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Preliminary Note on a Hitherto Unknown Form of the Eight-Armed , Genus Gonatqpsis, from Northern North Pacific

Takashi OKu'rANi

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(paJtt Plate 5)

During the course of study on in the stomach contents of sperm whales taken from the northern North Pacific and the Bering Sea (OKuTANi & NEMo'ro, 1964),

a single specimen of strange eight-armed squid was found. As the specimen was almost spoiled superficially, it was erroneously misidentified in the previous report. The re-

sult of close observation of the specimen finally revealed that this belongs to the genus () and shows some differences from the known three forms of the genus, namely, Genatopsis octopedatus SAsAKT, G. borealis SAsAKr and G. borealis makho OKuTANi & NEMoTo. It may be described as a new species or subspecies, but a new

name will be deferred until better specimens wil! be availab!e in future. The precise

locality of the specimen is not known, but it might be taken near the Aleutian Chain. The present report is aiming at providing an information of existence of a probable differentiated form of Gonatopsis borealis-group which may be one of the puzzling

groups of squid. It is interesting to find the fact that the present specimen retains the trace of degenerated tentacle as a fleshy process between third lateral and ventral

arms.

Observation of the specimen

The external shape agree with general Gonatid squid. The epithelium with dark purplish (in preserved condition) are almost stripped off on the , while it is retained on the head, funnel and proximal portions of the arms. The in- tegument is rather thick but very soft. The softness of integument may not be due

to digestive fluid of a , because other types of Gonatid examined on the

same occasion never lost robustness of integument even they were more badly digested

(Fig. 1). The dorsal mantle length measures 230mm. and width of the mantle at the an- terior end, about 90mm. The mantle tapers gradually towards the posterior end. The

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middle of the dorsal free rnargin terminates in a prominant triangular end, while ex- cavation on the ventral margin is very shallow. The fin is rhomboidal or sagittate, and is soft but muscular and thick. The length of the fin is about 100mm. and the width is presumed to be 160mm. or so; the marginal portion is badly nipped and torn. The head is not larger than the mantle opening. Neck is strongly constricted and clearly marked off from the head. Eye is very large, with a wide opening which has a deep sinus in front. A minute olfactory crest is present on both posterior ends of the funnel excavation wliich is very smooth and has no ridges at the circumference (Fig. 4). Funnel is of moderate size, with a large semilunar valve. Dorsal funnel organ is inverse V-shaped and a ramification measures about 25mm (Fig. 10). The ventral organ consists of a pair of ovoidal pads which measure 18mm. in major diameter and 8mm. in minor diameter. Funnel cartilage is slender, slightly curved renal form and 26rnm. in length (Fig. 6). The Iocking socket is very shallow and widened posteriorly. The plug on the mantle is very short and nearly hemi-rodshaped (Fig. 9). Nuchal cartilage almost quadrangular with rounded corners and its middle portion being feebly concave (Fig. 5). Arms are remained only in proximal portion and, consequently, armatures on the distal parts are not known. The measurements of remained part of respective arms are as follows:

right left

Dorsal 130 mm. 150 mm.

2nd lateral 140 105

3rd lateral 170 160

Ventral 110 100

The outer suckers are all lost, but weak and short pedicels on which suckers might be present are remained (Figs. 7, 8). All of arms except the dorsal ones seem to have a pair of rows of small hooks between outer rows of suckers on both sides of sucker-

bearing faces of the arms. The hooks are situated apart from each other in an oblique positions and 2-3 pairs on the proximal portions are immature hooks that retain nature of suckers. Of the dorsal arm, middle pair of armature is not hooks but small suckers.

Five to nine pairs of hooks or suckers of the middle rows are observed on the entire length of remained portion of the arms. Between the ventral and third arms, a pair of short fleshy process is present. It is laterally compressed and semi-quadrilateral in profile. The anterior margin is cut in a knife-edge, but the posterior to distal margin are widened and roundish with purplish chromatophores. This strange fleshy process is considered to be a remains of the degenerated tentacle (Figs. 2, 3). Buccal membrane seems to be supported with 7 ribs. Gladius is apparently a pen- niform one, but almost broken into pieces.

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Comparison to G. boreatis

Although the closest species to the present specimen is decidedly GonataPsis boreatis SAsAKi, there are found a number of different characteristics from G. borealis: Mantle : The mantle of G. borealis is quite muscular and robust even it is badly digested in sperm whale's stomach. There was not any examples that have such a soft and loose musculature as is observed on the present specimen. Olfactory crest: G. boreaiis has four crests on the posterier part of the head but

only a single minute crest was found on the present specimen, Locking cartilage: The general shape of funnel cartilage ef both species are similar each other, but the socket groove of th/ present specirnen seems to be shal- lower than that of G. borealis. The mantle plug of G. borealis is elongated wedge- shaped and that of the pres-.a.nt specimen is short hemi-rod-shaped. Armature of brachial arms: The principle of arrangement of hooks and suckers is common to that of G. borealis, ie. the dorsal arm has four series of suckers

only and other arms have two sL'ries of hooks in the middle and two pairs of suckers outside. Even on those arms, s:veral proximal pairs of hooks are immature and re- main nature of suckers. The most remarkable difference between G. borealis and the hooks present specimen is size and density of hooks. On the former, large and strong are arranged very closely each other and they cover the major pertion of the sucker- bearing face of arms, On the latter, small and weak hooks are so sparsely arranged The on the arms that the large portion of naked sucker-bearing face of arm is seen. comparison of armature on the distal portion could not be made as the only proximal portion of arms are remained on the present specimen. The most noteworthy finding on the present specimen is a remnant of degenerat- ed tentacles. Result of examination on small adolescent specimens Qf G. borealis

revealed that the species does not retain any remnants ef tentacle despite this seems to have normal tentacles in early stage of the life (OKuTANi 1966). The internal characteristics so far observed do not seem to be different from those of G. borealis. The visceral organs of the present specimen were badly invaded by number of large nemathelminths which are parasitic to the sperm whale.

Consideration

As far as the present specimen is concerned, a short fleshy appendage seems to be a normal remnant of degenerated tentacle and not a remains of accidentaly cut

tentacle. If this is not abnormal, this is an exceptional case among eight-armed squids

and rnay be an important phylogenic link between Gonatzts and GonatQPsis. This fact may be suggested that this specimen is a contingent or belongs one of probable poly-

typic subspecies of G. borealis.

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摘 要

北 部 太 平 洋 産 の マ ッ コ ウ ク ジ ラ の 胃中 か ら発 ．見 さ れ た イ カ 類 中 に GonatePsis 属 に 属 す る 未 記 載 の 1 種 を 一 認 め た 。 単 慓 本 で も あ り，か な り破 損 し て い る の で ， 現 段 階 で 新 種 名 を 与 え る こ と は さ し 控 え た が ， 複 雑

て い と こ の い で に 分 化 し る 思 わ れ る Gonatidae に 更 に よ う な 型 が あ る と う 情 報 を 与 え る 意 味 予 報 す る 。

octoPedatus bore α iis makho 標 本 は 同 属既 知種 ， G ． SASAKI，G ．borealisSASAKI お よ び G ． OKVTANI ＆ 一 NE 皿 orrO の 何 れ と も 異 る 特 徴 を も っ て い る が ， 明 ら か に G ． borealis 種 群 の 員 と 考 え ら れ る 。典 型 的 な G ．

borealis と は 次 の よ うな点 で 異 な る 。

（1） 外 套膜 ： G ．boreagis の よ う に 強 靱 な 筋 肉質 で な く柔 か く締 りが な い 。 こ れ は 必 ず し も マ ッ コ ウ タ ジ

ラ の 消 化 液 の せ い で は な い と 考 え られ る 。な ぜ な ら ば ， こ の 標 本 よ り更 に 消 化 度 の 進 ん だ 他 の Gonatidae と ． い え ど も筋 肉 質 の 陸質 が 失 わ れ て い な い 。

2 ： の は ． の と い （） 外 套 軟骨 器 漏 斗 軟 骨 器 形 状 G borealis そ れ 殆 ど 変 らな が ，外 套 軟骨 器 が 極 め て 短 く， 漏 ．斗軟 骨 器 の 溝 も 浅 い よ うで あ る 。

腕 ： 先 端 の 部分 は 各 腕 と も失 わ れ て い て 比 較出 来 な い e 残 さ れ た 部分 を 見 る 限 りで は ，吸 盤 と 鉤 の 配

列 の 原 則 は G ．borealis と 変 ら な い が ， G ． boreaiis の そ れ は 強 力 な 鉤 が 密 生 し て い る の に 比 し ，弱 く小 さ い

鉤 が 広 い 間 隔 を あ け て 並 ん で い る 点 明 らか な相 異 で あ る n

〔4） 触 腕 ： GonatoPsis 属 は 幼 時 触 腕 を 持 っ て い る と 推 察 さ れ る が ， 触 腕 を 失 っ た 痕 跡 は 何 も認 め る こ と

い の で で は こ 1cm の が 出来 な が 普通 あ る 。 本 標 本 れ が 長 さ 程 側 扁 し た 肉 質 の 附 属肢 的 な 痕 跡 と し て 残 っ て

い る 点 他 に 類 例 を 見 な い 特 徴 で あ る 。

References

OKul ］ANr ， T ．，1966 ： Planktonic larvae of decapodan from the Northern North Pac 三且c

summer seasons 1952−1959 Bu 〃 Toleai fteg Fisher Res 五 ab − in during ． 。 ． ． ． ．45 ； 61 79 ， 3pls ． OKuTANI ， T ．＆ T ． NE ｝loTo ，1964 ： Squids as the food of sperm whales in the Bering Sea and Ala． skan Gulf． Rept ． VVhal侈s ム〜召s． lnst．18 ： 111 −122 ，5pls ．

SAsAKL M り 1929 ： Amonograph of the dibranchiate cephalopods of the Japanese and adjacent

waters ア 4gr 1 − ． ／0u ．Co 〃 ．． ．Hokkaido 加 ρ．Univ ．20 ： 1 357， 30 pls．

Explanations of Plate 5

Fig． 1． Dorsal view of GenatoPsis sp ． found from the stomach of sperm whale from the North Pacific （DML ： 230 mm ．） Fig ． 2． Showing the fieshy appendage between ventral （IV ） and third arms （HI ＞． B denotes the buccal membrane ．

コ n FF 99 δ ロ Right appendage ， enlarged ， ca ．5mm ． in length ．

ユ ロ 4リ Surrounding of right eye showing the fleshy appendage between the ventra1 （IV ） and third （III） arms ．

Fig ． 567■ Nuchal cartilage ．

Fig ． ● Funnel cartilage ，

Fig． ・ The right dorsal arm ， showing sparsely distributed hooks and pedicels on which small suckers might be born indicated by arrows ． の （ ） FFFig 99コ 89 The middle part of left second arm ， ロ ロ り Mantle plug ． 。10． Funnel organs ． Fig ．1L Rostra，

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PIate 5

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OKC,I'ANI: Unknown Form of Eight-Armed Squid

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