Angursa seisuimaruae Fujimoto & Hansen 2019, sp. nov.

Angursa seisuimaruae sp. nov.

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Figs 6–7

Angursa sp. – Kimura et al. 2018: table 23.

Diagnosis

Angursa with club-shaped primary clavae longer than lateral cirri; pedestals of primary clavae and lateral cirri absent; D-shaped secondary clavae; three-lobed tertiary clavae; leg I sensory organs as subdivided spines; legs II and III sensory organs absent; leg IV sensory organs each as papilla enveloped in hemispherical cuticular sheath with short, apical spine; anal papillae absent; seminal receptacles open latero-ventrally with short, sinuous ducts.

Etymology

The specific epithet refers to the T/V Seisuimaru of Mie University.

Type material

Holotype

PACIFIC OCEAN • adult ♀; Northwestern Pacific, Japan, Sea of Kumano; between 33°59.5′ N, 136°56.7′ E and 33°59.7′ N, 136°56.7′ E; 768–796 m below sea level; 10 Nov. 2017; mounted in glycerol; Fujimoto leg.; KUZ Z2066.

Paratype

PACIFIC OCEAN • 1 adult ♀; same data as for holotype; KUZ Z2067.

Type locality

Sea of Kumano, Northwestern Pacific (between 33°59.5′ N, 136°56.7′ E and 33°59.7′ N, 136°56.7′ E; depth range, 768–796 m) (Kimura et al. 2018).

Description of holotype

Adult female with unarmoured, slender body (143 μm long; 35 μm wide between legs II and III) (Figs 6, 7A). Epicuticular pillars visible.

Cephalic region with unpaired median cirrus, paired internal cirri, paired external cirri, paired lateral cirri, paired primary clavae, paired secondary clavae, paired tertiary clavae, and mouth opening. Median cirrus (1 μm) positioned dorsally. Internal cirri (5 μm) inserted on anterior margin of body each consisting of scapus (2 μm) and distal flagellar part with blunt tip (2 μm). External cirri (9 μm) inserted ventrally each consisting of scapus (5 μm) and distal flagellar part with blunt tip (5 μm). Lateral cirri (4 μm) positioned dorso-laterally. Primary clavae (10 μm) positioned immediately ventral to lateral cirri and both organs inserted directly on body with no apparent pedestal (only very slight rise). Primary clavae club-shaped and distal half slightly bent posteriorly. Secondary clavae (Figs 6, 7B) present posterior to median cirrus as flat, D-shaped structures without epicuticular pillars. Tertiary clavae (Figs 6, 7C) indented around external cirri, giving impression of three-lobed structures (one lobe directed anteriorly, interior to external cirri; second lobe developed interior to first lobe; third lobe developed posterior to external cirri) without epicuticular pillars. Anteriorly directed mouth at antero-most position of body. Buccal apparatus dissolved and only pharyngeal bulb recognised (length 14 μm, width 11 μm).

Paired cirri E (18 μm) (Figs 6, 7D) as simple, tapering spines without recognisable annulation, inserted dorsally slightly anterior to leg IV.

Each leg consists of indistinct coxa, femur, indistinct tibia, and tarsus bearing four digits terminating in claws with two divergent points. Leg I sensory organ (10 μm) (Figs 6, 7E) present on femur as spine consisting of proximal portion and distal portion with blunt tip. Legs II and III lack sensory organs. Leg IV sensory organs (4 μm) (Figs 6, 7D) present at base of leg IV each as papilla enveloped in hemispherical cuticular sheath with short, apical spine. Internal digits have proximal pads and lack peduncles (Figs 6, 7E). External digits have arched peduncles at their base which never reach claws (Figs 6, 7E). Internal digits always longer than external digits and leg IV has longer digits than those of legs I–III (leg I, internal digits 9 μm/external digits 6 μm; leg II, 9/6; leg III, 10/6; leg IV, 13/7).

Rosette-like gonopore (4 μm in diameter) (Figs 6, 7F) situated 2 μm anterior to anus. Longitudinal cuticluar fold of anus reach dorsal side (Figs 6, 7D). Paired seminal receptacles (Figs 6, 7F) positioned near latero-ventral margin of body, at level slightly anterior to gonopore. Each seminal receptacle duct runs interiorly, antero-dorsally, and then postero-ventrally terminating in round vesicle.

Description of paratype

Cephalic region accidentally destroyed during cleaning of specimen before observation and mouth opening, buccal apparatus, median cirrus, secondary clavae, and tertiary clavae not recognized. Primary clava (11 μm) and scapi of internal, external, and lateral cirri recognized on torn cuticle. Presence of scapi suggests subdivision of lateral cirri as in the internal and external cirri. Gonopore and anus recognised before permanent preparation in lateral positioned body. Other characters confirm that of holotype (cirrus E, 17 μm; leg I sensory organ, 10 μm; leg IV sensory organ, 4 μm).

Remarks

Angursa seisuimaruae sp. nov. resembles A. abyssalis, A. clavifera, and A. capsula by the club-shaped primary clavae longer than the lateral cirri, the leg IV sensory organs in hemispherical shape, and the lack of the anal papillae (Renaud-Mornant 1981; Noda 1985; Bussau 1992). However, the new species is distinguished from all three species by its D-shaped secondary clavae and its three-lobed tertiary clavae (Noda 1985; Bussau 1992). Further, the new species’s seminal receptacle ducts are shorter than A. clavifera ’s spiral ones (Noda 1985).