Janiralata plana sp. nov.

(Figs. 3A, B, 4, 5, 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 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). 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). 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) 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): 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): 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): 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): 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): 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): 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): 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): 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): 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) propodus with a dorsolateral bloom seta.

Pleopod 1 (Fig. 6A): 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): 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): 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): endopod slightly curved and oval, ~3× as width; exopod slightly narrower than endopod.

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

Uropod (Fig. 4H): 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) 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)).