSUKO HIDAKA-UMETSU * & DHUGAL J. LINDSAY 1 School of Marine Bioscience, Kitasato University, Sagamihara, Kanagawa, Japan 2 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Kanagawa, Japan Received 8 November 2017; Accepted 25 January 2018 Responsible Editor: Jun Nishikawa Abstract: An individual narcomedusa assignable to Solmissus incisa sensu lato was observed having ingested a fish at 573 m depth near the southeast slope of the Kaikata seamount, Japan. Solmissus is a very common deep-sea narco- medusan genus that is widely considered to be a predator specializing on gelatinous plankton. Several cryptic species, with differences in the number of tentacles and form of manubrial pouches, are thought to be included in the nominal species Solmissus incisa. Therefore, the present study gives a short description of the morphotype of Solmissus incisa s.l. observed with a fish in its stomach, as well as several individuals of the same morphotype that had ingested gelati- nous prey. Key words: Izu-Ogasawara Islands, mesopelagic, piscivorous, Solmissus incisa, stomach contents Introduction Materials and Methods The common midwater narcomedusan genus Solmissus ROV Hyper-Dolphin video footage from a Super-HARP is widely regarded to be a predator specializing on ge- high-definition video camera (Lindsay 2003) were ana- latinous zooplankton prey (e.g. Raskoff 2002). The feed- lyzed for Dive 81 (Southeast slope of Kaikata Seamount, ing behaviour and stomach contents of 82 individuals of launched at 26°42.168′N, 141°06.425′E on 7 March 2002) Solmissus were reported by Raskoff (2002), based on ROV and Dive 83 (Northeast slope of Sumisu Caldera, launched observations in the Monterey Bay, California, and that at 31°29.070′N, 140°09.198′E on 9 March 2002). Physico- study found that 88.6% of prey items were gelatinous zoo- chemical data were collected using a SeaBird SBE19 CTD plankton, with not a single fish ingested and with the small (Conductivity, Temperature and Depth profiling system) number of non-gelatinous prey presumed to be bycatch and an SBE13 oxygen sensor attached to the vehicle on from the stomach contents of ingested gelatinous preda- all dives. Depth, temperature, salinity and dissolved oxy- tors. gen were correlated to the presence of a given animal by During cruise KY02-03 of the R/V Kaiyo to the Izu- matching the time on the CTD series to the timecode on Ogasawara Island chain from 18 February–13 March 2002, video. The original BCT-124HDL HDCAM tapes (1080i, the Remotely Operated Vehicle (ROV) Hyper-Dolphin re- 29.97 fps) were digitized using an AJA Ki Pro (Apple corded several Solmissus ingesting gelatinous prey such ProRes 4:2:2 codec, QuickTime .mov container). Still im- as salps and a narcomedusa, but also an individual that ages of 1920×1080 pixels were captured using Quicktime had ingested a fish. Herein we report, for the first time, an Pro 7.6.6 by copying the frame at native resolution and observation of piscivory by the mesopelagic narcomedusan pasting into an Adobe Photoshop CC (Ver. 2015) docu- genus Solmissus, along with observations of feeding on ge- ment, before applying auto tone, auto contrast, and auto latinous zooplankton by two other individuals of Solmissus color on the default values and saving as TIFF format. incisa s.l., with notes on their morphology. Information on the individuals treated in the present study and their file names is presented in Table 1. * Corresponding author: Dhugal Lindsay; E-mail, [email protected] 42 M. HIDAKA-UMETSU & D. J. LINDSAY Table 1. Solmissus incisa s.l. “white socks” individuals observed with material in their guts during the present study. Solmissus incisa morphotype “White Socks” Individual 1 Individual 2 Individual 3 Bell shape Disk-like, concave Disk-like, concave Disk-like, concave Height of bell/bell diameter 0.15 0.17 0.13 Number of tentacles 24 22 24 Tentacle length/bell diameter 1.26 1.45 1.10 Colour of tentacles tipped with white tipped with white tipped with white White portion/tentacle length 31–35% 24–39% 28–41% Shape of stomach pouches Pentagonal Pentagonal Pentagonal length of stomach pouch/bell diameter 0.20 0.23 0.14 stomach pouch length /width at widest point 1.25 1.30 ̶ stomach pouch length /width at base 1.66 2.16 ̶ width at base/space between 7.0 3.5 ̶ adjacent stomach pouches Bell height: lappet length: velum length 10 : 7.5 : 7.5 10 : 10 : 7.5 11.3 : 10 : 7.5 Gonads globular, opposed pairs globular, opposed pairs globular, opposed pairs Depth 573 m 614 m 619 m Dive Locality Kaikata Seamount Outside the Sumisu Caldera Outside the Sumisu Caldera Date March 7, 2002 March 9, 2002 March 9, 2002 Latitude, Longitude 26.70 N, 141.11 E 31.48 N, 140.15 E 31.48 N, 140.15 E Temperature 9.71°C 9.64°C 9.54°C Salinity 34.27 34.32 34.33 Oxygen 3.3 mL/L 2.7 mL/L 2.7 mL/L Filename HPD0081-20020307-115539- HPD0083-20020309-151503- HPD0083-20020309-151122- SHHD-Front-1920x1080_ SHHD-Front-1920x1080_ SHHD-Front-1920x1080_ HDCAM-1of3-TC115553916 HDCAM-1of2-TC15150316 HDCAM-1of2-TC15112201 to120221320DF-NoImpose- to15184114DF-Noimpose- to15144910DF-Noimpose- Solmissus_incisa_s.l.-Mitsuko_ Solmissus_incisa_s.l.-Mitsuko_ Solmissus_incisa_s.l.-Mitsuko_ Hidaka-KAPPAKURAGE- Hidaka-KAPPAKURAGE- Hidaka-KAPPAKURAGE- eating_fish_573m_24T.mov eating_salp_614m_22T_SS1. eating_Narco_619m_24T_ mov SS1.mov four marginal tentacles with distal quarter to two fifths of Results much stronger whitish colour than proximal length, pre- sumably caused by very high concentrations of nemato- Solmissus Haeckel, 1879 cysts. Gonads with a single egg, thereby being spherical Diagnosis or oval in shape when mature, in 2–4 oppositional pairs, Narcomedusae with perradial and undivided stomach placed opposite each other on the margins of each perra- pouches; with tentacles leaving umbrella opposite centre of dial manubrial pouch. each stomach pouch, equal in number to that of pouches; pouches not extending beyond points of origin of tentacles; Comments without peripheral canal system; without otoporpae. The stomach contents of these individuals were a fish belonging to the Order Stomiiformes [Maurolicinae or Description of present material (n=3) Phosichthyidae] (Fig. 1A, B), salps (Fig. 1C–E) and a nar- Solmissus incisa s.l. of 22–24 tentacles type (S. incisa comedusa (Fig. 1F), which were completely ingested. The T22–24) with flattened, disc-like exumbrella, concave at salps were not identifiable to a lower taxa, but it is highly apex. Mesoglea fairly thick but transparent and relatively possible that they were the blastozooids of Salpa sp. (J. soft. No visible nematocyst patches on surface of exum- Nishikawa, personal communication). The ingested narco- brella. Velum well-developed. Manubrium large, circular. medusa was one-third of the diameter of the Solmissus Twenty-two to twenty-four perradial manubrial pouches of individual that had ingested it, and had a rigid, biconvex rectangular to pentagonal shape. Twenty-two to twenty- umbrella of a width 3.3 times as wide as high. It had thick Solmissus also ingests fish 43 Fig. 1. Solmissus incisa T22–24 individuals with their stomach contents. Individual 1 with 24 tentacles observed at 573 m with an ingested fish (A) with a close-up of the stomach contents (B). Individual 2 with 22 tentacles observed at 614 m with ingested salps (C) with a close-up of the stomach contents and manubrial pouches (D) and in lateral view (E). Individual 3 with 24 tentacles observed at 619 m with an ingested narcomedusa (F). gelatinous swellings where the stomach pouches must have Discussion been situated before they were digested, and had 10 ten- tacles. Apart from the lower tentacle number it resembled Currently the genus Solmissus comprises six species, Solmissus marshalli Agassiz & Mayer, 1902 very closely. with three species [S. albescens (Gegenbaur, 1857), S. in- 44 M. HIDAKA-UMETSU & D. J. LINDSAY cisa (Fewkes, 1886) and S. marshalli] being widely accept- have small clusters of nematocysts on their exumbrellar ed and a further two [S. faberi Haeckel, 1879, S. bleekii surface” though Kramp (1957) explicitly states that the ex- Haeckel, 1879] generally considered doubtful. Solmissus umbrella of the former is smooth. The medusa in Raskoff's atlantica Zamponi, 1983 has been determined not to be a (2002) Fig. 2A has obvious nematocyst patches on the sur- valid species by Genzano et al. (2008), rather being pro- face of the exumbrella but the morphology of the stomach visionally assignable to the Aeginidae sensu lato and the pouches and bell shape are not reminiscent of S. marshalli, present authors concur. The description of S. albescens presumably indicating he considered it a small specimen has been emended by Gili et al. (1998), but the taxonomy of S. incisa s.l. The medusa in Raskoff's (2002) Fig. 3A–E of the remaining species is a quagmire of confusion. The seems to have both 16 tentacles and a thick and rigid ex- species S. marshalli was described based on a single indi- umbrella, suggesting that it is indeed S. marshalli, and vidual with a thick and rigid bell of 60 mm diameter and although the resolution is sub-optimal it does appear that a tentacle/stomach pouch number of 14 (Agassiz & Mayer there may be nematocyst patches scattered over the bell 1902). The widths of the distal portions of the stomach margin. In any case, until a thorough revision of the ge- pouches were figured to be 2–3 times as wide as the wid- nus is undertaken it seems prudent that photographs and/or est spaces between the pouches and the length of each descriptions of the material in question be provided when stomach pouch to be 1.3–1.6 times as long as its width at reporting on the ecology of Solmissus species, as has been its widest (Plate 5, Fig.