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Worldwide knowledge about the diversity of the cephalopods is limited although they represent an important fishery resource, and play an essential ecological role in the marine trophic web. Although adult squids can be relatively easily identified, determination of species of paralarvae and juveniles that are found in the plankton is still quite difficult. In Mexican Pacific waters, only a few attempts have been made to identify these early life history stages. Paralarvae for this study came from zooplankton samples collected with standard bongo net tows off the west coast of the Baja California peninsula in Mexico, from Ensenada to Punta Abreojos. The samples were collected by the IMECOCAL Program, as part of 4 oceanographic surveys carried out during the winter and summer of 1998 and 1999. Total abundance was 920 paralarvae/1000m³, from which 9 families, 12 genera, 12 species. Additionally, we identified ten new forms. Specimens only identified to family level were included in seven taxa. Three families of squids, namely: Onychoteuthidae (32%), Cranchiidae (28%), and Gonatidae (23%) accounted for a total of 83% of the relative abundance of paralarvae. Two species, Leachia danae and Helicocranchia beebei, plus 10 additional species of squids (identified from their paralarvae) are reported off the west coast of Mexico the first time. To date a total of 58 cephalopod taxa are known to occur in the area of study. This represents an increase of 26% in the number of species present off the west coast of the Baja California peninsula, and 20% of species reported in Mexican Pacific waters. Chromatophores were absent in almost all specimens because formalin was used for fixation of samples. As a result pigmentation patterns could not be used help identify paralarvae. However, additional morphological features such as sucker counts on the arms, shape of tubercles, plus morphometric and meristic methods were useful to identify squid paralarvae off Baja California.

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