Phascolion ( Lesenka ) salgadoi, Gómez-Vásquez, 2024

Phascolion ( Lesenka) salgadoi sp. nov.

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Fig. 7 View Fig

Etymology

Named after the researcher José Salgado-Barragán, a crustacean specialist from the Universidad Nacional Autónoma de México (UNAM) and a good friend who provided the specimens of this species. The epithet is a noun in the genitive case ( ICZN 1999, Art. 31.1.2).

Material examined

Holotype

MEXICO • Sonora, Guaymas Bay ; 24 Oct. 1991; depth 45 m; inside empty shells of Polystira sp. ; EMU-13448 .

Paratypes

MEXICO • 7 specs; same collection data as for holotype; UMAR-SIPU 131 • 6 specs; same collection data as for holotype; EMU-13449 • 7 specs; same collection data as for holotype; EMU-13450 .

Other material

MEXICO • 4 specs; same collection data as for holotype; UMAR-SIPU 132 .

Description (EMU-13448)

Body coiled to the left; trunk 25 mm in length ( Fig. 7A View Fig ). Light brown skin, translucent at mid trunk. Ventral region of trunk with numerous simple, round and flat papillae, mid trunk with scattered circular papillae with hardened U-shaped border with a tooth ( Fig. 7D View Fig ), denser and smaller on caudal region and on each side of ventral papillae. Introvert partially protruded; 12 short, thin digitiform peripheral tentacles encircling mouth. Scattered claw-shaped, dark hooks ( Fig. 7F View Fig ) of type I ( Cutler 1994), 37 µm long, occupying 10% of distal length of introvert. Anus on proximal portion of introvert, near edge of trunk; posterior introvert with bladder-shaped holdfast papillae ( Fig. 7E View Fig ), extending slightly to trunk.

Longitudinal musculature continuous; retractor muscle in a single column, attached to body wall at 90% of posterior trunk length. Esophagus attached to retractor muscle. A single nephridium of approximately 15% of trunk length attached in all its length to body wall; nephridiopore opens posterior to anus. Spindle muscle attached anterior to anus and attached to intestine in caudal region of trunk; intestine without coils, with same torsion as body ( Fig. 7B View Fig ).

Variation

Some of the hardened holdfast papillae have a U-shaped border. The density of papillae is variable among the specimens.

Habitat

Subtidal ( 45 m); inhabiting shells of the gastropod Polystira sp. ( Fig. 7C View Fig ).

Distribution

Gulf of California: only known from Guaymas Bay, Sonora.

Remarks

The specimens can easily be placed in the subgenus Phascolion ( Lesenka) by the presence of a single retractor muscle and by having less than 20 tentacles. Phascolion ( L.) salgadoi sp. nov. is similar to two subspecies: P. ( L.) valdiviae valdiviae Fischer, 1916 (from the Indian Ocean) and P. ( L.) valdiviae sumatrense Fischer, 1916 (from Sumatra). The two subspecies and the specimens examined here have U-shaped holdfast papillae, in addition to having a single retractor muscle; however, the specimens from the Mexican Pacific are geographically separated from previous subspecies. Also, they have several morphological differences from both subspecies.

Phascolion ( Lesenka) salgadoi sp. nov. differs from Fischer’s subspecies because they have dark hooks, while P. ( L.) valdiviae valdiviae has pale hooks and P. ( L.) valdiviae sumatrense lacks hooks. Phascolion ( L.) salgadoi does not show intestinal coils, the intestine instead following the torsion of the body, while the Indian subspecies has 20–22 coils. Regarding habitat, Ph. ( L.) salgadoi was found at a depth of approximately 45 m, living in an empty shell of the gastropod Polystira sp. , while the subspecies P. ( L.) valdiviae valdiviae was obtained at a depth of 158 m, living in shells of the scaphopod Dentalium sp. , which does not have whorls. The description of P. ( L.) valdiviae sumatrense did not mention anything about its habitat, except that the species was found at a bathyal depth ( 750 m) ( Fischer 1916).

Comparing Phascolion ( Lesenka) salgadoi sp. nov. with other species of the subgenus, the following differences are noted: P. ( L.) collare Selenka & de Man, 1883 has conical papillae and small type III hooks ( Cutler 1994); P. ( L.) cryptum Hendrix, 1975 has four main tentacles followed by accessory tentacles and it has no hooks; and P. ( L.) hupferi Fischer, 1894 has the anus at half of the introvert length and, like P. ( L.) rectum Ikeda, 1904, has neither hooks nor holdfast papillae ( Cutler 1994). On the other hand, P. ( L.) salgadoi possesses flat oval papillae with a hardened U-shaped border, bladder-shaped holdfast papillae, type I hooks, short digitiform tentacles and the anus is situated at the base of the introvert.