Aspects of the biology of the jewel squid Histioteuthis (Mollusca, Cephalopoda, Histioteuthidae) in Maltese waters

Abstract

The deep water cephalopods of the Central Mediterranean have not been extensively studied mainly due to the difficulty in accessing deep water. Neither of the two faunistic studies on the cephalopods of Maltese waters (Schembri & Schembri, 1997; Cachia et al., 2004) include any species of Histioteuthis. There are also no studies on any species of Histioteuthis in the Central Mediterranean. The present study records the genus Histioteuthis from Maltese waters for the first time and studies a limited number of specimens that were collected more or less incidentally, in order to identify the species present and to provide a detailed description of morphological characteristics shown by these species. This study was initially triggered by the collection of one specimen of Histioteuthis that could not be placed with certainty in any of the recorded Mediterranean species and it turned into a wider study when it was found that not much was known about these squid in the Central Mediterranean. All specimens were collected by trawling, either by local fishers or as part of the MEDITS trawl surveys made between 2007 and 2010. Specimens were frozen on collection and were then thawed and a number of morphological measurements were made and other parameters were observed. Cluster analysis and NMDS ordination on a specimen/parameter matrix were used to determine the number of Histioteuthis species present in the sample. A total of 69 Histioteuthis individuals were analysed: 32 females, 29 males, and another 8 that whose sex could not be determined. The dorsal mantle length ranged from 40 mm to 212 mm and the total weight ranged from 20g to 2490 grams. Cluster analysis resulted in two clusters which, on the basis of the morphological features of the constituent specimens corresponded to the two Mediterranean species: H. bonnellii and H. reversa. There were significant differences between the two species in the photophores round the left eye, those round the right eye, and on all arms, as well as in the radula, buccal membrane, tentacles, inner web and rings of suckers; however there were no significant differences in the configuration of the outer web. Significant differences were found between the total weight of the two species considered separately, however, no difference was found between the depth of collection for the two species. Significant differences were also found between the total weight and the maturity stage, and between the dorsal mantle length and maturity stage for the two species. However no differences were found between the total weight and dorsal mantle length in the two sexes or in the depth of collection when considered separately. Additionally, no significant difference was found between the depth of collection and the maturity stage and gender for either species.