Janiralata plana, Ohta & Takano & Kojima & Narimatsu, 2023

Janiralata plana View in CoL sp. nov.

( Figs. 3A, B View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 )

Type materials were deposited in the National Museum of Nature and Science, Tokyo (NSMT). The extracted DNA were stored at AORI, The University of Tokyo.

Material examined: Holotype: male, 5.3 mm, NSMT-Cr 31499 , off Otsuchi, Iwate, Honshu Island, Japan (39º19.49’–20.81’N, 142º35.71’–35.76’E; 1,337– 1,306 m: R/V Shinsei-maru cruise KS-20-15, station OT-1320) (type locality), sorted from soft sediment, collected by 3 m beam trawl on 2 October 2020. Paratypes: male, 6.4 mm body length, NSMT-Cr 31501, off Otsuchi, Iwate, Honshu Island, Japan (39º20.97’–19.96’N, 142º42.05’–41.73’E; 1,559 – 1,557 m: R / V Shinsei-maru cruise KS-20-15, station OT-1550-2) attached to aboral side of starfish Crossaster borealis , collected by 3 m beam trawl on 1 October 2020; female, 5.9 mm, NSMT-Cr 31500, from type locality, attached to aboral side of C. borealis . See Supplementary material Table S1 View Table 1 for voucher specimens.

RESULTS

Six Janiralata individuals were found attached to an unidentified sea anemone ( Hormathiidae ) and ten to the solasterid starfish Crossaster borealis . Two additional individuals were found in mud sediment without hosts. These may have been crawling freely on the bottom or fallen off hosts during sampling.

Genetic analysis

Diagnosis: Head without rostrum and anterolateral projection. Eye length not exceed half of head length. Body flattened, length ~3× as wide, translucent pale yellow, without brown chromatophores, dorsal surface smooth. Coxal plates smooth, visible on dorsal view. Pereopod 1 slightly shorter than posterior pereopods, propodus with 9 serrations. Pleotelson distal margin rounded. Male pleopod 1 apex curved medially, without conical knobs. Pleopod 3 exopod without plumose setae. Uropod biramous, endopod slightly longer than exopod.

Partial nucleotide sequences of the COI gene were successfully obtained from 16 individuals; the obtained sequences varied among the specimens from 505 to 785 bp presumably due to the preservation conditions. A 505-bp matrix was therefore offered for inferring the haplotype network ( Fig. 2 View Figure 2 ). Eight haplotypes were identified in total, which were deposited to the DDBJ/EMBL/GenBank databases with accession numbers LC773543–LC773558. The maximum uncorrected p -distance was 0.8% among the newly obtained sequences. Three haplotypes were shared by individuals from two neighboring sites ( Fig. 1 View Figure 1 ). No genetic trends were found among the individuals from the starfish, sea anemone, and bottom sediment.

The individuals were identified as a single species based on molecular and morphological data, and hereby described as Janiralata plana sp. nov.

Taxonomy

Family Janiridae G.O. Sars, 1897

Description of holotype and paratype males: Body ( Fig. 4A View Figure 4 ) flattened, length ~3× as wide, translucent pale yellow, without brown chromatophores, dorsal surface smooth. Pereonites 2–4 coxae bilobed, all coxae similar in size; all pereonites coxae visible dorsally. All pereonites without lateral or anterolateral processes. Pleotelson rounded, length ~0.9× as wide, distal margin slightly pointed, without any processes; lateral margins with numerous fine setae.

Cephalon slightly narrower than pereonite 1, trapezoidal, length ~1/2× as width; frontal margin slightly convex, without rostrum; anterolateral projections small, not acute. Eyes on dorsal side, small, dark brown, anterolaterally directed.

Antennulae ( Fig. 5B, C View Figure 5 ): article 1 conical with distal fine, simple seta; article 2 slightly shorter than article 1, distally with 2 long simple and 2 long bloom setae; article 3 as long as article 2, with 3 long distal setae; with 18 flagellar articles, each article excluding last 2 with short, simple distal seta and last two articles with an aesthetasc.

Antenna ( Fig. 4B, C View Figure 4 ): article 1 broad, with a distolateral seta; article 2 shorter than article 1, without setae; article 3 trapezoidal, with lateral simple and 2 distal unequal bifid setae, conspicuous scale with distal simple and 2 unequal bifid setae; article 4 shorter than article 3, with 2 distal setae; article 5 length ~6× as article 4, with 2 long lateral and 2 distal setae; article 6 longest, length ~1.2× as article 5, with 3 distal setae; flagellum multiarticulate, length ~3× as article 6, article 1 longest, last 20 articles with a few black chromatophores.

Left mandible ( Fig. 5G View Figure 5 ): palp article 1 without setae; article 2 with 2 long setulate setae and 3 short setae distolaterally; article 3 as long as article 1, with row of many short robust setae ventrally and row of many fine setae distally; incisor with 4 cusps; lacinia mobilis with 4 teeth, spine row with 7 robust setulate setae.

Right mandible ( Fig. 5H View Figure 5 ): palp article 1 with 3 long setae distally; article 2 with row of 5 simple setae distolaterally; article 3 with row of many simple setae laterally and 6 simple setae distally; incisor with 4 cusps, spine row with 9 robust setulate setae; molar process with some setae distally.

Maxillula ( Fig. 5E View Figure 5 ): inner lobe with 8 robust setae distally; outer lobe with 8 robust denticulate setae distally and many fine setae laterally and medially.

Maxilla ( Fig. 5F View Figure 5 ): inner lobe with 1 setulate robust seta and many fine setae distally, medially; 2 outer lobes each with 3 robust setae apically and many fine setae medially.

Maxilliped ( Fig. 5A View Figure 5 ): endite width subequal to palp, with 8 serrate and some simple setae distally, 3 coupling hooks medially. Palp with 5 articles, article 1 with a distolateral simple seta; article 2 with distolateral, some lateral, 2 medial, 4 distomesial simple setae; article 3 distally broad, with 2 distolateral and 14 distomesial simple setae; article 4 narrow, with 8 distal simple setae; article 5 as wide as article 4, with 6 distal and some lateral simple setae. Exopod triangular, slightly tapered distally.

Pereopod 1 ( Fig. 4D, E, F View Figure 4 ): basis length 2× as wide with a distal unequal bifid seta; ischium length ~2/3× as basis with a dorsolateral unequal bifid seta; merus triangular, long distally, with 2 simple distal setae and mediolateral and 2 mediodistal setae; carpus long, broadened at center, length equal to basis, mediolateral with ~20 robust short setae, 2 dorsal simple and 3 distal simple setae; propodus with a row of 9 subequal serrations on proximal third of ventral margin, slightly shorter than carpus, length 6× as wide, 2 dorsolateral and some mediolateral simple setae, distal margin with a unequal bifid seta and 2 simple thin setae of different length, medial margin with a stout and 2 simple thin setae; dactylus short, with 2 claws and 5 simple fine and a bloom setae.

Pereopod 2 ( Fig. 4G View Figure 4 ): basis resemble pereopod 1, with long dorsolateral unequal bifid seta and 2 spiniform mediolateral setae; ischium longer than pereopod 1, with long dorsolateral unequal bifid seta; merus resembles to pereopod 1; carpus long, not broadened at center, length 7× as wide, with 3 mediolateral and 2 mesial and dorsolateral short unequal bifid setae and 3 simple distal setae of different length; propodus long, length 10× as wide, some dorsolateral simple and 5 mediolateral unequal bifid setae; dactylus with 2 claws. Pereopods 2–7 all resemble each other but pereopods 5–7 (pereopod 6 figured; Fig 5D View Figure 5 ) propodus with a dorsolateral bloom seta.

Pleopod 1 ( Fig. 6A View Figure 6 ): distal tips laterally expanded, with projecting subtriangular lateral lobes tapered laterally, slightly curved anteriorly; distal margins with pair of small protrusions.

Pleopod 2 ( Fig. 6B View Figure 6 ): protopod length ~2× as width, with 7 distal setae; endopod slightly wider than appendix masculina, appendix masculina robust, elongated, surpassing distal margin of protopod; exopod distalmedially placed on protopod, no surpassing distal margin of protopod.

Pleopod 3 ( Fig. 6C View Figure 6 ): endopod ~1.6× as protopod, with 3 distal plumose setae; exopod with 2 articles, article 1 ~twice as article 2, with many lateral fine short setae; article 2 with many lateral fine setae and ~17 distomedial and medial simple short setae.

Pleopod 4 ( Fig. 6D View Figure 6 ): endopod slightly curved and oval, ~3× as width; exopod slightly narrower than endopod.

Pleopod 5 ( Fig. 6E View Figure 6 ): semicircular, ~2× as long as width.

Uropod ( Fig. 4H View Figure 4 ): length ~0.7× as pleotelson, bearing numerous long simple setae; biramous; sympod rectangular, elongated; rami tapered, slightly longer than sympod, endopod slightly longer than exopod.

Description of paratype female: Similar to holotype male. Pereonites laterally and dorsally smooth. Operculum ( Fig. 6F View Figure 6 ) distally concave; length as long as maximum width, marginally setose.

Etymology: The species name plana, Latin for “flat” or “plain”. It was appropriately named after the characteristic feature of the species: flattened and having no body projections or setae.

Remarks: The new species is assigned to the genus Janiralata based on the combination of the following characters: the absence of anterolateral and distolateral projections on the head and pleotelson respectively, smooth surface and leteral margins of the body, antennula article 1 slightly curved dorsally, and inward curved male pleopod 1 without conical knobs.

Wilson & Wägele (1994) divided the species of Janiralata into four morphological groups and the new species shows the following characters of the “ rajata -group”: reduced rostrum and reduced anterolateral projection of the cephalon, a distally-rounded pleotelson and pleopod 3 exopod without plumose setae. According to Wilson & Wägele (1994) and Kim & Yoon (2021), this group contains six species: J. koreaensis Jang, 1991 from Bijin Island, southern Korean Peninsula; J. microphthalma Kussakin, 1972 and J. modesta Mezhov, 1981 from Urup Island, Kuril Islands; J. obliterata Kussakin, 1972 from a seamount in the central Pacific; J. rajata Menzies, 1951 from northern California; and J. sagamiensis Shimomura, 2006 from Sagami Bay, Japan. Janiralata plana sp. nov. can be distinguished from five of these species by the following: a remarkably long uropod ( vs. J. microphthalma and J. obliterata ); no anterolateral projection on the cephalon ( vs. J. modesta and J. sagamiensis ); and slightly small eye lobes, not reaching half of the cephalon ( vs. J. rajata ). Janiralata plana sp. nov. most closely resembles J. koreaensis but differs as follows: dorsal surface without dark brown pigments; antennula article 1 slightly curved dorsally; and male pleopod 1 apex curved medially with no conical knobs ( vs. J. koreaensis ). Moreover, the distributions of these two species differ geographically and bathymetrically. Janiralata koreaensis has only been collected in South Korea at 8–80.4 m depths ( Jang, 1991; Kang et al., 2019). In addition to the named taxa, four undescribed species have been reported from the Santa Maria Basin in the northeastern Pacific ( Wilson, 1997). Janiralata plana sp. nov. can be distinguished from these undescribed species by the following characteristics: a smooth head without brown chromatophores or cephalic anterolateral projections ( vs. Janiralata sp. A and B in Wilson (1997)); and small eye lobes, not reaching half of the cephalon ( vs. Janiralata sp. C and D in Wilson (1997)).