Octopoteuthis Ruppell 1844

Introduction

Subadults and adults of Octopoteuthis lack tentacles. All the arms terminate in photophores and these photophores lack muscular lids. Instead, they possess mobile chromatophores that conceal the photogenetic tissue. Arm tips of Octopoteuthis are frequently broken off during capture. This "fragility" is probably a normal defensive weapon (see Behavior of O. neilseni).

The species in this genus are poorly defined and identification, therefore, may be difficult.

Diagnosis

An octopoteuthid ...

•  with small photophores at tips of all arms.
  

Characteristics

1. Tentacles
   1. Absent in subadults.
2. Photophores
   1. Slender, dark organs at tips of all arms.
   2. One or two large tail organs.

Comments

Species of Octopoteuthis have a variety of photophores in addition to those listed above as being characteristic for the genus. This diagram names the organs that are most easily found in dissection. The variation between species in photophore arrangement is poorly known. The most obvious difference is the presence of one or two tail organs.

image info

Figure. Ventral view of Octopoteuthis deletron showing photophores. Drawing from Young (1972).

Nomenclature

Pfeffer (1912), with reservations, described the genus Octopodoteuthopsis based on Verrill's Ancistrocheirus megaptera primarily due to the more widely spaced hooks in this species compared to Octopoteuthis sicula. Adam (1952) suggested that this and Octopoteuthis were synonymous but Voss (1956) maintained their distinctness. The two were treated as synonyms by Young (1972).

The type species of the genus, Octopoteuthis sicula, has been known as Octopodoteuthis sicula for many years due to an illegal emendation of the original spelling. Octopoteuthis persica Naef, 1923 was transferred to Taningia by Young (1972). Chun (1910) described a 3.8 mm paralarva from the Indian Ocean (34° 31'S, 26° 00'E) which Naef (1923) found to be different from the paralarvae he examined of O. sicula from the Mediterranean Sea. He named Chun's paralarva, O. indica but no subsequent work has clarified the use of this name. O. longiptera Akimushkin, 1963, from the South Atlantic, was described from a whale stomach, and considered a species dubia by Young (1972).

Species

According to Young (1972) the systematics within this genus rests primarily on three features: (1) the number of tail photophores; (2) the size of the tail in small specimens; (4) the presence of accessory cusps on the hooks in small specimens.

In the North Pacific two species are known: O. deletron with a single tail photophore and O. neilseni with two tail photophores.

image info image info

Figure. Ventral view of the mantle and fins of Octopoteuthis showing the two North Pacific species with virtually no tails but differing patterns of tail photophores: Left - O. deletron. Right - O. neilseni. Drawings from Young (1972).

 In the North Atlantic, three forms are known: One, O. sp. A with a single tail photophore, absence of accessory cusps on the arm hooks and a long tail, and two forms with two tail photophores. One of the latter, O. danae, has a tail of moderate length while the other, O. megaptera, (right drawing) has a long tail. The type species of the genus, O. sicula, is the senior synonym of either O. sp. A or O. danae.

image info image info image info

Figure. Mostly ventral views of mantles and fins of Atlantic species of Octopoteuthis.  Left - Octopoteuthis sp. A, 49 mm ML with a lateral view of a large arm hook from the same specimen. Center - O. danae, 53 mm ML. Right - O. megaptera, 38 mm ML.

O. rugosa, from the waters off South Africa and south Australia, is discribed only from very large specimens (14.5-23 cm ML) and cannot be adequately compared to many of the other species.

Nesis (1982) indicates that the presence of arm base photophores on arms III and IV is another specific character and these are absent in O. danae and O. megaptera.

Behavior

On several occasions, while observing O. neilseni aboard ship, a bright bioluminescent flash was observed from the caudal area, that presumably came from one or both of the tail photophores.

On one occasion an arm was cut off a moribund O. neilseni that was being observed in seawater in a pan. The portion of the arm that was separated from the squid immediately began to wiggle violently while the arm tip photophore flashed brilliantly. On one occasion an arm tip was found in the bottom of a shipboard tank that held a living O. neilseni. Each of these squid qenerally are retrieved from the trawl without several arm tips of differing length, and occasionally a specimen is captured with an arm tip in the process of regeneration. This evidence suggests that the arm tips can either be autotomized or are easily broken by an attacking predator and that the detached, flashing and wiggling arm tip acts as a lure to detract the predator,similar to the function served by the autotomized tail of a terrestrial lizard.

O. neilseni has been observed to counterilluminate in shipboard aquaria.