Treatise Online, no. 17, Part M, Chapter 3: Anatomy of Recent forms

Nixon, Marion

doi:10.17161/to.v0i0.4087

Cited by 6 publications

(8 citation statements)

References 60 publications

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“…Due to the similar function of hooks and suckers, that is, to grab and hold prey, both are primarily hunting weapons. It is interesting to note that tiny hooklike (<5 mm) structures can be found in the suckers of oegopsid Decabrachians (Nixon 2011), in which tentacular sucker rings can bear relatively large hooks (>5 mm). Those hooks are positioned curving inward, with the tip pointing in the direction of desired prey movement toward the mouth.…”

Section: Discussionmentioning

confidence: 99%

Grasping the shape of belemnoid arm hooks—a quantitative approach

Hoffmann¹,

Weinkauf²,

Fuchs³

2017

Paleobiology

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Chitinous arm hooks (onychites) of belemnoid coleoids are widely distributed in Mesozoic sediments. Due to their relative abundance and variable morphology compared to the single, bullet-shaped belemnite rostrum, arm hooks came into the focus of micropalaeontologist as a promising index fossil group for the Jurassic-Cretaceous rock record and have been the target of functional, ecological, and phylogenetic interpretations in the past (e.g. Reitner & Engeser 1982;Fuchs et al. 2013;Hammer et al. 2013). Based on three well-preserved arm crowns of the Toarcian diplobelid Chondroteuthis wunnenbergi, we analyzed the shape of a total of 87 micro-hooks. The arm crown of Chondroteuthis is unique in having uniserial (rather than biserial) hooks. The first application of elliptic Fourier shape analysis to the arm weapons of belemnoid coleoids allows for the distinction of four micro-hook morphotypes and the quantification of shape variation within these morphotypes. Based on the best preserved arm crown, we reconstructed the distribution of morphotypes within the arm crown as well as along a single arm. Our quantitative data support former observations that smaller hooks were found close to the mouth and at the most distal arm parts, while the largest hooks were found in the central part of the arm crown. Furthermore, we found a distinct arm differentiation, as not every arm was equipped with the same hookmorphotypes. Here, we report the functional specialisation of the belemnoid arm crown for the first time and speculate about the potential function of the four morphotypes. Our analyses suggest a highly adapted functional morphology and intra-specimen individual distribution of belemnoid hooks, serving distinct purposes mainly during prey capture, prey digestion, as well as reproduction. In this regard, hooks at the distal end of the arms show stronger curvature to effectively catch and hold the prey, while hooks closer to the belemnoids mouth are more suitable for prey dissection and for transporting food to the mouth. We speculate that this highly specialised arrangement is an adaptation of Chondroteuthis towards its uniserial hook-arrangement. This is supported by the fact that belemnoids with biserial hook armament do not show interindividual changes in micro-hook morphology (Engeser 1987).

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Section: Discussionmentioning

confidence: 99%

Grasping the shape of belemnoid arm hooks—a quantitative approach

Hoffmann¹,

Weinkauf²,

Fuchs³

2017

Paleobiology

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“…1 h–k), the decabrachian type of sucker (Fig. 1 a–d) is stalked (pedunculated) and equipped with a sclerotised cylinder (sucker ring) and a muscular piston that fits into this cylinder (e.g., Haas, 1989 ; Nixon, 2011 ). Despite this and a number of other morphological differences such as the sucker symmetry (e.g., Nixon, 2011 ), the two sucker types share a sucker cup (acetabulum) and an attachment ring (infundibulum).…”

Section: Suckersmentioning

confidence: 99%

“…1 a–d) is stalked (pedunculated) and equipped with a sclerotised cylinder (sucker ring) and a muscular piston that fits into this cylinder (e.g., Haas, 1989 ; Nixon, 2011 ). Despite this and a number of other morphological differences such as the sucker symmetry (e.g., Nixon, 2011 ), the two sucker types share a sucker cup (acetabulum) and an attachment ring (infundibulum). Ontogenetically, both sucker types are known to derive from transverse bulges very similar to those on the arms of Nautilus (Haas, 1989 ).…”

Section: Suckersmentioning

confidence: 99%

“…The idea of “chitinous” sucker rings is widespread (e.g., Boletzky, 2006 ; Doguzhaeva & Mapes, 2014 ; Engeser, 1990 ; Engeser & Clarke, 1988 ; Kear et al, 1995 ; Naef, 1922 ; Nixon, 2011 ; Pfeffer, 1912 ; Stevens, 2010 ). Although repeatedly emphasised by various authors (e.g., Nixon & Dilly, 1977 ; Nolte & Fioroni, 1983 ; Rudall, 1955 ; Young et al, 1998 ), it is here again crucial to clarify that chitin has never been analysed in decabrachian sucker rings.…”

Section: Sucker Ringsmentioning

confidence: 99%

“…These hooks are covered on the outside by a thin translucent dermal sheath; only the tips of the claws are free. Shape, number, and arrangement of these commonly called hooks vary considerably even along arms and tentacles (Nixon, 2011 ). The claw characteristically curves towards the hook base, which still exhibits an aperture as a reminiscence of the former sucker ring.…”

Section: Oegopsid Arm Hooksmentioning

confidence: 99%

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Evolutionary development of the cephalopod arm armature: a review

2021

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The cephalopod arm armature is certainly one of the most important morphological innovations responsible for the evolutionary success of the Cephalopoda. New palaeontological discoveries in the recent past afford to review and reassess origin and homology of suckers, sucker rings, hooks, and cirri. Since a priori character state reconstructions are still ambiguous, we suggest and discuss three different evolutionary scenarios. Each of them is based on the following assumptions: (1) Neocoleoidea uniting extant Decabrachia and Octobrachia is monophyletic (= proostracum-bearing coleoids); (2) extinct Belemnitida and Diplobelida are stem decabrachians; (3) proostracum-less coleoids (Hematitida, Donovaniconida, Aulacoceratida) represent stem-neocoleoids; (4) Ammonoidea and Bactritoidea are stem coleoids. We consider a scenario where belemnoid hooks derived from primitive suckers as well-supported. Regarding belemnoid hooks and suckers as homologues implies that belemnoid, oegopsid, and probably ammonoid arm hooks arose through parallel evolution. Our conclusions challenge the widespread opinion, whereupon belemnoid hooks evolved de novo, and instead support earlier ideas formulated by Sigurd von Boletzky.

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A new vampyromorph species from the Middle Jurassic La Voulte‐sur‐Rhône Lagerstätte

Rowe¹,

Kruta²,

Villier³

et al. 2023

Papers in Palaeontology

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Eight coleoid genera have so far been described from the Callovian‐aged La Voulte‐sur‐Rhône Lagerstätte (c. 165 Ma; Ardèche, France), a locality noted for its unique three‐dimensional preservation of soft tissues. Here, we used high resolution x‐ray‐based imaging methods, in conjunction with reflectance transformation imaging, to study the soft tissues of a previously undescribed coleoid from the La Voulte‐sur‐Rhône locality. This analysis identified both an ink sac and internal light organs, a combination of defence mechanisms present in the Recent, although not previously described from the coleoid fossil record, as well as the presence of Octobrachia‐type arm musculature and Vampyroteuthis‐like sucker attachments. The morphology of the gladius could not be attributed to any known coleoids and therefore justified the assignment of this single specimen to a new taxon: Vampyrofugiens atramentum. The addition of this new vampyromorph species not only increases the coleoid diversity known from the site, but also broadens the morphological variation observed in the co‐occurring coleoid taxa. These findings suggest that there was a high diversity of cephalopods occupying differentiated communities during the Middle Jurassic.

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Treatise Online, no. 17, Part M, Chapter 3: Anatomy of Recent forms

Cited by 6 publications

References 60 publications

Grasping the shape of belemnoid arm hooks—a quantitative approach

Grasping the shape of belemnoid arm hooks—a quantitative approach

Evolutionary development of the cephalopod arm armature: a review

A new vampyromorph species from the Middle Jurassic La Voulte‐sur‐Rhône Lagerstätte

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