Mobydickia poseidonii, Arnold & Nos & Sáez-Liante & Fernández-Álvarez, 2025

Arnold, Sam, Nos, David, Sáez-Liante, Raquel & Fernández-Álvarez, Fernando Á., 2025, Diversity in the squid family Ancistrocheiridae and description of a new family of the order Oegopsida (Cephalopoda), Zoological Journal of the Linnean Society 204 (3) : -

Mobydickia poseidonii sp. nov. Arnold and Fernández-Álvarez ( Fig. 7; Table 10)

Diagnosis: Same as genus.

Examined material: NHM 20240079. 1 individual of sex unknown collected by Malcolm R. Clarke from the stomach content of a male sperm whale; 175 mm DML; area encompassing the Bellinghausen Sea, the Drake Passage, and the Scotia Sea ( Fig. 8, see remarks), 1955/1956, Natural History Museum of London (NHM).

Type material: NHM specimen 20240079. There is only one specimen available, which was collected from the stomach content of a male sperm whale hunted between 1955 and 1956.

Type locality: Antarctic or sub-Antarctic waters, an area encompassing the Bellinghausen Sea, the Drake Passage, and the Scotia Sea.

Etymology: The specific epithet ‘ poseidonii ’ is named after the mythological character Poseidon from ancient Greek religions. According to the legends, Poseidon used his trident to create chaotic springs, earthquakes, drownings, and shipwrecks. The hooks of the arms of M. poseidonii , with their main cusps and accessory claws, resemble a trident. Poseidon is a male character, so the male gender genitive suffix was applied.

Proposed vernacular names: Poseidon’s squid (English), calamar de Poseidón (Spanish).

Description: Specimen of 175 mm DML ( Fig. 7A–D). The body is soft and gelatinous with a short tail and is white in colour. The mantle is relatively narrow with an MWI of 58.9%. No photophores are present on the skin, around the eyes, or on the examined internal organs of the specimen. Chromatophores are solely found surrounding each eye, on both the dorsal and ventral surfaces. The fins extend to less than half of the length of the mantle, with a FLI of 42.3% of DML. The head is relatively short and wide with an HLI of 15.4% of DML and an HWI of 34.3% of DML. The funnel is large, representing 28.6% of the DML. The length of the funnel component of the funnel-mantle locking apparatus ( Fig. 7E) is 16.6% of DML; the mantle component is 10.4% of DML and shallow, extending towards the anterior end of the mantle.

The gladius ( Fig. 7F) is long, representing 136.6% of DML and relatively narrow, with a GWI of 17.0% of DML. It has a dorsal keel depth of 1.7 mm. The rostrum and rachis are long, 3.6 mm and 32 mm, respectively. The rachis is very pronounced and angular.

The arms are long and similar in length, ranging between 98.3% and 102.9% of DML. At least 50 suckers in each arm, placed in two indistinct alternating rows. In the central area of arms I–III, the horny rings are developed into hooks ( Fig. 7G, H), with one larger main cusp and one smaller accessory claw on each side. Proximal and terminal horny rings of arms I–III are circular hard structures with a thicker area where the main cusp is found in the suckers from the midportion of the arms. The proximal suckers start smaller and increase in size until the maximum diameter and length at sucker 4, and then they gradually decrease. The posterior hooks are less pronounced hooks and until they become circular horny rings. Arms IV have only the flat circular hard structures with a thicker area present in the proximal and distal parts of arms I–III and are approximately one-fourth smaller than the suckers from the other arms ( Fig. 7I, J).

The LRL is 5.0 mm, which is equal to 3.1% of DML. The lower beak length is 254% of LRL, and the depth is 280% of LRL. The wings are wide, representing 120% of LRL. The hood is large, representing 110% of LRL, and the wing gap is 106% of LRL. The rostrum and shoulders are heavily pigmented, whereas the hood and lateral wings are moderately pigmented ( Fig. 7K, L). The upper beak is only darkly pigmented in the rostrum area ( Fig. 7M).

The radula has seven transverse rows of teeth ( Fig. 7N). The rachidian tooth is tricuspid with hooked lateral cusps and a mean rachidian length of 0.45 mm in the ventral part of the radula and 0.63 mm in the dorsal part. The L1 row is bicuspid with a hooked lateral cusp and an overall length of 82.0%–85.0% of RL ventrally and 81.8%–93.5% of RL dorsally, while the L2 row is unicuspid with a length of 97.6%–107.2% of RL ventrally and 133.4%– 152.5% of RL dorsally. The marginal rows are unicuspid with a length of 88.7%–89.3% of RL ventrally and 158.0%–172.0% of RL dorsally.

No gonads were found in this specimen, but it cannot be confirmed whether it represents an immature specimen or the gonads were missed during ingestion, as the mantle was opened and some internal organs were missing.

Distribution: Probably Antarctic and sub-Antarctic waters around the Bellinghausen Sea, the Drake Passage, and the Scotia Sea ( Fig. 8), further distribution unknown.

Remarks: The colour of the specimen is white ( Fig. 7A, C), and distinct chromatophores were only found in the ventral and dorsal head surfaces next to each eye. While it can be argued that this colour could have been the effect of being partially digested or of being preserved for a long period, it is true that (i) the skin was intact almost completely in well-preserved body parts; (ii) some chromatophores were present in the skin near the eyes, which was not distinctly less digested than in the remaining body; and (iii) other specimens collected from sperm whales stomach contents by the same author (Malcolm Clarke, 1913–2013), and kept in the same collection (one of which since the 1960s) and most likely under the same conditions, including some individuals with signals of longer digestion times, showed good preservation of both chromatophores and photophores. Therefore, the pale colour of this specimen and the absence of photophores most likely represent the true condition of the species.

The fins and tentacles are broken and, therefore, are not included in the description. The beak pigmentation has probably been altered due to the action of the digestive enzymes and acidic environment of the sperm whale stomach.

The arm armature of M. poseidonii distantly resembles those present in octopoteuthid squids, with hooks with a main cusp and accessory claws (Kelly 2019). The accessory claws might provide an enhanced grip. Most of the internal organs of M. poseidonii were missing. Thus, the gut content was not examined. It must be noted that M. poseidonii differs from octopus squids in many characters, such as the presence of tentacles, absence of photophores, and the beak, arm hooks, and gladii morphology.