Tremoctopus violaceus delle Chiaje, 1830

Jimenez-Badillo, Maria de Lourdes, Meiners-Mandujano, Cesar, Galindo-Cortes, Gabriela, Morillo-Velarde, Piedad S., Gonzalez-Gomez, Roberto, Barriga-Sosa, Irene de los Angeles & Pliego-Cardenas, Ricardo, 2021, The first record of Tremoctopus violaceus sensu stricto Delle Chiaje, 1830 in southwestern Gulf of Mexico gives a hint of the taxonomic status of Tremoctopus gracilis, ZooKeys 1012, pp. 55-69 : 55

Tremoctopus violaceus delle Chiaje, 1830 Figures 2 , 3

Material examined.

Mexico • 1 female, 640 mm TL; 135 mm ML; southwestern Gulf of Mexico, Veracruz, Antón Lizardo; 19°03'24"N, 95°59'17"W; 20 July 2019; Jiménez-Badillo, L; recovered alive by fishermen; GenBank: MT271737; specimen code CNMO 8042.

The analyzed octopod was an adult female (TL of 640 mm, MLd 135 mm, and TW 1.02 kg). It was found alive and was showing signs of disorientation and gross color pattern changes on the blanket from iridescent transparent to reddish-brown (Fig. 2A, D, F ). The specimen had no apparent damage. Upon approach and handling by the fisherman, the octopus became threatened, extended her web, and jettisoned her eggs (Fig. 2B-D . A few meters away from the octopus, there appeared what was probably the eggs attached to a rod-like structure, but this could not be collected only recorded by video. This observation provides evidence of autotomy as a means of protection of the egg mass (Fig. 2G-I ). The specimen is inferred to be sexually mature (Fig. 2E ). Water pores, the coiled web on the ventral side of the animal, and some chromatophores on the web, which are characteristic of the species, were seen and recorded by video (Fig. 2A-D, G ).

The fresh octopus had a brownish-purple color on the dorsal mantle and the head, while the ventral mantle was iridescent-silvery. The mantle was thick and muscular. The eyes were lateral. It had one pair of cephalic pores on the dorsal head between the eyes, and another, smaller pair on the ventral head adjacent to the funnel opening. The funnel extended beyond eye level and 14 gill filaments were counted. The arms were unequal in length and shape. The dorsal arms (arm pairs I and II) were much longer than the ventral arms (arm pairs III and IV); arms I and II were truncated. The suckers were biserial, decreasing in size towards the distal portion of each arm. One deep web was present between the four dorsal arms. The depth of the interdigital membrane was well developed and V-shaped. The nuchal folds numbered eight (Fig. 3A-E ). The radula had seven teeth as well as two thin, rectangular marginal plates per transverse row. The rachidian teeth were tricuspid with an A2 seriation. The first lateral teeth were much smaller than the second lateral and rachidian teeth. The marginal teeth were long and slender and spine-shaped (Fig. 4 ). The color pattern and the morphological features described above as well as the body measurements and morphometric indices presented in Tables 1 , 2 of the analyzed specimen fully correspond to T. violaceus , ( Thomas 1977; Roper and Voss 1983; Orsi 2009; Mangold et al. 2018).

The compiled sequence of the mtDNA16S region (470 bp) obtained in this study (GenBank accession number MT271737) shows over 90% similarities to the T. violaceus homologue sequences from South Korea (MN435565), Taiwan (KY649286; Chiu et al. 2018), and Hawaii (AJ252767). This is the first mtDNA 16S haplotype publicly available in GenBank of T. violaceus from the Gulf of Mexico. Other public sequences for the species correspond to haplotypes of cytochrome c oxidase subunits I (COI) and III (COIII) genes (AF377978 and GU288522, respectively), and the voucher UMML:31.312. The genetic divergence among the Gulf of Mexico (Atlantic Ocean) specimen and the reference sequences from the Pacific Ocean is 6%, with 31 variable sites. All the T. violaceus 16S sequences are clustered in a well-supported monophyletic clade (bs = 100) (Fig. 5 ); however, the Atlantic Ocean specimen is in a separate clade from specimens from the Pacific Ocean.

Figures

Figure 2. Photographic record of the Tremoctopus violaceus specimen (135 mm ML) in natural environment highlighting relevant characters for its taxonomic determination A ventral water pore B-D web of dorsal arms coiled on the ventral side and deployed when female was feeling threatened E egg mass F web displaying an iridescent greenish glow and a reddish brown color G-I evidence of autotomy: segments detached from interbrachial membrane showing slender arm, part of the connective tissue, circulatory system and chromatophores pattern characteristic of the species.

Figure 3. Photographic record of the Tremoctopus violaceus fresh specimen (135 mm ML) highlighting relevant characters for its taxonomic determination A, B dorsal and ventral view; arms unequal in length; one web between the four dorsal arms; two pairs of cephalic water pores, one pair located on dorsal surface of the head, slightly anterior to eyes at the base of first arms C second pair located ventrally, adjacent to funnel opening, at base of fourth arms; eyes large, laterally directed; funnel extends beyond eye level, distal one quarter free D bioluminescent tissue E biserial suckers on arms decreasing in size towards the distal portion F nuchal folds. To see the character dimensions, see Table 1. Scale bars: 10 cm (A-C).

Figure 4. Photographic record of A upper and lower beak B radula, seven teeth and two marginal plates per transverse row are appreciated. On the approach (bottom right) rachidian teeth tricuspid with an A 2 seriation is observed. For beak dimensions see Table 1. Scale bars: 1 mm (B).

Figure 5. Maximum likelihood phylogenetic tree based on 16 S sequences showing the relationships of Tremoctopus violaceus. Only bootstrap values above 90 are shown. Records from the Hawaiian Islands and South Korea-Japan were likely misidentified and correspond to T. gracilis.