Pale biological implications of some Upper Ordovician juvenile asteroids (Echinodermata)

Blake, D. B. 1990 10 15: Pale biological implications of some Upper Ordovician juvenile asteroids (Echinodermata). Lethaia , Vol. 23, pp. 347–357. Oslo. ISSN 0024–1164.
Two patterns have been recognized in the early dorsal skeletal development of modern asteroids. The skeleton of well-preserved juveniles of the Late Ordovician species Promopalaeaster finei is similar in fundamental ossiclar arrangement to one of these patterns, suggesting continuity of developmental sequence. Similarities include presence of large terminal ossicles and double rows of marginal ossicles. Ancient and modern juveniles differ in that in P. finei , podial pores leading to the interior of the arms are lacking, thus providing an ontogenetic argument that such pores are phylogenetically derived within the class. An unpaired interbrachial marginal, or axillary, is present distal to the oral frame; positioning supports earlier suggestions that the axillary is the homologue of the odontophore ossicle of modern asteroids. Comparisons between P. finei and another Ordovician species, Macroporaster matutinus , suggest the need for greater mouth frame flexibility contributed to the evolution of the modern odontophore. Axillary development is linked to the common absence of actinal ossicles from Paleozoic species. ▭ Asteroidea, Echinodermata, functional morphology, ontogeny, phylogeny, Ordovician, Paleozoic .     

Larval development of three blenniid species Aidablennius sphynx, Coryphoblennius galerita and Lipophrys canevai (Pisces: Blenniidae: Blenniini) in the western Mediterranean

The early stages of development of three blenniid species, Aidablennius sphynx (6.7–15.8 mm BL), Coryphoblennius galerita (4.3–13.9mm BL), and Lipophrys canevai (3.5–10.4 mm BL) are described from specimens collected in the western Mediterranean. The characteristics used for identification included meristic, developmental, morphological and pigmentation characters. Distinguishing characters of these species useful in differentiating them from other species of blenniids for which early stages are known in the Mediterranean are presented. Information on the occurrence of larvae and juveniles of these species off the Catalan coast (north-western Mediterranean) is also given.     

Morphological changes during metamorphosis in cod (Gadus morhua L.), with particular reference to the development of the stomach and pyloric caeca

Metamorphosis in cod, Gadus morhua L., was investigated with respect to morphological changes in the alimentary tract (mouth, stomach and pyloric caeca) and external characters (finfold and fin development). Morphometric measurements and histological investigations were made on both larvae and juveniles and all fish lengths are given as standard length. Median unpaired fins started to develop when the fish were 9–10 mm in length. The larval median finfold was resorbed when fish reached a size of 11–15 mm. The vertebrae were formed in fish of 11–20 mm. The supraterminal mouth, seen in larvae <12 mm, changed gradually to a sub-terminal position in juveniles larger than 65 mm. The development of the stomach and pyloric caeca started at 15 mm and the juvenile form was seen in fish of 40 mm. The ability to store and grind food particles in the stomach developed gradually as fish increased in size from 20 to 40 mm. Compared to many other teleost species, cod juveniles are relatively large when the stomach and pyloric caeca become fully developed. These findings may have important implications for both start-feeding of cod larvae and the weaning of juveniles on to artificial diets.     

The feeding ecology of juvenile mullet (Mugilidae) in south-east African estuaries

Changes in the feeding ecology of juveniles (10–59 mm standard length) of eleven species of Mugilidae were investigated in south-east African estuaries. Adults of all species spawn in the sea and juveniles enter estuaries at a length of about 10 mm. In estuaries they change their feeding habits in the following sequence: zooplankton to zooplankton in the benthos (10–15 mm), zooplankton in the benthos to meiobenthos (10–20 mm), and meiobenthos to sand particles and associated microbenthos (15–25 mm). All species show a similar pattern of change but interspecific competition is probably prevented by the rapid switch to the adult diet of microbenthos and sand particles and because species enter estuaries at different times according to spawning periods. The juveniles seek shallow quiet water areas of estuaries and it is suggested that the change from being planktonic macrophagous carnivores to benthic microphagous omnivores can only take place in the estuaries of the region. Conditions in the inshore waters of the Indian Ocean in south-east Africa are probably too rough for substrate feeding by juvenile mullet.     

Food and feeding ecology of Wilson's storm petrel Oceanites oceanicus at South Georgia

At South Georgia, the diet of Wilson's storm petrel was studied using the regurgitates of adults arriving to feed chicks. Feeding frequency and meal size were estimated by weighing chicks twice daily, or in some cases every 3 h during daytime. Crustaceans contributed 98% of the total number of individual items and 68% of the total weight consumed; fish, 1% of the number of items and 28% of the weight. The most abundant crustacean was the amphipod Themisto gaudichaudii, which accounted for 90% of the total number but only 44% of the total weight of crustaceans eaten. Most (79%) of the Themisto were juveniles. Euphausiids were much less numerous in the diet (5% by number) but were the main group by weight (55%); most (52%) were Antarctic krill, with juveniles and sub-adults (25–50 mm long) predominating. Mysids, copepods and barnacle larvae were also present. Fish were all myctophids (lanternfish), Protomyctophum normani and P. bolini being identified; specimens were 50–85 mm long and weighed 1–4 g. Meal sizes averaged 6-5-7-5 g (14–22% adult body mass); about 75% of chicks were fed each day (mainly at night), about 10% probably receiving meals from both parents. A review of storm petrel diets emphasizes the importance of fish to Oceanodroma species and of crustaceans to Oceanites, Garrodia and Pelagodroma. Euphausiids and amphipods (chiefly Themisto and Hyperia) are the main crustacean prey and range from 5–50 mm and 0-005-0-7 g. Myctophids are the main fish prey and range from 20–100 mm and 1–5 g. Meal size ranges from 15–25% adult body mass and chicks are fed on 50–85% of days. This low delivery rate is mainly responsible for the disproportionately slow growth and long fledging period of storm petrel chicks.     

Studies on the growth of juveniles of Cynoscion striatus in the sea and in aquaria

This paper reports on the studies on growth of juveniles, 20–140 mm in length, of Cynoscion striatus in the sea and in aquaria. The monthly growth of these juveniles in the sea was determined by means of the analysis of length-frequency distributions of 5500 individuals throughout the year. Fish in aquaria were measured and weighed every two weeks, and were fed on known amounts of food. The relationship between the length and the weight of fish, and between the length, width and thickness of the otoliths and the length of fish were calculated and were expressed as exponential functions. On the basis of the analysis of length-frequency distributions and of back calculations it was determined that the formation of the first annulus in the otoliths of juveniles of this species occurs in specimens of 45–100 mm in length and of 1.16–10.0 g in weight. In the majority of the individuals the first annual ring was formed at a size of about 70–80 mm. In juveniles of 79–102 mm, at a temperature of 15–22° C, the maintenance requirement was 0.189 g, and the gross efficiency is 0.310 g of shrimp per gram fish per week. The efficiency of food conversion is high, its value being of 18.8%. The increment in length in these juveniles was 2.01 mm per week and the increment in weight was 0.896 g per week.     

Ontogenetic development of weberian ossicles and hearing abilities in the African bullhead catfish

Background

The Weberian apparatus of otophysine fishes facilitates sound transmission from the swimbladder to the inner ear to increase hearing sensitivity. It has been of great interest to biologists since the 19^th century. No studies, however, are available on the development of the Weberian ossicles and its effect on the development of hearing in catfishes.

Methodology/Principal Findings

We investigated the development of the Weberian apparatus and auditory sensitivity in the catfish Lophiobagrus cyclurus. Specimens from 11.3 mm to 85.5 mm in standard length were studied. Morphology was assessed using sectioning, histology, and X-ray computed tomography, along with 3D reconstruction. Hearing thresholds were measured utilizing the auditory evoked potentials recording technique. Weberian ossicles and interossicular ligaments were fully developed in all stages investigated except in the smallest size group. In the smallest catfish, the intercalarium and the interossicular ligaments were still missing and the tripus was not yet fully developed. Smallest juveniles revealed lowest auditory sensitivity and were unable to detect frequencies higher than 2 or 3 kHz; sensitivity increased in larger specimens by up to 40 dB, and frequency detection up to 6 kHz. In the size groups capable of perceiving frequencies up to 6 kHz, larger individuals had better hearing abilities at low frequencies (0.05–2 kHz), whereas smaller individuals showed better hearing at the highest frequencies (4–6 kHz).

Conclusions/Significance

Our data indicate that the ability of otophysine fish to detect sounds at low levels and high frequencies largely depends on the development of the Weberian apparatus. A significant increase in auditory sensitivity was observed as soon as all Weberian ossicles and interossicular ligaments are present and the chain for transmitting sounds from the swimbladder to the inner ear is complete. This contrasts with findings in another otophysine, the zebrafish, where no threshold changes have been observed.     

Early life history strategies of notothenioids at South Georgia

Antarctic notothenioid early life history strategies are examined in general and then for common species at South Georgia. Channichthyids, bathydraconids, artedidraconids and some nototheniids have large eggs 3·0–4·9 mm whereas other nototheniids and arpagiferids have smaller eggs 1·6–2·7 mm. At South Georgia the larvae of species with large eggs hatched between August (late winter) and late November (late spring) at 11–16 mm standard length ( L _s). Larvae of species with small eggs hatched mainly during October and December at 4.5–9 mm L _s. Most of the larvae of all species attain urostyle flexion between October and January, and develop to the end of the larval stage between November and May. The duration of the larval stage varies from 2 months in species with smaller larvae to 6 months for some of the species with larger larvae. Two nototheniid species develop to the early juvenile stage before a channichthyid and a bathydraconid that hatch around 2 months earlier. During their first winter, the early-juveniles of most species with large eggs are pelagic, whereas those of species with small eggs may be pelagic or demersal. Four groups of strategies are proposed based on egg size and the winter ecotype of the early-juvenile stage.     

Presumed postlarval pentacrinoids from the Lower Devonian Hunsrück Slate,Germany

Several tiny crinoids with crowns as small as 1 mm, or less, in width are newly recognized from the Hunsrück Slate of southwestern Germany. The presence of erect arms above an amorphous calyx in some specimens can be inferred. Based on comparison with the size and gross morphology of developmental stages in living crinoids, these tiny Hunsrück crinoids are judged to be at an early postlarval stage that is analogous to the pentacrinoid stage just after development from the stalked, but armless, smaller cystidean larval stage found in both living comatulids and isocrinids. Some of these tiny crinoids have a stalk up to 4 mm long attached to a now pyritized former substrate. Their clustered occurrence suggests gregarious settlement of larvae. Taxonomic identification of these presumed pentacrinoids is not possible, even to the sub‐class level, although they are preserved with larger juveniles of the cladids Propoteriocrinus and Lasiocrinus. These larger juveniles exhibit 3‐D pyritized calcite plates, whereas the probable pentacrinoids appear to be preserved as flattened, micro‐crystalline pyritized dermal tissues that enclosed lightly calcified, porous ossicles. The pentacrinoids were likely buried within weeks or months of hatching, based on developmental stages in similar‐sized living crinoids. These tiny crinoids, presumably pentacrinoids, are a further example of the extraordinarily detailed preservation of delicate tissues in pyrite from the Hunsrück Slate. They are most likely the pentacrinoid stage from one or more of the crinoid taxa (30 genera) present in the Hunsrück Slate. Assuming these are not microcrinoids, they are the first report of pentacrinoids from the fossil record and document that a Palaeozoic sister group to modern crinoids had similar developmental stages.     

Cranial morphology and bite force in Chamaeleolis lizards--adaptations to molluscivory?

Anolis lizards have become a model system for the study of adaptive radiations as species with similar morphologies occupying similar habitats have arisen independently on all the larger islands in the Caribbean. However, on both, Cuba and Hispaniola unique forms have evolved that seemingly have no counterparts on any of the other Caribbean islands. Anoles of the genus Chamaeleolis comprise such a unique form and have been termed 'twig giants' because of their cryptic life style, slow locomotor mode, and short limbs. However, some of the most unusual features of these lizards are their large heads and molluscivorous diet. Here, we compare head shape, bite force, and muscle structure among sexes and age classes of Chamaeleolis lizards with Anolis crown giants. Our data show that Chamaeleolis lizards have a dramatically different head shape characterized by tall heads with a pronounced temporal ridge and long snouts. Analyses of bite force, surprisingly, show no differences between adult Chamaeleolis and Anolis crown giants. Juveniles of Chamaeleolis, however, have very tall heads for their size and bite harder than Anolis juveniles do. This can be related to the propensity of juveniles of this genus to eat snails, food items for which high bite forces are crucial. This observation is corroborated by the presence of well-developed jaw adductors in juveniles. Thus, our data suggest that the unusual phenotype of adults with large and tall heads may be due to selection on the juvenile life history stages.     

The status of Benthalbella infans (Pisces: Myctophoidei), its development, bioluminescence, general biology and distribution in the eastern NOrth Atlantic

Evidence of comparative and developmental morphology is presented from 99 specimens from the Atlantic and Indian Oceans to establish the conspecificity of Benthalbella dubius with B. irfans. The development of the species is described from the early post-larva (12.5 mm) through metamorphosis (60–80 mm) to the sexually mature adult (112–143 mm). Benthalbella infans is shown to be a hermaphrodite with simultaneous maturation of ova and spermatozoa, in common with other alepisauroid fishes. A fecundity estimate gave 2300 ova. The morphology and histology of the light organs are described, at cellular and sub-cellular levels, and the luminous tissue is shown to be derived from muscle blocks. The significance of these findings is discussed, the properties of the bioluminescent emission defined and measures of intensity recorded. Stomach contents were analysed. The significance of changes in body and eye orientation at ossification is discussed in relation to behaviour and specifically to that of feeding. The horizontal and vertical distribution of B. infans considered in the light of collections made in the eastern North Atlantic. The possibility of racial differences within the species is discussed, although no major niorphological differences were observed between Atlantic and Indian Ocean specimens. The diurnal depth distribution of the species is indicated (90–1500 m); post-larvae are shown to occupy the shallower reaches of the range, descending with advancing development. Evidence of vertical migration was observed only in adults and juveniles.     

Ontogenetic niche shifts in two populations of juvenile threespine stickleback, Gasterosteus aculeatus, that differ in pelvic spine morphology

Most research on ontogenetic niche shifts has focused on changes in habitat or resource use related to food resource distribution and heterospecific size-limited predation. Cannibalism, an intraspecific interaction, can also affect habitat selection or resource use by vulnerable size classes. Morphological defenses, such as spines, increase the effective size of an individual, making it more difficult to consume. The importance of such defense structures in affecting niche shifts in early life history stages is unclear. Using a combination of field observations and experiments in aquaria and wading pools, we examined the relative roles of cannibalism and morphology in determining juvenile habitat use in two populations of threespine stickleback that differ in pelvic spine morphology. Juveniles were categorized into three size classes: small (5–10 mm), medium (11–15 mm), and large (15–25 mm). In experiments assessing the relative vulnerability of juveniles to cannibalism by adults, we documented a significant difference among size classes in the number of juveniles eaten such that more large juveniles were eaten from the population lacking pelvic spines. The natural distribution of small and large juveniles in two distinct littoral microhabitats, open water and vegetation, was determined in each lake. In both populations, small juveniles were more abundant in vegetation. In the population with pelvic spines, a greater proportion of large juveniles was observed in open water than in vegetation. In the population without pelvic spines, the proportion of large juveniles did not differ between the two habitats. Experiments comparing juvenile habitat use in the presence or absence of adult conspecifics suggest that differences in habitat use may not only depend on the size of the individual, or the size of the individual relative to the size of the adult predator, but also on the degree of development or expression of defensive structures.     

Abundance, distribution, morphometrics, reproduction and diet of the Izak catshark

Holohalaelurus regani was caught in 38% of the 3314 bottom trawls conducted during routine demersal surveys o. the South African west and south coasts from 1986 to 1999. An index of biomass for H. regani has increased on the west coast, from 1606 t in 1986–1993 to 3012 t in 1994–1999, despite c. 130 t being taken annually as by–catch in the demersal fishery. On the south coast, there has also been an increase over the same period, from 793 to 1350 t. Females and juveniles were generally found in shallower water (<300 m) than males, suggesting an inshore nursery area. Male H. regani become mature at 450–500 mm LT, whereas females become mature at 400–450 mm LT. There is reproductive activity throughout the year and fecundity appears to be high. This species is a generalist feeder, with the diet comprising teleosts, crustaceans and cephalopods. H. regani also scavenges offal opportunistically. Its high fecundity, the relative protection of females and juveniles in shallow water that is rarely trawled, its opportunistic diet and its robust nature that may allow it to survive after it has been discarded, have enabled H. regani to increase in numbers, despite indirect fishing pressure.     

Life history and distribution of the small south-western Atlantic octopus, Octopus tehuelchus

Although this species has been reported from shallow waters down to 90 m depth, knowledge is almost entirely based on intertidal samples. In this study both intertidal and subtidal samples were taken during 1982–1987, in northern San Matias Gulf (41° S, 63° 30' W). This is a large-egged (eggs: 9–12 mm long ×–5 mm wide, stack of 4–6 mm long) and small-sized (up to 150 g) octopus. Egg laying occurs between autumn and winter. Embryonic development takes about four months (water temperature:–19°C). Large hatchlings (DML: 5·64 mm, TL: 14·23 mm, TW: 0·139 g) emerge over spring and early summer, and development is direct. Maximum size is reached after 17–18 months; mating takes place in summer. Females reduce their feeding activity when they reach maturity, and cease eating while brooding. Mean life-span is two years, but some individuals (mostly females) may live up to three years. Females approaching the beginning of the brooding period move to the subtidal zone, where males outnumber females until the end of summer and females (mostly brooders) then outnumber males. In the intertidal zone sex ratio was 1:1 from December to late March, but in April males outnumber females.
These life-history traits are compared with those of other large-egged octopuses and are discussed in relation to environmental conditions prevailing in the San Matias Gulf.     

Starving early juvenile sprat Sprattus sprattus (L.) in western Baltic coastal waters: evidence from combined field and laboratory observations in August and September 2003

Growth patterns inferred from otolith microstructure analysis were compared between sprat Sprattus sprattus early juveniles (26–42 mm total length, L _T) collected in August 2003 in shallow coastal waters of the Kiel Fjord, and sprat recruits (60–95 mm L _T) sampled in October during a pelagic trawl survey of the western Baltic Sea. At the end of August, a sudden and very rapid decline in otolith growth was observed in early juveniles but not in sprat recruits. Laboratory results indicated that the early juvenile fish were starving prior to capture. Specifically, when transferred to the laboratory, otolith growth rates immediately increased in fish provided ad libitum food rations, while otolith growth of starved fish continued to decline in the same manner observed prior to field collection. In addition, the vast majority of juvenile sprat had empty stomachs on the sampling day. Given that juveniles and recruits probably experienced similar temperature conditions, the rapid decline in juvenile growth rates presumably resulted from very poor feeding conditions in nearshore waters. Starvation during the early juvenile period has not been documented before, but may, at least in the case of Baltic sprat, comprise a density-dependent mechanism operating in coastal nursery areas in some years.     

Growth and morphological development of laboratory-reared larvae and juveniles of the Laotioan indigenous cyprinid Hypsibarbus malcolmi

The morphological development, including the pigmentation, body proportions, fins, and survival rate for 30 days after hatching, of laboratory-reared larval and juvenile Hypsibarbus malcolmi is described. Body lengths (BL) of larvae and juveniles were 2.0 ± 0.2 (mean ± SD) mm at 1 h after hatching (day 0) and 9.2 ± 0.6 mm on day 16, reaching 12.1 ± 0.9 mm on day 30. Yolk volume decreased linearly, with the yolk being completely absorbed by day 3 in all preflexion larvae (all specimens >3.2 mm BL). Feeding was observed on day 2 in fish which had rapidly undergone complete yolk absorption following mouth and anus opening on day 1, and on day 3 in all remaining fish. Myomere numbers were 20–21 + 11–12 = 31–33, although they were not clearly visible in juveniles. Melanophores were few on the body during days 0–2, but increased with growth and covered the entire upper dorsal body surface during the juvenile stage. Body proportions tended to become constant in juveniles. Notochord flexion began in larvae >5.2 mm BL on day 8, and was completed in larvae >8.4 mm BL on day 14. Specimens with full fin ray complements were initially observed on day 22 (10.4 mm BL in juveniles). All specimens >11.5 mm BL had attained the juvenile stage. A high survival rate of 92.7% was estimated on day 30.     

Identification of grey mullet (Teleostei: Mugilidae) juveniles from British waters

Examination of juveniles (25–50 mm t.l .) of the three species of grey mullet present in British and other nothern European waters has indicated that the melanophore pattern on the ventral surface of the head is a reliable and useful character for identification.     

Shell shape and habitat use in the North‐west Pacific land snail Mandarina polita from Hahajima,Ogasawara: current adaptation or ghost of species past?

The endemic land snail genus Mandarina of the Ogasawara Islands provides an excellent model system to investigate adaptive radiation. Previously, it has been shown that coexisting species of the islands segregate by microhabitat, so that they are either predominantly found on the ground in relatively wet and sheltered sites, dry and exposed sites, or else are arboreal. Moreover, shell morphology correlates with microhabitat, so that species in wet and sheltered sites tend to have high-spired shells with a high aperture, and those in dry and exposed sites tend to have relatively low-spired shells with a wide aperture. We have now found that on Hahajima, Mandarina polita have variable shell morphology, and there is a correlation between morphology and the depth of leaf litter, as well as the presence/absence of other terrestrial species. Specifically, when high-spired terrestrial Mandarina ponderosa is present, M. polita tend to be low-spired and have a large aperture, indicative of character displacement. When M. ponderosa is absent, the shell shape of M. polita is much more variable, the overall spire is higher, individuals are found in deeper litter, and there is a strong correlation between litter depth and spire height. We argue that these patterns are due to local adaptation, but it remains possible that they are an artefact due to the 'ghost of species past'.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 149–159.     

A new species of the deep-sea fish genus Paraliparis Collett (Liparididae) from the eastern North Atlantic, with notes on its ecology

A new species of liparidid, Paraliparis hystrix , is described from the slope waters (255–1140 m) to the west of Britain, in the area 49–59°N and 07–18°W. This pallid species is not uncommon, and is represented by a strong imbalance of females. Specimens close to ovulation have been collected in all seasons and have an estimated mean fecundity of 83 eggs.     

Microhabitat choice and high temperature tolerance in the land snail Theba pisana (Mollusca: Gastropoda)

Adults of the land snail Theba pisana near the species'northern limit (Tenby. South Wales) spend the daytime inactive attached to stems of tall vegetation, avoiding higher temperatures near the ground, while juveniles remain low down. This may be related to the lesser ability of juveniles to withstand desiccation for long periods, and/or to their requiremcnts for an easily accessible source of suitable food during growth. In the field and laboratory, adults (at least) respond to light and wind direction, avoiding the hottest and most exposed sides of stems on which they rest.
The upper lethal temperature of snails from S. Wales lies between 42 and 46 °C, depending on exposure time. Juveniles are more tolerant than adults, probably because of their greater ability to use evaporative cooling for short periods. Spanish T. pisana are more tolerant (upper lethal limit 46–50 °C) than Tenhy snails; this difference may have a genetic basis. Aestivating Spanish snails are more tolerant than active ones.
Climbing and orientation are essential for both adults and juvenilcs in the Mediterranean habitats where Theba pisana evolved, since ground temperatures can exceed the lethal limit. It is less important at the northern edge of the range, but is still retained by the adults.