(according to Hansen 1975). Anus dorsal. Unpaired dorsal appendages absent. Circum-oral (or post-oral) papillae present. Tentacles soft, pliable, and retractile.

Holotype : RSIO6017101, adult specimen, collection number: DY60-JL171-B01, 16.935°N, 134.911°E,12 January 2021, 2602 m; Paratype: RSIO3710601, adult specimen, collection number: DY37-JL106-B01, 13.017°N, 156.947°E, 1 May 2016, 2408 m.

RSIO590504, adult specimen, collection number: DY59-ROV05-B04, 16.916°N, 134.916°E, 20 July 2020, 2692 m; RSIO590506, adult specimen, collection number: DY59-ROV05-B06, 16.933°N, 134.916°E, 20 July 2020, 2453 m.

Body elongated and subcylindrical when fixed. Skin red with violet, thin, soft. No obvious large papillae arranged on dorsal surface. Some minute papillae, conical with tips, on the anterior dorsum. Brim narrow, thin, flattened. Mouth ventral, anus terminal. Eighteen tentacles; circum-oral papillae present. Dorsal ossicles include rods and primary crosses with four arms. Rods present in tentacles. Ossicles of ventrum not observed.

(RSIO6017101). Length was approximately 25 cm before preservation in 10% seawater formalin. Color violet in life (Fig. 2C); skin transparent, thin, soft, and gelatinous after fixing. Brim retracted less than 0.7 cm in width. Approximately nineteen pairs of dorsal papillae poorly developed, minute, closely placed in two bands along anterior dorsal radii. Another four single minute papillae on posterior dorsal edge. Approximately 28 pairs midventral tube feet arranged in two rows. Mouth ventral, with circum-oral papillae. Anus terminal, unguarded. Due to the contraction, tentacles could not be clearly observed. Few ossicles observed. Dorsal ossicles in the anterior body wall, consisting of primary crosses with spiny arms, and spinous rods (Fig. 4A–F). Rods approximately 400 μm long, arms of crosses approximately 200 μm long. Tentacles with rods, 400–500 μm long (Fig. 4G–J). Other body parts devoid of ossicles.

Figure 2. 

A, B Benthodytes jiaolongi sp. nov. (RSIO3710601, holotype) in situ on the seamount Weijia Guyot C specimen (RSIO6017101, paratype) in situ on the Kyushu-Palau Ridge D specimen (paratype) before preservation in 10% seawater formalin.

RSIO3710601. Specimen approximately 22 cm in length, 5 cm wide at maximum point. Color red-violet in situ at the seabed (Fig. 2A, B); pale violet at sea surface, with transparent skin; white color after preservation in 10% seawater formalin for 5 years. Paired dorsal papillae as present in holotype absent, minute papillae also not distinguished. Owing to long-term preservation, quantity of midventral tube feet could not be determined, but were arranged in two rows. Brim could not be distinguished. Mouth ventral, with circum-oral papillae, anus terminal. Eighteen tentacles retracted to stalk. Ossicles not observed.

Figure 3. 

Benthodytes jiaolongi sp. nov. A dorsal view B ventral view.

RSIO590504.Specimen approximately 22 cm in length before preservation in 10% seawater formalin. Color red-violet on deck, skin transparent; white color after preservation. During sampling, a piece of sponge was stuck in the ROV pump sampler, and the specimen was damaged by the sponge, meaning that the tentacles could not be determined and the dorsal tips could not be distinguished. Quantity of midventral tube feet could not be determined. Mouth ventral, anus terminal. Ossicles not observed.

RSIO590506. Specimen approximately 13 cm in length before preservation in 99% alcohol and heavily damaged. Color red-violet at sea surface, skin transparent. The specimen was stained with sponge as was RSIO590504 and many external characters could not be distinguished. Mouth ventral, anus terminal. Few rods observed on dorsal region (Fig. 4A-C). Rods approximately 400 μm, spine terminal. Ossicles from body wall not observed.

Figure 4. 

A–C scanning electron micrographs of dorsal body wall ossicles from Benthodytes jiaolongi sp. nov., RSIO590506 D–F dorsal body wall ossicles from Benthodytes jiaolongi sp. nov., RSIO6017101 G–J ossicles of tentacles.

The name is derived from the first Chinese HOV ‘Jiaolong’.

Benthodytes typica Théel, 1882 (by original designation).

Kyushu-Palau Ridge, tropical Western Pacific. Depth: 2453–2692 m.

Known from Weijia Guyot and Kyushu-Palau Ridge.

Hansen (1975) revised the genus Benthodytes and proposed that this genus, except Benthodytes superba Koehler & Vaney, 1905, could be divided into two distinct groups based on the ossicles and external morphology.

The first group was characterized by the regular crosses, ossicles with bipartite central apophysis and well-developed dorsal papillae. This group included five species: B. incerta Ludwig, 1894; B. lingua Perrier, 1896; B. valdiviae Hansen, 1975; B. sibogae Sluiter, 1901a and B. plana Hansen, 1975. Benthodytes sanguinolenta Théel, 1882 and B. typica Théel, 1882 formed the second group characterized by strongly reduced rod ossicles, and minute dorsal papillae.

Recently, five more species were identified: B. gosarsi Gebruk, 2008; B. wolffi Rogacheva & Cross in Rogacheva et al. 2009; B. violeta Martinez, SolísMarín & Penchaszadeh, 2014; B. manusensis Xiao et al., 2018; B. marianensis Li et al., 2018. They can be assigned to first group.

Benthodytes jiaolongi sp. nov. clearly belongs in the genus Benthodytes and is close to Benthodytes sanguinolenta Théel, 1882 and Benthodytes typica Théel, 1882, for the minute papillae and reduced rod ossicles.

Benthodytes typica was described by Théel in 1882 based on specimens collected by the Challenger Expedition. The original description indicated approximately eight, minute, retractile processes located on each of the dorsal ambulacra and unbranched spinose calcareous spicula scattered on the integument. Hansen (1975) re-examined B. typica and reported that the specimens showed considerable variation. Benthodytes papillifera Théel, 1882 was described based on 13 specimens taken from three Pacific Challenger stations. Théel (1882) described this species as being similar to B. sanguinolenta based on the tentacles and tube feet. Hansen (1975) re-examined specimens from each of the stations and proposed that the variation in B. papillifera represented the geographic variation of B. typica. In the original description of Benthodytes glutinosa Perrier, 1896, Perrier (1896) indicated that the differences from B. typica were the more elongated shape and the complete absence of dorsal papillae. Hansen (1975) considered this species to be a synonym of B. typica.

In general, the morphological features of B. typica can be summarized as follows: 3–7 pairs of minute papillae arranged on the dorsal surface and rods scattered on the body integument and tentacles. Benthodytes jiaolongi sp. nov. differs from B. typica in its arrangement and number of dorsal papillae and composition of ossicles. The dorsal minute papillae of Benthodytes jiaolongi sp. nov. are arranged in two bands along the anterior dorsal ambulacra, and those of B. typica are arranged in a row with 3–7 pairs of papillae. The rods of B. jiaolongi sp. nov. are present in the tentacles and dorsum, and the primary crosses are only present in the dorsum. However, B. typica only present rods scattered on the ventrum, dorsum and tentacles.

The characteristics of B. sanguinolenta as described by Théel (1882) included the many minute retractile processes scattered on the dorsal surface; the form of calcareous deposits could not be distinguished. According to a re-examination by Hansen (1975), the dorsal minute papillae were arranged in two radial bands and the rods were only present on the midventral tube feet and tentacle discs of specimens from station 663. Rogacheva et al. (2009) recorded B. sanguinolenta and the main characteristics can be described as: minute dorsal papillae arranged in two bands or between the two bands; approximately 1–4 papillae placed in a band, narrowing to one or two papillae at the posterior end; ossicles were not found. The differences in the characteristics between the new species B. jiaolongi sp. nov. and B. sanguinolenta can be listed as follows: (1) Dorsal papillae of B. sanguinolenta are arranged in two bands, whereas those of the new species were arranged in two rows on the anterior dorsal ambulacra; (2) Ossicles of the new species were only present in the tentacles and in the dorsum. Rods are present in the tentacles and dorsum, and primary crosses are only present in the dorsum; whereas the rods are only present in tube feet and in the tentacles in B. sanguinolenta.

Catalog number: RSIO6018004, adult specimen, collection number: DY60-JL180-B04, 13.569°N, 134.352°E, 25 January 2021, 2469 m; Catalog number: RSIO6017005, adult specimen, collection number: DY60-JL170-B05, 12.079°N, 134.860°E, 8 January 2021, 2361 m.

RSIO6018004. Specimen resembles a barbell after collection, approximately 20 cm in length before preservation 10% seawater formalin (Fig. 5C, D). Before preservation, height of appendage was approximately 50 mm, and width at base approximately 30 mm (Fig. 5C, D). Dorsal skin transparent with brownish red color on seabed and dark brown on deck. Warts covering dorsal skin and appendage; giant ossicles in warts visible (Fig. 5E, F). Approximately 30 pairs of degenerated tube feet arranged in two rows along middle of ventrum. Sixteen tentacles forming a circle. Brim broad and covered with warts on dorsum.

Figure 5. 

A, B Psychropotes verrucicaudatus Xiao, Gong, Kou & Li, 2019 (RSIO6018004) in situ C, D specimen (RSIO6018004) before preservation E, F red arrows point to the giant ossicles, specimen (RSIO6018004) after preservation in 10% seawater formalin. Scale bars: 5 cm (A–E); 1 cm (F).

A giant cross with four arms visible in each wart. Arms 800–1000 μm in length, and maximum width between large arms approximately 500 μm. Arm flexion approximately 250 / 400 μm (Fig. 6A–D). Height of central rudimentary apophyses approximately 200–300 μm. Ventral ossicles divided into two types: primary cross with spiny arms (Fig. 8A, C) and cross with three arms (Fig. 7B), length of arm approximately 200 μm. Primary crosses with spinous arms in dorsum (Fig. 7D–F) and brim (Fig. 7H–J); arms up to 200 μm in length. Dorsal ossicles with spinous rod, 170 μm in length (Fig. 7G), and large primary crosses with spiny arms in brim (Fig. 7K). Tentacles with rods with irregular shape (Fig. 7L–R). Large rod with two apophyses at the end, approximately 900–1000 μm in length (Fig. 7L-M); small rod with apophyses in middle area was approximately 200 μm in length (Fig. 7N). Other rods with spiny arms, 500–800 μm in length (Fig. 7O-R).

Figure 6. 

Psychropotes verrucicaudatus A–D giant ossicles from the dorsal warts.

RSIO6017005. Specimen approximately 18 cm in length, height of appendage approximately 40 mm, and width at base approximately 20 mm. Mouth and anus ventral. Skin transparent, light brown color. Dorsal skin and appendage covered with warts; warts also present in dorsum of brim. Giant ossicles visible in warts. Tentacles damaged, more than 12. Ossicles as in RSIO6018004.

Figure 7. 

Psychropotes verrucicaudatus ossicle from A–C ventral body wall D–G dorsal body wall H–K brim L–R tentacle.

Jiaolong Seamount, South China Sea, Western Pacific Ocean, sandy bottom, depth 3615 m.

Psychropotes longicauda Théel, 1882.

Known from Jiaolong Seamount of South China Sea and Kyushu-Palau Ridge.

The specimens were clearly a new record for the South China Sea, as the species was previously known only from the Jiaolong seamount. The present specimens differed from those of Xiao et al. (2019) in external morphology and the ossicles. Due to the bad preservation, Xiao et al. (2019) could not observe the ossicle assemblage of the warts, which was possible in the specimens here under study.

The intraspecific differences can be listed as follows: (1) In the present specimens, the skin was transparent and the color was darker than that of the type specimen; (2) The width of the appendage at the base was also larger than that of the type specimen; (3) The length of the primary crossing arms distributed in the dorsum, ventrum, and brim was longer than that of the type specimen. Furthermore, the spinous rod of the dorsal ossicles was not present in the type specimen, and the ventral body wall of the specimens did not possess the tripartite ossicles of the type specimens; and (4) Most of the ossicles of the tentacles in our specimens were the same as those of type specimen, but longer.