Berryteuthis magister, Berry, 1913

Zimina, V. R., 2024, Statocysts of cephalopods can function with asymmetric statoliths: on the discovery of an anomality in statolith ontogenetic development in squid Berryteuthis septemdentatus (Coleoidea: Gonatidae), Invertebrate Zoology 21 (1), pp. 67-80 : 75

B. magister

0,106±0,01 0,197±0,01 0,540±0,04 40 t-statistics 7,842 14,733 5,16

P(T<=t) two-sided

2,38*10 -11 7,68*10 -24 2,39*10 -6

Abbreviations:l— mean length of paralarval statolith;w — mean width of paralarval statolith;n— number of statoliths.

statolith was 196.5 µm; average width: 106 µm. The width to length ratio was 0.54. All in all, thin sections of 40 B. magister statoliths were analysed. Results and t-statistics are presented in Table 2.

ABNORMAL STATOLITH. During our study one pair of statoliths extracted from maturing female B. septemdentatus with a mantle length of 198 mm and age of 191 days was found to be asymmetric: the left statolith had normal shape specific for this species, while the right statolith had abnormal shape due to develop- ment anomalies: it initially appeared as three crystallization points ( Fig. 6A ) located at 169, 46 and 215 µm apart from each other. First two crystallization points ( Fig. 6A ) represent the nucleioftwoanomalousembryonicstatoliths. In the larger embryonic statolith ( Fig. 6A ) the first growth mark corresponding to paralarva hatching is located at 49, 100, 74, 53 µm from the nucleus (measurements 104 clockwise on Fig.6A ).In the smaller embryonic statolith the distances from the nucleus to the first (hatching) growth mark are 47, 61, 23 and 45 µm (clockwise). The larger embryonic statolith is 169 µm in length and 120 µm in width, for smaller embryonic statolith similar meanings are 107 and 72 µm. Width to length ratios were 0.71 and 0.67 for both statoliths respectively. At the moment of hatching, each of these statoliths did not have tear-drop shape that is characteristic for the genus Berryteuthis . The third crystallization point ( Fig. 6A ) formed a bubble-like structure on the smaller embryonic statolith ( Fig. 6B ). The two separate paralarval statoliths merged into a single statolith only on the fourth day after hatching ( Fig. 6B ), the length of this statolith was 337 µm. Merging of two paralarval statoliths resulted in formation of a single anomalous dumbbell-shaped statolith. It is important to note that this anomaly resulted in the formation of an ugly statolith in adult- hood with an altered general shape ( Fig. 7B ). In adult statolith, an abnormal convexity is visible in the area of transition of the statolith’s body into rostrum, while in normal statoliths of this species such convexity is absent. This modified zone is marked by 3 longitudinal sutures lines originating from the boundary of two paralarval statoliths, the distance between these sutures is 274, 565 and 136, 177 µm for larger and smaller statolithsrespectively ( Fig. 6C ).Thus, anomality in the appearance of three growth points and two paralarval statoliths of modified shape induced to the change in the crystallization process for this defective statolith as a whole.As can be seen from the growth pattern of abnormal statolith, this squid for the first 4 days after hatching had two statoliths in the right statocyst chamber and one statolith in the left chamber. Such anomality resulting in appearance of asymmetric statoliths within one pair has never been described yet in coleoid cephalopods.

The statolith in the left chamber of statocyst had no anomalies in its development ( Fig. 7A ), but at first sight it seems that paralarval statolith in this specimen was more rounded than usual for B. septemdentatus ( Fig. 8 ). The length of this paralarval statolith was 242 µm and the width was 131 µm. Thus, the width to length ratio was 0.54, while in the rest 38 B. septemdentatus specimens studied the width to length ratio averaged 0.5. Distances from nucleus to first-check mark were 49, 125, 58 and 118 µm. It can be noted that the distance from the crystallization point to the hatching line in direction to lateral dome in all there paralarval statoliths from this pair of statocysts is almost identical: 49 µm and 47 µm for the defective one and 49 µm for the normal.

Figures

Fig. 6. Nuclei of abnormal B. septemdentatus statolith, light microscopy. A — three crystallization points (also called nuclei), lines radiating from the nucleus (marked from 1 to 4 clockwise) indicate the measurments of embryonic statolith (distances between nucleus and first check mark); B — dumbbell-shape paralarval statolith, black tips indicate to the first three growth lines after hatching when paralarval statoliths were separate: white tip indicates to the formation of the first common growth increment (on the fourth day after hatching) when two separate paralarval statoliths merged into a single dumbbell-shaped structure, lines show bubble-like structure; C — longitudinal sutures lines running from the boundary of two paralarval statoliths, lines show distances between sutures lines:1 and 2 are 274 and 565 µm, respectively; 3 and 4 are 136 and 177 µm, respectively. Abbreviations: n1 — nucleus number one or the first crystallization point; n2 —nucleus number two; n3 — nucleus number 3. Scale bars: A —50 µm, B — 50 µm, C — 150 µm. Рис. 6. Ядра аномального статолита B. septemdentatus, световаЯ микроскопиЯ. A — три точки кристаллиЗации (также наЗываемые Ядра), отреЗками расходЯЩимисЯ от Ядра и маркированные по часовойстрелкеот1до4, покаЗаныиЗмерениЯЭмбриональногостатолита(расстоЯние отЯдрадо первой отметки выклева);B — гантелеподобныйличиночный статолит,черные стрелкиукаЗывают на первые три неЗависимых прироста, белаЯ стрелка укаЗывает на первый обЩий прирост, сформированный на четвертый день жиЗни, когда два раЗдельных личиночных статолита срослись вместе, обраЗовав гантелеообраЗную структуру, линии покаЗывают пуЗыревидную структуру; C — микроструктура продольных Швов вдоль двух личиночных статолитов, световаЯ микроскопиЯ, линии покаЗывают расстоЯние между Швами. 1 и 2 равны 274 и 565 µm, соответственно; 3 и 4 равны 136 and 177 µm, соответственно. ОбоЗначениЯ: A — n1— первое Ядро, или перваЯ точка кристалиЗации; n2 — второе Ядро; n3 — третье Ядро. МасШтаб: A — 50 µm, B — 50 µm, C — 150 µm.

Fig. 7. Comparison of two statoliths, light microscopy. A — general view of normal statolith, light micros- copy; B — abnormal statolith with modified zones. Grey rectangle on modified zone. Scale bar: 300 µm. Рис. 7. Сравнение двух статолитов, световаЯ микроскопиЯ. А — обЩий вид нормального статолита; В — иЗмененнаЯ форма аномального статолита. Серый прЯмоугольник покаЗывает Зону иЗменениЯ внеШнего облика статолита. МасШтаб: 300 µm.

Fig. 8. Normal paralarval statolith B. septemdentatus. Lines show approximate boundaries of paralarval statolith. Scale bar: 50 µm Рис. 8. Нормальный личиночный статолит B. septemdentatus. Линии отображают примерные границы личиночного статолита. МасШтаб: 50 µm.