Philip V. Mladenov

Mechanisms of arm-tip regeneration in the sea star, Leptasterias hexactis

SummaryWound healing and regeneration following amputation of arm-tips of the sea star, Leptasterias hexactis, are described using light microscopy, SEM, TEM, and [3H] thymidine autoradiography. The process can be divided into a number of stages. Initially, the wound is closed by contractions of the stump-tip. Re-epithelialization then occurs through migration of epidermal cells from adjacent areas over the wound to form a thin wound epidermis. This is converted into a thicker, permanent covering in concurrence with the onset of cell cycle activity in the wound epidermis and adjacent epidermal regions. Histolysis and phagocytosis of damaged tissues occur beneath the new epidermis and a small connective tissue scar develops at the wound site within which muscle differentiates. At this time, elevated levels of [3H]thymidine incorporation are initiated in the sub-epidermal tissues of the arm-tip. A variety of differentiated cell types enter the cell cycle including cells of the parietal peritoneum, lining of the radial water canal, and the dermis. Cell division is accompanied by the development of a small new arm-tip complete with terminal ossicle, terminal tentacle, and optic cushion. The radial water canal, radial nerve, and perivisceral coelom extend by outgrowth into this newly developing tip. Accelerated growth of the regenerate then occurs in a zone just proximal to the new tip. There is no evidence of a blastema-like mass of rapidly dividing undifferentiated cells at the tip of regenerating arms. Arm-tip regeneration in this sea star may therefore be best described as a morphallactic-like process in which a true blastema is not formed, but in which scattered cell proliferation plays an essential role.

Improved method for benzoyl chloride derivatization of polyamines for high-peformance liquid chromatography

Abstract A rapid and sensitive method for derivatization of polyamines (putrescine, cadaverine, spermidine and spermine) by benzoyl chloride is described. Derivatization was improved by dissolving benzoyl chloride in methanol thereby enhancing the reaction with polyamines. The benzoylated polyamines are eluted by reversed-phase high-performance liquid chromatography using methanol-water (60:40) as the mobile phase. The sensitivity of this method is 100 pmol. The benzoylated polyamines are stable for at least two weeks. The application of this derivatization method to detect different polyamines in vertebrate and invertebrate tissues (mouse and sea star) is described. Sea star tissues had higher levels of polyamines than did mouse tissues.

Asexual reproduction in the west indian brittle star Ophiocomella ophiactoides (H.L. Clark) (Echinodermata: Ophiuroidea)☆

Abstract The biology of asexual reproduction in the fissiparous brittle star Ophiocomella ophiactoides (H.L. Clark) at Jamaica, W.I. was studied during June, July, August and December, 1981 and July, 1982. Most O. ophiactoides were in various stages of recovery following fission, having three long and three shorter arms. Recently split specimens with only three arms and half of a disc were present in winter and summer suggesting that asexual reproduction occurs throughout the year. A small number of five- and seven-armed individuals resulted from natural variability in fission and regeneration processes. Fission in O. ophiactoides proceeded unilaterally, with one side of the disc first apparently softening to form a furrow which then progressed across the disc to separate the brittle star into two halves. Initiation of fission appeared to be internally controlled. Fission occurred before the new arms were fully regenerated. This minimized the interval between successive fissions and so maximized increase in numbers due to asexual reproduction. The fission plane was not predetermined but variable which ensured that many halves acquire a mixture of both longer and shorter arms. It was deduced from data on arm configuration and regeneration rates that the interval between fissions was of the order of 89 days. A single specimen potentially may divide and produce 15 new individuals each year. The population size structure showed that larval recruitment was absent or minimal. Populations of O. ophiactoides at Jamaica must be maintained by asexual reproduction.

DEVELOPMENT AND METAMORPHOSIS OF THE BRITTLE STAR OPHIOCOMA PUMILA: EVOLUTIONARY AND ECOLOGICAL IMPLICATIONS

The development to metamorphosis ofthe shallow-water tropical-Atlantic ophiu roid Ophiocoma pumi!a is described for the first time. This species possesses an eight-armed planktotrophic ophiopluteus larva that has a potential pelagic existence of three months (26—27.5°C), considerably longer than other brittle star species so far studied. This likely accounts for the amphi-Atlantic distribution of 0. pumila. During metamorphosis, all of the larval arms are resorbed into the developing ophiuroid rudiment although the right antero-lateral arm disappears last. The metamorphosing larva transforms into a highly mobile vitellaria possessingtransverse ciliary bands and tube feet. Ophiuroid vitellariae have hitherto been described only for species with abbreviated lecithotrophic development. The vitellaria of 0. pumi!a can delay settlement for at least a week and probably functions as a pre-settling exploratory stage. The discovery of both an ophiopluteus and a vitellaria in the ontogeny of a brittle star strongly supports the proposal that ophiuroid vitellariae are related to ophioplutei and are not a divergent larval series. Abbreviated development in brittle stars with vitellariae may be the outcome of heterochrony caused by an acceleration of metamorphosis. Little is known about ophiuroid metamorphosis so it is possible that the ophioplutei of many other species pass through a vitellaria stage towards the end of their pelagic existence.

Studies of the fissiparous holothurian Holothuria parvula (Selenka) (Echinodermata: Holothuroidea)

A Bermudan population of the fissiparous holothurian Holothuria parvula (Selenka) was sampled over a 13-month period (1984–1985). Fission was most frequent in the summer when water temperatures were > 25 °C. During fission, the holothurian split into roughly equal parts, and there was little difference in survival of the oral and anal ends. Regeneration of a new gut is a priority and feeding was possible within 2 months of fission. The majority of growth following fission occurred between April and July, just prior to the peak occurrence of fission. Many individuals were fully regenerated within a year, so fission is possibly an annual event. Individuals showing evidence of multiple fission were found. The capacity for sexual reproduction was limited and it appeared to occur mainly during the summer, which was also the peak period for asexual reproduction. No small (< 18 mm) individuals were ever found suggesting that larval recruitment to this population had not recently been successful. The population has probably been maintained recently by fission.

Reproductive ecology of an obligately fissiparous population of the sea star Stephanasterias albula (Stimpson).

A population of the fissiparous sea star Stephanasterias albula (Stimpson) was studied at North Lubec, Maine, U.S.A. This population consisted of a dense (up to 40/m2 localized group of roughly 5500 small (R, the length of longest arm from disc center to arm tip, nearly always <18 mm) contagiously distributed individuals. Very small individuals (R<3mm) were totally absent suggesting that larval recruitment had not occurred recently. Fission is a seasonal phenomenon that takes place most frequently in the spring and summer. Incidence of fission appears to be correlated with seasonal changes in photoperiod. Rates of regeneration following fission are sufficient to allow individuals of S. albula to split once every 1 or 2 yr. Examination of 1-μm plastic sections from even the largest specimens revealed no trace of a differentiated reproductive system and of associated aboral haemal and coelomic rings, strong evidence that S. albula is obligately fissiparous. The ecological and developmental consequences of this finding are considered.

Brooding biology of the sea star Pteraster militaris (O.F. Müller): energetic and histological evidence for nutrient translocation to brooded juveniles

Abstract Adaptations of the sea star Pteraster militaris (O.F. Muller) for brooding postmetamorphic juveniles in an aboral chamber are examined. Brooding was extremely widespread among adult females, occurring in 75 of 99 individuals examined between February 1986 and July 1987. Premetamorphic offspring comprised > 80% of all brooded progeny. Offspring may be brooded to a juvenile size of R = 4.5 mm from an egg of ≈ 1.1 mm in diameter, although the majority of juveniles left the brood chamber at sizes less than R = 2.1 mm. There is a size-independent upper limit on the number of juveniles that can be successfully brooded by a female. The mean energetic content of freshly spawned eggs (10.2 J) was considerably less than that of brooded juveniles (54.2 J). This suggests that there must be some postvitellogenic transfer of nutrients from parent to brooded juvenile. Histological examination revealed the presence of a complete and apparently fully functional digestive system in brooded juveniles as small as R = 1 mm. Thus, both histological and energetic analyses indicate the possibility of active feeding by brooded juveniles. There are numerous potential mechanisms by which nutrients may be procured by the brooded juvenile. Observations indicate that brooded juveniles are cannibalistic ectoparasites, grazing on irritation-induced hyperplastic regions of the maternal dermis. Direct ingestion of other maternal tissues, such as pyloric caeca that has been extruded into papullae and on the epithelium lining the brood chamber, may also occur. Brooded juveniles may also ingest particulate organic matter derived from abortive embryos or larvae, faecal material and mucus secreted by the epithelium of the brood chamber. Uptake of dissolved organic matter may also be of importance to brooded juveniles.

Fine structure of the doliolaria larva of the feather star Florometra serratissima (Echinodermata: Crinoidea), with special emphasis on the nervous system

The epidermis of the doliolaria larva of the Florometra serratissima is differentiated into distinct structures including an apical organ, adhesive pit, ganglion, ciliary bands, nerve plexus, and vestibular invagination. All these structures possess unique cell‐types, suggesting that they are functionally specialized in the larva, except the vestibular invagination that becomes the postmetamorphic stomodeum. The epidermis also contains yellow cells, amoeboid‐like cells, and secretory cells. The enteric sac, hydrocoel, axocoel, and somatocoels have differentiated but are probably not functional in the doliolaria stage. Mesenchymal cells, around the enteric sac and coeloms, appear to be actively secreting the endoskeleton and connective tissue fibers.

Purification and partial characterization of an autotomy-promoting factor from the sea star Pycnopodia helianthoides

Echinoderms possess collagenous connective tissues that are capable of rapid, nervously mediated changes in their tensile strength. Arm autotomy in sea stars is facilitated by a rapid decrease in the tensile strength of connective tissues in the arm base. In this study, an autotomy-promoting factor (APF) has been isolated from the fluids released by scalded or autotomizing sea stars (Pycnopodia helianthoides). When injected into the coleom, APF elicits a complex behavioral response that culminates within minutes in multiple arm autotomy and a generalized softening of the body wall. Injection of fluid from intact, untreated sea stars does not promote the autotomy response. APF is a water soluble, heat-labile substance derived from the body wall. It is ammonium sulphate precipitable and its activity is reduced or destroyed by several proteolytic enzymes. On the basis of its gel permeation elution pattern, APF has Mr of about 1200 Daltons. APF can be purified to a single peak of activity by reversed-phase HP...

Polyamines and cell proliferation in the sea star Pycnopodia helianthoides

1. Diamines (putrescine and cadaverine) and polyamines (spermidine and spermine) were extracted from tissues of the sea star Pycnopodia helianthoides, separated and quantitated using reversed-phase high-performance liquid chromatography (RP-HPLC). Simultaneous measurements of levels of protein and DNA and rates of incorporation of 14C-thymidine were carried out. 2. The most abundant polyamine in tissues was spermidine (0.3873-2.5282 nmol/mg tissue) followed by spermine (0.103-1.5517 nmol/mg tissue), putrescine (0.2096-0.5322 nmol/mg tissue) and cadaverine (0.022-0.6064 nmol/mg tissue). 3. An unknown molecule with derivatization and elution behaviour similar to that of polyamine standards was detected in all tissues. 4. Protein levels ranged from 20.47 mg/g tissue in the body wall to 48.44 mg/g tissue in the pyloric caecum. 5. DNA levels were lowest in the ovary (0.25 mg/g tissue) and highest in the testis (5.62 mg/g tissue). 6. Incorporation of 14C-thymidine was highest in the testis. Testicular tissue had the highest spermidine/spermine ratio (5.4). A significant correlation between the spermidine/spermine ratio and 14C-thymidine incorporation (expressed either as DPM/g tissue or DPM/mg protein) suggests that polyamines are implicated in the regulation of cell proliferation in the sea star P. helianthoides.