Euborlasia lidiae sp. nov.

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Figs. 2A–D; 3A–G; 4A–G

Type material: Holotype, CNP-INV 1773, serial transverse sections from the head tip to the foregut region (31 slides), collected in November 2011, “La mina” beach (49° 09′24″ S, 67°37′46″ W), San Julián, Santa Cruz, Argentina, intertidal, mussel bed, under rocks; collected by JEFA.

Other material examined (Paratypes): Four specimens collected by JEFA. CNP-INV 1711: “Villarino” beach (42° 24′33″ S, 64°17′ 34″ W), San José gulf, Puerto Madryn, Chubut, Argentina . CNP-INV 1727: “Camarones” bay (44°45′ 02″ S, 65°34′04″ W), Chubut, Argentina . CNP-INV 4106: “Puerto Lobos” beach (41°58′50″ S, 65°04′01″ W) Chubut, Argentina . CNP-INV 4107: “Cerro Avanzado” beach (42°50”S, 64°51’51”W), Puerto Madryn, Nuevo gulf, Chubut, Argentina .

Type locality: “La mina” beach (49°09′24″ S, 67°37′46″ W), San Julián, Santa Cruz, Argentina.

Sequences: PV397468 (COI) and PV397474 (16S) for CNP-INV 1773 (Holotype).

Etymology: The specific epithet is in loving memory of Dr. Lidia Kazimierki (1944–2018) who continuously supported and encouraged JEFA work.

Description

External features: Body bulky, with anterior region of body cylindrical and posterior region flattened. Body length ca. 15 –25 cm long and 1.5 –3 cm wide. Dorsal and ventral sides of head with numerous brown or olive-green spots on whitish background color; anterior tip of head whitish; dorsal side of rest of body predominantly brownolive in color with light inclusions; in foregut region, ventral side of body also dark spotted, while intestinal region creamy pink, with sparse pale olive spots (Fig. 2A). Body coloration visible even after fixation in formalin. Head not demarcated from trunk (Fig. 2A–C). Mouth longer than body width; anterior end of mouth aperture situated anteriorly to posterior ends of lateral cephalic slits (not overlapping) (Fig. 2B, C). Caudal cirrus absent. Ocelli absent.

Internal morphology (Figs 3, 4): Epidermis 63–79 μm thick, with rounded-shaped blue, orange, and small redstained gland cells and ciliated cells (Fig. 3A). Cutis separated from body-wall layer by connective tissue, including separate longitudinal fibers (Fig. 3B). Body wall musculature with outer longitudinal, diagonal, middle circular, and inner longitudinal muscle layers. Circular musculature as thick as outer longitudinal musculature (Fig 3B). Diagonal muscles layer between outer longitudinal muscle and circular muscles layer (Fig. 3B, C). Nerve plexus wedged between two layers of diagonal muscles: very thin and incomplete outer and thinner inner layers (Fig. 3C, D). Inner longitudinal musculature thinner than middle circular musculature (Fig. 3B, E). Cephalic lacuna extending above rhynchodaeum, posteriorly bifurcated and situated on each side of rhynchodaeum (Fig. 3F, G). Vascular plexus around foregut present (Fig.3E). Foregut epithelium with subepithelial glands (Fig. 3E). Cephalic slits and canals of cerebral organs with two (dorsal and ventral) pouches (Fig. 4E). Cephalic-slit epithelium containing flask-shaped red, pinkish staining, globular and serous glandular cells; relatively densely arranged along cephalic slits canal, and found in epidermis on other parts of body (Fig. 4E). Nephridial canals found in foregut region.

Proboscis pore terminal. Rhynchocoel circular muscles intertwined with longitudinal muscle fibers and foregut circular muscle below rhynchocoel blood villus (Fig. 4A). Proboscis with morphology typical for genus (Fig. 4B); obvious muscular crosses absent, but diagonal strand between diagonal and inner circular muscular layer detected (Fig. 4C). Connective-tissue layer present between inner circular and longitudinal musculature (5–8 µm). Epithelial ridge present, with rod-shaped pseudocnidae 7–8 µm long (Fig. 4D). Transverse muscle fibers net, cephalic glands, and nerves present in precerebral region (Fig 3G). Dorsal brain commissure thicker than ventral one (Fig. 4F). Neither neurochord cells nor neurochord observed (Fig. 4G).

Habitat: Intertidal zone, among mussel beds and under rocks in muddy sediment; commonly found in sympatry with Parborlasia fueguina Serna de Esteban & Moretto, 1968 and Lineus sanguineus (Rathke, 1799) .

Distribution: Southwestern Atlantic coasts, along the Chubut and Santa Cruz provinces, from Puerto Madryn (42.5°S) to San Julián (49°S). The species was recorded from six different localities (from north to south): Puerto Lobos, Puerto Madryn, Playa Villarino, Camarones, San Julián, and Puerto Deseado.

Remarks: We placed the new species in the genus Euborlasia based on the following morphological features: bulky body, body coloration pattern (mottled), absence of caudal cirrus, proboscis with one layer of longitudinal musculature, cutis separated from body-wall outer longitudinal muscle layer by connective tissue, and position of the nerve plexus between two layers of diagonal muscles. The last feature appears to be a synapomorphy of the clade Euborlasia + Corsoua (Hookabe & Kajihara 2020a; 2020b).

Euborlasia lidiae sp. nov. differs from the other described species of the genus in its body coloration. Euborlasia elizabethae, Euborlasia nigrocincta, and Euborlasia variegata possess narrow bands or rings arranged at regular intervals on the body surface (Hookabe & Kajihara 2020a). Euborlasia maycoli and Euborlasia inmaculata possess white dots, being fewer or less densely distributed in E. inmaculata . For Euborlasia thori, the body coloration of live specimens remains unknown. Regarding Euborlasia maxima and Euborlasia hancocki, their coloration differ subtly from that of E. lidiae . While their original descriptions resemble that of E. lidiae sp. nov., they were based on previously fixed specimens, making a reliable comparison with the new species difficult. Additionally, the geographical distributions of E. maxima and E. hancocki are distant from the South Atlantic Ocean. E. maxima has only been recorded from its type locality in California, USA (Coe 1905, 1940, 1944), while E. hancocki has been reported from different locations in the Pacific Ocean, including Mexico, China, Panama, and Peru (Hokkaido & Kajihara 2020a). Taken together, these morphological distinctions and the known geographic distributions provide sufficient evidence to confirm that E. lidiae sp. nov. is a distinct species. Euborlasia lidiae sp. nov. possesses an anterior-posterior pattern of background coloration (whitish to creamy pink), mottled with olive-brown dots, lower in density at the anterior end, and with the tip of the head whitish. A comparison of ten species belonging to Euborlasia is detailed in Table 2, excluding E. gotoensis and E. proteres, as these species possess outer longitudinal musculature in the proboscis and therefore do not belong to Euborlasia . It should be noted, that the remaining species included in the comparison (10) were described from specimens collected in locations far from the Atlantic coast of South America. This further supports the recognition of E. lidiae as a distinct new species.

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AbsentProboscis without muscle crossPresent study

Molecular phylogeny and distances

The Maximum Likelihood (ML) and Bayesian Inference (BI) trees showed congruent topologies and supported multiple lineages previously defined by Kajihara et al. (2022), including A, H, I, J, K, and N, all with full support (100/1) (Fig. 5). Within Lineage O, Euborlasia lidiae sp. nov., Euborlasia maycoli, and Euborlasia cf. elizabethae form a well-supported clade with Corsoua takakurai (89/0.99). Several nodes within lineage O exhibit high support values (95/0.99).

The interspecific genetic distances (p -distance) for 16S are 10% between E. lidiae and E. maycoli, 20% between E. lidiae and E. cf. elizabethae, and 16 % with Corsoua takakurai; while for COI, they are 13.0% and 14.5%, respectively and 16% whit C. takakurai . Interspecific distances for all species in the analysis were also calculated (Table S1 & S 2).