Pelagic Squid Research Articles

Endohelminth parasites of some midwater and benthopelagic stomiiform fishes from the northern Gulf of Mexico

Mesopelagic fishes represent significant ecological links between mesozooplankton and the larger pelagic squids, fishes, and marine mammals. As such, these fishes also play a significant role as intermediate or paratenic hosts for parasites that require a crustacean intermediate host and mature in marine mammals or pelagic fishes. We examined a total of 208 individuals representing 5 species of Sternoptychidae and 88 individuals representing 2 species of Phosichthyidae from 20 locations in the northern Gulf of Mexico (nGOM). Six of the 7 species we examined are mesopelagic and one species was benthopelagic. We found the larval stages of Anisakis brevispiculata, Anisakis typica, Hysterothylacium fortalezae (all Nematoda: Ascaridoidea); Bolbosoma sp. (Acanthocephala: Polymorphidae); and Tetraphyllidea (Cestoda) plus an immature specimen of Brachyphallus sp. (Digenea). Molecular sequencing was used to identify the ascaridoids and Bolbosoma sp. and to confirm the identification of 3 host sternoptychid species. The mesopelagic fishes hosted Anisakis brevispiculata (that matures in pygmy and dwarf sperm whales) and Hysterothylacium fortalezae (that matures in pelagic fishes, primarily mackerels), whereas the benthopelagic species was parasitized by Anisakis typica (that matures in dolphins). We suggest this pattern of infection indicates a pelagic life—cycle for Anisakis brevispiculata and Hysterothylacium fortalezae and a demersal life—cycle for Anisakis typica. Our study represents the first published sequences from the nGOM for the fishes Argyropelecus aculeatus, Maurolicus weitzmani, and Polyipnus clarus and the first molecular identification of larval ascaridoids from mesopelagic fishes in the nGOM.

Wind-driven upwelling effects on cephalopod paralarvae: Octopus vulgaris and Loliginidae off the Galician coast (NE Atlantic)

Circulation patterns of coastal upwelling areas may have central consequences for the abundance and cross-shelf transport of the larval stages of many species. Previous studies have provided evidences that larvae distribution results from a combination of subtidal circulation, species-specific behaviour and larval sources. However, most of these works were conducted on organisms characterised by small-sized and abundant early life phases. Here, we studied the influence of the hydrography and circulation of the Ría de Vigo and adjacent shelf (NW Iberian upwelling system) on the paralarval abundance of two contrasting cephalopods, the benthic common octopus (Octopus vulgaris) and the pelagic squids (Loliginidae). We sampled repeatedly a cross-shore transect during the years 2003–2005 and used zero inflated models to accommodate the scarcity and patchy distribution of cephalopod paralarvae. The probability of catching early stages of both cephalopods was higher at night. Octopus paralarvae were more abundant in the surface layer at night whereas loliginids preferred the bottom layer regardless of the sampling time. Abundance of both cephalopods increased when shelf currents flowed polewards, water temperature was high and water column stability was low. The probability of observing an excess of zero catches decreased during the year for octopus and at high current speed for loliginids. In addition, the circulation pattern conditioned the body size distribution of both paralarvae; while the average size of the captured octopuses increased (decreased) with poleward currents at daylight (nighttime), squids were smaller with poleward currents regardless of the sampling time. These results contribute to the understanding of the effects that the hydrography and subtidal circulation of a coastal upwelling have on the fate of cephalopod early life stages.

Population dynamics of the squids Dosidicus gigas (Oegopsida: Ommastrephidae) and Doryteuthis gahi (Myopsida: Loliginidae) in northern Peru

Pelagic squids of continental shelf ecosystems mostly include oceanic and migratory species of the family Ommastrephidae and neritic species of the family Loliginidae. These two families have contrasting life history strategies; ommastrephids spawn in the open ocean and are thought to have a high dispersal potential, while loliginids spawn on the bottom and are likely to have a low dispersal potential. Consequently, these squid species should display different patterns in their population dynamics, which can be inferred through commercial catches. To study the population dynamics of the Ommastrephidae and the Loliginidae families, monthly time series catches of Dosidicus gigas and Doryteuthis gahi were used. These artisanal fishery catches were made in northern Peru from 1999 to 2010. They were standardized to construct autocorrelation functions so that the relationship between catch dynamics and short-term environmental change (thermal anomalies of sea surface temperature were used as a proxy) could be studied. The results revealed that increases in catches of D. gigas and D. gahi are not related to thermal anomalies, but rather a pattern of drastic fluctuations in D. gahi catch sizes are seen. In, both species, temporal relationships indicate that the annual growth rate and changes in abundance can modelled as a function of the catch density observed in previous years. We propose that these population differences result from the contrasting life history strategies and differential habitat use of these two squid species.

Branchial NH 4 + ‐dependent Acid‐base Transport Mechanisms and Energy Metabolism of Squid ( Sepioteuthis lessoniana ) Affected by Seawater Acidification

CO2 induced pH fluctuation in the extracellular compartments are a unifying physiological phenomenon that all animals are confronted with. Cephalopods have evolved acid-base regulatory abilities to accommodate temporal pH fluctuations via highly pH sensitive hemocyanins. Interestingly, it has been suggested that metabolic energetic limitations may be a critical factor when exposed to acidified seawater. Here we show the effects of short-term (few hours) to medium-term (up to 168 h) seawater acidification on pelagic squids, Sepioteuthis lessoniana. Routine metabolic rates, NH4+ secretion and extracellular acid-base balance were monitored during exposure to control (pH 8.1) and acidified conditions of pH 7.7 and 7.3 along a period of 168h. Metabolic rates were significantly depressed by 40% after 168 hours in pH 7.3 conditions exposure. The extracellular pH is fully restored within 20 h and is maintained along the period of 168 h, and the accompanied acid-base transporter transcripts were up-regulated including V-type H+-ATPase (VHA), Rhesus protein (RhP), Na/HCO3- cotransporter (NBC) and cystolic carbonic anhydrase (CAc). Immunohistochemical analyses demonstrated co-localization of Na+/K+-ATPase (NKA), VHA in basolateral and Na+/H+-exchanger 3 (NHE3), RhP in apical membranes of the branchial epithelium. Protein levels of branchial VHA and RhP were increased in response to acidified conditions. The present work demonstrated the NH4+ based proton secretion via RhP may contribute to a well-developed acid-base regulatory machinery in branchial epithelia of cephalopods.

Isolation and characterization of microsatellite loci in the purpleback flying squid (Sthenoteuthis oualaniensi).

The purpleback flying squid (Sthenoteuthis oualaniensis) is a pelagic squid with tremendous potential for commercial exploitation. We isolated and characterized 21 polymorphic microsatellite loci for S. oualaniensis using a (GT)13-enriched genomic library. The number of alleles per locus varied from 6 to 32. The observed and expected heterozygosities ranged from 0.188 to 0.890, and 0.537 to 0.968, respectively. No significant linkage disequilibrium was detected at these loci. Five loci significantly deviated from the Hardy-Weinberg equilibrium, and four loci may have exhibited null alleles. These microsatellite markers will facilitate further studies in population genetics and the sustainable utilization of S. oualaniensis.

An ethogram of the Humboldt squid Dosidicus gigas Orbigny (1835) as observed from remotely operated vehicles

Many cephalopods can rapidly change their external appearance to produce multiple body patterns. Body patterns are composed of various components, which can include colouration, bioluminescence, skin texture, posture, and locomotion. Shallow water benthic cephalopods are renowned for their diverse and complex body pattern repertoires, which have been attributed to the complexity of their habitat. Comparatively little is known about the body pattern repertoires of open ocean cephalopods. Here we create an ethogram of body patterns for the pelagic squid,Dosidicus gigas. We used video recordings of squid made in situ via remotely operated vehicles (ROV) to identify body pattern components and to determine the occurrence and duration of these components. We identified 29 chromatic, 15 postural and 6 locomotory components forD. gigas, a repertoire rivalling nearshore cephalopods for diversity. We discuss the possible functional roles of the recorded body patterns in the behavioural ecology of this open ocean species.

Development and characterization of twenty-three microsatellite markers for the purpleback flying squid (Symplectoteuthis oualaniensis)

The purpleback flying squid (Symplectoteuthis oualaniensis) is a pelagic squid that is facing the serious threat of large-scale commercial exploitation in the South China Sea. In this study, microsatellites were developed for the first time in this species using biotinylated probes for hybridization and library screening. Twenty-three polymorphic microsatellite markers were isolated and characterized in a wild population. The number of alleles varied from 5 to 28, and the observed and expected heterozygosity ranged from 0.220 to 0.867 and 0.374 to 0.958, respectively. Significant deviations from Hardy–Weinberg equilibrium values were detected in six loci. These markers will facilitate further studies in conservation of genetic diversity and sustainable utilization of S. oualaniensis.

Branchial NH4+-dependent acid–base transport mechanisms and energy metabolism of squid (Sepioteuthis lessoniana) affected by seawater acidification

Cephalopods have evolved strong acid–base regulatory abilities to cope with CO2 induced pH fluctuations in their extracellular compartments to protect gas transport via highly pH sensitive hemocyanins. To date, the mechanistic basis of branchial acid–base regulation in cephalopods is still poorly understood, and associated energetic limitations may represent a critical factor in high power squids during prolonged exposure to seawater acidification. The present work used adult squid Sepioteuthis lessoniana to investigate the effects of short-term (few hours) to medium-term (up to 168 h) seawater acidification on pelagic squids. Routine metabolic rates, NH4+ excretion, extracellular acid–base balance were monitored during exposure to control (pH 8.1) and acidified conditions of pH 7.7 and 7.3 along a period of 168 h. Metabolic rates were significantly depressed by 40% after exposure to pH 7.3 conditions for 168 h. Animals fully restored extracellular pH accompanied by an increase in blood HCO3− levels within 20 hours. This compensation reaction was accompanied by increased transcript abundance of branchial acid–base transporters including V-type H+-ATPase (VHA), Rhesus protein (RhP), Na+/HCO3− cotransporter (NBC) and cytosolic carbonic anhydrase (CAc). Immunocytochemistry demonstrated the sub-cellular localization of Na+/K+-ATPase (NKA), VHA in basolateral and Na+/H+-exchanger 3 (NHE3) and RhP in apical membranes of the ion-transporting branchial epithelium. Branchial VHA and RhP responded with increased mRNA and protein levels in response to acidified conditions indicating the importance of active NH4+ transport to mediate acid–base balance in cephalopods. The present work demonstrated that cephalopods have a well developed branchial acid–base regulatory machinery. However, pelagic squids that evolved a lifestyle at the edge of energetic limits are probably more sensitive to prolonged exposure to acidified conditions compared to their more sluggish relatives including cuttlefish and octopods.

Slow swimming, fast strikes: effects of feeding behavior on scaling of anaerobic metabolism in epipelagic squid.

Many pelagic fishes engage prey at high speeds supported by high metabolic rates and anaerobic metabolic capacity. Epipelagic squids are reported to have among the highest metabolic rates in the oceans as a result of demanding foraging strategies and the use of jet propulsion, which is inherently inefficient. This study examined enzymatic proxies of anaerobic metabolism in two species of pelagic squid, Dosidicus gigas and Doryteuthis pealeii (Lesueur 1821), over a size range of six orders of magnitude. We hypothesized that activity of the anaerobically poised enzymes would be high and increase with size as in ecologically similar fishes. In contrast, we demonstrate that anaerobic metabolic capacity in these organisms scales negatively with body mass. We explored several cephalopod-specific traits, such as the use of tentacles to capture prey, body morphology and reduced relative prey size of adult squids, that may create a diminished reliance on anaerobically fueled burst activity during prey capture in large animals.

Branchial NH

BackgroundCephalopods have evolved strong acid–base regulatory abilities to cope with CO2 induced pH fluctuations in their extracellular compartments to protect gas transport via highly pH sensitive hemocyanins. To date, the mechanistic basis of branchial acid–base regulation in cephalopods is still poorly understood, and associated energetic limitations may represent a critical factor in high power squids during prolonged exposure to seawater acidification.ResultsThe present work used adult squid Sepioteuthis lessoniana to investigate the effects of short-term (few hours) to medium-term (up to 168 h) seawater acidification on pelagic squids. Routine metabolic rates, NH4+ excretion, extracellular acid–base balance were monitored during exposure to control (pH 8.1) and acidified conditions of pH 7.7 and 7.3 along a period of 168 h. Metabolic rates were significantly depressed by 40% after exposure to pH 7.3 conditions for 168 h. Animals fully restored extracellular pH accompanied by an increase in blood HCO3− levels within 20 hours. This compensation reaction was accompanied by increased transcript abundance of branchial acid–base transporters including V-type H+-ATPase (VHA), Rhesus protein (RhP), Na+/HCO3− cotransporter (NBC) and cytosolic carbonic anhydrase (CAc). Immunocytochemistry demonstrated the sub-cellular localization of Na+/K+-ATPase (NKA), VHA in basolateral and Na+/H+-exchanger 3 (NHE3) and RhP in apical membranes of the ion-transporting branchial epithelium. Branchial VHA and RhP responded with increased mRNA and protein levels in response to acidified conditions indicating the importance of active NH4+ transport to mediate acid–base balance in cephalopods.ConclusionThe present work demonstrated that cephalopods have a well developed branchial acid–base regulatory machinery. However, pelagic squids that evolved a lifestyle at the edge of energetic limits are probably more sensitive to prolonged exposure to acidified conditions compared to their more sluggish relatives including cuttlefish and octopods.

Cephalopods in the diet of young-of-the-year bluefin tuna (Thunnus thynnus L. 1758, Pisces: Scombridae) from the southern Tyrrhenian Sea (central Mediterranean Sea)

Information on distribution and abundance of cephalopods inhabiting pelagic water masses is often not available because of the difficulty of applying conventional methods in this remote habitat. An alternative source of information is represented by stomach content analysis of pelagic predators that are known to be efficient cephalopod prey collectors. This study focuses on the occurrence of cephalopod prey in the diet of young-of-the-year bluefin tuna (Thunnus thynnus L. 1758, Pisces: Scombridae) in the southern Tyrrhenian Sea (central Mediterranean). Overall, 139 fishes were sampled by trolling lines or purse-seine in a Fish Aggregating Devices (FADs) area and as by-catch of the purse-seine sardine fishery, from 1998 to 2000 between July and November. Cephalopods found in the stomach contents were identified to the lowest possible taxon and, when digestion was too advanced, beaks from stomachs were considered as the best taxonomic feature for classification. Of a total of 1233 cephalopod prey, 1144 individuals were identified, belonging to 15 species. Onychoteuthis banksii was the most common prey (%N = 58.39), followed by Heteroteuthis dispar (%N = 23.03). This importance was confirmed also in terms of biomass with O. banksii and H. dispar that respectively reached 39.41% and 21.23% in weight, followed by Todarodes sagittatus (%W = 20.16). In general, young-of-the-year bluefin tunas are able to feed on a large spectrum of cephalopod prey in the study area, usually relying on juvenile specimens and epipelagic and mesopelagic shoaling species. In fact, the identified preys mainly belong to muscular squids (71%) and sepiolids (25%), but pelagic octopuses, buoyant squids and juvenile demersal octopuses were also recorded. These data provide further information on the feeding habits of T. thynnus, relative to a poorly investigated life stage. The improving knowledge on trophic relationships of young tunas and their reliance on cephalopod taxa is an important step in supporting management of this fishery resource.

Diet composition of the Guadalupe fur seal (Arctocephalus townsendi). Where and what do they eat?

The Guadalupe fur seal (Arctocephalus townsendi) is a specialist predator feeding on prey present in one trophic level. Data related to the diet of the Guadalupe fur seal are few. It is still unknown where most of the individuals forage or the composition of their diet. On Isla Guadalupe, the San Benito Archipelago and the Farallon Islands, fur seals primarily feed on pelagic and coastal squids. However, differences between colonies were found probably caused by differences in diversity and abundance of prey species over the continental shelf and the pelagic environment, and maybe due to the plasticity of the species in their foraging behavior. Diet composition of the Guadalupe fur seal might reflect adaptations to local and temporal environmental conditions. The aim of this work was to consider historical information, add new information, identify main prey species, and determine where in the marine regions the Guadalupe fur seals feed.

Ocean nomads: Distribution and movements of sperm whales in the North Pacific shown by whaling data and Discovery marks

AbstractWe investigated the distribution and movements of sperm whales (Physeter macrocephalus) in the North Pacific by analyzing whaling data and movement data of whales marked with Discovery marks. Prior studies suggested that there were discrete “stocks” of sperm whales, assuming that the intervals between historical areas of concentration indicated subpopulation boundaries. Our analyses clearly refute this assumption: whaling and marking data suggest no obvious divisions between separate demes or stocks within the North Pacific. Sperm whales appear to be nomadic and show widespread movements between areas of concentration, with documented movements of over 5,000 km, time spans between marking and recovery over 20 yr, and ranges that cover many thousand km2. Males appear to range more widely than females. Sperm whales likely travel in response to geographical and temporal variations in the abundance of medium‐ and large‐sized pelagic squids, their primary prey. Our analyses demonstrate that males and females concentrated seasonally in the Subtropical Frontal Zone (ca. 28ºN–34ºN) and the Subarctic Frontal Zone (ca. 40ºN–43ºN), and males also concentrated seasonally near the Aleutian Islands and along the Bering Sea shelf edge. It appears that the sperm whales targeted by the pelagic whalers range widely across this ocean basin.

Life History of Risso’s Dolphin (Grampus griseus) (G. Cuvier, 1812) in the Faroe Islands

Risso’s dolphins (Grampus griseus) were taken for the first time by the opportunistic drive fishery in the Faroe Islands in two separate incidents: three in September 2009 and 21 in April 2010, with in total 16 females and eight males. Their sizes ranged from 193 to 308 cm in length and 60 to 395 kg in weight for females, and 186 to 323 cm in length and 70 to 505 kg in weight for males; the maximum weights are heavier than previously documented for this species. The smallest mature female was 277 cm long, while the youngest and also lightest mature female was 8 y old and weighed 280 kg. Sperm competition and a promiscuous mating system were suggested for the species based on large testicular masses. The diet was composed of cephalopods from both the water column (Todarodes and Loligo) and the ocean floor (Eledona and Todaropsis). Although both schools landed showed a mixed diet, the September school diet centred on a pelagic squid (Todarodes sagittatus), while the April school diet centred upon a benthic octopod (Eledona cirrhosa). Since August 2009, Risso’s dolphins have been observed on five occasions in waters around the Faroese north of 61o 34' N, the northernmost observation situated at a latitude of 62o 23' N. Sightings of the species off Shetland occur mostly between April and September, with a peak in August and September, the observations in Faroese waters (2 in April, 1 in August, and 2 in September) falling within this period. While the species had not previously been observed in this area north of the Shetland-Faroe Channel, these observations in Faroese territorial waters indicate a likely northward extension of the known range of the species.

A multi-gene phylogeny of Cephalopoda supports convergent morphological evolution in association with multiple habitat shifts in the marine environment.

BackgroundThe marine environment is comprised of numerous divergent organisms living under similar selective pressures, often resulting in the evolution of convergent structures such as the fusiform body shape of pelagic squids, fishes, and some marine mammals. However, little is known about the frequency of, and circumstances leading to, convergent evolution in the open ocean. Here, we present a comparative study of the molluscan class Cephalopoda, a marine group known to occupy habitats from the intertidal to the deep sea. Several lineages bear features that may coincide with a benthic or pelagic existence, making this a valuable group for testing hypotheses of correlated evolution. To test for convergence and correlation, we generate the most taxonomically comprehensive multi-gene phylogeny of cephalopods to date. We then create a character matrix of habitat type and morphological characters, which we use to infer ancestral character states and test for correlation between habitat and morphology.ResultsOur study utilizes a taxonomically well-sampled phylogeny to show convergent evolution in all six morphological characters we analyzed. Three of these characters also correlate with habitat. The presence of an autogenic photophore (those relying upon autonomous enzymatic light reactions) is correlated with a pelagic habitat, while the cornea and accessory nidamental gland correlate with a benthic lifestyle. Here, we present the first statistical tests for correlation between convergent traits and habitat in cephalopods to better understand the evolutionary history of characters that are adaptive in benthic or pelagic environments, respectively.DiscussionOur study supports the hypothesis that habitat has influenced convergent evolution in the marine environment: benthic organisms tend to exhibit similar characteristics that confer protection from invasion by other benthic taxa, while pelagic organisms possess features that facilitate crypsis and communication in an environment lacking physical refuges. Features that have originated multiple times in distantly related lineages are likely adaptive for the organisms inhabiting a particular environment: studying the frequency and evolutionary history of such convergent characters can increase understanding of the underlying forces driving ecological and evolutionary transitions in the marine environment.

Predation on cephalopods by Weddell seals, Leptonychotes weddellii, at Hope Bay, Antarctic Peninsula

Cephalopods play a key role in marine environments as food resources for top predators such as marine mammals and seabirds. However, detailed information on their trophic relationships with Antarctic seals is scarce. The aim of the present study was to examine the cephalopod portion of the diet of adult and subadult Weddell seals, Leptonychotes weddellii, at Hope Bay, Antarctic Peninsula, through the analysis of scats collected during three consecutive summers (2003, 2004 and 2005). Cephalopods occurred in almost 45% of the 217 samples collected during the whole period of study. A total of 662 beaks (358 upper and 304 lower) were removed from scats containing cephalopod remains (n = 93). Octopods were largely dominant in comparison with teuthoids constituting in numerical abundance over 95% of the cephalopod prey. The octopod Pareledone turqueti was the most frequent and dominant prey species representing, respectively, 57.9 and 71.1% in numbers and biomass of cephalopods consumed. Species belonging to the group of papillated Pareledone were second in importance. The results were compared with information from previous dietary studies of L. weddellii at other localities of Antarctica. Based on the examination of the cephalopod prey taxa identified in this study, it is suggested that during the study period Weddell seal individuals foraged mainly on benthic prey resources close to the coast, in inshore waters where octopods were dominant in comparison with pelagic squid.

Large aggregations of pelagic squid near the ocean surface at the Antarctic Polar Front, and their capture by grey-headed albatrosses

Abstract Rodhouse, P. G., and Boyle, P. R. 2010. Large aggregations of pelagic squid near the ocean surface at the Antarctic Polar Front, and their capture by grey-headed albatrosses. – ICES Journal of Marine Science, 67: 1432–1435. Satellite-tracked squid predators and fish-finding acoustics were used to locate squid concentrations at the Antarctic Polar Front, then to sample them with a midwater trawl. Near-surface hauls were dominated by the squid Martialia hyadesi similar in size to those fed to grey-headed albatross chicks. The characteristics of the squid and their proximity to the surface suggest that the birds locate squid concentrations by olfaction and catch them by plunging.

Squid as a resource shared by fish and humans on the Falkland Islands’ shelf

Nektonic squids are the dominant group in the Falklands Islands’ fishery representing >75% of the total annual catch. Among these squids, the benthopelagic Loligo gahi is an important link between zooplankton and fish in the shelf food web. It is preyed upon by diverse and numerous demersal and benthopelagic fishes, penguins and marine mammals, and is harvested by fishermen. Pelagic squids, Illex argentinus, Onykia ingens, and Gonatus antarcticus though seasonally very abundant, are scarce in fish diet because of the absence of specialised pelagic predators. This ecological niche is shared between humans (targeting Illex) and penguins (targeting Onykia and Gonatus). Martialia hyadesi though was abundant in some years in the past, it has now virtually disappeared from the shelf ecosystem. The biomass produced by L. gahi remains in the Falkland waters, whereas that of pelagic squid is transported out of the shelf either to the northern Patagonian slope ( I. argentinus) or to deeper waters around the islands ( O. ingens and G. antarcticus). Generally squids occupy the ecological niche of epipelagic fish on the Falkland shelf and slope.

Molecular inference of phylogenetic relationships among Decapodiformes (Mollusca: Cephalopoda) with special focus on the squid Order Oegopsida

Squids, cuttlefish and bobtail squids comprise the molluscan superorder Decapodiformes (Mollusca: Cephalopoda). Although these animals exemplify the morphological and ecological diversity seen in Cephalopoda, no previous study has focused resolving decapodiform relationships, particularly within Oegopsida, a large order comprised of pelagic squid. To further clarify the phylogenetic history of Decapodiformes, and Oegopsida in particular, molecular data for five genes (18S rRNA, 28S rRNA, Histone H3, 16S rRNA, COI) was collected for 90 taxa representing all major lineages and families and evaluated using parsimony, likelihood, and Bayesian analysis. Although ordinal relationships were sensitive to analytical method, several conclusions can be inferred: the pelagic order Myopsida is closely related to the benthic sepioids, whose relationships were ambiguous, and Bathyteuthoidea is distinct from Oegopsida. Within Oegopsida several clades are consistently recovered, some with previous morphological support (e.g. chiroteuthid, lepidoteuthid, histioteuthid families) while others suggest novel relationships (e.g. Architeuthidae + Neoteuthidae). This study, with its broad coverage of taxa, provides the first in-depth analysis of Decapodiformes with special focus on the morphologically and biogeographically diverse Oegopsida, confirms several sister-taxon relationships, and provides new hypotheses of cephalopod evolution in the open ocean.

A comparison of information-theoretically optimal classifications with estimates of phylogenetic relationships in the squid family Cranchiidae (Cephalopoda: Oegopsida)

Criteria by which some biological classifications may be judged better or worse than others have been debated for centuries, but since 1859 most systematists have striven to create taxonomies that reflect genealogical relationships, and the familiarity of such terms as “monophyletic”, “paraphyletic” and “polyphyletic” reflects a widespread concern about the nature of correspondences between classifications and phylogenies. Some systematists, however, have expressed pessimism about the ability of modern researchers to discover true phylogenies, and question the utility of phylogenetic classifications even were it possible to ascertain their historical accuracy. J. S. L. GILMOUR, an early and articulate critic of evolutionary taxonomy, proposed that biological classifications be comprised exclusively of “. . . natural groups [that] class together individuals which have a large number of attributes in common” (GILMOUR 1940: 466). The utility of natural groups, so defined, is usually equated with the information about characters conveyed by knowledge of group memberships (SOKAL and SNEATH 1963; FARRIS 1979). That classifications should (1) correspond to known or inferred phylogenies and (2) be maximally informative about characters are both intuitively appealing ideal properties, and it is therefore of interest to inquire whether or not they need be viewed irreconciliable as optimality criteria. In this paper we define ways in which classifications can correspond to tree diagrams of evolutionary history, propose quantitative measures of taxonomic information content and examine the relationships between phylogenetic reconstructions and informative classifications of pelagic squids in the family Cranchiidae.