Gyorome guttatum gen. et, 2024

Komeda, Sota, Ohtsuka, Susumu & Huys, Rony, 2024, A new genus and species of oceanic planktonic Tisbidae (Crustacea, Copepoda, Harpacticoida) with enlarged modified eyes, ZooKeys 1191, pp. 307-338 : 307

publication ID	https://dx.doi.org/10.3897/zookeys.1191.114974
publication LSID	lsid:zoobank.org:pub:97EA749E-1CE0-4299-86FE-F7F107705759
persistent identifier	https://treatment.plazi.org/id/20C65F2B-C974-40F9-B6E8-E7167EB00802
taxon LSID	lsid:zoobank.org:act:20C65F2B-C974-40F9-B6E8-E7167EB00802
treatment provided by	ZooKeys by Pensoft
scientific name	Gyorome guttatum gen. et
status	sp. nov.

Treatment

Gyorome guttatum gen. et sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Type locality.

Japan, Kuroshio region (Off Mie Prefecture, 33°10'N, 136°00'E), epi- or mesopelagic zone (0-935 m depth).

Type material.

Holotype: Undissected ♀ (1.80 mm) in vial (NSMT-Cr 31562). Allotype: ♂ (1.47 mm), dissected prosome, urosome and appendages mounted on glass slide (NSMT-Cr 31563). Paratypes: One dissected ♀ (1.77 mm) mounted on glass slide (NSMT-Cr 31564), one undissected ♀ (1.64 mm) preserved in 10% neutralized formalin-seawater solution in vial (NSMT-Cr 31565).

Description of adult female.

Total body length ranging from 1.64-1.80 mm (n = 3). Habitus (Figs 1 View Figure 1 , 2A, B View Figure 2 ) cyclopiform and yellowish. Prosome (Fig. 2A, B View Figure 2 ) significantly expanded bilaterally, ovoid in dorsal aspect producing vaulted appearance; integument of cephalothorax (except anterior portion) and somites bearing legs 2-4 with dense pattern of minute surface denticles (Fig. 2A View Figure 2 ). Cephalosome completely fused to first pedigerous somite, forming cephalothorax; ventral surface between maxilliped and leg 1 with distinct protuberance; posterodorsal margin with semicircular lobate extension covering anterior third of leg 2-bearing somite. Anterior part of cephalosome with middorsal pair of baculiform ocelli (BO in Fig. 2A, B View Figure 2 ) and one pair of globular organs (GO in Fig. 2A, B View Figure 2 ) each surrounded by thin semi-parabolic plate (SP in Fig. 2A, B View Figure 2 ) either side of baculiform ocelli; lipid droplets (LD in Fig. 2B View Figure 2 ) filling up space between and posterior to semi-parabolic plates; ovaries (OV in Fig. 2B View Figure 2 ) occupying larger part of posterior half of cephalothorax. Rostrum (Fig. 2C View Figure 2 ) small and triangular, pointing downwards; labrum (LB in Fig. 2D View Figure 2 ) a rounded lobe with spinules around distal margin; paragnaths (PG in Fig. 2D View Figure 2 ) represented by semicircular lobes fringed with setulae posteriorly and laterally.

Pedigerous somites bearing legs 2-4 completely separated (Fig. 2A, B View Figure 2 ); with well-developed pleurotergites, gradually decreasing in width; pleural areas of somites bearing legs 3 and 4 protruding posteriorly.

Urosome (Fig. 3A, B View Figure 3 ) cylindrical, comprising fifth pedigerous somite, genital double-somite, and three free abdominal somites; all somites with dense pattern of minute surface denticles (Fig. 2A View Figure 2 ). Leg 5-bearing somite with lateral setular tufts in anterior half. Original segmentation of genital double-somite marked by transverse suture and accompanying spinules dorsally and dorsolaterally; posterior margin with spinules all around; copulatory pore small, located midventrally, immediately posterior to genital slit; copulatory duct well developed, with slight bilateral constriction halfway down its length. Genital double-somite and free abdominal somites with numerous minute tubercles laterally; fourth and fifth urosomites with continuous row of spinules around posterior margin; anal somite with setulae posteromedially and with paired rows of spinules near bases of caudal rami.

Caudal ramus (Fig. 3C, D View Figure 3 ) ~ 3.3 × as long as wide (measured in dorsal aspect); with seven setae, setae I-III and VII slender and naked, setae IV-V broken, represented in all specimens by short basal parts, setae VI slender and pinnate; seta I longer than caudal ramus, originating laterally in proximal third of ramus; seta II arising from outer distal corner; bases of setae IV and V positioned slightly ventral to that of seta VI; seta VI long (Fig. 3A, B View Figure 3 ), ~ 2.5 × length of ramus length; seta VII located dorsally near inner margin at ~ 70% of ramus length; dorsal posterior margin of ramus with two elongate, branching tube-pores (inner one distinctly longer than outer one), covering bases of setae III-VI; ornamentation consisting of spinules on ventral surface of ramus and around bases of setae I-III and, to a lesser extent, VII.

Antennule (Fig. 4A View Figure 4 ) 8-segmented, ~ 0.25 × as long as body length; armature as follows: 1-(1), 2-(15), 3-(4), 4-(3 + ae), 5-(2), 6-(3), 7-(1), 8-(5); all setae naked; segment 1 with inner spinules; aesthetasc on segment 4 well-developed and 0.8 × as long as antennule; segments 7 and 8 incompletely fused, original segmentation indicated by transverse surface suture.

Antenna (Fig. 4B, B View Figure 4 ') without ornamentation on coxa. Basis unarmed, with setules on posterior surface. Endopod 2-segmented; proximal segment unarmed, with setules along abexopodal margin; distal segment with one minute and two well developed elements laterally and six setae apically, inner margin with short spinules proximally and outer margin with longer spinules in proximal half. Exopod 4-segmented; segments 1-3 with one lateral seta; segment 4 with three apical setae and spinules along inner and outer margins.

Mandible (Fig. 4C View Figure 4 ). Gnathobase with three well developed bicuspid teeth, three smaller teeth with terminal setular tuft, one hirsute dorsal seta, and transverse row of fine, densely arranged setules. Basis unarmed. Endopod unsegmented, with two proximal setae along inner margin and four distal setae; outer margin with row of setules. Exopod unsegmented, with one inner and two distal setae.

Maxillule (Fig. 4D View Figure 4 ) 3-segmented, comprising praecoxa, endopod, and compound segment representing fused coxa, basis and exopod. Praecoxal arthrite with two naked setae on anterior surface; medial margin with one plumose seta; distal margin with two naked and three pinnate spines (fused at base to arthrite). Compound segment with few spinules along inner margin; coxa represented by subcylindrical endite with two setae; basal endites with three setae; exopod completely incorporated in segment, represented by single seta. Endopod distinct, with two setae.

Maxilla (Fig. 4E View Figure 4 ) 2-segmented, comprising syncoxa and allobasis. Syncoxa with setules along outer margin; medial margin with proximal protuberance bearing spinular row; coxal endite represented by small process with one plumose apical seta. Allobasis produced into curved claw with fine pinnules along outer margin and short plumose seta just over halfway claw length.

Maxilliped (Fig. 4F View Figure 4 ) 3-segmented, comprising syncoxa, basis and endopod. Syncoxa small, articulating with subcylindrical pedestal bearing long spinules at outer distal corner; with few spinules along medial margin. Basis elongate, ~ 3.5 × as long as maximum width; unarmed; medial margin slightly expanded, with sparse long spinules in middle third and shorter spinules further distally; outer margin with two groups of long spinules as figured. Endopod small, subrectangular; outer margin with one unipinnate seta; distal margin with long, slender claw accompanied at base by plumose seta; claw with two closely set spinules halfway the inner margin.

Legs 1-4 (Fig. 5A-H View Figure 5 ) with large coxa, narrow basis and 3-segmented rami; without minute surface denticles. Coxa with several spinule rows along outer margin (particularly P2-P4) as figured. Basis with short spine (leg 1) or long naked seta (legs 2-4) on outer margin; inner lobate expansion with numerous long and/or short setules/spinules. Endopod longer (leg 1) or distinctly shorter (legs 2-4) than exopod.

Leg 1 (Fig. 5A, B View Figure 5 ). Basis with long inner spine, extending to middle of enp-2, bipinnate except for plumose proximal quarter; distal margin with anterior spinules near articulation with endopod. Exopodal segments with spinules along outer margins; exp-2 not markedly longer than other segments, with setules along inner margin; outer spines without spinular combs. Endopod indistinctly 3-segmented with transverse surface suture marking original segmentation between enp-2 and -3; outer margins of all segments with spinules, additional spinules along inner margins of enp-1 and -2; enp-1 expanded in distal half forming lobate extension along medial margin; enp-3 small.

Legs 2-4 (Fig. 5C-H View Figure 5 ). Exp-2 markedly shorter than proximal and distal segments. Exopodal spines more robust than in P1. Spinular ornamentation present along outer margins of all exopodal and endopodal segments, and along inner margin of exp-1; few spinules also discernible along inner margin of exp-2. Posterior surface of P3-P4 exp-3, P2 enp-1-3, P3 enp-2 and P4 enp-2-3 with additional spinules. Armature formula as for genus.

Leg 5 (Fig. 5I View Figure 5 ) 2-segmented, comprising baseoendopod and 1-segmented exopod. Baseoendopod apparently fused basally to somite; endopodal lobe obsolete, armature represented by one very long seta (twice length of exopod); outer basal seta very long and naked. Exopod elongate, gradually widening towards distal margin; ~ 2.8 × as long as maximum width; with setules along outer margin; armature consisting of one inner, one outer and two terminal setae (all elements sparsely bipinnate); small apical tubercle discernible between outer and outer terminal setae.

Sixth pair of legs (P6 in Fig. 3B View Figure 3 ) fused medially, forming common plate closing off genital slit; each leg represented by one long outer and one short inner setae. Egg-sac not observed.

Description of adult male.

Total body length 1.47 mm (n = 1). Sexual dimorphism in prosomal ornamentation, antennule, maxilliped, P2 endopod, P5, P6 and urosomal segmentation.

Prosome resembling that of female except for denticles covering dorsal surface of cephalothorax and pedigerous somites much denser and middorsal protrusion around posterior margin of cephalothorax not expressed (Fig. 6A, B View Figure 6 ). Urosome (Fig. 6C, D View Figure 6 ) 6-segmented; denticles covering surface sparser than on prosome; spermatophore located in left half of genital somite; caudal ramus similar to that of female.

Antennule (Fig. 7A, A View Figure 7 ') 8-segmented, ~ 0.4 × as long as body length; armature as follows: 1-(1), 2-(11), 3-(9), 4-(6 + ae), 5-(1), 6-(0), 7-(2), 8-(7 + ae); segment 1 with spinular pattern on ventral surface; segment 6 with spinules; geniculation between segments 6 and 7; terminal portion of segment 8 digitiform and slowly curved.

Maxilliped (Fig. 7B View Figure 7 ) 4-segmented; palmar margin of basis with lobate spinular expansion in distal third; medial margin of endopod produced into triangular unguiform projection.

Legs 1-4 similar to female condition except for inner basal spine of leg 1 without setulae or spinules (Fig. 7C View Figure 7 ) and inner seta of proximal endopodal segment of leg 2 (Fig. 7D View Figure 7 ) displaying pinnate ornamentation along distal half of outer margin (instead of plumose in female).

Leg 5 (Fig. 7E View Figure 7 ) 2-segmented as in female; endopodal seta much shorter, only ~ one-third the length of exopod; exopod ~ 3.1 × as long as maximum width; outer margin with spinules.

Sixth pair of legs (P6 in Fig. 6D View Figure 6 ) symmetrical, each represented by ovoid plate closing off genital aperture and bearing three naked, well developed setae.

Etymology.

The specific name is derived from the Latin Gyorome guttatum meaning spotted or speckled and alludes to the dense denticular ornamentation on the male prosome (Fig. 6A, B View Figure 6 ).