Segonzackomaius sursus Kou, Chan & Li, 2025, sp. nov.
Creators: name: Kou, Qi
name: Chan, Tin-Yam
name: Li, Xinzheng
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Nematocarcinidae
Segonzackomaius
Segonzackomaius sursus

description: Segonzackomaius sursus sp. nov.
urn:lsid:zoobank.org:act: F0447E47-D959-4EF3-A9E3-EA3F337C5C9F
(Figs. 1–5)
Segonzackomaius altus — Burukovsky, 2013: 164–166, figs. 1B, 2. [Not Segonzackomaius altus (Spence Bate, 1888)]
Material examined. Holotype. Female (pcl 36.0 mm), the Philippine Basin, RV ‘ Marine Geology 9’, stn DX2, 16°25’42”N, 134°55’25” E, ~ 3,300 m, bottom trawl, 16 September 2023, MBM 304655.
Other specimens. Taiwan: 1 male (pcl 29.0 mm), 2 females (pcl 22.5, 24.5 mm), TAIWAN 2008, stn CP 413, 22°15’4” N, 121°54’59” E, 4412–4446 m, French beam trawl, 12 June 2008, NTOU M01677.
Etymology. From Latin sursum, meaning upwards, referring to the upwards recurved rostrum of the new species.
Diagnosis. Rostrum ascending, almost reaching distal margin of antennal scale, about 0.65 times of carapace length; dorsal margin armed with 5–9 fixed teeth; ventral margin armed with 6–8 fixed teeth in distal half. Carapace armed with 9–11 small, movable teeth on post-rostral ridge; suborbital angle and pterygostomial angle subacute. Pleon with third somite tergite produced posteromesially; fifth pleuron with posteroventral angle subacute, inner surface posteriorly with teardrop-shaped tubercle. Telson overreaching uropodal endopod; armed with 5 pairs of dorsolateral spinules.
Description of female holotype. Body (Fig. 1) robust; integument soft, not membranous, surface smooth.
Rostrum (Figs. 1, 3A, B) slender, ascending, about 30° against horizontal plane of dorsal carapace margin, almost reaching distal margin of antennal scale, 0.65 of carapace length; dorsal margin armed with five small fixed teeth; ventral margin with six small fixed teeth, proximal half unarmed, fringed with two rows of long plumose setae; lateral surface with low blunt ridge confluent with orbital margin. Carapace (Figs. 1, 3A, B) with nine small movable post-rostral teeth, widely separated from posterior most rostral tooth, posterior most post-rostral tooth arising at anterior 0.14 carapace; post-rostral ridge low, extending to 0.40 of carapace; with distinct postorbital, cervical, post-cervical, hepatic, branchiocardiac grooves; cervical groove dorsally shallow; branchiocardiac groove not accompanied by sharply delineated ridge; orbital margin evenly concave, without suborbital lobe; suborbital angle with minute antennal spine; pterygostomial angle with small, subacute spine; anterolateral margin oblique, slightly sinuous.
Thoracic sternum (Fig. 3C) with three bilobed prominences on sixth to eighth somites; lobes of anterior two prominences rounded, separated by deep concavity; lobes of prominence on eighth somite bluntly triangular.
Pleon (Fig. 1) without dorsal carina. Pleura of anterior four somites broadly rounded. Posterodorsal margin of third somite (Fig. 3D, E) strongly produced, reaching anterior fourth of fourth somite, rounded posteriorly. Fifth pleuron (Fig. 3D, F) with subacute posteroventral tooth on both sides, inner surface posteriorly with teardrop-shaped tubercle. Sixth somite (Fig. 3D, G) 1.96 times as long as fifth somite, 2.72 times as long as wide; posterolateral process and posteroventral angle blunt; ventral surface with single row of long setae on either side of midline, almost parallel; posteroventral spots lacking; pre-anal tooth acute, directed posteriorly.
Eye (Fig. 3B) subpyriform, almost reaching tip of stylocerite; cornea well pigmented, 1.80 times as wide as eye-stalk.
Antennular peduncle (Figs. 3B, 4A) stout, reaching midlength of antennal scale. First article 1.85 times as long as second article, with broad distolateral tooth; stylocerite reaching 0.85 of first article length, acuminate; distal two articles subequal in length, 1.40 times as long as wide; third segment with subtriangular distomesial process.
Antennal peduncle (Figs. 3B, 4B) with basicerite stout, armed with acute ventrolateral distal tooth, ventral surface smooth; carpocerite short, reaching tip of stylocerite. Antennal scale 0.62 of carapace length, 4.20 times as long as wide; lateral margin slightly sinuous; distolateral tooth small, not reaching tip of broadly rounded lamella.
Mouthparts typical of family. Mandible, maxillule, labium, maxilla, first maxilliped and second maxilliped as shown in Fig. 5.
Third maxilliped (Fig. 4C) slender, with endopod not reaching tip of antennal scale, consisting of four articles; ultimate article lanceolate, with several terminal spines, mesial surface with rows of dense stiff setae forming grooming apparatus; penultimate article 1.34 times as long as ultimate article; antepenultimate article flattened dorsoventrally, lateral margin straight, with row of three spinules on lateral surface; epipod present, shorter than coxa; exopod about 0.80 length of antepenultimate article of endopod.
First to fifth pereopods with ischium to dactylus missing. Epipod (Fig. 4D) present on first to fourth pereopods, strap-like, non-hooked, shorter than coxa; exopod (Fig. 4D) present on first to fourth pereopods, decreasing in length posteriorly, about 3.50 to 2.00 times as long as coxa.
First to fifth pleopods (Fig. 1) biramous; protopod stout, subrectangular, with longitudinal ridge on lateral surface. First pleopod (Fig. 4E) with endopod shorter and broader than exopod, 4.00 times as long as greatest width, tapering, without appendix interna; exopod 2.00 times as long as endopod. Second pleopod (Fig. 4F) with endopod and exopod lanceolate, subequal in length, 8.20 times as long as greatest width; endopod with well-developed appendix interna, 0.30 times as long as endopod, tip inflated, slightly curved, bearing cluster of small hooks. Third to fifth pleopods similar, exopod slightly longer and broader than endopod.
Uropod (Fig. 4G) with stout protopod terminating posterolaterally in blunt tooth; exopod longer and broader than endopod, with distinct suture; lateral margin of exopod slightly convex in proximal half, terminating in tiny, acute tooth, movable spine arising mesially, longer than posterolateral tooth; endopod lanceolate, reaching 0.85 of exopod length.
Telson (Fig. 4H) with apex broken off, remnant 5.22 times as long as greatest width, overreaching posterior margin of uropodal endopod, almost reaching posterior margin of uropodal exopod, gradually tapering posteriorly; dorsal surface slightly concave in anterior third, with five pairs of dorsolateral spinules at posterior two-thirds, spinules regularly spaced with each pair aligned symmetrically.
Branchial formula as follows.
Mxp1–Mxp3, first to third maxillipeds; P1–P5, first to fifth pereopods; Plb, pleurobranch; Arb, arthrobranch; Pod, podobranch; Ep, epipod; Ex, exopod; +, present; –, absent.
Distribution. Western Pacific from the Philippine Basin to southeastern Taiwan, at depths of 3,300 –4,446 m.
Coloration. Body and appendages crimson red, except antennal peduncle and base of antennal scale whitish. Cornea of eye with golden brown reflection, eyestalk dark red (Fig. 2C).
Remarks. Segonzackomaius sursus sp. nov. differs from the type species, S. burukovskyi (Komai & Segonzac, 2005) in the somewhat ascending rostrum (vs almost straight) armed with 5–9 dorsal teeth and 6–8 ventral teeth (vs with 3 dorsal teeth and 4 ventral teeth); post-rostral ridge armed with 9–11 small, movable teeth (vs with 6 movable teeth); lobes of prominence on sixth thoracic sternite rounded (vs terminating in acute spine); posterodorsal margin of third pleomere tergite strongly produced (vs weakly produced); fifth abdominal somite with subacute posteroventral tooth on both sides and with teardrop-shaped tubercle on inner surface (vs with one or two acute posteroventral teeth and without tubercle on inner surface); and first to fourth pereopods with exopod longer than length of coxa and basis combined (vs exopod shorter than coxa) (cf. Komai & Segonzac 2005).
The material reported by Burukovsky (2013) as Segonzackomaius altus from Taiwan is almost identical to the specimen from the Philippine Basin and differs from the holotype of S. altus in having a shorter and ascending rostrum, which is about 0.65 the length of carapace (vs almost horizontal, about 0.90 times carapace length). Furthermore, the proximal half of the ventral margin of the rostrum is unarmed in the new species, while the ventral teeth are distributed along the distal 0.80 of the rostrum in the holotype of S. altus (cf. Spence Bate 1888, pl. 132-4). According to the original description, S. altus “... may be at once recognised by the ... shortness of the telson, which does not quite equal the length of the inner branch of the sixth pleopod, ...”. However, the telsons of the Philippine Basin and Taiwan specimens distinctly exceed the uropodal endopod (Figs.1, 2C, 3D, also see Burukovsky 2013: Fig. 2B).
The low genetic distance (COI sequence divergence 2.5% with an identical 16S sequence) between the Philippine Basin and Taiwan specimens (also see molecular analyses below) suggested that they are conspecific. As the ascending and proportionally shorter rostrum occurs in both sexes, this character can be considered as rather stable and not affected by sexual dimorphism. Although no molecular data is available for the holotype of S. altus, it is determined that the Philippine Basin and Taiwan specimens with relatively shorter rostrum and longer telson represent a different species. New materials of S. altus with genetic data will be likely to support the present taxonomic treatment.
description: Published as part of Kou, Qi, Chan, Tin-Yam & Li, Xinzheng, 2025, A new species of the rare genus Segonzackomaius Burukovsky, 2011 (Decapoda, Caridea, Nematocarcinidae) from the Northwest Pacific, pp. 373-386 in Zootaxa 5627 (2) on pages 376-382, DOI: 10.11646/zootaxa.5627.2.8, http://zenodo.org/record/15326101