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This genus presently contains two species.

Containing group: Onychoteuthidae

Introduction

Callimachus species are small squids; the maximum adult size recorded is a female of ML 150 mm (C. rancureli), and males have been observed to mature at ML ~80 mm.  This genus is easily recognized by its short, broad shape and oval fins. Another diagnostic feature of Callimachus is the short, thin, blunt rostrum that is oriented perpendicular to the gladius.

The type species, C. rancureli, may have a very broad geographical distribution; its type locality is the tropical Indian Ocean, but additional Callimachus specimens have been collected in the tropical North Pacific and from the tropical Atlantic.  This broad distribution suggests that several additional species will probably be recognized in this genus.  Rancurel's (1970) specimens from the tropical South Pacific appear referable to C. youngorum (Bolstad 2010), and more undescribed species may also exist. 

Diagnosis

An onychoteuthid with...

• Oval fins, not drawn-out posteriorly (unique character).
• Gladius elongate-rhombic shaped (unique character) and visible beneath skin in dorsal midline.
• Primary occipital folds only.

Characteristics

1. Arms
   1. Dorsal protective membranes of arms II and III greatly enlarged (ca. 2X) relative to their ventral protective membranes, and with long, well-defined trabeculae.
   2. Suckers lack distal fleshy knob (see Onychoteuthis).
      

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      Figure. Oral view of proximal regions of arms II (upper) and III of C. youngorum, Hawaii, 65 mm ML, male. Photograph b R. Young.

2. Tentacular club
   1. A few marginal suckers present in subadults, presumably lost in adults.


3. Occipital region
   1. 3 primary occipital folds; large occipital membrane from fold 3 extends dorsally and curves to join occipital crest without forming a distinct fourth fold. Olfactory organ lies at posterior end of fold no. 2.


4. Head
   1. Beaks: Descriptions can be found here: Lower beak; upper beak.
      
   2. The margins of the funnel groove are straight and define a sharply pointed V-shape. 
      

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      Figure. Ventral view of head and funnel of C. youngorum, Hawaii, 65 mm ML, male. Photograph by R. Young.

5. Fins
   1. Oval with large anterior lobes; not drawn-out posteriorly (see title illustration). The apical fin-angle is approximately 180°.


6. Photophores
   1. Absent. Note, in the photograph above, that the eye which has popped outside the eyelid, has no photophores on its ventral surface.


7. Gladius
   1. Short, blunt rostrum directed perpendicular to tip of gladius.
   2. Gladius visible in dorsal mid-line except at posterior tip of mantle.
      

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      Figure. Lateral view of the posterior end of the gladius of C. rancureli showing rostrum, Hawaii, 37 mm ML. Photograph by R. Young.

Nomenclature

There is disagreement about the generic placement of the species rancureli and youngorum.  Okutani (1981) originally attributed his new species rancureli to Onykia, based on its overall external resemblance to juveniles of that genus (ovate to paddle-shaped fins, presence of marginal suckers on the tentacle club). However, its retention of these features into maturity, its small size, smooth skin and the unique elongate-rhombic gladius readily separate it from Onykia.

Some authors believe C. rancureli to be a senior name for Walvisteuthis virilis Nesis & Nikitina, 1986, a species originally described in its own family, the Walvisteuthidae, based on a single mature male.  This specimen, the holotype, was somewhat similar to onychoteuthids but it had a number of very peculiar features that caused the authors to erect the new family: enlarged distal suckers on Arms III, dentate suckers on all arms, and club morphology com­prised solely of sparse, small, irregularly set suckers.  Those who propose C. rancureli and W. virilis to be synonymous  consider these peculiar features to be modifications that arise at sexual maturity, and since these differences would certainly require a separate genus from other known onychoteuthids, they suggest that Walvisteuthis is the appropriate generic name.

Bolstad (2010) considered these peculiar features too un-onychoteuthid-like to accept the synonymy, and erected the genus Callimachus for the species rancureli and youngorum, based on the following rationale: "Since W. virilis is known only from adult male specimens, while C. rancureli is known from subadult and spent females, and smaller individuals of both sexes, the morphological differences observed to date could conceivably represent sexual dimorphism. The unusual tentacle clubs on the W. virilis holotype may have been regenerating at the time of capture, since their overall appearance is similar to that of a regenerating club observed in Onykia robusta [Bolstad 2010, fig. 35D]. However, given that the characteristic onychoteuthid hooks are absent from the holotype of W. virilis, while several characters that would be unique within the Onychoteuthidae are present (the strongly enlarged distal suckers on Arms III, the dentate arm suckers), and that no material of W. virilis was available for examination in this study, Walvisteuthidae is retained as a separate family at present. The species rancureli and youngorum are certainly onychoteuthids, but cannot be accommodated within any existing onychoteuthid genus as presently recognised. They are therefore attributed to a new genus, Callimachus."

Life History

Paralarvae of this genus are known as small as 1.9 mm ML. The smallest paralarvae are extremely slender with a mantle width about 25% of the ML. Between this size and about 4-5 mm ML (Fig. A) they are easily recognized by their slender appearance and a distinctive elongate patch of large chromatophores along the dorsal midline. The eyes are dorsoventrally elongate and strongly bulge from the head. Club suckers are in two series, large (about the same size as the arm suckers) and prominent. At roughly 4-5 mm ML (Fig. B) the paralarvae begin a strong morphological change. They start to become relative broad, the eyes become hemispherical and the fins become much more prominent. At 7 mm (Fig. C) the squid is very broad for its length. Chromatophores are small and scattered but larger on the dorsal surfaces than ventral surfaces. On the ventral surface of the head the chromatophores are deep within the tissue and not readily visible in preserved specimens. By 12 mm ML the V-shaped funnel groove and the distinctive rostrum are present and hooks are beginning to form in the medial-ventral series on the club.

Distribution

These squids are found world-wide in tropical to temperate seas.

Other Names for Callimachus (Bolstad, 2010)

• Onykia rancureli
• Walvisteuthis rancureli
• Walvisteuthis hawaiiensis
• Stubby hooksquid
• Walvisteuthis Nesis & Nikitina, 1986