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.

Ricardo Pliego-Cárdenas,Piedad S. Morillo-Velarde,Roberto González-Gómez,Irene de los Angeles Barriga-Sosa,César Meiners-Mandujano,María de Lourdes Jiménez-Badillo,Gabriela Galindo-Cortes

doi:10.3897/zookeys.1012.55718

Abstract

Knowledge on species taxonomic identity is essential to understand biological and biogeographical processes and for studies on biodiversity. Species the genus Tremoctopus have been confused in the past and are inconsistently identified. To clarify of the taxonomic diagnosis Tremoctopus violaceus Delle Chiaje, 1830, an evaluation of morphological and meristic characters, as well as morphometric indices and genetic analyses, was undertaken. The analyzed octopod was an opportunistically collected mature female of 640 mm in total length, with a mantle length of 135 mm and a total weight of 1.02 kg. Evidence of autotomy as a defensive mechanism for protecting the egg mass is presented. The 16S haplotype sequenced from this specimen represents the first one publicly available for this species from the Gulf of Mexico. The genetic divergence between this haplotype and those reported from the Pacific Ocean is representative of interspecific variation in other taxa, which suggests that “T. violaceus” in the Pacific Ocean (KY649286, MN435565, and AJ252767) should be addressed as T. gracilis instead. Genetic evidence to separate T. violaceus and T. gracilis is presented. The studied specimen from the Gulf of Mexico represents the westernmost known occurrence of T. violaceus and the first record from the southwestern Gulf of Mexico.

Highlights

Tremoctopodidae is one of the four families within the superfamily Argonautoidea Cantraine, 1841 (Mollusca, Cephalopoda), all of which are characterized by marked sexual size dimorphism, with small or dwarf males and larger females, some of which reach 2 m long (Naef 1923; Norman 2000)
The Tremoctopodidae is represented by a single genus, Tremoctopus, with four species currently recognized as valid: Tremoctopus gelatus Thomas, 1977 which is meso-bathypelagic, gelatinous, with circumtropical and temperate distribution; Tremoctopus robsoni Kirk, 1884 which was described from waters off New Zealand; Tremoctopus gracilis (Eydoux & Souleyet, 1852) which occurs in the Pacific and Indian oceans; and Tremoctopus violaceus Delle Chiaje, 1830 which is an epipelagic (1–250 m depth), muscular, heavily pigmented, and restricted from 40°N to 35°S in the Atlantic Ocean, including the Gulf of Mexico, Caribbean Sea, and Mediterranean Sea (Voss 1967; Thomas 1977; O’Shea 1999; Quetglas et al 2013; Mangold et al 2018)
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

Summary

Introduction

Tremoctopodidae is one of the four families within the superfamily Argonautoidea Cantraine, 1841 (Mollusca, Cephalopoda), all of which are characterized by marked sexual size dimorphism, with small or dwarf males and larger females, some of which reach 2 m long (Naef 1923; Norman 2000). The difficulty in separating these taxa based solely on male morphology, as well as the absence of molecular phylogenetic analyses of the genus, has caused taxonomic confusion. This is evident in occurrence records of these two species that lie outside the geographical limits indicated by Thomas (1977) and Mangold et al (2018). Examples of such cases are records published by Zeidler (1989), García-Domínguez and Castro-Aguirre (1991), Norman et al (2002), Chesalin and Zuyev (2002), Nabhitabhata et al (2009), Chiu et al (2018), and many historical records in the Ocean Biogeographic Information System (OBIS 2020)

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Conclusion