Acromegalomma scutolenis, Rebello & Nogueira & Carrerette, 2025

Acromegalomma scutolenis sp. nov.

Figures 14–16 View FIGURE 14 View FIGURE 15 View FIGURE 16 ; 17 View FIGURE 17 (A–E); 18 (P–T); 19D; Table 2 View TABLE 2

Material examined. Holotype. MNRJP-8322 , complete specimen, in soft-sediment (sand), 20.807ºS 40.648ºW, 1–2m deep, May, 2023, Praia de Parati , Anchieta, Espírito Santo, Brazil GoogleMaps . Paratype. MNRJ P992 , incomplete specimen, in continental shelf, 20.590ºS 39.916ºW, 142–146 m deep, June to July, 2013, Espírito Santo Basin , Espírito Santo, Brazil GoogleMaps .

Diagnosis. Spherical eyes on dorsalmost radioles; lateral radioles with spherical and oval eyes; collar dorsal margins fused to faecal groove, collar dorsal lappets and dorsal pockets both present; anterior peristomial ring not exposed; caruncle present; ventral lappets triangular; thoracic ventral thoracic shields all entire, smooth; inferior thoracic notochaetae Type C sensu Giangrande et al. (2015).

Measurements. Holotype body 22.8 (18.5) mm long. Radiolar crown 7, 4 mm long (9,2 mm). Thorax 5.1 (4.7) mm long, 1.9 (1.3) mm wide.

Description. General aspects and color patterns. Elongated body, yellow to ochre, with well-marked collar dorsal margins and well-defined segments; thorax 3x longer than wide. Branchial crown longer than thorax, 1/3 of total body length, also yellowish, with 4–5 brown bands, distalmost largest, extending for space of origin of up to 12 pairs of pinnules, basalmost band shortest ( Figs 14B, D View FIGURE 14 ; 15A–B, D, F View FIGURE 15 ). One pair of large and prominent dorsal eyes on dorsalmost pair of radioles; tiny subdistal compound eyes on lateral radioles, 1 per radiole, missing on some dorsal and ventralmost radioles ( Figs 14B, D View FIGURE 14 ; 15A–B, D View FIGURE 15 ; 19D View FIGURE 19 ).

Radiolar crown. Crown longer than thorax, semicircular radiolar lobes, with 14 (14–16) pairs of radioles. Subdistal compound eyes on dorsalmost and lateral pairs of radioles, except on four dorsalmost (beginning from second pair) and four ventralmost pairs ( Fig. 19D View FIGURE 19 ); eyes of dorsalmost pair of radioles large and spherical, eyes of lateral pairs of radioles smaller, spherical to oval ( Figs 14B, D View FIGURE 14 ; 15A–B, D View FIGURE 15 ; 17O–Q View FIGURE 17 ). Tips of radioles of dorsalmost pair short, radiolar tips gradually longer ventralwards ( Figs 14B, D View FIGURE 14 ; 15A–B, D View FIGURE 15 ; 17O–Q View FIGURE 17 ). Dorsal lips erect, triangular, about 1/3 of radiolar crown length, with radiolar appendages (mid-rib) and one pair of pinnular appendages ( Fig. 15F View FIGURE 15 ). Ventral lips about 1/3 of dorsal lips length, broadly rounded. Basal ventral flanges absent.

Peristomium. Anterior peristomial ring not exposed ( Figs 14A, E, F View FIGURE 14 ; 15E, F View FIGURE 15 ; 17N View FIGURE 17 ); remarkably short caruncle, triangular, half-length of second thoracic segment, with rough surface, due to irregularly sinuous crests ( Fig. 14E View FIGURE 14 ). Collar dorsal margins fused to faecal groove, dorsal lappets rounded and V-shaped dorsal pockets ( Figs 14A, E–F View FIGURE 14 ; 15E, F View FIGURE 15 ; 17N View FIGURE 17 ). Collar ventral lappets longer than first ventral shield, rounded, overlapping, mid-ventral incision reaching anterior margin of first ventral shield ( Figs 14C View FIGURE 14 ; 15C View FIGURE 15 ; 17M View FIGURE 17 ), ventral sacs and ventral parallel lamellae present ( Fig. 14E View FIGURE 14 ); collar lateral margins straight, covering origin of radioles ( Fig. 15E, F View FIGURE 15 ).

Thorax. Chaetiger 1: notochaetae all elongate narrowly hooded ( Figs 16A View FIGURE 16 ; 18P View FIGURE 18 ), those of superior row longer; first ventral shield with rounded anterior margin and short medial incision ( Figs 14C View FIGURE 14 ; 15C View FIGURE 15 ; 17M View FIGURE 17 ). Chaetigers 2–8 (2–7): all thoracic tori about same length, not reaching shields, extending for 3/4 of distance between notopodia and ventral shields lateral margins. Notochaetae of superior group elongated, narrowly hooded, 4–6 chaetae per fascicle, inferior notochaetae with thick and short, distally rounded shaft, ending by mucronated hood, Type C sensu Giangrande et al. (2015), 10–12 per fascicle ( Figs 16B–C View FIGURE 16 ; 18Q View FIGURE 18 ). Uncini with main fang surmounted by numerous rows of minute teeth, covering half of main fang, handles 1.5x length of main fang, 15–22 uncini per torus; companion chaetae with teardrop-shaped membranes and handles as long as those of uncini ( Figs 16D View FIGURE 16 ; 18R View FIGURE 18 ). Interramal eyespots absent throughout.

Abdomen. Segments: 66 (65–66). Neurochaetae broadly hooded, those of posterior rows longer, 10–12 chaetae per fascicle ( Figs 16E View FIGURE 16 ; 18S View FIGURE 18 ). Uncini with main fang surmounted by 8–10 rows of minute teeth, covering half of main fang, and shorter handles than those of thoracic uncini ( Figs 16F View FIGURE 16 ; 18T View FIGURE 18 ) 10–13 uncini per torus.

Pygidium. Broadly rounded, pygidial eyespots absent.

Tubes. Mucous, with shell fragments and coarse sand embedded.

Methylene blue staining pattern. Thoracic shields stain uniformly, first shield entire, with M-shaped anterior margin, subsequent ventral shields rectangular with concave lateral edges, smooth. Abdominal shields each divided into two at midlength, by faecal groove. Entire dorsum and lateral sides of body pale, unstained ( Figs 2 View FIGURE 2 ; 14C View FIGURE 14 ; 15C, E View FIGURE 15 ; 17M View FIGURE 17 ).

Etymology. The specific epithet is formed by the terms “ scutum ” = shields + “ lenis ” = smooth, referring to the smooth ventral shields, without ornamentations of any type, such as ciliary patches or fissures, as in members of the other species described herein.

Habitat. 2–146 m deep, in soft-sediments.

Distribution. Only known from the type locality (Praia de Parati, Anchieta), and surrounding areas, in Espírito Santo Basin, Espírito Santo, Southeastern Brazil, Southern Atlantic Ocean.

Remarks. Out of all the currently known species of Acromegalomma , members of A. scutolenis sp. nov. resemble specimens of A. adriaticum ( Giangrande, Caruso, Mikac & Licciano, 2015) , A. fauchaldi ( Giangrande, Licciano & Gambi, 2007) , and A. messapicum ( Giangrande & Licciano, 2008) , in having eyes on the dorsalmost and lateral pairs of radioles, collar dorsal margins fused to the faecal groove, with dorsal pockets, and thoracic tori all of the same length; of these three species, only A. fauchaldi was originally described from an American locality, while both the other species both were described from the Adriatic Sea, in the Mediterranean ( Giangrande et al. 2007; Giangrande & Licciano 2008; Giangrande et al. 2015). Additionally, members of all these three species lack a caruncle, while specimens of A. scutolenis sp. nov. possess a conspicuous caruncle.

Furthermore, members of A. scutolenis sp. nov. do not have anterior peristomial ring exposed, as also occurs in specimens of A. fauchaldi , whereas individuals of both A. messapicum and A. adriaticum have anterior peristomial ring exposed dorsally. Finally, thoracic tori of chaetigers 2–3 occupy half of the distance between notopodia and corresponding ventral shields lateral margins in members of A. messapicum and A. fauchaldi , and extend for 3/4 of that distance in individuals of A. adriaticum and A. scutolenis sp. nov.

Acromegalomma schwindtae Tovar-Hernández, de León-González & Bybee, 2017 is the only species of this genus originally described from the Southern Atlantic waters so far ( Tovar-Hernández et al. 2017). ( Table 2 View TABLE 2 ). Major differences between specimens of A. schwindtae and A. scutolenis sp. nov. are: (1) eyes only present on the dorsalmost pair of radioles in members of A. schwindtae (dorsalmost and lateral pairs of radioles in the new species); (2) members of A. schwindtae have dorsalmost radioles with long tips, tips diminishing gradually towards ventralwards (tips progressively longer ventralwards, in specimens of A. scutolenis sp. nov.); and (3) dorsal lappets absent and anterior peristomial ring exposed dorsally between dorsal pockets in representatives of A. schwindtae , while dorsal lappets are present and the anterior peristomial ring is not exposed in members of A. scutolenis sp. nov.