Parastygarctus potercha Trokhymchuk, Hansen, Pysarenko, Subota & Kieneke, 2026, sp. nov.

Parastygarctus potercha sp. nov. Figs 7, 8, 9, 10, 11, Table 4 Diagnosis. Parastygarctus with three body plates, each with two pairs of lateral acute processes: short and ventral anterior, long and dorsal posterior. Caudal plate with three pairs of processes: a pair of lateral spine-like processes, a pair of dorsolateral processes bearing cirri E, and a pair of spine-like posterior processes. Primary and secondary clavae oval and pedunculated. The first three pairs of legs terminate with three claws: outermost and middle claws with dorsal filaments. Leg IV with two claws bearing dorsal filaments. Female seminal receptacles as small vesicles with short sinuous ducts. Type locality. Station 850, 17°11.31'N, 21°57.20'W, 102.4 m b. s. l., Senghor Seamount, summit central, September 2009, biogenic coarse sand, MUC sample. Paratypes were collected from stations 848, 849 and 850, from 101.3 m, 102.0 m, and 102.4 m b. s. l. respectively, Senghor Seamount, summit central, September 2009, biogenic coarse sand, MUC samples. Type material. Holotype: • 1 ♀ (M 79-3-850-2_13v74, SMF 1493) on slide. Paratypes: • 1 ♀ (M 79-3-850-2_14v74, SMF 1494) on slide; • 2 ♂♂ (M 79-3-848-5_1v26, SMF 1427; M 79-3-850-2_10v74, SMF 1490) on slides; • 1 juvenile (M 79-3-850-2_2v74, SMF 1483) prepared for SEM, on stub; • 4 juveniles (M 79-3-849-2_1v35, SMF 1453; M 79-3-850-2_11v74, SMF 1491; M 79-3-850-2_12v74, SMF 1492; M 79-3-850-2_15v74, SMF 1495) on slides; • 2 undetermined sex (M 79-3-850-2_16v74, SMF 1496; M 79-3-850-2_61v74, SMF 1541) on slides; • 1 undetermined sex (M 79-3-850-2_3v74, SMF 1604), digital specimen. Description. Holotype. Mature female (69.0 µm long, 21.0 µm wide) with cuticular armour divided into cephalic plate, three body plates, two intersegmental plates and caudal plate. Cephalic plate divided into five lobes: one medial, two medio-lateral, and two lateral. Each lateral lobe bears a posterior spine (Fig. 8 A). Elbows (antero-lateral lobate processes of lateral lobes) are slightly prominent. Each of the three body plates has two pairs of spine-like lateral processes: a small anterior, arising ventrally, and a large posterior, arising dorsally (Fig. 8 A). Caudal plate has a pair of spine-like lateral processes (Fig. 8 A), a pair of dorsolateral processes bearing cirri E (Fig. 8 B), and a pair of spine-like posterior processes (Fig. 8 E). Cuticle with fine punctation. All cephalic cirri consist of scapus with distal swelling and flagellum. Internal cirrus is 7.0 µm long. External cirrus is 10.5 µm long. Median cirrus (8.5 µm long) arises from a circular plate. Primary clava (4.7 µm long) consists of peduncle and oval papilla. Cirrus A (9.8 µm long, the left one has a broken flagellum) inserts separately from primary clava. Secondary clava (4.0 µm long) is similar in shape as primary clava (Fig. 8 C). Mouth cone is retracted. The structures of bucco-pharyngeal apparatus are not visible. Cirrus E (23.0 µm long) arises from lateral process and consists of smooth proximal portion, annulated scapus and flagellum (Fig. 8 B). Sensory organs only on legs IV. Leg IV sensory organ (1.7 µm long) as spherical papilla arising on short peduncle. The first three pairs of legs bear only three claws (5.5 µm, 4.5 µm, and 4.0 µm for first, second, and third pairs respectively), with outermost and middle having dorsal filaments. Leg IV bears two claws, which are the biggest and the widest (6.5 µm long) and have dorsal filaments. Small rosette-shaped female gonopore (Fig. 8 E). Seminal receptacles as small vesicles (Fig. 8 F, G). Seminal ducts are sinuous and short. Anus closed by two large lateral lobes and small anterior lobe (Fig. 8 D). Anus is 6.0 µm posteriorly to gonopore. The holotype exhibits paedomorphic patterns in having a small body size and a low number of claws on both legs I – III (only three claws per limb) and legs IV (only two claws per limb), but at the same time possessing a gonopore and seminal receptacles. Remarks on paratypes. In total, 11 paratypes were investigated. The paratypes correspond to the morphology of the holotype (Figs 9, 10, 11). Only a weak sexual dimorphism is observed. Males are slightly larger and have a shorter anus – gonopore distance of approximately 4.0 µm (Fig. 10 D). Pharyngeal bulb locates in the level between first and second leg pairs in male specimens (Figs 9, 10 B), however, there is no information on female specimens. Male gonopore formed a broad tube with oval opening (Fig. 10 D). During SEM examination of a juvenile specimen (Fig. 11) we were able to better examine cephalic structure and claws. Differential diagnosis. The presence of two pairs of lateral spines of the body plates is shared by Parastygarctus higginsi Renaud-Debyser, 1965, P. biungulatus Morone De Lucia, Grimaldi de Zio & D’Addabbo Gallo, 1984, P. svennevigi Hansen, Kristensen & Jørgensen, 2012, and P. mediterranicus D’Addabbo Gallo, De Zio Grimaldi & Sandulli, 2001. Parastygarctus potercha sp. nov. can easily be distinguished from all congeneric species by the unique claw formula having only three claws per leg on leg pair I – III and two claws per leg on leg pair IV. Parastygarctus potercha sp. nov. and P. biungulatus both have three pairs of caudal plate processes. However, in P. potercha sp. nov. the dorsolateral processes bear the cirri E whereas in P. biungulatus cirri E attach directly to the caudal plate. Furthermore, the posterior spine-like processes are much shorter and thinner in P. potercha sp. nov. compared to those of P. biungulatus. Etymology. Potercha, plural poterchata (Latinised from Ukrainian " потерча", "потерчата") is the ghost of a dead, unbaptised child, unique to Ukrainian folklore. The species name refers to the paedomorphic appearance of this species.